Hilo build aka Gus 1.5ish

Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Sun Mar 08, 2015 11:31 pm

I should mention that that is the resolution of the arm extension s̶o̶ ̶a̶s̶ ̶I̶ ̶u̶n̶d̶e̶r̶s̶t̶a̶n̶d̶ ̶t̶h̶e̶ ̶g̶e̶o̶m̶e̶t̶r̶y̶ ̶t̶h̶e̶ ̶r̶e̶s̶o̶l̶u̶t̶i̶o̶n̶ ̶o̶n̶ ̶t̶h̶e̶ ̶d̶r̶a̶w̶ ̶p̶l̶a̶n̶e̶ ̶g̶o̶e̶s̶ ̶u̶p̶ ̶t̶h̶e̶ ̶f̶u̶r̶t̶h̶e̶r̶ ̶y̶o̶u̶ ̶g̶e̶t̶ ̶a̶b̶o̶v̶e̶ ̶t̶h̶e̶ ̶s̶h̶o̶u̶l̶d̶e̶r̶. you actually gain xy resolution and lose z resolution

I'm also trying to decide where to put the end stops. What is the maximum reasonable arm extension angle? Mechanically I should be able to open them to 20deg from straight before belts start to hit.
Last edited by rustynoob on Mon Mar 09, 2015 7:05 pm, edited 1 time in total.
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Re: Hilo build aka Gus 1.5ish

Postby Nicholas Seward » Mon Mar 09, 2015 12:26 am

300um/step is a bit much but it will allow for testing.
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Mon Mar 09, 2015 7:01 pm

so I think I'll keep my current design and upgrade my pulleys from 20 to 16 tooth pulleys and eventually upgrade the steppers to 400 steps/rev motors. I can get it working now with my current motors. All of that only gets my resolution down to 120 microns but I think that should be good enough. I guess if I really want to make it better for anyone who follows my design I should go with a belt reduction drive or shorten the arm. Shortening the arm reduces build volume so the belt reduction seems like the way to go. It just won't be as pretty...
I think I've almost talked myself into a redesign. Maybe I'll play around with it and see what I can come up with before I make any decision.
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Re: Hilo build aka Gus 1.5ish

Postby Nicholas Seward » Mon Mar 09, 2015 7:08 pm

The belt reduction could allow you to move the motor to a location closer to the lower pivot. It will also make it easier to place you secondary drive pulley in the center of the gear.
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Tue Mar 10, 2015 9:01 pm

so If use 16t pulleys and shrink the arm pivot to center down to 100mm and if micro stepping voodoo is reliable at 4 then I have a resolution of 50um. This requires the least changes to my design. How good is the voodoo? Do you think this will work?
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Sun Mar 15, 2015 12:12 am

belt arm bw.jpg
My latest arm design
belt arm bw.jpg (124.4 KiB) Viewed 33748 times

I finally finished reworking my design. Still need to make a place for the end stop sensor and maybe tweak the motor mount a little.
This design takes 3 more bolts and 12 more flange bearings than the old one but it gets the resolution down to 60 um without relying on micro stepping. I feel like that should be plenty.
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Sun Mar 29, 2015 1:41 am

and the prototype arm is all printed. I'm still waiting on the right pulleys and need to print the large one.
WP_20150328_15_23_44_Pro.jpg
Arm overview
WP_20150328_15_23_44_Pro.jpg (1.32 MiB) Viewed 33699 times

There are a few things I will update for the real thing. The belt spreader needs to be a little wider
WP_20150328_15_24_44_Pro.jpg
belt spreader 1
WP_20150328_15_24_44_Pro.jpg (1.38 MiB) Viewed 33699 times

WP_20150328_15_24_25_Pro.jpg
belt spreader 2
WP_20150328_15_24_25_Pro.jpg (1.38 MiB) Viewed 33699 times

It is hard to see in the photos but it is in a hard place to get good photos of. The belt comes off the spreader narrower than drums it wraps around on the way to the attachment points so as the spreader approaches maximum wrap it starts to bind on the lip making it not run smoothly at the ends.
The placement of the spreader is going to be critical as well, at least on the end near the elbow, because if it is not directly in the center it starts to wrap on one of the pulleys before the arm is fully extended and throws things off.
Also there are a few minor changes to make some features print better but I think It would work just fine as is.
Last edited by rustynoob on Sun Mar 29, 2015 1:51 am, edited 1 time in total.
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Sun Mar 29, 2015 1:45 am

I also designed a filament drive because I got bored waiting for parts to arrive.
WP_20150328_15_25_43_Pro.jpg
filament drive
WP_20150328_15_25_43_Pro.jpg (1.31 MiB) Viewed 33699 times

It has two mistakes but I think i will be able to use it as is. The hole for the Bowden tube press fit is the wrong size. I think If I ream it out it should work and the bearing was supposed to be on the inside but I didn't make room for the flange on the inside ... oops.
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Sun Apr 12, 2015 3:02 am

Development is coming along nicely. I just picked up the arm pieces for the last two arms today and put them together. It is a bit of a pain to put the belts on but I got it all together. I am still waiting for the bearings for the hub so I won't be able to do much real testing until I'm get them. in the mean time I may print out some dummy bushings so I can do some basic testing.
This is the build so far.
WP_20150411_16_23_51_Pro.jpg
WP_20150411_16_23_51_Pro.jpg (364.8 KiB) Viewed 33616 times

WP_20150411_16_24_02_Pro.jpg
WP_20150411_16_24_02_Pro.jpg (310.01 KiB) Viewed 33616 times

on a side note. 7/8" plywood is a bit thick. I had to counter sink the bolt holes on the top in order to have enough threads to put the nuts on the bottom.
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Re: Hilo build aka Gus 1.5ish

Postby rustynoob » Sun Apr 12, 2015 3:30 am

I should probably add that I have only run the one arm at the moment and using a ruler with millimeters determined that using 1/32 micro-stepping I have about 250 steps/mm.
Some things that may cause me trouble are:
1.The bolts having too much slop in the bearings. When I tighten it down it seems to be rigid but I am not convinced that there will be no twisting from that.
2. The gear joints seem to not be aligned quite properly. Some how all the arms are twisted slightly so that when closed so there is an offset of about 3 mm. This consistent so could theoretically be accounted for in software but I expect to cause issues calibrating. If worst comes to worst I will have to redo half of the gears.
3. The arms may be too flexible. You have to apply enough force to flex the arms that I do not think this is going to be an issue but it is something I am aware of that could cause problems in getting good dimensional accurate parts.
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