Servos Suited for Legs

Question

Can anyone provide some advice on high torque servos suitable to use for robot legs? I just finished installing the standard EZ robot HDD servos - one in each hip and one in each knee. When powering up, the robot will topple over as these servos are not strong enough to hold it up (the start up position is 90 degrees). My robot is 4' high and the top half weighs a lot more than its legs. I want the robot to slide walk, not lifting the leg at all. CR servos will be in the feet.

Any advice would be appreciated.

Jeremie · Answer

There are a few options out there. There are a number of Dynamixel servos from Robotis that would likely fit the bill. Otherwise, you can look at the servos that are used in the inMoov project, but be aware that they are a much larger form factor. HS-805BB and TS-80 are some servos that are used by the inMoov. I would suggest though to find a digital servo because the noise with analog servos for a walking robot would be unbearable. You could also look at augmenting the EZ-Robot HDD servos with 3D printed gearing to increase the torque. The worm gear in the inMoov shoulder is a good example. There is also the openDog project by James Bruton for another idea for driving robot legs. Any way you look at it, legs for a 4-foot tall robot is a large challenge, you will likely need to engineer a few different prototype ideas.

Jeremie · Answer

I forgot that James Bruton also did a humanoid leg project, and there was a 5-foot robot with legs here in the community as well. The robot here moved by slide walking as you described. Hopefully, another community member can remember that post.

Nomad 6R · Answer

afcorson did you print the chest ? very cool robot.

Mickey666Maus · Answer

Nice robot, but those servos will not have enough power to operate it...you should have done some testing before building the whole thing I guess! But don't let this bring you down, failing is always a good lesson and I am sure you will be improving your build soon! Hope to see updates on this one, its beautiful!!

Jeremie · Answer

I found it! It's HAL the robot that walks and talks https://synthiam.com/Community/Robots/HAL-THE-ROBOT-THAT-WALKS-AND-TALKS-18477

Perry_S · Answer

That's a great bot and I'm surprised nobody has made the link as to what it is yet. As a hint, I would love to see it with a Dr. Theopolis around his neck. Beee De  Beee De Beee De

EzAng · Answer

Hi Nomad, Hi, Perry_S, you said you have the same 3d printer as I have, any does and don'ts?, pointers? EzAng

Perry_S · Answer

Hi EzAng - no real advice. I was able to just use mine out of the box. Use Simplify 3D as a slicer.

DJ Sures · Answer

I can picture the movie in my head but the name escapes me. Don’t tell me though. My brain is gonna get it without googling.  I keep picturing the robot bending at the waste and being super stiff in the show. Just can’t seem to get it clear enough in my head. Stay tuned for my eureka moment lol on topic of the servos - I think you’ll need to visit what the inmoov and similar style robots are doing. Because a servo won’t really have the juice at the price point for what you’ll want.

Nomad 6R · Answer

i think the biloid premium version is a good excample. maybe you need to makea c-type robot and use heavy robotis servo's. aldo they are very expencive.

Perry_S · Answer

Come on DJ. Not a movie, think TV. Think spandex.

Dave Schulpius · Answer

I'm pretty sure the movie is Buck Rogers in the 25th Century.

Dave Schulpius · Answer

I'm not sure how these would work for legs but you could use Servo City gear boxes with the recommended servos installed. There are many choices of gear ratios, continuous or with positioning feedback and comes in different mounting options. The ones with the most torque are 3304 oz-in, 0.98 sec/60. These have 7-1 ratio. The problem is the higher the torque the slower the speed. Their pricey between $110 - $270 each depending on how strong you want them. Here's the link: https://www.servocity.com/servo-gearboxes/ Have fun!

DJ Sures · Answer

Dave I was supposed to guess!

DJ Sures · Answer

Oh and also wasn’t a similar robot in space balls?

RoboHappy · Answer

Yes DJ, you are correct I highly recommend those Servocity gearmotors, as I am using them on HEMI. The torque on them are awesome.

Dave Schulpius · Answer

Sorry @DJ. I thought the challenge was open to anyone. However it sounds like you won anyway.  I didn't remember the one from Spaceballs till you mentioned it. Congrads! LOL.

DJ Sures · Answer

What was Perry thinking of with a tv show wearing spandex?

Perry_S · Answer

Buck Rogers was a TV series and not a movie. I used to watch it every Sunday Night. I particularly liked Dr. Theopolis who was like a council member robot that this robot (Twiki) wore around his neck.

As far as the spandex comment, they had some pretty awesome costumes in the show. At least awesome to the 13 year old boy I was at the time. The show was kinda known for it.

And don't forget the very evil Princess Ardala

DJ Sures · Answer

I had no clue buck Rogers was also a tv series. I watched the movie a couple times - but had no idea it was a series. Guess I know what I’ll be watching this winter

Nink · Answer

I own a robot that walks :-)

afcorson · Answer

Thanks for all the comments and links. I will follow up the link to ServoCity. The servos in the legs can be swapped with other servos easily enough, although they are strong enough to move the legs if the robot was placed on a harness. The arms I have tested with the EZ robot servos and they work well enough. Twiki's parts were bought from Resident Dreamer, but I am only using the body.  I made all the other components as they needed to be light and articulated.

afcorson · Answer

Thanks for all the comments and links. I will follow up the link to ServoCity. The servos in the legs can be swapped with other servos easily enough, although they are strong enough to move the legs if the robot was placed on a harness. The arms I have tested with the EZ robot servos and they work well enough. Twiki's parts were bought from Resident Dreamer, but I am only using the body. I made all the other components as they needed to be light and articulated.

afcorson

Servos Suited For Legs

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