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Stanley - the capstan based quadruped

A maker friendly capstan based BLDC driven quadrupedal robot kit. Based on mjbots electronics

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Our goal is to get as close to the performance of the MIT mini cheetah as possible while keeping the cost down and the entire build accessible to the average maker. The use of Capstan Drive's allowed us to lower the price of the entire build. Two fabrication techniques are being used - FDM 3D printing which almost every maker now has access to, and 2D milling in FR4 - which is less available, but it is cheap to order these parts in a local shop. Drivers used are mjbots moteus r4.5, the main computer is a Rpi4. The motors are 90KV 8308's

The current stage of the project:

Done:

  1. Design a single capstan reducer and build a test stand for it - perform tests and improvements.
  2. Design and build a 2Dof leg - with the knee and hip joint.
  3. Write a python script for communication with the moteus r4.5 controllers over the USB-CAN_FD adapter
  4. Solve inverse kinematics and scripts for jumping and various other demonstrations.
  5. Perform testing on the 2Dof leg - continuous jumping for 1h - inspect, iterate.
  6. Design and build a 3Dof leg - adding the ab/ad joint.
  7. Perform testing on the 3 Dof leg - continuous jumping for 1h between randomly chosen points.
  8. Make design corrections based on the test and retest. Also perform mass reduction improvements.
  9. Design the chassis.
  10. Print a mock-up of the chassis before ordering the "real thing" in FR4 to verify the design .
  11. Get all FR4 Parts and assemble The First Stanley.
  12. Lay down cables.
  13. Get the internal CAN communication working.
  14. Get the Xbox360 Controller working with RPi4B.
  15. Solve inverse body kinematics, make a demo.
  16. Create a parametric step trajectory generator, make Stanley walk for the first time.
  17. Tune the walking algorithm.
  18. Add jumping functionality.
  19. Test different types of cables, choose the best one.
  20. Make assembly improvements.
  21. Create prototype payloads for JetsonNX and Intel cameras.
  22. Create side covers that better protect the insides of Stanley
  23. Redesign cable tension system for easier assembly.
  24. Create assembly tools.

To do:

  1. Increase reduction ratio to 1:8.
  2. Make Stanley’s legs longer.
  3. Make the AbAd actuator more compact.
  4. Introduce new, lighter motors (probably).
  5. Make more space inside Stanley for compute and batteries.
  6. Further assembly improvements.
  7. Reduce the number of types of screws used in the design
  8. Develop Mobile Application to control .Stanley missions.
  9. Create SDF for simulations.
  10. ...

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Discussions

rraetz wrote 08/11/2021 at 06:56 point

Amazing project, but a bit disappointing that you don't release any files... Are you planning to monetize it or is there any other reason? 

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Ahead wrote 10/26/2021 at 01:03 point

We are working on a kit and organizing new material.  We will be releasing some files at one point.

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jnesselr wrote 08/07/2021 at 18:11 point

Apparently the files existed and were then removed at some point? What's the reasoning behind that? I'd love to look at the files in a bit more detail. It looks like you might be using Fusion 360, is there a way to look at the entire file/assembly of that?

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Damian Lickindorf wrote 08/07/2021 at 19:01 point

nope, the full design was never published.

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jnesselr wrote 08/07/2021 at 19:10 point

Is there any particular reason why? ie, why not open source it so others can build it.

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ntrewartha wrote 08/07/2021 at 11:28 point

Is there a kit available - I have no 3D Printer?

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Ahead wrote 10/26/2021 at 01:04 point

We are working on a kit and we will be announcing something soon.

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Tor wrote 08/06/2021 at 16:03 point

I love this project. Great work so far.

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tuban96 wrote 05/14/2021 at 15:42 point

Any news on this project? I see there are no [longer] FIles available.

Can each leg rotate about the body axis independently? In the video, they all move together, but it seems like maybe they can.

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abhiramrayadurgam12345 wrote 04/13/2021 at 16:45 point

what is the estimated total budget for this project?

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fox007ggr wrote 01/29/2021 at 01:28 point

What is the name of the project on GitHub?

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marazm wrote 01/10/2021 at 10:49 point

Jaki ma udzwig ten robot. Da się nim przenieść powiedzmy lekarstwa, albo wodę? wystarczyłby np. 2 litry wody + kanapka. Wtedy można było by to coś wykorzystać do transportu a ludzie zapewne chieli by zając się programowaniem. Gotowe moduły mógłbys sprzedawać jak Józef Prusa swoje drukarki

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Jamie McLaughlin wrote 01/09/2021 at 10:35 point

Amazing project!  Are you planning on making the models available at some point?  I'd love to experiment with the design.

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Damian Lickindorf wrote 01/14/2021 at 14:35 point

Please read the "Files:" section of the Description

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Nick wrote 07/31/2021 at 06:56 point

There are no Files in the 'Files' section ...

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Damian Lickindorf wrote 07/31/2021 at 16:13 point

@Nick that comment is out of date, files for this project will not be released.

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Nick wrote 08/09/2021 at 00:49 point

That is disappointing to hear that they wont be released. It looks like an awesome project.

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David Greenberg wrote 01/08/2021 at 17:50 point

I really like your design. Do you have any posts I could read about why you chose to use capstans over wobblers?

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Damian Lickindorf wrote 01/08/2021 at 18:21 point

Wobblers?! 

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David Greenberg wrote 01/08/2021 at 19:01 point

Haha, it's a funny name I've heard is slang for cycloidal gearboxes, another small way to get a big reduction. I know that harmonic drives (which now sums up the 3 compact low-to-zero backlash gearboxes I know of) can be annoying due to the constantly changing flexion of one component, which can drive up costs. I think yours is the first capstan quad I've seen, and I'd love your thoughts on why capstans over cycloidal drives. I can send you some links to cycloidal drive quads if you haven't seen that design.

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Damian Lickindorf wrote 01/09/2021 at 01:16 point

@David Greenberg You could compare against many things, cycloids aren't even a worthwhile comparison cause the range of reduction ratios they offer has very little overlap with what u get with capstans. First the ratio - you need less than 1:9 to have a proper Quasi Direct Drive actuator, to achieve the torque transparency required to apply advanced controllers like the MIT mini cheetah one. (this is not true for all scales, but at this scale it is). So here cycloids are out of question already - just because of the ratio - they are also bad for many other reasons I won't get into. The only worthwhile comparison is to the planetary gearboxes in the actuators used in MIT mini cheetah and all similar bots. A planetary reducer is a better solution, it might be the best available - but only if you can fabricate your bot in metal. I decided to limit myself to 3D printing - and when we consider 3D printed planetary gearboxes - they would need to be really bulky, contain a lot of bearings and would wear quickly, plus will never be truly 0 backlash. A Cable drive can be as efficient as a planetary (also as torque transparent) - and at the same time, it does not suffer because of the limits of 3D printing. There are no contact spots that are under loads as high as the loads on teeth of a planetary gearbox. Thanks to this a highly torque transparent yet lightweight and robust to high dynamic loads can be manufactured using only 3D printing.

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David Greenberg wrote 01/09/2021 at 01:20 point

Your reasoning makes a lot of sense. If you have any references on other downsides of cycloids, I'd be interested in reading, especially as to whether the downsides are fabrication or control related.

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Damian Lickindorf wrote 01/09/2021 at 01:54 point

@David Greenberg the downsides are mainly low efficiency, and high massif higher efficiency is attempted (you could easily fit 50 bearings into a cycloidal gearbox if you want all contact to be rolling contact). I have experience making cycloids, they are good for robotics, even cobot-style robotics - but legs need much more than that in terms of torque transparency.

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rraetz wrote 01/08/2021 at 09:00 point

This is amazing! I had a very similar design in my mind for a long time, but never had the time to realize it. I'm an engineer working in haptics where capstan drives are used quite often and I am conviced that they are very nicely applicable to quadruped robots. So I am really stoked to see your amazing implementation of this kind of transmission. Looking already forward to seeing your next progress update! 

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ekaggrat singh kalsi wrote 01/08/2021 at 00:29 point

really cool work . !i wish i could afford to make one :(

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Damian Lickindorf wrote 01/08/2021 at 02:04 point

I did my best to go as low with the price as i could, while still making a true high performance BLDC based quadruped. Below ~2400usd you need to go with hobby servos or dynamixels. There are also cheaper bldc options if you're willing to solder your own ESC's - take a look at the open dynamics initiative 

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Dan Maloney wrote 01/07/2021 at 17:24 point

Nice design, I appreciate the attempt to keep it affordable.

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Damian Lickindorf wrote 01/08/2021 at 02:04 point

Thanks :D was trying my best! 

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