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

[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]

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

[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 :-)

[Trucker_Jo]

Interesting, thanks for showing us the details!

[SteinHDan]

First test digging dirt!





https://youtu.be/YNJewdL_CPk

[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 :-)

[Lil Giants]

Originally Posted by SteinHDan

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.

Do you have flat spots on the shaft for the set screws to anchor to? Blue locktite is adequate to keep set screws tight! But the locktite will also seep around shaft & mounted part too making it a real bytch! to get apart again. Maybe you don't want to add that just yet during testing phases, eh?

[SteinHDan]

Yep, that's good advise.There is a flat spot, but I just hadn't tightened it and I only added the left set screw, not the right. Lot's of screws loose at this point, like you say, it gets taken apart all the time when when building and testing like this. I'll get it all tight at the final assembly and add some blue locktite for good measure! :-)

Stein

[SteinHDan]

Added a simple mount for the brain (CPU) of the excavator. At the same time I replaced the Raspberry Pi 2 with the version 3. It's mostly the same, but a little bit quicker and has WiFi and BlueTooth built in.

- Raspberry Pi 3


The mount is very simple. Four self-tapping screws to hold the PCB and then two nylon M4 bolts to hold the mount on the base plate.








The audio (engine sound) has its output through that 90-degree 3.5mm jack on the top.

[SteinHDan]

Bolting together the arm

The arm sandwich of 3mm aluminum sheets with 3D-printed ABS in the middle is held together by 34 M4 countersunk stainless steel bolts and sleeve nuts.

There are different length bolts used throughout the arm:
- 23 x 50mm (for the main part)
- 5 x 75mm (80mm cut to length) for the stick hub
- 4 x 80mm for the stick mount
- 2 x 55mm for the stick angle sensor mount

Ebay links:
- Bolts: http://www.ebay.com/itm/231787670429
- Sleeve nuts: http://www.ebay.com/itm/191771467782

[SteinHDan]

I added a gas spring from the boom to the stick. I only found the correct length, stroke and force on Aliexpress:

- 6kg (60N) gas spring: http://www.aliexpress.com/snapshot/7601366858.html

The sleeves and spacers are cut from 8mm and 12mm stainless steel tubes. The pin is also gotten from Ebay:

- 8mm (ID 4mm) tube cut to 13mm length: http://www.ebay.com/itm/121600172085
- 12mm (ID 8mm) tube cut to 4mm legnth: http://www.ebay.com/itm/121762512929
- 8x30mm pin: http://www.ebay.co.uk/itm/121851516316

[SteinHDan]

I also added a gas spring to the bucket, mostly for the visual appearance as the bucket is already way more powerful than it needs to be.

The spacers are made the same way as previously, cut tube to length.

Ebay links:
- 8mm (ID 6mm) tube cut to 4mm length: http://www.ebay.com/itm/121762445745
- 12mm (ID 8mm) tube cut to 4mm legnth: http://www.ebay.com/itm/121762512929
- 6x30mm pin: http://www.ebay.co.uk/itm/121868709865
- 8x80mm pin: http://www.ebay.com/itm/291511678072
- Eyelets: http://www.ebay.com/itm/151838223022

The lower eyelet is drilled out to 8mm to fit the 8mm pin in the bucket linkage.