Hilo build aka Gus 1.5ish

Hilo build aka Gus 1.5ish

Postby rustynoob » Wed Feb 18, 2015 4:41 am

So I'm starting a Gus build, I've ordered a bit of the hardware and started printing parts and, I've been looking over the forums and I'm thinking about making two modifications to the arms and would love input. First I want to use a belt drive as discussed in another thread, and second I think rotating the block and tackle bolts about 45 deg should give more even leverage across the arms range of motion and perhaps help to reduce the small remaining nonlinearity. I would love any feedback you could give. I know Gus 2.0 is on his way but with the indefinite timeframe I think ill have to go with Gus 1.5ish

I welcome your feedback and look forward to finishing this build.
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Re: Hilo build aka Gus 1.5ish

Postby Nicholas Seward » Wed Feb 18, 2015 4:45 am

Awesome! What do you mean by rotate 45 degrees? (The bolts and the arm pivot have to be in a line that go through the gear center or it will break the linearity of the response.)
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Wed Feb 18, 2015 5:06 am

I mean rotating them around the center moving the bolt near the arm toward the build platform and the outer bolt away from the platform. I had a nice picture but my laptop died before I got around to making my post. It may be that 45 deg is to much. You could also say rotating the arm and the gear relative to each other about 30 to 45 deg. The idea is with the arm at its halfway point the bolts on the two arms should be parallel. This would make the current print for the arm massive but if I bolt it together like the 2.0 arm it shouldn't be to bad. I was working on it in inventor before my computer started crying about the battery.
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Re: Hilo build aka Gus 1.5ish

Postby Nicholas Seward » Wed Feb 18, 2015 5:15 am

I think you may be violating linearity. Are the two bolts and the arm pivot all in a line? If not, the math gets hard and calibration will be super extra tricky.
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Wed Feb 18, 2015 6:50 pm

I guess I skipped to much of the arm design thread when I was reading it and hadn't thought through the geometry quite well enough. I guess I will have to just do the belt drive for now. I thought there might be some reason it was done the way it is and that's why I posted here before I went wild printing parts... That and i hadn't finished designing them quite yet.
Now to hash out the details of the belt drive...
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Re: Hilo build aka Gus 1.5ish

Postby Nicholas Seward » Wed Feb 18, 2015 7:23 pm

No worries. The design of a Proportional Gear Drive Joint or PGDJ is far from intuitive. This threadwill help.

The next problem you might have is by having a variable amount of belt in contact with pulleys. (This will introduce a small variability that will drive someone trying to calibrate the machine crazy.) For instance, if the belt terminates on the slave arm. However, if the belt goes around an idler on the slave arm and then terminates by wrapping around a static drum of the same size as the idlers then you are golden expect that the belts has to stay in plane. (My plan was to actually terminate the belt with a printed y that you could use to tie strings onto and then wrap the strings around static drums on each side of the idler on the motor arm. Let me put this a different way. Belt leave the drive pulley->redirected by idler on motor arm->redirected by idler on slave arm->converted from belt to two strings->strings wrap around static drums on each side of the motor arm idler. Repeat for other side.)

Wish it was easier but then it wouldn't be as fun. :-)
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Thu Feb 19, 2015 6:52 pm

So this is basicly what I have in mind for the belt termination. I'm thinking of using some steal from an old pc case or something for the metal clip and then possibly printing a plastic piece to make a rounder surface for the belt wrap around before going through the notch where the teeth should keep it from slipping.

I guess string or wire would work t0o but I worry about stretching, slipping and breaking.

belt termination.png
belt termination idea
belt termination.png (19.94 KiB) Viewed 56153 times


The effect of the plastic piece could be achieved by bending the metal around the inside of end instead of just cutting it of but then it could deform under pressure and cause the belt to go slack.

also some sort of retention clip may be nice to keep things from moving around to much, a zip tie or some safety wire should do the trick nicely.
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Sat Feb 21, 2015 1:14 am

I'm almost done redesigning the arm. I just need to finish the motor mount and double check my numbers. I'll post a picture when I'm done... Probably after the weekend.
In the mean time could someone measure the width of the top of shoulder with the bearings. I'm making the shoulder and worst joints double sided and I want to make sure they fit.
So does the mailing stock out at all and do I need washers to keep things from rubbing.
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Re: Hilo build aka Gus 1.5ish

Postby timrwilliams » Sat Feb 21, 2015 10:43 am

The width of the top shoulder joint with 2 x 608 bearings - I have 25.1mm.
Splitting the shear joints seems a good idea and was one of Nicholas' original redesign suggestions.
I tried to do this in my Mk2 test arm, and because I wanted a modular design with some interchangeability, I ended up with 4 x 608 bearings per joint. This seems a bit excessive?
Apart from checking that the motor/slave arm pair was a drop-in replacement for the original pair (which it seemed to be!) I have not progressed much further.
I wish you good progress with your print/build.
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Re: Hilo build aka Gus 1.5ish

Postby Nicholas Seward » Sun Feb 22, 2015 12:42 am

ToWrapOrNotToWrap.png
ToWrapOrNotToWrap.png (39.23 KiB) Viewed 56122 times


The termination you mentioned above will break linearity. I know the way you have it drawn makes it look like the belt won't aim straight at the pivot but it will. Even if you the belt is somehow aimed so that it is coming in tangent, you need it to wrap and unwrap on the terminating drum so the math works out.

I hope this makes sense. I will be glad to clarify if it doesn't.

One idea could be to split end of the belt longitudinally. You could then have a little plastic piece to hold the two half width ends apart so they can wrap on either side of the motor arm idler pulley.
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