Pulley Drive system 4:1

discussion of design changes / improvements / suggestions
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wlanfox
Posts: 74
Joined: Sat Oct 20, 2012 10:49 am

Pulley Drive system 4:1

Post by wlanfox » Mon Dec 01, 2014 11:38 pm

Released 1st version of Pulley Drive 4:1 (posted also at the G+ Shapeoko Forum)

Can be downloaded here : https://github.com/shapeoko/Shapeoko_Ex ... Drive_4to1

What does this do for you? if you are using 400st/rev steppers, now you have 1600st/rev. Also torque is improved 4x. 100 micron resolution with #Shapeoko ??!! Yes I can :D. At this point I can drive the motors with this configuration at 1000mm/min, I am happy with this since I usually cut at 400mm/min-500mm/min.

What is given up? maximum speed, bu that is fine (at least fro my usage) since even if you could drive your machine at say 3000mm/min do you really ever use it that way? For my use I normally cut at 500mm/min - 400mm/min and travel at around 800mm/min.

The configuration shown uses outside-belts configuration; this is not require, I design it so it can be a direct replacement to the regular stepper motors. For in-belt configuration just don't make the idle wheel blocks. The upper screw have the NEMA23 profile and is just a direct mount or replacement for stepper motors. The pulley the drives the belt is a 20 teeth just as regular #Shapeoko . Without the idle wheel blocks it will look like this early prototype (picture below).

Here is the measurement data at different micro stepping and pulley ratios, all are GT2 2mm pitch belts and pulleys and driven with #TinyG :

1:1 No Pulley Drive: http://goo.gl/CVmw0y
4:1 Pulley Drive: http://goo.gl/GTSRel

In the github repository you will find:
BOM (parts and sources)
STL files (ready for fab)
CAD files (FreeCAD)

Image

early prototype:
Image
Last edited by wlanfox on Tue Dec 02, 2014 1:01 am, edited 4 times in total.

twforeman
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Re: Pulley Drive system 4:1

Post by twforeman » Mon Dec 01, 2014 11:59 pm

Very cool. I remember seeing this project when you started it.

Any backlash issues in the belt drive?
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wlanfox
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Joined: Sat Oct 20, 2012 10:49 am

Re: Pulley Drive system 4:1

Post by wlanfox » Tue Dec 02, 2014 12:11 am

twforeman wrote:Very cool. I remember seeing this project when you started it.

Any backlash issues in the belt drive?
No my backlash actually improved, if you look at data (I measured these many times). With no Pulley Drive just motor and 20 teeth pulley at 2x micro step the max backlash was 0.12mm with the 4:1 drive same micro stepping the max backlash was 0.09mm. Which makes me think that the backlash I am seeing is step error based, and with the 4:1 drive that is reduce since say 10 steps error will be much less pronounced when your step per rev is 1600 as oppose to 400. One thing that most people don't realize is that the spec for the regular stepper motor is usually 5% step error with no load and 10% step error with load. Some background info http://www.geckodrive.com/support/step- ... ution.html

LouisV
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Re: Pulley Drive system 4:1

Post by LouisV » Tue Dec 02, 2014 5:02 pm

That's very cool. I can see how this level of resolution could be useful in certain applications. It would certainly be a cool upgrade to add to any machine. Keep us updated. :)

Enraged
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Re: Pulley Drive system 4:1

Post by Enraged » Tue Dec 02, 2014 7:05 pm

Nice work! Do you have 2D DXF or DWG files of the parts? It would make it easier to program to cut on the Shapeoko itself. STL files are faceted, so a round hole in an STL file isn't actually round, it has many flat faces. Provided that the file was saved with a high enough resolution this isn't usually a problem, but with a DXF or DWG file you can program you CNC machine to cut a circle or a curve, which helps a lot with bearings fitament as well as cutting times.

wlanfox
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Joined: Sat Oct 20, 2012 10:49 am

Re: Pulley Drive system 4:1

Post by wlanfox » Tue Dec 02, 2014 10:56 pm

Enraged wrote:Nice work! Do you have 2D DXF or DWG files of the parts? It would make it easier to program to cut on the Shapeoko itself. STL files are faceted, so a round hole in an STL file isn't actually round, it has many flat faces. Provided that the file was saved with a high enough resolution this isn't usually a problem, but with a DXF or DWG file you can program you CNC machine to cut a circle or a curve, which helps a lot with bearings fitament as well as cutting times.
No don't have DXF or DWG, but SVG should also work, attached is a zip file with the svg files for the plates.
Attachments
fab-parts.zip
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