A redesign of the GUS Arm for easy external stringing

Re: A redesign of the GUS Arm for easy external stringing

Postby tommythorn » Thu Apr 21, 2016 8:34 pm

Thank y'all, I misread the file names (read biggearmod_fixed.stl as "bigger mod" :) )

I asked because I had a lot of trouble with the original GUS' extruder (and franky even with the direct extruder on my current printer). Wade looks promising, but I think I've seen versions with better gears (lulzbot perhaps). A belt driven one sounds very interesting, please tell us more!
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Re: A redesign of the GUS Arm for easy external stringing

Postby Viproz » Thu Apr 28, 2016 12:00 pm

Printing goes along nicely, I now want to start printing the arms but I have a few questions :

How do you print them in general ? I'm guessing with support material but everywhere or just for the big overhang ?

I saw that on the extruder they used a neat way to facilitate printing the part, in all holes that become smaller later in the print they use a little wall so that the slicer can make a bridge there and by doing that they eliminate the use of support material.

I wanted to get your input before starting editing it in the part file since there seems to be a lot of operations on the arms (it's going to take me a bit of time to edit every hole).
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Re: A redesign of the GUS Arm for easy external stringing

Postby Jfriesen » Thu Apr 28, 2016 5:44 pm

I just used auto generated support in Cura. I set the break away support to everywhere and support infill to 20%. I also used 1.5 mm wall thickness and 1 mm top and bottom thickness with 0.25 mm layer height. My regular infill percent was 30% and my printer nozzle was 0.5mm. With these settings in Cura the arms came out great on my taz5 printer, hope that helps.
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Re: A redesign of the GUS Arm for easy external stringing

Postby Viproz » Thu May 12, 2016 6:34 pm

It seems like there are some issues in the assembly file with parts, I am writing them as I go here : https://docs.google.com/spreadsheets/d/ ... =621368198

Also I see thet the spool holder is different in the assembly compared to the stl, which one work better ?
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Re: A redesign of the GUS Arm for easy external stringing

Postby Jfriesen » Fri May 20, 2016 4:57 am

Sorry I've been out of the game again for a bit. FYI my printer is still working very reliably with no apparent cable wear. As far as the spool mount goes, both work fine. I created the new one to let the spool sit a bit lower. Feel free to use either!

Thank you for compiling this list. I will address all these issues in a few days and update the repository.
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Re: A redesign of the GUS Arm for easy external stringing

Postby ekaggrat » Fri Sep 02, 2016 7:35 am

i finally got a version of marlin running with the delta calculations inbuilt. Now i have a issue of the movement being not flat but domical.

how do you correct for that error..

i was off the build for quite some time due to other distractions. !!

glad to see that your printer is working fine...

thanks
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Re: A redesign of the GUS Arm for easy external stringing

Postby Jfriesen » Fri Dec 02, 2016 10:01 pm

Calibration for me mostly centered on gathering lots of accurate measurements on the actuators, and then accurately calibrating the vertical height offset from the build plate.

First I independently measured the homed lengths of each actuator and adjusted them each to be as even as possible. You can also do software trim but this is more annoying, better to just calibrate the machine. I measure this length with calipers between the two bolts when the arms are dis-assembled from the machine. Next I would use the printer board to move the arms to a shorter length, commanding 300mm shorter for instance, and then see how far I was off. I could then use these two measurements to adjust the steps per mm for each arm.

Once these are all accuratley calibrated I re-assembled the machine and sent it to the home position. I think the dome you are seeing could be caused by an incorrect vertical offset. You want to make sure that when you home the arms and measure the distance between the nozzle and the build plate that the distance there matches the readout from your machine. You also want to make sure that when you step the machine down to Z = 0 the nozzle is at the build plate height. The key here is you know the three arm lengths from previous measurements and so with one more measurement you should be able to determine the build plate height and how that needs to be adjusted.

To summarize I calibrate in this order:
-Maximum arm length for each arm (from the center point of each bolt)
-Steps per mm for each arm
-Vertical Height offset

After I get those three down I then I level the build plate manually using the adjustment screws. Perhaps I'll make a video of my calibration process. I've just been too busy! Once you get the geometry right the printer will print reasonably level (at the far outer reaches of the build volume I still see some errors around 0.5 mm in height).
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Re: A redesign of the GUS Arm for easy external stringing

Postby ekaggrat » Tue Jan 03, 2017 2:00 am

thanks i will try that.. has been a long pause on this project.. :mrgreen:
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Re: A redesign of the GUS Arm for easy external stringing

Postby jwm » Fri Jan 06, 2017 1:51 am

I'm finally starting my GUS 2.5 build. My original printer didn't have enough build volume so I printed a completely new core XY printer that was large enough to print the Gus parts and am now starting on those. (Bootstrapping in true reprap fashion)

You mentioned before in this thread that you modified the build to only require 12 pulleys instead of 16, but I can't see which 4 I can omit, is there an updated stringing diagram?

My intermediate printer was a FuseBox if anyone was curious, blows my wobbly prusa Mendel v1 out of the water. I can highly recommend it as an easy build that's straightforward to modify to fit your junk drawer vitamins.
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Re: A redesign of the GUS Arm for easy external stringing

Postby Jfriesen » Mon Jan 09, 2017 7:37 pm

I had modified the design to reduce the pulley count as mentioned, but I found that this modification caused some issues with the revised string routing, and the resultant cable rub induced a ton of wear on the interference points at the contact of the strings. I would not recommend using those changes. Better to have more pulleys and a printer that lasts somewhat indefinitely than one that breaks every couple of prints due to cable wear.

I had extra pulleys so I didn't concern myself too much with reducing the count, but you can easily reduce the required number by two per arm by simply printing two dummy pulleys and replacing these with the two final pulleys that feed into the guitar tensioner and the string anchor point. Just make sure the dummy pulleys have the same diameter as the originals. These pulleys do not spin at all during normal operation so it won't add any friction into your arm drive.
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