# Where finding powerful and special servomotors ?

Hello,

i need special motors for my humanoid robot project to reproduce this movement https://upload.wikimedia.org/wikipedia/commons/2/2e/Pronation_and_supination.jpg arm and others also, how to call this type of servo ? I also wanted to know where I could find very powerful servo, looking around 1000kg.cm, any ideas?

1000kgf-cm is 100Nm which could easily break you, its far far more torque than the human wrist
can handle for instance. Its about what you need to fit an axle nut to a road vehicle. Do you
really know what these torque values mean?

Generally with non-standard applications you need to build your own gearmotor and position
feedback system, or spend money on an industrial servomotor. Noone's going to manufacturer
a vast range of servomechanisms to match every possible robot articulation topology and size,
you either build something from standard parts or pay for bespoke manufacture, which implies
high volume production to be economic.

Simple rough guide to torque:

0.1Nm = forefinger+thumb turning something
1Nm = one hand driving a screwdriver comfortably
10Nm = two hands on a car steering wheel

BTW a 8mm steel axle carrying 100Nm will be twisted about one radian per foot of length, if
that gives you some idea of 100Nm - everything would need to be chunky, in practice that
would mean you'd use a gearbox to increase the torque, and try to integrate its output
directly onto the piece being moved. I can see this sort of torque being appropriate for
a shoulder joint, not ulna-radius twisting though!

Use 1/2 scale RC boat sail winch servos and a gearbox. The sail servos are multiple-turn. And bigger is better!
Brushless servos are also available.

Thanks a lot for your answers, i am sorry i forgot to tell you why i needed this power, i want my 1m30 robot cans pull up at a rate of 1 per second, with a 30 cm arm back (slightly less) and a weight of just 20 kg, servos distributed on the two arms I need is 300 kg.cm 0,5tr / s, i was wrong.

It isn't humanly possible to exert anything like that torque using pronation or supination of the forearm,
nor is it the way a load is lifted. Loads are lifted by flexing the elbow using the biceps and shoulder
muscles. Are you confusing the two motions?

No pronation and supination do not have matter with 300kg.cm 0,5tr/s i need. I don't find servomotors with this torque having a good price, i think it would be better if i use DC motor and turn it in servomotor, whre can i find DC motors like this one of leg's Atlas robot last generation in this picture http://a57.foxnews.com/images.foxnews.com/content/fox-news/tech/2016/02/24/this-humanoid-atlas-robot-can-take-punch/_jcr_content/par/featured-media/media-0.img.jpg/0/0/1456334981015.jpg?ve=1?

Nobody ?