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Software and control design for the MIT Cheetah quadruped robots
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- BuildIts Feed Reaction wheel motor assembly 2 weeks ago
March 4, 2019
Hello there, mini cheetah.
36 comments:
Congratulation!
From your thesis: "The particular model used nearly identical in shape and performance to the T-Motor U8, which was used in the direct-drive legged robot Minitaur[20], but available for for between $60 and $90, less than 1/3 the cost of the U8." Do you have a link to the actual motor used?
I originally purchased them on Ebay formerly here (https://ebay.to/2XF3iMb), seller offered a bulk discount. Now I'm getting them directly from iFlight. They've also been on sale on Hobbyking a few times for $60, but are out of stock now.
Impressive work! I'm really happy that I found your blog after watching official "mini cheetah" video on youtube :)
Ha! I suspected it might be you behind the Mini Cheetah videos that started popping up in my feeds. Congrats, great work! Regarding the Front Housing part of the actuator, did you use a 4- or 5-axis on the Haas for the side vents? Or was it some kind of indexing fixture?
I did it on the 4th axis of a Dyna 1007 which has been converted to Linux CNC controls
Hi Ben, Really thanks for the amazing work, this provide more flexibility for people working on it. Will the whole thing be open-sourced? I am out of school already and working on STEM education now, but I am still a great robotic enthusiast. It will be great if I can build one at home and helps improving it. BTW, is the back flip from trail and error?
The backflip was done with offline trajectory optimization. There was a lot of trial in error in simulation to get that to work well, but on the actual robot it just worked. It is not open source right now - that's not really my call. I do hope to make the design available eventually though.
Just take a look at flipping part in your thesis. It's said that the code to generate this motion is open-sourced but i can not find the right link for this part in Appendix A. Do you plan to share it?
Hi Thomas, Sorry for the mistake in the text. I'll check with the other people I worked with on that project and see if they're okay with sharing it.
Hi, Ben You did a really awesome job, thanks for you sharing. I would like to know which simulation software are you use? and some details about the accurate dynamics? Thanks in advance!
Our simulator is all custom. The rigid body dynamics are computed with spacial vectors with some additions (http://royfeatherstone.org/spatial/)
Thanks your reply first! I mean, after you get the link accelerations, then you use what to draw it? OpenGL, ODE, MoJoCo or something? And you also have to solve the collision and friction problems, why not use a existing simulator? Or do you have the plan to opensource or release your custom simulator?
The graphics are drawn with OpenGL. We don't need particularly fancy contact dynamics - we have two different ones, one with a compliant ground, and one with hard contacts (which is faster) I do not know if there are plans to open source the simulator. That's not really my work.
Thanks Ben! Really appreciate for your answer. Now I just have two questions here: 1. About the rigid body dynamics, do you write your own featherstone-algorithm, or use some libraries like RBDL? 2. I wonder if there has some links or references for contact dynamics(your two different ones). You know, the contact dynamics is always quite difficult to simulate, I really want to know how to make it works like yours! Thanks in advance!
Hello Ben, just simply put - truly amazing work. I would like to try and build one for a test bed, however I could not find any CAD data for the mechanical components, such as the housing, gearbox or rotor modification. Would it be possible for you to upload these? Thanks!
Sorry, not at this time. I hope to eventually though.
Is it because you don't have them, or cannot share them through some licensing issues?
Are there any other elements that are not provided or just the CAD files for the actuator housing? From a quick scan of your thesis and github it looks like most everything else is provided?
Your work is astonishing and I hope you will continue to develop cutting edge robotics. Your blog has been a great inspiration for other students of robotics like me.
Was the gearbox lubricated? If so, willing to share with what?
I'm using a thick molybdenum disulphide grease: https://www.amazon.com/Yamalube-ACC-MOLDM-GS-10-Molybdenum-Disulfide-Grease/dp/B005XA2EQK
Great work. the bot is very dynamic and compact, it looks way better than cheetah 3.I am an UG student in mechanical from india and i am very much into this legged robots, can you explain what are the topics i should develop knowledge on to make a legged bot, and also could you suggest some source for learning dynamics of walking of legged bots
I've got a similar motor to your iFlights, a BE8108, and I am having a terrible time trying to liberate the stator from the aluminum back housing. I've tried heat, cold, PB blast off, acetone, combinations thereof, all with no luck. I'm about to just use a cutoff wheel, but figured I would see if you could reveal what technique you used with your motors to extract the stator?
First cut through the aluminum cylindrical part holding the stator in 3 or 4 places. Be careful not to cut into the stator. I originally did this by passing a hacksaw blade through the hole in the center, and later by plunging through on a CNC Mill. Then use a flat screwdriver and hammer to bend the 4 sections of the aluminum inwards. Then the stator should fall right off. To hold the motor while doing these operations, I passed a big bolt through the bearings in the center, tightened a nut on it, and held that in a vice.
Yeah, the hacksaw seems to have done the trick, although my hand hurts enough now that yeah, a mill will be the way to go for more than 1 or 2. Thanks!
Truly great work.
That's pretty incredible - particularly how you are using more stock components and less expensive custom ones. I've been following your work since the Rubik's contraption, and it is so impressive. Just wanted to say how awesome this is - can't wait to see a pack of 10 of them running around!!!
Hi Ben. Truly amazing work! I have a question about the source files that you posted on github. It seems that the firmware running on the motor (3phase_firmware) and the eagle scheamtics (Cheetah driver integrated V4) aren't matching. Eg. in hw-setup.cpp the ADC pins are defined as PC_0 and PC_1 but in the schematics PC_0 and PC-1 are not connected. There are other discrepancies as well. Am i looking at the correct and lates files? I am to build a baby cheetah and any work that i can leverage would be awesome. Thanks, eddy
The latest drivers are these ones: https://github.com/bgkatz/3phase_integrated/tree/master/New%20Version And the latest firmware is here: https://os.mbed.com/users/benkatz/code/Hobbyking_Cheetah_Compact_DRV8323/ The previous version used a different gate drive ic (DRV8301), so pin configurations were a little bit different.
You guys are amazing. When I read the post and watched the videos of your robot, I felt like a kid again. You represent the dream of hundreds of young engineers around the world. MIT is the best and you are representing this institution in a excellent way. Congratulations!
Can we see some more progress of woofer?
YOu must be proud that you're already copied in China: https://www.youtube.com/watch?v=oDept9NPNps
Hi, Ben It's a really amazing job. I noticed MA700 has been uesed as position sensor on the latest version, but it seems still use AS5147 as position sensor in the fireware you provided on Mbed(https://os.mbed.com/users/benkatz/code/Hobbyking_Cheetah_Compact_DRV8323/), can you provide the fireware including MA700 codes? Thank you so much.
Mini Cheetah Clone Teardown, By None Other Than Original Designer
[Ben Katz] designed the original MIT Mini Cheetah robot, which easily captured attention and imagination with its decidedly un-robotic movements and backflips. Not long after [Ben]’s masters thesis went online, clones of the actuators started to show up at overseas sellers, and a few months after that, clones of the whole robot. [Ben] recently had the opportunity to disassemble just such a clone by Dogotix and see what was inside.
Amusingly, one of the first things he noticed is that the “feet” are still just off-the-shelf squash balls, same as his original mini cheetah design. As for the rest of the leg, inside is a belt that goes past some tensioners, connecting the knee joint to an actuator in the shoulder.
As one may expect, these parts are subject to a fair bit of stress, so they have to be sturdy. This design allows for slender yet strong legs without putting an actuator in the knee joint, and you may recall we’ve seen a similar robot gain the ability to stand with the addition of a rigid brace .
It’s interesting to read [Ben]’s thoughts as he disassembles and photographs the unit, and you’ll have to read his post to catch them all. But in the meantime, why not take a moment to see how a neighbor’s curious sheep react to the robot in the video embedded below? The robot botches a backflip due to a low battery, but the sheep seem suitably impressed anyway.
21 thoughts on “ Mini Cheetah Clone Teardown, By None Other Than Original Designer ”
This is why you should either patent your stuff or make it “as a service”. Bill Gates can buy anything and play any video game he wants. By comparison Richard Stallman can’t even afford decent clothes. If Linux was paid software it would be better.
If Linux was paid software, it wouldn’t be what it is. It’d be Windows, with all the lock-in and “keep up with the rat race” that it includes.
I’ve been using Linux since about 1996. I prefer it to Windows, though I have to use Windows at work.
I prefer the ideals that Stallman and Torvalds represent over the lack of ideals that Gates represents. “Gimme more money” just doesn’t inspire me.
Some people do things to learn. Some people do things to help other people. Some people do things just to get more cash.
It takes all kinds of people to get things done in this world, but I know I prefer those whose main goal isn’t merely to fill their own pockets as full as possible.
Great answer!
To what purpose, what service? This project is the result of a master thesis IIRC, it doesn’t really fill any marketable need. It is a really good applied research project that could be the starting point of other marketable developpements. Leaving it open is a way of boosting innovation, and makes a lot of sense when an organization is there to research and not specifically to make money (even if they are always happy to get more funding). The fact that it’s pretty hard to actually find those clone robots available after a couple of years also shows that the market is not really there. Look at boston dynamics, they are still struggling to market their robots.
In the same way, if Linux was paid software, maybe it wouldn’t exist at all today. In what market Linux would have been competitive at the time? Was there room for a new competitor? I’m not sure, but what I am sure of is that Linux plays a bigger role in computing than any other OS competitor in the current times.
The “as a service” business model is actually an interesting lead on how to market free software: provide knowledge about your system for people to understand it and potentialy improve it or create new uses, while making it easier for a person to pay you regularly instead of deploying it themselves. Of course you have to absorb the NRE costs compared to any competition that could just copy your service, but there are ways to counter that (mainly closing parts of the functionnalities sadly).
As for Stallman and Gates, your comment is funny, but they simply followed different goals. Not everything is about getting more money than needed.
(Also, good luck enforcing a patent in China, your best option is probably to keep everything secret.)
I think the point is that innovative companies like you cited in Boston Dynamics are unlikely to be able to continue to innovate if knock off clones of their products keep appearing from China. You can’t survive if you pay for all the R&D and someone else gets to commoditize your product.
The point of the author in working on his master’s degree probably has something to do with wanting to be compensated at some point to pay for his education. Maybe he does not need to be Bill Gates but he probably would like to eat and be able to afford a nice vacation some day. No one can really afford to be absolutely altruistic when performing their craft.
Indeed, but the mini cheetah wasn’t a development from Boston dynamics. I was only referring to this company to illustrate the lack of existing market. Their work is not open AFAIK, and it potentially won’t make them successful if there are no problems to solve economically with their solutions. Funding this kind of project publicly to open the results may be the best option, in order for future commercial developers to find a way to use (part of) it and market it.
I think we shouldn’t be that afraid of the copying of the results of such projects. They are far from commercial products, and a big part of the valorization of such results actually comes from the know-how of people working on them. If you’ve read Ben Katz’s blog entry, you’ve seen that he immediately noticed some dumb vestigial design aspects that he would have immediately changed. The Chinese didn’t because they don’t understand the project as much as the original team. And if they did and actually changed the design, it would be to the benefit of everyone (ideally, if they respect the licensing terms). In that way, a future company hiring Ben Katz or people having worked on the origonal project would have a significant edge over potential copying competition, at least for a couple of years. I get that it’s not reassuring to investors when you don’t have a nice description of your valued and locked down IP to show them, but it shouldn’t be frightening to engineers.
As for the author of the project, I don’t know about the MIT rules, but I would be extremely surprised if the original author has any ownership on the intellectual property generated by his project. Making the results open may actually be the only way for him to keep using the results of his work…
Also I’m not talking about being altruistic. To reassure you, people working in research center are still paid, just not necessarily to generate directly profitable results. You could also argue that he found retribution in the fame he got from the project, the knowledge he acquired, the entry in the resume and the degree he received. I have no doubt a graduated MIT engineer will find ways to be able to eat and take some vacations ;).
The inescapable fact is that if you open source your design it is a lot harder to make a profit on it. You have all the NRE and research costs and your competitors don’t, hence they can sell it for less and still make a profit. If it is open source anyone can make it themselves. In the case of software it completely removes the ability to profit from it unless you offer some form of technical support. Considering robotics is very software based it isn’t a good idea to open source any of it if you want to make a profit.
In order for open source to be profitable you need to provide something the user can’t provide for themselves. For physical parts that is easy, most people don’t have access to or it is to expensive to have the part machined or injection molded. For software when anyone can download and run it you can’t make much profit, a lot of companies that make open source software ask for donations, that should tell you something about it’s potential profitability.
For software there are certain steps you can take to make it profitable, again to do with providing things that the user can’t, like web hosting or technical support.
You can never avoid the copying problem though. The only way around it is keeping at least part of the system closed source but even then someone might find a way to reverse engineer it and the open source community wouldn’t like it much.
Often universities allow students to patent their designs and can even help the students with the patent process, it all depends on the project proposal and the agreement with the university and any agreements with anyone that funded the project. It absolutely is possible and often encouraged to patent any new ideas you have during your time at university and I know of a few students at my university that have turned a project into a full business, I think the university offers its support for a fraction of the company and staff working at the university are open to create their own deals (some have companies themselves that are independent of the university). The goal of universities is to teach and to do research, none of it needs to be open source
Simply put Ren, people that create as a passion instead of a career drive science and technology.
People that create for a career instead of a passion drive the economy.
Look at the 3d printer world for a good example. The hobbiests drive the industry forward
In what world?
Are hobbyists creating polyjet 3D printers? Are they creating functional metal 3D printers?
I don’t think so, all the advanced and new features tend to come on expensive closed systems first, this even applies somewhat to slicers.
Hobbyists may be driving demand, but for the most part they aren’t driving the industry forward. Most new open features tend to come from research labs or master’s thesis anyway, not really from hobbyists.
If linux was paid software, it would have never achieved adoption and would become a proprietary shitpile even if it did survive ten years (more likely it would be nothing more than a stub article in computing history by now). SaaS is dreck and represents a slide into techno-Lysenkoism. Total drain of competence on a long enough timeline
Well BSD is free and just look at how it’s taking the world by storm. Maybe, being free isn’t enough for success.
The reason why BSD isn’t taking the world by storm is because of the success of Linux, and the success of Linux is due to AT&T’s attacks against BSD in its early days.
iOS and macOS are based on BSD… they haven’t maybe ‘taken the [whole] world by storm’ but I’d say they’re doing pretty well?
If RMS cannot afford decent clothing it’s of his own doing.
My favorite parts is how the product manual talks about their “patented technology” dual absolute encoder and their “three years of painstaking development”. Typical. Even if the original author did not patent the device, they should have at least given a shout out for using his idea. If China will not respect other people’s work they should be removed from the WTO.
Agreed. The CCP should have been economically forced into breaking up after the 1989 Tiananmen Square Massacre, similar to what happened to the Eastern Block in soviet Europe.
They like to pretend they’re “one people one China” but there are 50 or more different ethnic groups and anywhere from 3 to 23 (or more depending on who you ask) different regions. It is past time for those regions to be independent nations. Let Xi the Pooh keep Beijing, the rest of the world can fence it off and treat it like a nature preserve, a living example of what NOT to do.
The sensoring of the actuator is actually partly innovative. But it would have been nice to open it (and maybe mandatory, depending on the license).
About China, I have mixed feelings in this regard. On one hand they can simply rip people’s work and make more margin because of their extremely low cost of production, killing the devs, but on the other hand I had interactions with Chinese companies about having access to their source codes that I wouldn’t dream to have with EU or US companies. In one case, it was because they weren’t respecting an open license, and they fixed the situation immediately. The lack of openness was more due to a lack of care but they were happy to comply. I have yet to encounter such interactions outside of China…
I’m not going to totally defend China’s approach to intellectual property, but what often gets elided in these discussions is that IP isn’t a free-for-all in China, they just have a different system. Bunny Huang has a nice explanation of this: https://www.youtube.com/watch?v=y5QkM2Work0
Remove China from the WTO to protect western laborers and inventors? LMAO what do you think global trade is for? Helping you?
Kinda reminds me of the tendons in a horse’s leg. There’s really not much down there except.. well, biological equivalents of drive belts, tensioners, and pulleys. Which is also why the legs never heal right. They barely even have blood below a certain point.
It is always interesting to me how much history is lost. How can you “clone” something that is open source, and openly shared? Most quadruped research was funded by DARPA, and the research was all done out in the open, and documented in many papers, and git repositories. “Chinese clone” always has a negative connotation?
I’ve written about some of the past here: https://github.com/MAVProxyUser/ConsumerQuadruped
Mind you… these companies that fail to directly credit MIT (until forced) like Unitree, are being unscrupulous to say the least. https://github.com/unitreerobotics/unitree_legged_sdk/issues/55
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This thesis details the hardware and control development for a low-cost modular actuator, intended for use in highly dynamic robots.
Abstract. This thesis documents the development and implementation of software and controllers for the MIT Mini Cheetah and MIT Cheetah 3 robots. The open
This thesis documents the development and implementation of software and controllers for the MIT Mini Cheetah and MIT Cheetah 3 robots. The open
Here's my thesis on the actuator and robot design. I designed and built all the all the hardware, both mechanical and electronics (with some
The last iteration of the MIT Cheetah is a smaller version called the MIT Mini Cheetah. B. Katz designed it as part of his Master's thesis project [43] .
We implement this framework on a quadruped robot Mini Cheetah [4] . The robot therefore could walk quadrupedally ... Thesis. Full-text available. Sep 2017.
[Ben Katz] designed the original MIT Mini Cheetah robot, which easily ... Not long after [Ben]'s masters thesis went online, clones of the
Mini cheetah: A platform for pushing the limits of dynamic quadruped control. B Katz, J Di Carlo, S Kim. 2019 international conference on robotics and
with MPC and tested on the Mini-Cheetah quadruped robot. To demonstrate the robustness and versatility, the controller.
This specific methodology flow results in robots like MIT Cheetah [9], Penn Minitaur [12], and GOAT, the robot introduced in this thesis.