1/16 Scale FrankenDiff
 

I'm going to be doing several Bruder conversions in the near future, since I'm retiring next week. I don't have the skill to scratch build, and I like the idea of using the Bruder stuff as a starting point. Bruder at 1/16 scale really doesn't look right when you use 1/14 scale running gear, plus the cost of the running gear is more than I'm willing to spend.

Soooo... my wandering mind latched onto the idea of Frankensteining a reasonable looking truck rear end out of other available low-cost bits. I probably got the idea from "mick thebass" on YouTube when he modified a couple of low-buck 1/12 scale WPL diffs and used them on his articulated Bruder dumper. He did some really neat stuff if you haven't checked him out. He hasn't updated his channel for a couple of years so I'm afraid he might not be with us anymore - which is too bad. The guy was a master at stuffing 10 pounds into a 5 pound sack.

I thought about using the Kong 1/12 scale diff, even got one to see if it'd work. It's a GREAT looking axle, smooth as silk, about the right size, and the price isn't too bad. But as far as I know they only make the rear axle version, they don't make a center axle version. I don't know about you guys, but the thought of building a truck that's SUPPOSED to have double drivers, and then having one axle sitting there doing nothing doesn't appeal to me.

So, back to the Frankendiff. I'm starting with your basic plastic diff for a WPL 1/12 scale car, it's guts are about the same size as the Kong axle. The actual axles will need to be shortened, but that'll be fairly simple machining to cut them to length, turn down the ends, thread them M4, and drill new holes for the drive pins. I'm just going leave it an open diff for now, no lockers.

Nope, the complicated part is the 3D modelling of the front and rear halves of the differential housing so that the WPL guts will fit into them. (While simultaneously learning Alibre, I use-ta-use Designspark3D.) The pinion housing is the most complicated part and I re-did that last night - I was NOT happy with the first attempt. I think I should be able to get the rear cover done tonight, it's pretty simple.

Then I'll 3D print a prototype and see what parts need to be fixed. I'll take some pictures when I've got some physical parts.

Eventually I'd like to cast the parts in ZA-12, both for durability and the extra weight. (But plastic will do for now.)

Re: 1/16 Scale FrankenDiff
 

Welcome to the good life. I was able to take early retirement 8 years ago and I have enjoyed every minute of it. What got me into this hobby was the fear of 'what am I going to do with all this time' after averaging 50+ hours a week for the last 30 years. Has not been a problem. Get to do everything I like to do, research, design, build, play with electronics, play with machining, experiment with new methods, etc, etc, etc. Most weeks, come Friday, I wonder where the time went.

See you apparently decided to go with Alibre as your 3d cad program. It's been a good program for me, hope you enjoy it.

Re: 1/16 Scale FrankenDiff
 

Zabco:

I went with Alibre for a couple of reasons, you can get a perpetual license, and you can get an off-line version of that license - one that doesn't need to phone-home every 30 days. I refuse to rent a cad package, and I also refuse to let somebody else hold my files hostage. I pulled the trigger on the Alibre purchase this morning, only had 4 days left on the trial. I've REALLY got to learn Best Practices, and actually use them, instead of just poking and prodding at it like I have been.

I printed out a prototype of the front half of the diff to see how things fit. Let's just say that my measurements were apparently less than accurate. Or at least my 3D model is less than accurate. I guess I got some 'slpainin to do to it. Over the weekend I hope to get to the point where the WPL guts will fit between the front and rear halves of the diff.

I left side to side clearance for fit of the pinion to ring gear, as well as front to back clearance for the pinion to ring gear. I figured I'd print a prototype and let the diff find its' happy spot, then measure how much I needed to adjust the model.

I've definitely got a problem with the diff carrier bearing fit - they don't. Looks like I measured the bearing ID and OD, then drew the 3D model using the ID dimension instead of the OD.

Then I've got this STUFF in the middle of the axle itself, that I can't for the life of me figure out WHY it's there. On both axles there a hole with a very short pin inserted in it, imagine a 6mm long pin through a 5mm axle and you've got the picture. I'd include a picture, but that axle is at home and I'm NOT. There's a plastic collar that slips over the pin and retains it, but the pin also limits how close the outboard edge of the collar can get to the diff carrier. Just outboard of that junk is a plain bushing, yup - a bushing. There are bulkheads on both sides of the bushing fixing it in place. The inboard bulkhead also does a very rough job of limiting the side to side position of the diff assembly by limiting how far outboard that plastic collar can move.

I can't think of ANY good reasons why the crap is there. The best explanation I can think of is that WPL uses this assembly in other differentials and it's needed in that other application. We all know that WPL uses bits and pieces from this model and that, slaps them together, and calls them a new model. In the next round of design I'm going to chuck all that crap in the middle of the axle into the trash-can and see if anything breaks. I've still got bearings supporting the diff carrier and bearings on the outboard ends of the axles. That's all that most full-size cars and light trucks have. If it's good enough for them it's good enough for me.

It's supposed to be rainy Saturday night and Sunday, we'll see what I can get done on the Frankendiff.

Re: 1/16 Scale FrankenDiff
 

Same reasons I went with Alibre also.

Yep, bearing support for axle shafts in middle and end should be only thing you need. That's all the Tamiya rear ends have and they seem to hold up just fine to all sorts of abuse.

Re: 1/16 Scale FrankenDiff
 

I got some stuff printed out over the weekend. It's been a while since I created a new album, I THINK I've got it set for sharing, let me know if I remembered all the hoops I need to jump through so that anybody else can see the photo.
https://photos.google.com/share/AF1Q...l0RnQ5b3hWdnVR

What you are hopefully seeing is the front and rear halves of the diff housing screwed together, along with the pinion housing screwed on the front. I've lost track of the number of times I've printed the diff halves, definitely more than I can count on one hand, even if I was the 6-fingered man. I was having bed adhesion problems at first, it's been a while since I printed anything. But I DID dust the bed off first, that just wasn't enough. That was Round 1.

Then it JUST wasn't measuring up, too small. That was Round 2. Yeah, I forgot to scale it up in the slicer - it's been a while since I printed anything. I scaled it to 103% in the slicer and printed Round 3. Hoo-Boy-Howdie Round 3 measured at 120.18mm, close enough to 120mm for me. Do the guts fit....NOPE. How come, the ring gear has a 25mm OD and it's in a 26mm hole, it should fit. IF the ring gear was centered in the opening it would fit, but when the ring gear is offset from center - not so much.

Re-design the diff carrier space in the front and rear diff halves and re-print - Round 4. Things were looking up after Round 4, outside dimensions checked out OK, the donor diff guts and bearings appeared to fit in their respective pockets. Will the front and rear halves fit together? NO, the diff halves do not fit together!!!!!

I started measuring the bearing pockets, since the bearings are the only things that could be keeping the case halves from mating together. The bearing measurements and the model measurements match. I don't like either of the explanations that I was able to come up with; 1) either the slicer is doing something funky when it's scaling the part, or 2) the part isn't shrinking linearly.

The only thing I could think of was to start tweaking bearing pocket dimensions and see if that worked:
Round 5 - too small.
Round 6 - better but still too small.
Round 7 - WHOOOPS - over-compensated.
Round 8 - Sorta worked. The diff halves do clamp together, but the axles not longer turn as easily as they used to turn. I wondered if I was clamping the bearings too tightly? I backed off the screws and sure enough things started turning easier. It's hard to believe that a pair of M2 sheet metal screws and a 2 piece plastic clamp could apply enough pressure to load the bearing shells like that. I'll tweak the pocket dimensions one more time and try Round 9 tonight.

Don

Re: 1/16 Scale FrankenDiff
 

When you create the .stl file from your 3d model in alibre a stl configurations box should pop up. Make sure and use a value no greater than 1 degree for the faceting parameters setting. stls do not contain true circles, only straight lines. A value of 1 degree would create a circle comprised of 360 straight lines. If your faceting was set to say 6 degrees then the circle would only consist of 60 lines. The lines would be longer but more importantly the center distance between two opposing lines (the diameter of your circle) would be less than the desired diameter. This would compress your bearing when you tightened up the two axle halves.

Re: 1/16 Scale FrankenDiff
 

Awesome you took the CAD plunge. Alibre was at the top of my list too.


Id wager your printer is culprit. Some are better than others. Should be able to tune scaling in each direction. I've never totally solved it. Bearing pockets need a pretty tight fit. The slight compression of each layer squeezes it a bit wider.

3D printing is certainly a bit more involved than push button, receive part.

Is it possible to assemble the axle halves, and thru drill/ream the bearing pockets? Or are the end opening too small?

Re: 1/16 Scale FrankenDiff
 

With your growing lack of tolerance for fighting the printed part tolerances: What if you rough assembled the axle guts, moderately warmed them with a heatgun, and tried to close the axle case halves around them? Let the parts soften and clearance what they need, then you can evaluate where it made marks.

Which style WPL axles actually have a Differential instead of Spool?
I had wondered how much the extra bearings in the wpl axles was there to stiffen up the cases instead of support the axles?

Re: 1/16 Scale FrankenDiff
 

Nice discussion we've got going on here, deeply appreciated.

Blender:
I use Simplify3D for my slicer and I can scale all the axis independently if I want. I've tweaked the basic setup of the printer, it's a Wanhao D6 clone by Monoprice, so that I get accurate external dimensions. The diff halves should measure 120mm across, the circular part of the housing should have a 37mm OD and it should be 7mm thick, they measure 120.18mm, 36.98mm, and 7.21mm respectively. The first 2 are close enough for me. I'd like to get the Z height a little closer, but since my version of S3D does not allow for variable layer thickness, I've got to accept that the thickness could be off by a layer thickness, 0.2mm is what I'm currently printing at. External is fine, it's the internal pockets that are the problem. Drilling/reaming the 9mm outer bearing race pockets wouldn't be a problem. The only way I could see to get to the inner 12mm pockets would be some sort of line boring set-up, and I've only got the 6mm hole for the axle to work through.

Zabco:
I've been using the default set-up for the STL's, which I think is 4 degrees. Since I've been poking and prodding at all 4 of the parts, and have to reprint them all, I'll look at making a higher resolution STL.

Frizzen:
This is a replacement WPL diff for the "1:16" scale trucks.
https://www.ebay.com/itm/22618175378...Bk9SR-DG5t3EZA

I don't remember the exact part number, but this is REALLY similar to what I am using for a donor axle.
https://www.ebay.com/itm/20485224934...3ABFBMkKPg3cRk

Re: 1/16 Scale FrankenDiff
 

Two steps forward, one step sideways, and one step back.

I measured all of the internal pockets on the diff halves, they were ALL consistently about 97.4% of the model size. That's the size I would expect them to be when you allow for shrinkage. I'm beginning to wonder if my version of S3D scales internal dimensions? I really need to try scaling the slicer to about 150% and see what the pockets look like then as an experiment - without printing anything.

Anywho... I scaled the critical pocket dimensions to 103% in the model, the same as my scaling factor in S3D and printed the diff halves again - things are REAL close. The inner bearing pockets are a little bit too tight, and the outer bearing pockets are a little too loose. When I tighten all the screws holding the halves together the outer bearings will slip out of the pocket, and the inner bearings will not turn freely - but I think that's MY fault.

The outer bearing pocket dimension when scaled was 4.84mm and change, I just rounded it up to 4.85mm. The inner bearing pocket dimension when scaled was something like 6.12mm and change, I just rounded it down to 6.1mm. I'm going to print this one more time, but this time I'm going to round the pocket dimensions to the 3rd decimal place and see how that works.

Don

Re: 1/16 Scale FrankenDiff
 

Getting close! Almost every FDM printer I've used will make IDs too small. Normally I drill them out. Even the industrial printer's SLA parts I've ordered are a bit of a wildcard in term of tolerance.


When bearing pockets are too big, I'll do a single wrap of tape on the outside before installation. Tape choice based on how far out the pocket it maybe scotch, maybe painters tape. I'm also not above a drop of CA glue either.

Re: 1/16 Scale FrankenDiff
 

Something just didn't feel right to me, I had play in the pockets up and down, but not from front to back. So I got out the Opti-visor and gave things a look-see.

In most of the pockets there was a booger about 1-3mm wide in what would be the top of the arch when the pockets are printed. This area would be the bottom side of a bridge when printing. My printer does pretty good, but the bottom of the first layer of a bridge is NEVER pretty.

My current plan is to increase the radius about a 0.5mm in that area. I'll still get a booger when the printer bridges in that area, but the booger shouldn't be touching the bearing any more. And since I'm measuring about 0.2mm of total play I'll reduce the radius of the bearing pocket by about 0.1mm.

I've got a problem with the pinion housing's print too, turns out I'm trying to print a circular opening in a horizontal surface in mid-air. (Without support) That NEVER works out for me - should have seen that one coming.

Don

Re: 1/16 Scale FrankenDiff
 

OK, I have a mostly functional 3D printed Frankendiff. I modified the bearing pockets, as described above and that eliminated the booger caused by the bridging layer. Scaling the bearing pocket diameters to 3 decimal places instead of rounding them to 2 places seems to have cured the bearing fit problem in the diff housing.

I added a couple of fillets to the cut-out for the inner bearing in the pinion housing and printed it again - it didn't fit right. That was really no surprise since I couldn't get a good measurement of the depth to the inner bearing pocket. So I just guessed - I was about 0.75 mm too shallow. Well that didn't work as planned either, that extra 0.75 mm of cut depth managed to break through to the outside. When I fixed that, that fix broke almost ALL of the fillets to the rest of the housing.

By the time the shouting was over I had basically re-designed the entire diff. But it looks much prettier now, and the 3D model is a LOT simpler. Before it just looked, I don't know - chunky/clunky? It more closely resembles the Kong axle now, except that I can make a center axle out of mine by getting a replacement pinion and the bearings, and printing another pinion housing.

Re: 1/16 Scale FrankenDiff
 

Congrats!

Re: 1/16 Scale FrankenDiff
 

Sounds like it's been good practice. Any pics of the diff housings through the learning curve?

Thanks for the tip on those parts.

Re: 1/16 Scale FrankenDiff
 

Pictures.... about that, there's been a hiccup.

I retired about a week ago and I've discovered since then that I REALLY depended on those work computers. Almost all of the forums that I'm a member of were pointed to those e-mail addresses, and those high-speed morons were remembering the passwords for me. Those computers are no longer accessible to me now. I think I've worked my way through most of the forums now, but I'm still working on getting back into my pictures.

Regarding the donor axles, right out of the box they are about what you'd expect from cheap Chinese knock-offs. Let's just say not very good, as in really crunchy. You can BARELY turn the pinion shaft on them. When I opened up the first one I found that the ring gear and the pinion gear are both die-cast. They both had been very crudely clipped off their sprues - with no effort made to clean off the sticky-outy bits. Cleaning those nubbins off and getting the pinion depth set made a huge difference.

It's still a little crunchy when I make the diff work. I'll probably have to look at the spider gears next, since they are also probably die-cast. And probably just as rough as the ring and pinion were. I'll have to tear the diff apart anyway when I machine the axles to length.

Don

Re: 1/16 Scale FrankenDiff
 

Yea, practically every web site wants a login anymore. Way too many user ids and passwords to keep track of. I created a spreadsheet to keep track of them and it's probably the most often opened file on my PC, but an absolute lifesaver.

Re: 1/16 Scale FrankenDiff
 

Mine's a text document, with a very obscure name, that's on a thumb drive which never leaves my possession.

My work computers used to require us to change our password every 90 days. You couldn't repeat more than a small number of consecutive letters from your old password, and you couldn't reuse any of your last 12 passwords. I kept the list of my old passwords in the same document.

Re: 1/16 Scale FrankenDiff
 

Pictures, I think I've got pictures - if I can just decode how to insert them.

https://lh3.googleusercontent.com/pw...-no?authuser=0
If this works, you should be able to see the Frankendiff Mk-I. Well that seems to have worked. This was the 1st version of the diff, and it looks OK - just kinda mmeeehhhh.

Enter the Frankendiff Mk-II.
https://lh3.googleusercontent.com/pw...-no?authuser=0
This is the current version, and it looks more like the Kong diff which will be in the next image.

https://lh3.googleusercontent.com/pw...-no?authuser=0

I initially called this my Wall of Shame, but it's more a collage than a wall. On the left side from bottom to top you have:
1 - The MK-I front diff housing. If you look closely you can see that I have recessed pockets for the screw heads, more on this later.
2 - The Mk-I rear diff housing. It's ALMOST identical to the front half, except the mounting screws go into blind holes.
3 - This is the final version of the Mk-I diff. Everything fits, and it WOULD have worked - it just looks like something you could build out of a box of Tinker-toys.
4 - At the head of this column is the Kong axle, the thing that started this journey into madness. It's a nice axle, and at $A40-$50 USD fairly cheap. But it's unobtainium as a center axle.

Just to the left of the Kong axle is the back-side of the Frankendiff MK-II. I took the rear cover off so you could see that I also re-designed the ring-gear/diff pocket for the Mk-II. The Mk-I housing would allow a noticeable gap to show at the top and bottom of the center section. The Mk-I's rectangular diff pocket didn't give me any place to correct that gap. The Mk-II's diff pocket gave me room to stash 2 more screws under the pinion housing, closing up those gaps.

What are the differences between the Mk-I and the Mk-II! A LOT, but with the exception of the 2 extra screws in the center section all the changes were just to make it look better. I slimmed the diff halves by a total of 2 mm, then added pads on the outer ends like the Kong diff has. That meant I had to redesign the pinion housing and the rear cover to compensate for the 1 mm change on each side. I also got rid of the recessed pockets, nothing like a full-sized mockup to show where you need to make better choices.

The bottom row on the right side is the pinion housing iterations, these were:
1 - The oldest version - the bearing pocket ID's were too small. I also had recessed pockets for the screw heads. It looked good on the screen - real-life, too thin.
2 - The next version - the bearing pocket ID's were too big.(Round off error, my fault. Also got rid of the recessed pockets.)
3 - The next to the last version - the outer bearing pocket fit just fine, the inner one not so much. 3D printers just REFUSE to properly print something when it starts in mid-air. The latest version is still screwed onto the Mk-II diff.

The next row on the right side is the rear cover iterations, left to right:
1 - The oldest version - just didn't look right, it needed something.
2 - The next version - I added a boss. Why's it need a boss? For the drain plug silly! (Didn't print well, that starting to print in mid-air thing again.)
3 - The last version - including the drain plug.

In the upper RH corner is my latest descent into madness - hubs, wheels, tires, and unseen but holding up the wheel is the front axle that will be donating its' spindles/knuckles. The doo-dad that looks like a brake drum is the 1st iteration of the front hub, as usual the bearing pockets were too small. I overcompensated on the next version, but it was close enough that I could shim it with a piece of tape to put everything together. It looks good- and it would work. But the effort needed to get the 3 parts lined up to start that dinky little M2 screw was enough to convince me to make the wheel and hub 1 part - with a separate cover to hide the M4 Nylock nut.

The tire you see is the Lesu 1/16 scale "narrow" tire. I ordered a set of both the "narrow" and the "wide", to see how they looked - since the specs on them are sketchy at best. There's only a 1-2 mm difference in width between the two sets, not enough to justify the extra $5 per pair of tires. In addition to the minimal difference in width, they need different wheel profiles. The "narrow" tire needs a 39 mm OD on both sides for the wheel profile. The "wide" tire needs 39 mm on one side, and 40 mm on the other side - go figure.

Don

Re: 1/16 Scale FrankenDiff
 

I really like what you have come up with, they really look good. Even a drain plug in the rear cover. I had the same issue with multi-piece wheels and hubs when I was designing the dayton style wheels for my Mack. I'm going the make them just like the originals I thought. Well I'm blind in one eye and can't see with the other and yea, trying to get everything lined up and those damned little screws in is a real pain.

Re: 1/16 Scale FrankenDiff
 

Those parts are looking great! Sounds like the different versions have all lead up to some pretty nice axles. Wheels and diff covers look sweet

It's pretty bad when the model parts need to have a setscrew as a stud, or use a paperclip as drift punch just to align everything

Re: 1/16 Scale FrankenDiff
 

Last night I worked on the rear wheels, got the design done and started it printing before I went to bed. I think it looks pretty good, but it's got two major boo-boos and one "that just doesn't look right" issue.

Major problem #1 was the depth of the pockets. I pocket the wheel openings and the screw holes at the same time, and must not have been paying that much attention to the actual depth. The wheel openings were a little shallow but still OK, but the screw holes were only 1-2 mm deep.

Major problem #2 was that the 12 mm hex driver didn't fit, it was too small. I have been using Simplify3D for years, but it seems to have an issue with internal pocket and bore dimensions. I scale the model in the slicer to 103%, this gives me a final print that is dimensionally accurate to the 3D model within a few hundredths of a mm, at least externally. Internal pockets and bores were always too small. I've found that if I manually scale the dimensions of the critical bores and pockets to 103% before I send the model to the slicer things work out much better. When I checked the model I had scaled every critical bore and pocket to 103%, except the pocket for the 12 mm driver - you just can't fix stupid sometimes. I'm beginning to wonder if S3D just offsets all the dimensions away from the core of the print when it scales? (Maybe there's an advanced setting that I haven't found yet to cover that?)

My just doesn't look right issue was there's too much gap between the tires. I had it at about 5 mm, which turns out to be too wide. I reduced that to about 2-3 mm, we'll see how that looks on the next print.

Speaking of the next print, I just aborted it. I noticed on the slicer print preview that there were only 2 perimeter walls between the screw hole and the bore for the locknut, there should have been room for 3-4 perimeter walls there. Turns out I had used the clearance diameter of the screw, instead of the minor diameter. At least the print had progressed far enough that I could check the fit of the 12 mm driver - fits like a glove. Oh well, fix model, re-slice, re-print.

Don

Re: 1/16 Scale FrankenDiff
 

All educational opportunities, best way of learning. Strange though the way your slicer is doing scaling. I use Cura or PrusaSlicer, which is forked from slic3r, depending on which printer I am going to use and have never had that issue. When I size a cavity in one of my designs that's pretty much exactly what I get in the final print.

Re: 1/16 Scale FrankenDiff
 

OK, progress has been made - but it's been a LOT like doing the Hokey-Pokey. This is my current progress:
https://lh3.googleusercontent.com/pw...-no?authuser=0

From right to left we have the following:
1 - This is the cover for the locknut, The screws that hold this on will simulate the lug-nuts.
2 - This is the first version of the duals as described in Post #22. It didn't fit!
3 - This is the version that attempted to fix the issues from Post #22, it mostly worked. I tweaked the bores in the 3D CAD model by hand and realized this will be a royal PITA on a more complicated model - more on this later.
4 - This is my better idea, it ALMOST worked - more on this later also.
5 - Which you can't see, is bolted onto the other end of the axle and fixes the problem with #4.

This is the later. A couple of days ago I started a thread on another forum about slicer issues - with internal bores and pockets not being dimensionally accurate when scaled, here's the link:https://www.homemodelenginemachinist...-issues.36499/

I use Simplify3D for my slicer and I have always had to oversize the holes if I wanted things to fit together. It sounds like Cura has the same problem. I know from the diff housings that when I use S3D to scale the model to 103%, the external dimensions are within 1/4mm of the 120mm desired width of the housing - which is close enough. All of the internal bores and pockets measured too small though. The really confusing thing was that they were all too small by about same amount. They were all about 97% of the desired size. I got to wondering how the slicer was handling the internal bores and pockets when scaling, and if this was the problem with undersized holes all along. So, like Ford, I had a better idea. I took the task of scaling the part oversize, to allow for shrinkage, away from the slicer and gave it to the CAD program - which I reasoned was better equipped to handle the task. I reset the bores and pockets to their original values and scaled the part to 103% before I exported it to the STL file. #4 is the result, and it almost worked. Remember Major problem #2 from the above post? Yup, I do-ded it again. I didn't allow for any clearance Clarence! The 12mm hex driver would have been a press fit, and that's not good. I fixed the clearance issue and that resulted in #5.

Having wheels on both sides does tell me that I need to go back to the drawing board though. I currently measure about 200mm across the wheels and axle, I need to be at about 185mm. Now the question is where can I lose that 7.5mm on each side?

I added this image, to show that #5 exists and to show the gap between the duals. I think the gap looks about right. But I could shave a couple mm out of the gap, it's about 4mm-ish now. I could easily modify the wheel offsets 5mm and it wouldn't be too noticeable. I've got 100mm between the wheels now and the Bruder frame rails are 80mm outside to outside, so that leaves me a 10mm gap between the tires and the frame rail. If I move the wheels in 5mm that still leaves a 5mm gap, which should be enough for spring shackles and other odds and ends. I'll also have to move the angled transitions on the axle housings in 5mm, to give me a place to mount the springs, but that I'll fix when I re-do the pocket dimensions for the scaling fix.
https://lh3.googleusercontent.com/pw...-no?authuser=0

Re: 1/16 Scale FrankenDiff
 

Progress HAS been made! This is a family photo of the gang - so far.
https://lh3.googleusercontent.com/pw...-no?authuser=0

From back to front on the left side are:
1) The Kong axle with the modified rear wheels. I got my order of tires, so I can actually put tires on everything now.
2) The modified Frankendiff, still haven't shortened the axles though.
3) The prototype of the front axle - it still needs work. It's only got one wheel mounted because I don't have any more 5x9x3mm ball bearings. They are on order, should be here this week?
4) The other front wheel, with hub cover just laying in place.

On the right side are the next donor diff, and the left-overs from the donor front axle.

I've redesigned the rear axle's front and rear halves, making some minor tweaks.
1) I moved all the case mounting screw locations away from the axle bore, They were close enough to the bore that when the screws were threaded in, the inner wall would expand into the axle bore and bind on the axle.
2) I changed the angled transition to allow a convenient spot to bolt the springs to the axle.
3) I took the donor diff apart to see if the binding that I feel was coming from the spider gears - it was/is. There's no clearance in the gears. In fact if the screws that hold the spider gears cover in place are tightened down you can completely lock-up the differential. When I shorten the axles I'll take a little off the back side of the gears. That should make things work a little better.

The front axle needs a little help yet - it's 10mm too narrow. When I initially designed the front axle the plan was to use the steering arms, spindles and king-pins from the donor axle, which measured 205mm outside to outside. I need 175mm-ish, so I had to take 30mm out of the axle. The donor axle had spring perches that are spaced 80mm apart, which is right where I need them, but I need to lose 30mm somewhere. So I played with the design a while. This looked kinda OK on screen, so I printed it out. When I started to install the spindle assembly into the axle the spindle would flop around in the steering arm, they allowed PLENTY of clearance in this one Clarence! So, I am NOT going to use the original steering arms. While designing the new arms I came up with the idea of changing the front wheel offset by 5mm, to tuck the steering knuckle into the back of the wheel - so I did that too. And that my friends is why the front axle is 10mm too narrow. It's a simple fix and the axle only takes about 1/2 hour to print - just forgot about re-printing it.

Unfortunately the "Bag of Misfit Parts" continues to grow.

Don

Re: 1/16 Scale FrankenDiff
 

My 5mm ball bearing order arrived, so I put both front wheels on the axle. Here's a shot that shows a comparison of the overall widths of the axles.
https://lh3.googleusercontent.com/pw...-no?authuser=0

Well.... The rear axle is pretty close, and there's less than 1mm difference between my red axle and the silver Kong axle. But the front axle - not so much, the front axle didn't work exactly as planned. You know the old joke about cutting something off twice and it's still too short? Well, I printed the axle twice and IT'S still too short! Only this time I don't think that it's all my fault. I noticed that the display on my 8" caliper will periodically jump 5-10mm. All of the outside to outside measurements on the wheels are over 150mm, so I've got to use the 8" caliper. It's a Harbor Freight special, so we'll see how good the lifetime warrantee actually is.

Here's a shot that shows the size of the Lesu tires compared to the Bruder tires.
https://lh3.googleusercontent.com/pw...-no?authuser=0

This will probably be the first conversion victim. This will be one of the simplest, as in addition to forward/reverse and left/right, it will only require the drum to turn.(And maybe lights?)

Don

Re: 1/16 Scale FrankenDiff
 

I thought the "Bag of Misfit Parts' were to go with the "ghosts of projects future". Todays project doesn't need a 'Dr Seuss differential' with 7 pinions and 3 wheels, but who knows what might later? Or strap the bad parts to some pallets, now it's cargo.

Those axles & wheels are looking nice! Those seem to be a great fit on the bruder

That sucks about the measurements! The dial-calipers from Harbor are pretty solid. I've never messed with their digital calipers, because i don't really even care for digitals from good brands that are in a calibration program.

Re: 1/16 Scale FrankenDiff
 

I don't use the calipers for any critical measurements. Harbor Freight WOULD have replaced them, but nobody within 100 miles had any 8" calipers to replace them.

I tried using a spline in Alibre to get the curve I wanted on the front axle ends. I found out that they can behave unpredictably when you modify parameters, at least the way I used it they can. It would be nice if somebody would actually WRITE a user's manual.

Re: 1/16 Scale FrankenDiff
 

It doesn't always pay to buy cheap. I bought a Starret digital caliper for about $100 thirty odd years ago. Big money at the time. Other than having to replace the battery a couple of times it has worked great and is my go to for precise measurements. I have other measuring tools including analog and digital micrometers but the Starret is what I keep using. Was money well spent.

Re: 1/16 Scale FrankenDiff
 

I love the little 4" caliper that I got at HF years ago, but I think I just got lucky with it. I need a caliper that I can trust for a reliable measurement over 4", so I bought an 8" Mitutoyo last night.

Re: 1/16 Scale FrankenDiff
 

Yea, Mitutoyo makes very good measuring tools. I've got one of their digital micrometers. Dang thing will read down to like 0.00001 inch. Does like it's batteries though, always try to remember to remove battery if I'm not going to be using it for awhile.

Re: 1/16 Scale FrankenDiff
 

My digital angle gage is hard on batteries too, and it goes through three 2032's at one time.

I'm waiting on more parts to arrive, I was looking for a replacement pinion so I could build my center axle. Turns out the only way I could find the pinion was either as part of the replacement differential assembly, or as a complete rear axle. This diff assembly was only a couple of bucks less than the entire rear axle, and didn't even include any bearings. So I ordered enough rear axles to be able to do the next truck too. I've got some square aluminum tubing coming that I'll split and use for the frame rails, also got enough of it for the next truck.

While I'm waiting, I'll start on the rear suspension. I plan on making something like a Hendrickson Walking Beam suspension. I downloaded their tech manual last night and it's got enough illustrations that I've got a pretty good handle on how things are supposed to go together.

I do know that I'll need to make a couple of minor modifications to my axle housings, to give me locations to mount the axle brackets for the equalizer beam mounts, and the torque rod mount.

Don

Re: 1/16 Scale FrankenDiff
 

Don - sent you a private message.

Re: 1/16 Scale FrankenDiff
 

For the last couple of days I've been playing with assemblies in Alibre. So far I'm batting 1000, I've managed to break every one of them that I've tried - but I'm learning from my mistakes. That doesn't mean I'm making less mistakes, it just means that when they happen now they are WAY more impressive. This is my latest test assembly, I'm still trying to figure out how to save the current view.
https://lh3.googleusercontent.com/pw...-no?authuser=0
I hope I didn't screw up the previous posts, when I previewed my post I noticed that I hadn't scaled the image for posting. Somehow instead of deleting just the unscaled image, I managed to delete the entire Frankendiff album. I put it back, reloaded the photos, and shared it again - hopefully all is well. Where's the EASY button when you really need it?

Now all I've got to do is figure out how to get my spring hangers, springs, and equalizer beam center pivot to fit into a 32x65x10mm volume.

Don

Re: 1/16 Scale FrankenDiff
 

Assemblies in Alibre can be one of the more frustrating things to do in that program. If two parts are off by only the smallest fraction of an angle, they won't go together. If two holes are out of alignment by as much as half the thickness of the hair on fly's ***, they cant be made concentric. Absolutely no more than three constraints on any component. Always anchor one of the first components you add, otherwise you chase components all over the screen. You can add constraints between components and planes or axis lines as well as other components. With constructions that have a lot of components make small sub-assemblies and then assemble the sub-assemblies. Sometimes you just have to try a number of different constraint configurations to find one that works.

The real nice feature of assemblies is that you can edit individual parts, or create new parts, from within the assembly. For example in the assembly you posted, if you want to add a cross member to your frame you can create the cross member, put it in position where you want it and then edit the frame rail to put the mounting holes to match the location of the holes in the new cross member. When you save the assembly the cross member will be saved as a new part file and the frame file will be updated with the new holes. FM

Have fun.

Re: 1/16 Scale FrankenDiff
 

Zabco:

I found about the sub-assemblies after about the 2nd or 3rd time my suspension assembly tried self-destructing the axle on me. I tried to pivot the axle around the equalizer beam pivot, and just about every part of the rear axle moved separately - and I couldn't undo it. The rear axle, the center axle, the equalizer beams, and the torque rods are all separate sub-assemblies now. I did discover that when you insert sub-assemblies they are rigid until you tell them to be flexible. It took me a while to find out why the axle beam mount brackets would pivot in the equalizer beam assembly, but when that sub-assembly was inserted into another assembly they wouldn't pivot.

This frame is just a test jig so I haven't made it a sub-assembly. It will be a sub-assembly when I start working on the actual frame though. The frame rails shown are sized to the 1-1/4" square aluminum tubing with 0.063 walls that I got. The rails and the cross-member are the only parts that are currently anchored.

I've been poking and prodding at my current suspension assembly so much that I've gotten it completely confused. I think I am going to throw this version away and start fresh - and LEARN from my mistakes, instead of repeating them. That's tonight's task, now I've got to finish the yard work.

Don

Re: 1/16 Scale FrankenDiff
 

All educational opportunities. What I love about all this. Keeps my brain functioning.

Re: 1/16 Scale FrankenDiff
 

I've given up on making a functional suspension assembly - at least for now. It seems like every time I add another part to the assembly, and try to constrain that part, it breaks a half a dozen other constraints. For now I'm just going to use the assembly to provide feedback for the design of the beam pivots, springs, and spring hangers. I already found out that I'll need to make spacers for my torque rods, to get them to the correct length. My torque rods are a pair of M3 ball links that are screwed together with M3 threaded rod, and a 1/16" spacer between them.

I know that when the axles articulate, things are going to want to twist around. That's why they use the rubber bushings on the real deal. I've been wondering how I could easily duplicate that. I first thought of using silicon fuel tubing, but quickly scratched that idea - the tubing was too thick. My current plan is to use O-rings with a 1mm cross section, on both sides of the equalizer beam. I'll use a piece of brass tubing as a bushing. The bushing will also keep the threads of the mounting bolts from cutting into the plastic parts or the O-rings. If I oversize the 3 bores in the equalizer beam, that'll give it a little room to wiggle around when the axle articulates - I think.

I guess the proof will be in the building.

Don

Re: 1/16 Scale FrankenDiff
 

If the Oring idea doesn't work out, you might be able to build up something like a bushing with Heatshrink tubing.

Re: 1/16 Scale FrankenDiff
 

Progress is being made, even if I don't have any pretty pictures to prove it. (I forgot to get a snapshot of the suspension assembly before I called it a day.) I will try to update the assembly drawing tomorrow, there's a bunch of stuff that's been added. I've added the cross-member that supports the frame end of the torque rods. I even edited the cross-member to put the holes for the torque rod bracket mounting bolts in the right spots. I've added the torque rods, the torque rod brackets on both the axles and the cross-member. I've added the spring hangers, springs, and spring perches - though they've only been added to one side so far.

I've kinda figured out how I'm going to make the leaf springs. The current plan is to sacrifice the tines from an old lawn broom to make the spring leaves. The tines are about 5mm wide and 0.5mm thick. The SEEM pretty flexible, but they still may be entirely too stiff.

I'm debating whether I want to try making U-bolts for the springs or not. I've got a bunch of bike spokes left over from re-lacing a couple of 20" bike wheels for another project. That would give me plenty of raw stock for making the U-bolts. For a limited production run like this, 3D printed forming dies will be up to the task.

Don