90 ton 1/14 metal excavator scratch build w/embedded PC

[Machfab]

Originally Posted by SteinHDan

Hi Machfab!

> Will the gamepad/pc controller give you proportional control of the gearmotors or just on/off control?

The gamepad gives full proportional control for all the gear motors, including the track motors. I'm using the front analog triggers for the track motors, and I use the two front buttons to reverse the track directions. The swing, boom, stick and bucket controls are on the two joysticks and equal to running a normal excavator (ISO-mode).



This particular gamepad (the Logitech F710) doesn't stand back in sensitivity or accuracy in control from any of my normal RC transmitters. But most cheaper gamepads have less accurate analog control and also a larger deadspace in the middle / neutral position.

I would say the pros and cons VS a normal RC transmitter:
- Pros: Smaller, cheaper, 2 analog joysticks, 2 analog triggers, 1 digital four-directional pad and 10 digital buttons
- Cons: Short range (10m), no telemetry


Machfab, are you by any chance affiliated with http://machfabengineering.co.uk/ ? I just asking, because it would be interesting to get a quote on how much it would cost to get all the aluminum parts cut at a professional shop. I'd buy a set myself if someone could make it (depending on the price of course).


Best regards,
Stein :-)

No, not them. Just own a machine shop here in the US.
Also a user of Fusion360
Plan to do this build. Very nice! Thanks

[SteinHDan]

I've added some bronze self-lubricating bearings to the bucket linkage. I don't think they were really required, and it goes against one of the goals of this project, to keep it simple, but it just pains me to know that there is a load-bearing joint without any form of bearing in it. So it had to be done! :-)













The parts:
- Clips: HSP 02053 Body Clip
- Bearings: 8 x 10 x 12 oilless bronze bearing

[RobotArms24]

Can you explain a bit about infill on 3d parts please. Is it something you put in the model, or something the printer settings control? What does it look inside when its partially filled in? Is it honeycomb or some other pattern? How would the strength of say 25% infill compare to 100% infill?

Thanks

[SteinHDan]

Hi RobotArms24!


The infill is set in the printer settings (not in the model) and it's typically only used for FFM-machines (the typical home desktop 3D printers). Shapeways will always make a solid model, I believe.

I usually print with something called "fast honeycomb". There are lots of alternatives, but I feel that fast honeycomb is a good combination of strength, speed, weight and also the zig-zagging gives less pull on the edges and less warping of ABS prints.

I use a software called Simplify3D. They have a lot of good information on their web site. This is a video on infill:
- https://www.youtube.com/watch?v=BMWTK2ZgJCM

And they also have and this very helpful 3D-printing troubleshooter:
- https://www.simplify3d.com/support/p...oubleshooting/

I don't know exactly the strength of different infill percentages, but to the hand it feels linear, i.e. 20% feels twice as strong as 10%.


Best regards,
Stein :-)

[SteinHDan]

Starting to paint the metal parts on the boom, stick and bucket linkage. Need a couple more layers on the stick parts.
The paint color is the closest match I could find to the ABS filament color in the previous step. It's this one:
- Dupli-Color 577789 AC 3-0600
Sanded (120 sand paper) and primed with aluminum etch primer first.

It's a shame, really, to cover shiny metal in this way ;-)

[SteinHDan]

Mounted the counterweight to the base plate. After testing with 4, 6 and 8 kg ballast, it seemed 6 kg (13 lbs) gives the best balance.

I bought 2 kg (4lbs) lead plates from a local scuba-diving shop:
- http://dykk.no/main.aspx?page=article&artno=MTDA-1

I don't like exposed lead because of the health hazards, so I covered it in liquid plastic and added a shrink wrap tube on top of that. Probably overkill and you can probably use whatever to cover the lead, but I had these things at hand.
- Polytek EasyFlo 60 Liquid Plastic
- PVC Plastic Heat Shrink Tube F/W:95mm

Then I printed a 3D clamp (ABS, 30% infill) that has two very long M6 110mm hex bolts going through it.
- M6 110mm stainless steel hex bolt

Finally adding some common furniture anti-skid rubber pads to both the clamp and the lead to avoid the lead sliding in the clamp.

[bigford]

looking great I cant wait to see it dig dirt!!

[SteinHDan]

Thanks, Bigford! The snow has melted away here now, so as soon as I have it assembled again I'll make a video of it digging dirt. :-)

[SteinHDan]

Mounting the motor controllers (ESCs)

I wanted to mount the motor controllers in a compartment that had plenty of air flow, as they are the components that need the most cooling. I put them where the radiators are on the real version and I was able to add four controllers that can then control eight motors of up to 30 Amps each. Only six is required for the main motors. The two extra channels will be used for attachments and a surprise! :-)

I also wanted to be able to get easy access to the controllers and easily replace one if I need to. So I made a seat and four slot-in module mounts:




The motor controller modules each slide down into this seat:




And the air flow will be ok I think with the vents as they are placed on the original:






Each module consists of the motor controller as described previously and a 3D-printed (15% infill) module mount that attaches to the controller with two M3 nylon bolts. I use nylon here to avoid any kind of electrical connection in the screw.
















Each module is secured with one self-tapping screw. Only this screw needs to be removed to slide the module up and out again:




The seat attaches to the base plate also with just one M4 50mm bolt:








I'm pretty happy that I got all the motor controllers into this one spot, because it leaves more room for the other stuff. Even as large as this model is, it's going to get tight when everything is in place.

[outcastrc]

Those mounts turned out fantastic!

[DADSGARAGE]

Very interesting design, really like all the printed parts, well done!!!

[SteinHDan]

I really wanted this excavator to have proper sound. Deep and powerful bass. Not toy-like. I looked around a bit to try and find a large speaker that would fit, but came up empty. So I printed one instead. My biggest print to date. 21 hours and 290 grams of ABS. :-) (25% infill)

The speaker driver is this one:
- Pioneer TS-G1045R 4-Inch 210 W 2-Way

On the back there is a speaker terminal that I bought on Ebay:
- 44.8x21mm 2pin Red and Black Push Type Speaker Terminal

And then there are four self-tapping screws in the front, two on the terminal, and three that fasten the speaker box to the base plate.




I cut off the mounting tabs on the speaker driver, because I needed the screw holes to be closer to the cone. The flange on the self-tapping screws is now what holds the speaker driver in place:




Soldered the wires that came with the speaker to the terminal:






Attaching the speaker box to the base plate with three self-tapping screws. I added a soda can too, as I've seen a few others do that lately. My build is dwarfed by DADSGARAGE's and Cooper's though, but still it's not that small. :-)

[Trucker_Jo]

Great job with all of the 3D printing, it's very fun to see what people can come up with and easily create. If the sound doesn't seem quite correct with your setup, put some insulation inside of the box like bed top foam or something like that.

[SteinHDan]

Hi Trucker_Jo!

Yes, it's pretty cool, but this print was a pain. I started it and it ran for 5-8 hours four times before I got one successful print. The problems were lifting edges, support coming loose, support lifting and SD card error. :-)

I'm definitely going to add some dampening material inside. Initially, I tried to print something like that, but it didn't work that well, and I decided to do it the traditional way, and then completely forgot about it. Thanks for reminding me! :-)

Here are some images of my attempts at printing the inner dampening:




Stein :-)

[SteinHDan]

Thanks, DADSGARAGE! I'm following your build with excitement! :-)

[Lil Giants]

Overall looks to be pretty smooth... some springiness when stick is pushing hard, but still very impressive for electric rotation. Well done Stein!

[SteinHDan]

Thanks, Joe! That means a lot, coming from you!


I've not seen the springiness in the stick before since I haven't been pushing anything hard, but it's caused by the combination of the 6kg gas spring and the backlash in the gears. When there is no load, the gas spring pushes the stick to hang on the gears. when the stick is pushing hard, it takes over and the stick is pushed by the gears. When lifting the arm up, the gas spring is free to push the stick back over the backlash and to have it hang on the gears again.

I think I'll try to just lower the force on the gas spring to get rid of this problem or make it less of a problem. I'll try with a 3kg gas spring first. I though bigger would be better, because the gas spring offsets the force to give the stick more pull force. But it doesn't need that, and it's causing this problem, so it should be smaller.


Best regards,
Stein :-)

[SteinHDan]

If someone is wondering why the excavator is standing on planks, then the reason is that I didn't want it to get dirt into every corner of the track when it's going right back onto my work bench.

Stein :-)

[Lil Giants]

I don't recall reading where you added a gas spring, but great idea to take up the slack in the gear back lash to keep the movement tight.

Whether 3kg or 6kg gas spring, the difference in length of backlash travel will always be the same... might as well leave the 6kg in place.

[SteinHDan]

Yes, true, I just thought the 3kg would be less violent when it engages. It should probably be a pulling spring instead of a pushing spring so that the backlash is only seen when pushing hard with the stick and not when pulling hard. I'll see what I can do about it.

I also found that the set screw was loose, so the backlash is only about half of what you see in the video when the set screw is tight.

I have done a few things that I haven't documented here yet. The gas spring on the stick, a gas spring on the bucket, a mount for the CPU (the Raspberry Pi) and angle sensors for the bucket and stick. I'll get those updates up here shortly. :-)


Stein :-)