Where to look to buy a very powerful servo?

I require a servo motor of around 100nm.. maybe slightly less, but a very powerful one. Where would you guys look for this and how much would you pay?

I require a servo motor of around 100nm

This is an undefined statment!

Please look at the specification of servo motors on any supplier website, then ask the correct question. :slight_smile:

You seem to be looking for something like this monster.

Or ... make your own

shazhazel:
… a servo motor of around 100nm… …

Let’s just get one thing sorted out. Do you mean something like an RC servo that moves 0 to 1800, or a continuously rotating drive-type motor?

I do apologise for any mistakes, I’m still fairly new to motors… in simple terms, imagine a motor at the knee of a human. From the human sitting down with the knees bent at 90 degrees, it needs to assist the person standing, so the knees would be at 180 degrees now.

Keeping in mind the human weight plus the distance of the force etc, after some calculations i figured that 100nm would be sufficient in most cases.

I’m currently building a small scale prototype with 2.5nm servos and i do have proof of concept.

johndg:
Let’s just get one thing sorted out. Do you mean something like an RC servo that moves 0 to 1800, or a continuously rotating drive-type motor?

0 - 180, so RC

You don’t need a motor with that torque rating - the one I linked to produced the torque at IIRC 3000rpm.
A gearbox is a torque multiplier. If you wanted the joint to move through 900 in say, 7.5 sec, that’s 2rpm, so if you had a 3000rpm motor with a 1500:1 reduction gearbox, that’s only 100 * 1 / 1500 = about 0.07 Nm (70 mNm) from the motor. Ok, I’ve cited an extreme case, but do you see where I’m going? It’s still a pretty chunky gearbox - a worm drive would serve best.
(BTW, someone should check my sums; I’m old, it’s late, and the back of this envelope is pretty crumpled).

You need to specify not only the shaft output torque in Newton meters (N m) but also the speed of shaft rotation (which determines the required motor power output).

If a person rises from a seated position (knees 90 degrees) to standing (knees 180 degrees) in 1 second, the equivalent shaft rotation speed is 1/(4 seconds) or 15 RPM.

johndg:
You don’t need a motor with that torque rating - the one I linked to produced the torque at IIRC 3000rpm.
A gearbox is a torque multiplier. If you wanted the joint to move through 900 in say, 7.5 sec, that’s 2rpm, so if you had a 3000rpm motor with a 1500:1 reduction gearbox, that’s only 100 * 1 / 1500 = about 0.07 Nm (70 mNm) from the motor. Ok, I’ve cited an extreme case, but do you see where I’m going? It’s still a pretty chunky gearbox - a worm drive would serve best.
(BTW, someone should check my sums; I’m old, it’s late, and the back of this envelope is pretty crumpled).

i got a little lost at the calculation but i never realised that gears are torque multipliers! Thank you for that - I think its now time for me to do some research on gears and how they function within a motor.

Also - that motor would be great but its selling for close to £1,000. I think gears are my best bet

Have you researched the existing devices that do what you are designing? They ALL use cable systems to limit the weight on the legs. Don't forget to include the power supply for your motor.

Paul

Paul_KD7HB:
Have you researched the existing devices that do what you are designing? They ALL use cable systems to limit the weight on the legs. Don't forget to include the power supply for your motor.

Paul

I have. I can’t figure out what is exactly going on but i seem to find pullleys, bearings and cables being used - followed by backpacks which i am assuming carries the power supply and motor(s). I’m guessing flex cables are going from the motor shaft down into the legs(?)
Am i mistaken?