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3D-printable high torque servo/gear reduction

with only 8 3D-printed parts, this servo is very easy to assemble and very robust.

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This servo/gear reduction uses mostly 3D-printed parts. The servo uses a 775 36V 9000rpm brushed DC-motor wich is driven by a BTS7960B motor driver wich is controlled by an arduino mega 2560. The stall torque of the servo is about 55kg/cm wich is about 5.39 Nm. the peak current is about 18 amps when using a 6s LIPO battery (about 22-24V). the reduction ratio is 30:1. I originally wanted to use some 20mm ball bearings for the outputshaft but they didn't arrive in time so I ended up using two 20mm holes and some lubrication so the shaft can rotate freely. For the intend of filming the internals of the servo for possible faillures, I printed some collored gears and lasercut a 5 mm acrylic lid. Unfortunatly I didn't get to film any awsome footage of gears exploding because they were far to strong ;-). Even at a peak torque of 54kg/cm they didn't show the slightest form of flexing or cracks. For the full discription see the details :-)

This servo/gear reduction uses mostly 3D-printed parts. The servo uses a 775 36V 9000rpm brushed DC-motor wich is driven by a BTS7960B motor driver wich is controlled by an arduino mega 2560. The stall torque of the servo is about 55kg/cm wich is about 5.39 Nm. the peak current is about 18 amps when using a 6s LIPO battery (about 22-24V). the reduction ratio is 1:30. I originally wanted to use some 20mm ball bearings for the outputshaft but they didn't arrive in time so I ended up using two 20mm holes and some lubrication so the shaft can rotate freely. For the intend of filming the internals of the servo for possible faillures, I printed some collored gears and lasercut a 5 mm acrylic lid. Unfortunatly I didn't get to film any awsome footage of gears exploding because they were far to strong ;-). Even at a peak torque of 54kg/cm they didn't show the slightest form of flexing or cracks. The two middle gears (blue and red one) use a stainless steel shaft of 6mm diameter. The holes of the gears are designed at 6.2mm diameter so they would fit nicely around the 6mm shaft but some additional filing/sanding might be required. The same might has to be done for the 20mm shaft holes. 

STL-files can be found here: https://www.thingiverse.com/thing:3292860

Get your Maker Parts here: https://www.makerpartsonline.com

The video can be found here: 

AutoCAD DXF - 3.86 kB - 12/17/2018 at 22:04

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Standard Tesselated Geometry - 1.74 MB - 12/17/2018 at 22:03

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Standard Tesselated Geometry - 1.26 MB - 12/17/2018 at 22:03

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Standard Tesselated Geometry - 824.11 kB - 12/17/2018 at 22:03

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Standard Tesselated Geometry - 879.96 kB - 12/17/2018 at 22:03

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rk.freitas2 wrote 01/10/2019 at 18:07 point

Nice Job! Do you have a STP part/assembly?

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Dan Maloney wrote 12/21/2018 at 02:00 point

Looks good! One question: How are you getting feedback on the shaft position? I don't see a pot or encoder.

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brian brocken wrote 12/26/2018 at 18:14 point

Yeah I knew that one was comming haha. Thats the reason I gave the title the '"/gear reduction". I still need to find a place to mount the potentiometer. I might have to redesign the case a little bit in order to do this. I plan on using this servo in a project where I need position feedback. So the potentiometer will definitly be implemented in the design. You can follow this project so you get notified for future updates.

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Martin wrote 04/25/2019 at 12:14 point

Perhaps a magnetic (hall effect) rotation sensor is a good solution. You fit a magnet to the shat, the sensor can be on the outside of the enclosure, if the wall is not too thick.

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István Nótai wrote 12/18/2018 at 14:43 point

Really nice work, looks fast and smooth, thanks for sharing!

I'm curious how long can you stall the servo before, it starts to overheat and melt the housing and how much the whole servo weights.

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brian brocken wrote 12/18/2018 at 16:56 point

Thank you! The motor was about body temperature after all the heavy lift testing. I wouldn't recomend to stall the servo for a large period of time because the motor will burn out. I think the motor would rather burn out instead of the plastic melting although this could be a possibility. The servo weighs about 719 grams.

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