Re: 1/16 Scale FrankenDiff
 

Regarding the Sherline carriage lead-screw issue, when I started taking it apart last night I discovered that the issue went away when I took the hand-wheel off. Upon closer examination of the hand-wheel and the lead-screw shaft I found a nick on the face of the hand-wheel and a burr on the lead-screw. The burr on the lead-screw was caused by the grub screw, but I've got no idea what could have caused the nick on the hand-wheel. I stoned off the raised areas and when I reassembled things that particular problem was gone.

I've been plottin' & conivin' for a while as to how I can adapt the Frankendiff into a powered steer axle. Blender's build of a 1/14 scale TH407C telehandler gave me the idea I needed. He used Losi CVD front axles to build his steer axles. Since I've already got a butt-load of the WLToys 12428 replacement rear axles I decided to get a set of replacement front axles to see if they'd be usable. After doing a little (very rough) 3D modeling, it looks like things will work out. They both use a ball and socket joint in the knuckle, but the Losi uses a CVD joint while WLToys uses a CVA joint. A CVD joint has the ball on the axle with the socket on the half-shaft. A CVA joint flips that around and has the ball on the half-shaft with the socket on the axle. Here's a picture of the WLToys CVA joints.
https://lh3.googleusercontent.com/pw...-no?authuser=0
At the top is the assembled CVA joint, in the middle is the axle with the socket, and on the bottom is the half-shaft. At the left is the dog-bone that would normally attach to the front diff. This 14mm section on the left is totally useless to me, I only need about the last 25mm on the right. The center section of the half-shaft currently has a 3.18mm OD. My current plan is to turn part of the center section and part of the tapered area just to the right of it down to a 3mm OD. This will then be Loctited into the outboard end of the modified donor axle, just like I did when shortening the donor axles for the rear diffs.

Edit: Due to the black finish I was worried at first that the axles might be hardened. However when I checked them with a file I found out they aren't. The dog-bone section was easily removed with a hacksaw.

Re: 1/16 Scale FrankenDiff
 

Lord only knows what happened to the site this time. Was completely gone this time, not even any html code showing up when I tried to inspect the site. Glad to see it's back though and hoping it holds together for awhile yet. Still the best site for real information about building trucks and equipment.

Your axle really looks good Don, great job! Also sounds like you've got a good handle on the steerable axle as well. Can't wait to see how it comes out.

As to the Sherline, I'm glad to hear that removing the burr on the hand wheel fixed the problem. Thought you might have a bent lead screw when I started reading. Don't know about the bearings. Sherline claims they are lubed for life. Course no accounting for what the previous owner did to it. May want to drop Sherline a not asking about it.

Re: 1/16 Scale FrankenDiff
 

I was afraid I had a bent lead-screw too. Yes the bearings are supposed tp be lubricated for life, but, they are shielded bearings - not sealed. If they sit for several years without being used, the grease will dry out and harden. According to the part number they are standard precision bearings. Once upon a time in the west I used to repair machine tools for a living, so swapping spindle bearings is not outside my comfort zone. At least now the parts are a LOT lighter, and they're not covered in nasty smelling coolant.

I just got done modifying the first CVA half-shaft.
https://lh3.googleusercontent.com/pw...-no?authuser=0
The modified half-shaft is just slipped into the brass tube for now, I'm just getting started on the working 3D model that will be used to print the parts. I've got bushings and shoulder bolts on order for the knuckle pivots, so I can accurately model things now. I model things in mm because that's how most 3D printers think. I really wonder sometimes when reverse engineering this stuff, some of the measurements make no sense. Like why is part of the half-shaft turned to 3.18mm, and why is the socket bored to 7.62mm. Earlier today it finally dawned on me, 3.18mm is 0.125", and that odd 7,62mm bore is 0.3". When I convert all the odd Metric measurements to Imperial units they come out nice and neat.

Re: 1/16 Scale FrankenDiff
 

I spent most of the day yesterday fighting with Alibre locking up. I'm trying to do the final 3D design for the powered steer diff parts. The design I showed a couple of posts ago was quickly thrown together to see if I could even make it work. NOW I need to cross the I's and dot the T's so that it will all work together, and that means accurately modeling all the individual parts. That's actually a good thing as I found a couple of gotchya's while doing it.

One of those gotchya's was determining how much I needed to shrink/stretch the ends of the diff front and rear housings to accommodate the single front wheel instead of the dual rear wheels, and still maintain the same wheel track. It turns out I needed to take 13.5mm off each side. I know that doesn't make sense that I need to move the end of the diff housing inboard when going from duals to singles, but I spent a couple hours convincing myself that moving things 13.5mm inboard was actually right.

The second gotchya was when I realized that the screws holding what I'm calling the diff pivot in place (that's the part where the steer axle pivots in order to steer) would be hitting the outboard bearing - that would not be good. So I had to change the design of the diff pivot, it's now about 6mm longer. THIS change interfered with the outboard screws holding the front and rear diff halves together. Since the diff pivot slides over the ends of the front and rear diff halves holding them together, those screws aren't really needed any more. Problem solved, but I did have to change the 3D models for both halves to reflect this.

The third gotchya is what does the length of the brass tubing splice need to be? My modified rear axle measures 147mm from end to end. My modified axles were 70mm nominal in length, so that means the spider gears were occupying 7mm of space in the middle. My 3D printed non-powered front axle needs to be 172mm from end to end. If I subtract the 7mm for the spider gears, and divide by 2, the stack-up for my front axle length should be 82.5mm? (Why do I feel like Rodney Dangerfield in "Back to School" right now?)

Plus I realized that there's nothing keeping the outboard bearings of the steer axle from sliding outwards. On the rear axles the hex driver holds the bearing in place, on the front axle there's nothing but air in that location. Oh well, that's a problem for future me to solve.

Don

Re: 1/16 Scale FrankenDiff
 

Don't you love it. Think you got one simple change to make and it cascades into an avalanche. Good thing this is a hobby, I'd hate to have to charge someone for the time involved in some of these changes.

As to your bearing problem. Would it be possible to cut a small groove in the axle shaft just outboard of the bearing and install a C or E clip to act as a stop. This is how the bearings in Tamiya trailer axles are held in place.

Re: 1/16 Scale FrankenDiff
 

Somehow today I did something stupid. I must have changed the font size or something for this site because the text on this website is now huge. But it's only on this website, any other website appears normal, and I've got no clue how to get this back to normal.

Re: 1/16 Scale FrankenDiff
 

Never-mind, I figured it out. Somehow I had bumped the Zoom up to 200%.

I'm still fighting with Alibre's assemblies, trying to figure out what I can and cannot do with it. (I think part of the problem is that I'm NOT modeling any mechanical fasteners. This just might be what's driving Alibre up a wall.) This is a shot of the suspension assembly up to this point with the front axle just hanging out in mid air - things are shown at the approximate ride height.
https://lh3.googleusercontent.com/pw...-no?authuser=0

I've got the front diff mostly complete internally, I've got the flexible CVA axles & half-shafts modeled. I haven't completely modeled the brass tubes and inboard parts of the axle shafts yet. I do have the brass tubes modeled to give me a nominal over-all axle length of 82.5mm. I did this as a sanity check to see if I had about 7mm between the axle ends like there was with the rear diffs. The distance between the axle ends measures 7.143mm - as Mr. Miagi would say "CROSE ENOUGH!"

I'm working my way out now, I've got to design the steering knuckle/steering arm widget. I've got a rough idea of what will work, but I need to refine it. It needs to fit the tie-rod in so that it clears both the top on the pinion cover, and the bottom of the frame rails - with some clearance to allow for suspension travel. Now I need to find the specs on the bushings and shoulder bolts I ordered - so I'll know what modifications they will need.

Don

Re: 1/16 Scale FrankenDiff
 

Ugh, this sounds like a whole lot of fun.

How often are you stopping to take a break to push that Bruder truck around while making engine noises?

Re: 1/16 Scale FrankenDiff
 

That phase will probably start when I actually begin bolting pieces to the frame rails. Instead of just making making pretty pictures on the monitor.

Re: 1/16 Scale FrankenDiff
 

I think that I just might be starting to get a handle on this Alibre assembly crap.
https://lh3.googleusercontent.com/pw...-no?authuser=0

You are looking at a functional 3D assembly model. I can spin the wheel on the axle. When I turn the steering knuckle the wheel moves with it, and the tie-rod brings the knuckle on the other side along for the ride.

I did have to give up on the idea of putting the tie-rod above the drive shaft though, there just wasn't enough room. Where it is currently located the tie-rod is about 4-5mm below the driveshaft and won't touch any thing trough its' full range of travel. The bottom of the tie-rod is still above the bottom of the differential though so the tie-rod shouldn't get caught on any thing.

Re: 1/16 Scale FrankenDiff
 

Wanted to reply to your post on the 28th Don but I was at the Lafayette RC truck show this weekend and only had access to open public wifi and I don't like submitting passwords over those.

Alibre's assemblies can be a huge PITA. Most times they fall right in place and other times they just aaaarrrrrggghh. A few things I've learned about them over the years.

You can only have 3 constraints between any two objects or assembly.

Sometimes just changing the order you create the constraints will make a difference.

Under each part listed on the work history on the left side of the screen will be a list of each constraint you created for that part as well as a list of all the constraints created for the assembly as a whole. If a constraint has failed for some reason it will be shown in red. I usually just delete these as they can cause confusion when trying to figure out how things went together.

Get one part in place, usually 0,0,0 and anchor it. If you don't you run into the possibility of parts suddenly flip, flopping around and you can't figure out how the heck that happened. And usually the only way to correct it is to delete parts and start over.

It's often easier with complex systems to make parts into sub-assemblies and then assemble the sub-assemblies in a final assembly. But there is a catch to this method. In your last post as an example, you explained how you had the steering knuckles and tie rods able to move back and forth. If you were to make that drawing a sub-assembly and then add it to an assembly of say, the entire frame, those knuckles and tie rod will no longer be able to move. They will be frozen in whatever position they were in when you last saved the file. Only parts added in the current assembly will be able to move.

I don't know to how many decimal places Alibre takes their precision but it must be quite a few. If you try to constrain two parts and the difference in distance or angle is off by the slightest amount they will not go together. For example if I want to assemble a cross beam to a frame and they both have a square 4-hole layout that bolts would be put through to bolt the parts together I would probably assemble them in Alibre by first mating the two flat faces together, then make a coincident constraint between two of the holes in the frame and the bear. But the parts would still be free to move about each other around that bolt hole. To fully fix the beam in place I need to add a third coincident constraint between another pair of bolt holes. Three point of constraint and the two parts can't move in relationship to each other. But when I designed the beam I got the distance between the two pairs of holes .0001mm shorter than the same pair of holes in the frame. Such a tiny amount of length that you couldn't see it in the real world and a bolt would still easily fit, Alibre won't accept it. Round-off errors if you do your math outside of Alibre can cause a real problem. I don't know of any setting that you can change to allow a certain amount of 'play' between parts. The same is true when trying to mate parts with angled surfaces that are already constrained to other parts.

The nice thing about the assembly window is that you can create new parts or edit existing parts within the assembly. In my example above where I can't make the third constraint because of the slight difference in distance I could edit the beam by deleting the holes in the beam, place new holes on the face of the beam and make them individually coincident with the holes in the frame and then do an extrude cut on the beam. Perfect match, constraint made and when I save the assembly file the part file for the beam will be updated.

If all else fails, make a plane and use it to constrain a part. Planes have to be created relative to another plane, face or line of an object. So Alibre knows exactly where the plane is located. You can then do a direct of offset constraint between the plane and the part or sub-assembly you are having problems with.

Re: 1/16 Scale FrankenDiff
 

Constraining things to a plane is what I do - sometimes.

I placed an axis in the centerline of the axle bores, and I've got an axis on the pinion shaft centerline for each axle. The origin for my suspension assembly is the tail end of the center of the frame rails at ground level. I've got offset planes where the center of each axle shaft should be located. I've also placed a plane at the ride height. I've constrained the axles so they can move vertically along the locating plane and the pinion axis is constrained to the YZ plane, this keeps the axle where it belongs front to back and side to side.

I constrain the axle shaft axis to the ride height plane when I initially place the parts/sub-assemblies. When I want to check suspension clearances I suppress that constraint. When working in the various sub-assemblies I will constrain the various parts to get them properly oriented, anchor the part, then delete the effected constraint/s.

I did something similar with the front axle assembly. When I was initially placing the CVA axle and the CVA half-shafts their axis were constrained to be coaxial. Once I had everything placed properly I suppressed the coaxial constraint, and constrained the axle so that it could pivot around what are effectively the king-pin bushings.

I stumbled across a "Flexible" check-box and hoped I'd found the mother-lode regarding the "moving" sub-assembly parts no longer moving issue. Alas, there was no joy in Mudville that night since it made no difference. I've been doing a little digging on-line and it seems that I was on the right track.
That option IS supposed to fix the no longer flexible issue - but it doesn't always work.

I was able to use the assemblies to check clearances, what broke the rear suspension assembly was trying to get the walking beam to play nicely. I'm pretty sure the full scale rubber bushings are there to absorb any minor alignment problems, and I've got silicon O-rings to substitute for those bushings in the model. I just don't think Alibre assemblies were designed to simulate something like that.

Re: 1/16 Scale FrankenDiff
 

Sounds like you have a real good handle on the assembly process in Alibre. Just wish it all would work. Where is this 'flexible' check box? I don't recall ever seeing such a thing. Or is it only in the full blown version and not in Atom?

Re: 1/16 Scale FrankenDiff
 

I've got Design Pro V22, so I don't know about Atom. In Design Pro if you right click on the assembly in the Design Explorer, you get a drop down menu - Make Flexible is one of the options in that menu.
https://lh3.googleusercontent.com/pw...-no?authuser=0

Don't know if that helps.

Re: 1/16 Scale FrankenDiff
 

It does indeed, last place I had thought to look. Had gone through all the preference menus and couldn't find anything. Will have to do some experimentation as I have never tried it. Weird in that I use the functions on either side of it all the time and never really noticed it.

FYI - I talked with Travis Biddle while at the Lafayette RC show this past weekend. Travis is the guy who owns this web site. Asked him how much longer the site will remain active. He didn't say when it would go dark but that it's days were probably numbered. Lack of use, number of known bugs in the program and no one wanting to hose forums anymore. If you want to save anything you've posted on here you better back it up somewhere. I've always kept copies of my postings and thankful that I never used photobucket for my images. I'll keep coming in here till it goes down but I am considering options. I already am a member on Scale Builder's Guild and they have a section for trucks and equipment. And I know there are a couple of other similar sites. Wait and see what happens.

Re: 1/16 Scale FrankenDiff
 

I know that Blender, Frizzen and I have all posted over on the Semi Truck and Construction Equipment forum of RCGroups. I'd never heard of the Scale Builders Guild until now, I just registered there. I'll have to take some time and go through it later. I never used Photobucket either, but they sure did screw up a LOT of forums.

Re: 1/16 Scale FrankenDiff
 

The two programs are pretty much the same. I've still got a copy of Cubify Design (from when 3DSytems owned the software) and it works the same way. I played around some today with the 'flexible' function. It does work but is somewhat persnickety about how you set up the assembly. I drew up a basic engine using 3 cylinders with wrist pins and connecting rods. A piston with connecting rod and wrist pin was created as one assembly. A crankshaft with 3 - 120 degree connecting shafts as a part, and a basic engine block as the third component. Started a new assembly by bringing in the crank and constraining it to the Z axis and centered on 0,0. Then imported three copies of the piston assembly. First I connected each piston without enabling flexible to the crankshaft with a vertical constraint. As expected, the assembly locked up with the second piston and would not rotate. Next I enabled flexibility. Connected first piston assembly to crankshaft and constrained to vertical position directly over center of crank. Piston would move up and down with crank rotation. Added second piston same way and crank would rotate. Thought that this was going to work ok. Added third piston and the assembly locked up and would no longer rotate. All three pistons were in alignment and connecting rods were free to swing back and forth. Happened to glance at left hand column and noticed I had a number of constraints shown in red meaning they were bad.

Thought about what was going on and came to realization that I was over constraining the piston assemblies. What I forgot is that they already had some constraints carrying over from their original construction. Adding the three additional constraints placed on them in the new assembly and they froze. Deleted the piston assemblies and all their related constraints. Imported the engine block and centered it in X and Y over the crankshaft and anchored it in place. The engine block would serve to align each piston directly over the crank, properly space each piston along the crank and serve as the vertical guide for the pistons. Add each piston assembly back, enabled flexible, put concentric constraint between each piston and cylinder bore and a concentric constraint between crank and connecting rod. That's all, no other constraints. Added other two piston assemblies in same manner. "Grabbed" the crank and gave it a twist and it spun with all pistons going up and down as the should. So the 'flexible' function does work but you just have to be very careful in how additional constraints are applied. And, I think, not constrain part that will move to planes or axis.

Re: 1/16 Scale FrankenDiff
 

For the last couple of days I've been working on Sherline mods. One of the mods I did earlier was to add some cheap Chinese scales with remote readouts to the carriage and cross slide, that was a game changer. But I learned some things about those scales that I wasn't happy with. First, they're battery powered and no AC adapter is available. My scales also do not have an Auto-Off feature. I don't know how many times I've gone down to the shop the next day only to discover I'd left the stupid things on. The most aggravating thing is that the carriage scale will periodically reset to zero.

I did some research and found out that the Shahe clone scales, which is what these are, can be sensitive to electrical noise - there's no shielding on these things. I did mention they were cheap didn't I? 'Cause I got two 8" scales for 36 bucks and change, including shipping. I am replacing them with Igaging EZ-View Plus scales which have better resolution, shielded cables, and an available AC adapter. I got a 6" scale, a 12" scale, and the AC adapter - all for about twice the price of the Shahe clones. As an added perk, Igaging actually gives you instructions on what scale functions are available and how to use them.

I was having trouble wrapping my head around what everything would look like, so I decided to 3D model it. For the last couple of days I've been modeling my Sherline's bed, the base I've got it mounted on, the carriage, the cross-slide, the new 6" scale and read-head, and the new 12" scale and read-head. I modeled the scales and read-heads as separate parts so they would work correctly in the assembly. Once I got the parts modeled it was time to start arguing with Alibre about what I can and cannot do with constraints in assembly drawings. I've learned some lessons from the other assemblies I've done about being methodical and renaming the constraints to something that will make sense to you in the future.

I added the base to the assembly and then I anchored it. I then added the Sherline bed, and used offset constraints to position it. Then I anchored it also, and deleted the constraints I broke when I anchored the parts. I added the carriage and used coincident constraints on the dovetails to keep the carriage in its' proper location. I then added an offset constraint between the carriage and the headstock end of the bed, and played with the limits until I had the carriage restricted to it's normal movement. I did the same for the cross-slide and got the carriage and cross-slide working together as they should.

Then I started adding scale bits that were just hanging out in mid-air; getting them to move like they should without breaking anything else. Once I had everything dancing about in a coordinated fashion I started designing the brackets that would connect Tab A to Slot B. This is where I'm at now.
https://lh3.googleusercontent.com/pw...-no?authuser=0

I've still got to finish the design of the bracket that ties the cross-slide scale to the cross-slide. The cross-slide read-head is fixed and the scale moves through it. The carriage is the opposite with the scale fixed to the base and the read-head moving on it. I still have to design the brackets that will anchor the carriage scale to the base. I just noticed that I never modeled the two existing screw holes in the carriage. I'm going to use those screw holes to mount the read-head bracket. I'll need to reposition and redesign that bracket to use those screw holes. I guess I'll have to send a change order to the customer for the extra engineering time.

Don

Re: 1/16 Scale FrankenDiff
 

The iguaging scales are very popular in the home machinist hobby world. If you want an even better readout google 'yuris toys'. Yuri developed a, relatively, inexpensive way to combine the scales with an old android based tablet and some and some additional hardware to create a very good DRO for lathes or mills. Has his own forum on the www.hobby-machinist.com website.

Re: 1/16 Scale FrankenDiff
 

The new Igaging EZ-View Plus scales use a different protocol than their older DigiMag scales did. I know Yuri is working on it but I'm not sure if he's got his Touch DRO working with that protocol yet.

I got the 3D design done done for the lathe scales and printed the parts out last night.
https://lh3.googleusercontent.com/pw...-no?authuser=0

The 2 parts that I couldn't design any adjustment into are the ones that don't fit. Turns out it was operator error, I didn't model them correctly. I fixed the models and the parts are re-printing now, they should be done in a couple of hours. Then I can start installing the new scales.

After that, about the only thing left for Sherline modifications are new headstock bearings, which arrived in the mail today.

Re: 1/16 Scale FrankenDiff
 

The scales upgrade on the Sherline is mostly complete. Here's what things look like from the front.
https://lh3.googleusercontent.com/pw...-gm?authuser=0
As you can see, I'm no longer losing 35-40mm of carriage travel at the tailstock end due to the cross-slide scale. And the cross-slide scale is no longer a shelf where chips and dust will accumulate. That cute little 000 Phillips screwdriver on the lathe base and two extra screws came with the scales, you need it to open the battery cover.

This is what the back side of the scale install looks like - from the headstock end. The carriage scale in no longer a wide shelf that chips and dirt will land on. Both the cross-slide and the carriage scale have the actual "scale" facing away from the spindle, so they aren't directly exposed to hot chips.
https://lh3.googleusercontent.com/pw...-gm?authuser=0
That black object on the LH side of the cross-slide read-head is an end stop. Before I installed that, it wasn't uncommon for me to retract the cross-slide far enough to disengage the lead screw from the lead nut. While that wasn't a show-stopper, it was irritating. That won't happen any more.

This is the temporary location of the displays.
https://lh3.googleusercontent.com/pw...-gm?authuser=0
The brackets that came with the scales didn't work for me. They allowed you to swing the display from side to side on an arm that was 8-9" long. They did not allow any tilting of the display for a better viewing angle. I 3D printed a pair of stubby arms, about 2" long, that allow me to tilt the displays to the best angle - whether I'm standing or sitting.

There's still a few things on the To-Do list:
1) Find a more permanent home for the displays. Right now I'm leaning toward mounting them on the peg-board using some of that brown non-conductive organic material - probably about where the pin-punch set is hanging behind the 3-in-1 oil.
2) Do some cable management, not gonna get crazy with the excess cable like I did the first time. Behind the peg-board is a blocked off door that at one time went into the coal-room, for when the boiler was coal-fired. I may just let the extra cable hang in that space, it's not like I can actually use the space for any thing else.
3) I've got to find another plug and get the AC adapter modified so it will be able to power both units. Somebody might already make a Y-adapter in the right size, I'll have to check Digi-Key and Allied-Electronics to find out

Like Superfast Matt I tend to get things to the point where I can use them, then they never truly get finished. But they are good enough to use, and right now this one is "Good Enough".

I've also got the replacement spindle bearings for the Sherline, I got tapered roller bearings to replace the noisy deep-groove ball bearings, That project is on the "Someday" list too.

Don

Re: 1/16 Scale FrankenDiff
 

Looking good Don. Like your solution to handling the cross slide scale. Can those scales be trimmed to shorter lengths?

Re: 1/16 Scale FrankenDiff
 

Yes they can be trimmed. I cut about 3" off the original scales with a hacksaw. That got the job done, but the epoxy/glass board the actual scale's on was tough to cut. I used an angle grinder and the spinning wheel of death to cut the Igaging scales, that went MUCH easier.

I found that Igaging uses SS instead of aluminum for the scale support bar, so the cut-off wheel was probably a good choice. Because I reconfigured the cross-slide scale I was able to shorten the Igaging by about 1-1/2". But I started with a 6" Igaging scale, not an 8" like the original scales.

Re: 1/16 Scale FrankenDiff
 

Thanks Don. Have thought about doing similar to my lathe. Couldn't do the cross slide like you did. I bought mine set up for CNC and the servo mount prevents inserting anything into the the T-slots from the front. So can't plug up the rear access. Did come with the zero reset hand wheels which helps, don't have to remember what setting I started from.

Re: 1/16 Scale FrankenDiff
 

At one time I was considering putting the carriage and cross-slide scales parallel to each other. I was thinking of using something like a Sullivan Gold-N-Rod to link the cross-slide to the scale, to simplify making the 90 degree turn with the linkage. If I remember correctly the outer casing is only about 1/4" in diameter. Something like that might work for you.

Re: 1/16 Scale FrankenDiff
 

Further development on the steer axle is on hold for a week or so. The motor/2-speed gearbox, that I initially wanted to power the model with, uses a single 370 sized motor and has 3mm output shafts. While the 370 sized motor MIGHT have been up to the task, I don't think the 3mm output shafts would have been - since all of the differentials have 5mm input shafts.

I've got an LDRC LD1201 Unimog replacement motor/gearbox ordered. It uses a pair of 370 size motors driving a 2-speed gearbox with 5mm output shafts. One of the outputs looks to be centered, and the other appears to be offset to the side. If it is offset then I'll have to slide the pumpkin to one side on the front and rear housings for my steer axle. Unless I can find some drawings on-line, I won't be able to do any more work on the steer axle until I can get some measurements from the gearbox.

Re: 1/16 Scale FrankenDiff
 

That is a very interesting idea. I've never used a Gold-N-Rod before as i've never been into airplanes but know what they are. Thanks Don, gonna have to do some thinking on this.

Re: 1/16 Scale FrankenDiff
 

No problem.

A gentleman on HMEM suggested that if I lowered the cross-slide read-head I would free up that back corner of the cross-slide for normal use. I already had everything printed by that time and didn't feel like re-designing it - AGAIN. If I ever do this again, I'll probably hang both read-heads at the level of the carriage scale with both slides parallel. Then I'll use the Gold-N-Rod trick to actuate the cross-slide scale. I just had a thought, is the "Make Flexible" check box in Alibre to simulate a connection like a flexible pushrod?

Re: 1/16 Scale FrankenDiff
 

I don't think the 'flexible' option would work for something like that. It only allows movement in sub-assemblies function in another assembly but only within the limits of the applied constraints. You could model and move a straight line movement like a piston rod in a cylinder because it only moves in one axis. No way that I know of for it to model movement through multiple bends. Would be kind of neat though.

I really need to have access to both T-slots in my cross slide as I usually have my cutoff tool mounted in slot closest to head stock so I can get it as close to chuck as possible. Often have to have my QCTP in back slot depending on tool holder being used so, again, I can get cut off tool as close to chuck as possible.

Re: 1/16 Scale FrankenDiff
 

It doesn't really matter about the "flexible" setting, that was just one of those wild-haired ideas that smack me in the head once in a while - kinda like Gibbs and DiNozzo.

Re: 1/16 Scale FrankenDiff
 

Wilf on MEM got a flexible pushrod to work using SolidEdge 2025. I don't think my version of Alibre has the brains, or the brawn to handle it.

Anywho...I updated the 3D model of the chassis to use the appropriate frame rail lengths, and axle spacing, for Bruder's MAN mixer. The thing's starting to look more like a truck now, I've hidden the passenger's side frame rail so things are easier to see. I've also included the motor/gearbox so I could re-design the steer axle pumpkin location.
https://lh3.googleusercontent.com/pw...-no?authuser=0

That's done now, and we need to be verwee-verwee quiet, because we're hunting drive shafts. However, I'm having about as much luck finding one that will work as Elmer ever did getting the wabbit. I've got a couple different flavors of SCX10/TRX4 drive shafts on order, to see which will be easier to modify to fit. It would be nice if somebody made flange mount U-joints, but I don't see that happening - and I'm not building a museum scale model.

The center axle to rear axle drive shaft is the real problem. In order to be able to install that shaft WITHOUT removing an axle, that sucker needs to collapse down to under 39mm. It looks like I might as well be hunting for Unicorns. I'll probably just have to resign myself to the fact that shaft will need to be installed WITH the axle.

Don

Re: 1/16 Scale FrankenDiff
 

OK, I've found out that I'm going to have to revisit my chassis design a little. So far I've been sticking to the measurements taken off the Bruder MAN mixer, but that's gonna have to change a little. I'm going to have to modify the axle spacing/locations a little. I cannot find an off the shelf axle that will fit the existing center axle to rear axle spacing. I currently have an absolute minimum drive shaft length of 42mm. When you add in the 7mm I need to be able collapse the drive shaft to take it out. then I need a drive shaft that has a minimum length of 35mm. I was able to find drive shafts in the 30-36mm range, but they only had a 2mm ID with a 6mm OD. Nope, that ain't happenin'. I did find a Lesu drive shaft with a 5mm bore in the 45-50mm range, and have one headed my way. It costs 3 times as much as any of the other drive shafts, but none of them can be made to fit.

My current plan is to add 5mm to the spacing between the center and rear axle, and play with their locations a little so I don't mess up the drive shafts coming off the transfer case. By adding the 5mm to the axle to axle spacing, I SHOULD get into the middle of the range of motion for the Lesu drive shaft. Unfortunately it also means that the drive shaft and the axle have to be installed/removed as a unit.

Re: 1/16 Scale FrankenDiff
 

Well hopefully you won't have a need to remove the rear axles very often, if ever. Can't remember the last time I had to remove one of mine, or even mess with the drive shaft itself.

Re: 1/16 Scale FrankenDiff
 

Don, in your driveshaft search did you run across any with a 4mm bore? Been looking for another project, but haven't seen much. Everything is 5mm that I found, or 4mm/3mm mismatch.

Re: 1/16 Scale FrankenDiff
 

Blender:

I sure did. Here's an Ebay listing with 5mm, 4mm, 3mm, and 2mm drive shafts - but they call them "steering shafts".
Drive shafts

The LDRC Unimog twin motor/gearbox that I'm using has 4mm output shafts, the WPL motor gearbox that I originally planed on using had 3mm output shafts. Since all of my axles have 5mm input shafts, I thought the WPL gearbox might have been a little on the wimpy side.

Don

Re: 1/16 Scale FrankenDiff
 

That's perfect! Thanks. Even has some length options.

Re: 1/16 Scale FrankenDiff
 

One difference that I did notice between the 2 different sets of drive shafts I ordered is that one of the manufacturers wasn't particularly careful about getting the U-joints clocked properly. One of their drive shafts is OK, but the other is about 10 degrees off. I know on a full-sized vehicle, that WILL cause vibration issues. On a model that may not matter, but why chance it?

Re: 1/16 Scale FrankenDiff
 

I have found out that I needed to slightly modify my Frankendiff pinion housing design. The hole for the drive shaft's drive pin wouldn't line up with the hole in the pinion shaft. I must have fat-fingered a dimension because the outer bearing needed to be moved 1mm toward the axle shaft. I just had to decrease the extrusion that formed the nose of the pinion housing from 9mm to 8mm. While I was at it, I went back thru the design and removed anything that I'd done to optimize the design for FDM printing.

I've got a resin printer now and one of these days I gonna hafta put on my Big Boy pants and actually USE it.

Re: 1/16 Scale FrankenDiff
 

Sometimes I think Quality Control is a totally unknown concept in certain parts of the far-east. Some of the stuff is high quality, but there are a LOT of times when what you actually get is a kit of mostly usable parts. ALL of the SCX10 rear axles I ordered came from different vendors, but apparently the same supplier, and none of them were really usable when they arrived. All of them are almost impossible to turn. I chased that problem back to the fact that they arrived with an interference fit between the spider gears in the differential. I had to remove 0.3mm from the backside of each axle gear before things started to work properly. BUT, they are fixable.

I ordered some plastic bushings for the knuckle pivots on the powered steer axle I'm building. They were SUPPOSED to have a 3mm ID, it's actually under 2.8mm. Fortunately the OD is correct so they also are fixable.

I ordered drive shafts from 3 different manufacturers, 2 out of the 3 suppliers have the knuckles properly phased to minimize vibration. The third supplier... not so much. The knuckles are are least 10 degrees out of phase, and I'm not sure if there's going to be any fixing it.

And then, I've got a gotcha that's kinda my own creation. ALL of the drive shafts that I ordered are SUPPOSED to fit an SCX10, come with a 5mm bore and have drive pins that are threaded M4 on one end with the other end turned down to 2.5mm. My axles are SUPPOSED to be SCX10 replacement axles, but they all have holes for 2mm drive pins in the 5mm OD pinion shaft. I could bore the pinion shafts out to 2.5mm, since the Kong axle that I have has a 5mm pinion shaft with a 2.5mm drive pin hole. The Unimog replacement twin motor/2-speed gearbox that I got as a power unit has 4mm OD output shafts that are threaded M2.

So, here's my first dilemma, do I modify the pinion shafts? Or, do I modify the drive pins? Initially I was leaning towards modifying the drive pins, now I'm not so sure. If I modify the pinion shafts, I just punch the drive pin holes out to 2.5mm and call it a day. If I modify the drive pins by turning them down to 2mm, then I also have bush the hole in the drive shaft down to 2mm. Otherwise they'd be, to quote Wes from Watch Wes Work, "floppin' around like a hot dog in a hallway." Metal fatigue would probably cause the 2mm pin to break off in a short time. I think I just talked myself into modifying the pinion shafts.

My second dilemma is that the output shafts on the Unimog transfer case have a 4mm OD. Bushing the transfer case end of the drive shaft down to 4mm is no problem. They also have a pre-machined flat that is threaded M2. My first thought was to bore the M2 threads out to 2mm, since they are effectively that size now. I was planning on just having one drive pin that would work on either end, but that's just gonna make a lot of extra work for myself. I think what I'll do for the transfer case drive pins is cut a chunk off the 2.5mm end of the pin and turn the stub down to about 1.5mm - or whatever will fit in the M2 threads. The set screw on the flat will be the actual clamping/driving force, the little stub is just extra insurance if the set screw comes loose.

Don

Re: 1/16 Scale FrankenDiff
 

Lesu makes a driveshaft with a 40-45mm range, but I've only got 37mm between the center axle and the rear axle. If I move the center axle forward it will center the tires better in the fender. However, if I do move the center axle forward then I won't be able to collapse the driveshaft from the transfer case to the center axle far enough to be able to install/remove it without taking something else out. I can't move the transfer case because it's currently centered between the front and center axle, allowing me easy access to both drive shafts.

So what am I gonna do? I'm gonna leave the center axle right where it is, but everything else that's behind the cab is getting moved back by 5mm. The mixer, the fenders, the rear axle, the tail-lights, the whole schmear. I checked my 3D model and the only parts that I really need to change are the frame rails, and the equalizer beams, which all need to grow another 5mm in length.

While I was modifying things in the 3D model, I fixed a few other things. When I started working on the Frankendiff I didn't have a resin printer, so I just optimized everything for the foibles of an FDM printer. Now that I have a resin printer I don't have to do that anymore. Unless I'm actually going to use the FDM printer that is, THEN I'll need to. Re-designing the equalizer beams was not an issue, I was never happy with them anyway. I was never satisfied with the appearance of the first layer that was printed on supports, and there's NO way to print those beams without using support. So I just made the inside of the beams flat and didn't need any support. I haven't determined where the vast majority of the holes in the frame rails actually need to be yet, so changing the rail length was no big deal.

Maybe on the next truck I'll get ambitious and assign parameters to everything so I can design future chassis parts by filling in the blanks on a spreadsheet. This one's gonna be a little more old-school. Not clay tablet and sharp stick type old-school - since I am using 3D CAD to design it, more like 80's and 90's type old-school.

Don