Selection not working in cheetah3d4/11/2023 ![]() As Sangbae points out, a rugged robot means that you can work less in simulation, which is much more fun (and potentially more productive) and seriously how else do you come up with all of those outtake videos? Not breaking is a big deal for research robots, because it means that you can try things on them, or trust your students to try things on them, without first setting up quadruplicate e-stops, putting on body armor, getting out your checkbook, and standing next to the fire alarm. But once the degrees of freedom get to be too much, hydraulics has a huge advantage. There are other prices to pay for hydraulics, of course, so I think up to a certain number of degrees of freedom, I think electric actuators would be hands-down better in every aspect. That’s where hydraulics starts becoming attractive, because you have this one big power source, but the actuators are relatively small, and a lot smaller than an electric motor with equivalent torque. But if you have 24 degrees of freedom, and you need to have multiple degrees of freedom in the wrist and ankle and neck… there are so many degrees of freedom all jumbled up in one ball and socket joint, that’s where electric motors tend to suffer. So up to 12 degrees of freedom, that’s no problem, and I think electric motors are the way to go. I think the question becomes interesting when it comes to humanoids, because humanoids require so many degrees of freedom. It’s not very noticeable, but Mini Cheetah has shoulders that are bigger relative to its body length, making it more powerful.Įlectric motors scale up so easily that making a horse-sized robot, you’d be able to make it run as fast as a horse. The secret is details in the design: If you look at the shoulder of Mini Cheetah, they’re bigger, relatively, than in Cheetah 3. Electric motors scale up really well, and I was honestly surprised at Mini Cheetah’s performance, because electric motors scale down badly. He thinks there are some scaling issues, but I disagree. I had a discussion about this with Marc Raibert-he and I have slightly different opinions. Why are electric actuators best for robots like Cheetah and Mini Cheetah? Hydraulic motors are still being used in most high performance dynamic robots. The hope is to have, according to Sangbae Kim, “a robotic dog race through an obstacle course, where each team controls a Mini Cheetah with different algorithms, and we can see which strategy is more effective” Basically, we’ve reached a level where it’s so reliable that we can give it to other groups that are suffering a lot with their hardware. We’ve done 3-hour long demos with no problem. With Mini Cheetah, you can run it like 5 hours a day. If you have a robot like Cheetah 3, what is the actual time that you’re running it? It’s probably 1 percent or less, because it’s hard to run, it’s dangerous, or if something breaks, it’s down for a month. If you talk to anyone working with robots they can tell you how painful it is: Robots are fragile, dangerous, not enough torque, hard to model. ![]() Sangbae Kim: This is mostly for research acceleration. IEEE Spectrum: Why make a smaller version of Cheetah? The backflip you see in the video was, somehow, accomplished on the first attempt, and for its next trick, Mini Cheetah is being taught to perform the very cat-like maneuver of landing on its feet after being thrown into the air.įor more details, we spoke with Sangbae Kim, a professor of mechanical engineering and head of MIT’s Biomimetic Robotics Lab. The motors (now off-the-shelf and cheap rather than custom made and expensive) have a single stage 6:1 gearbox, and we’re told that they have a maximum joint speed of 40 radians per second, which is (in technical terms) frickin’ fast. ![]() So last week we spoke a little bit with Sangbae and asked him a few questions about Mini Cheetah’s design and his future plans for the robot.įor some context about this robot, MIT notes that Mini Cheetah weighs about 20 pounds, with 12 modular motors that give each leg a powered hip joint (with 2 degrees of freedom) plus a knee joint. We wanted to make sure you saw the video as soon as possible, which is why we featured it in Video Friday, but of course we wanted to know more about the robot. Earlier this month, MIT posted a video of Mini Cheetah, a small quadruped robot from the lab of Sangbae Kim.
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