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

[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]

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]

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

[Trucker Al]

Very cleaver.... you and this build amaze me ! Keep it up...

[SteinHDan]

Added angle sensor to the bucket.

The bucket angle sensor attaches in the same way as the stick angle sensor, but the cover is different. Its only purpose is to hold the sensor in place and protect it. Not my prettiest piece of work, but it'll get the job done.

[SteinHDan]

Thanks, Trucker Al!

I really like this forum. The positive atmosphere and the combined competence of everyone here fuel many of the builds, I think.


Best regards,
Stein :-)

[bigford]

that's cool dan!! you lost me with all the computer stuff but still a real cool build

[crusher]

As I have written before your build is great , ton of info for us beginners, can I ask a couple of questions, what DP or MOD did you base your swing gears on, I am trying to cut a pair but cannot seem to come up with a workable combination,( do not have cnc) I am also very interested in 3D printer work, about how long does it take to produce your track pads and if I may ask what make of printer do you use? Thanks for any info you may have.
Terry

[markturbo]

Excellent work, you are on a whole other level.

[SteinHDan]

Hi Crusher!

I used the Spur gear generator add-in in Fusion 360 to generate the gear, but there are also many online generators:
- http://geargenerator.com/
- https://woodgears.ca/gear_cutting/template.html
- http://hessmer.org/gears/InvoluteSpurGearBuilder.html

For my main gear, these are the parameters:
- Diametral pitch: 3.175 cm (1.25 inches)
- Number of teeth: 44
- Pressure angle: 20

For the pinion gear it's the same parameters but just 7 teeth.

Then I used the 50 rpm (no load) gear motor to drive these gears to get the wanted swing speed:
- 50 RPM * ( 7 / 44) = 7.95 RPM (no load)

The swing speed from the CAT 390F official specifications is 6.2, so with load I believe my speed matches that pretty well.


I did it like this mostly because I couldn't find a gear ring that would fit and also in a way that I could cut it on my CNC. I wanted an internal gear, but my cutting bits for my CNC aren't small enough to cut inner gears, so it had to be an external gear. But I think external gears look cool, though, so all was not lost. :-)

Later I've been thinking that I should rather not cut the gears myself, but use some more time to find gear rings on the net that I could use.


I'm really happy about the track pads. They really hold up great! Not one have broken so far, even as the machine now weighs 30kg (60lbs). I was initially planning to mill them all from aluminum, but now I'm thinking that if some break, I just print some new ones.

On my 3D printer, it takes about two days of continuous printing to print 80 track pads. I have a Makerbot Replicator 2X.
- http://store.makerbot.com/replicator2x

But that's quite an old 3D printer. I think these days, you can get better offers. The only important thing is that you can print ABS, because it's so much tougher than PLA (less brittle). And you need a heated build plate for ABS printing. Maybe one of these could do the job:
- Ultimaker 2
- Zortrax M200 Pro
- FlashForge Creator Pro

I've not tried any of them, but I've heard some good things about them and the specs look ok. There's probably lots of reviews on youtube.


Best regards,
Stein :-)

[SteinHDan]

Thanks, BigFord and MarkTurbo! :-)

Stein :-)

[Cat966c]

That thing is a beast!

[crusher]

Thank you very much for your reply re swing gears, much appreciated.
Terry

[Tk421reporting]

I love that you made a system that you can use a controller with, I was wondering for awhile if it was possible within reason and you have proved (and gone far beyond) that it is.
Ill be copying this system as well as some more ideas of yours when I start my build a ways from now (which i will put in the build page)
Its really helpful with all the links to everything you have done and detailed comments on it, thanks for that, it will help me tons, I cant wait for the final version =)

[SteinHDan]

Thank you for those kind and encouraging words, Tk421reporting!

I'm looking forward to following your build!

Stein :-)

[SteinHDan]

I'm working on the house body now, and even though I wrote this in another thread already, it really belongs in this thread.

To try to get the right dimensions on all the small scale features, I typically try to find a couple of measurements from a spec sheet, and then scale a photo or diagram as a canvas in Fusion 360 to match the known sizes.

E.g. from the spec sheet of the CAT 390F excavator, I can see that the length from the center to the very back (the tail swing radius) is 4.70 meters, and the height from the ground up to the counterweight is 1.64 meters. I insert the canvas and then scale it to match the known measurements (just divide by 14, since the scale is 1/14).

After the canvas has been scaled properly, I can draw in the 3D-objects on top of it to match the sizes of the features.


Insert canvas:






Switch to orthograpic view:




Draw in the objects:





Switch back to perspective view:




Hide canvas:




Voilà!



Best regards,
Stein :-)

[SteinHDan]

On this site you can find specs for most types of construction equipment:
- http://www.ritchiespecs.com/

For example, you can find the specs for this model, the CAT 390F:
- http://www.ritchiespecs.com/specific...modelid=108962

[SteinHDan]

The angle sensors are now in place and I've added the code in the motor controllers to:
- Read the angle sensors
- Set a max movement limit
- Set a min movement limit
- Set a customizable hysteresis to avoid rapid on/off switching at the end stops if the sensor fluctuates.
- A way to read the current position from the host CPU (the Raspberry pi).

I also added acceleration and variable braking. Both are compatible with the Pololu quik controller. The acceleration was needed to avoid jerkyness when entering or leaving the end limits. The braking helps a lot when holding the arm statically and avoids back-drive of the gear motors.

The end stop logic works as I hoped, and I no longer have to worry about crashing into the end of the travel.

Just for fun, I added a visualization of the excavator on a web page. It's just the same 3D model from Fusion 360, but exported to STL to be loadable by three.js in a web page. The web page uses WebSocket to read the current position of the joints from the excavator over WiFi.

Here is a short video:





https://youtu.be/Z60gWvpeJ8I


Stein :-)

[Trucker Al]

Fantastic !!