Help! I need to source a large, high torque easily source-able servo motor.

3D Printing
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Help! I need to source a large, high torque easily source-able servo motor. The end goal for this is to attach it to a printed gearbox to move a very large humanoid leg.

It needs to work something akin to the image below, which is what I currently use for the arms in my bot. This is not fast enough with enough torque to drive a leg.
Can anyone point me in the right direction?

EDIT:
the motor I use at the moment is a super large hitec 20kg servo. This was the best in class for reasonably priced servo tech, but it is not enough.

11029202eeabdf61dec5a8acef288e51.png
11029202eeabdf61dec5a8acef288e51.png665×763 52.8 KB

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A good place to start is see what folks like Adafruit and Solarbotics offer.

For example: http://www.adafruit.com/products/1142

3

Hit the RC hobby sites. There are quite a few high torque, high strength, metal gear servos available these days.
I see ads for them in every issue of Robot and Servo magazines.

4

I should have noted I have checked the obvious places :slight_smile: I will be designing a whole new gearbox, so it doesn’t even matter too much what servo it is, as long as it is reasonably quick and high torque

5

@Andrew_Plumb
10kg/cm would be torn apart in seconds :frowning:
I currently use Hitec servvos that pull 25kg/cm. Problem with these servos is that in order to maintain speed with good output torque, the input servo needs to be good and strong.
Cheers!

6

What about Epicyclic (planetary) gearing?

7

Why use such a servo? Get a normal BLDC with a planetary gear, take an incremental sensor and build a strong “servo” that way yourself! It’s a bit more expensive but you’ll definitely have a much stronger drive than with a servo off the shelf.

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@Hendrik_Wiese
It is something that I have thought long and hard about. Especially as I run the OpenServo project, which is designed to do exactly what you propose.
Issue I have is I want to keep this project as simple and commodity as possible so people can easily recreate it. The less custom stuff the better.
I am not ruling the idea out at the moment :slight_smile:
Thanks for the input!

9

Honestly, what most pros use are hypocycloid or harmonic drive gearing system paired with an encoder.

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@Marco_Alici
Excellent! Thanks for the pointer

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@ThantiK
Agreed. Even better alternative to the planetary gearing system.

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You’re welcome, @Barry_Carter !
I worked in roll up shutter design for a while, where multi-step planetary gearboxes are used. :slight_smile:

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Why print the gearbox?
Just because you have a hammer, not every problem is a nail.

14

I have recent servo spreadsheet here:

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@Marcus_Wolschon
I could just as easily mill it. I have a 3 axis. It isn’t so accessible to others once you start asking them to mill pieces of a machine, or stump up £££ for a gearbox. I am working on an experiment of how much of a robot design can be printed :slight_smile:

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@Billy
sweet, thanks

17

Valid argument.

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Maybe you can change the gear ratio? Either gor more speed or for more torque. You can’t have both…

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How much of an issue are backlash and speed?
I guess a leg must be pretty fast.

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@Marcus_Wolschon backlash is not so much an issue, but obviously as little as possible. Speed and torque are the main requirements here.