Backdrivable reduction mechanism

[medo79]

Dear All,
I am looking for a lightweight backdrivable reduction mechanism with 1:100 reduction ratio. Is there any option to for lightweight and backdrivable reduction mechanism?
regards,

 

[desertfox]

A gear train? would there be any torque you require?

desertfox

 

[Occupant]

Or how about harmonic gearing?

 

[medo79]

but harmonic drive is not backdrivable. I am looking for backdrivable mechanism.

 

[medo79]

The required torque is 40 N.m continuous torque and 110 N.m peak torque.

 

[BobM3]

Planetaries can get you 100:1 and are back-drivable.

 

[MikeHalloran]

If you're intending to backdrive it all the time, you should call it a speed increaser rather than a reducer, so as to avoid confusion, and so that any potential suppliers better understand what you want to do.



Mike Halloran
Pembroke Pines, FL, USA

 

[spigor]

I have a prototype of such a drive sitting on my shelf. We should get in contact directly to discuss it further.

 

[drawoh]

but harmonic drive is not backdrivable. I am looking for backdrivable mechanism.

Harmonic drive is backdrivable. I have designed a system with harmonic drive, and there is no problem turning it by hand. In some applications, it is even used as a speed increaser.

JHG

 

[medo79]

Is Harmonic drive is backdrivable? What about the resistance torque from output to input? Is the resistant torque small?
I will use it as speed reducer in a part of cycle and as backdrive in other part of the cycle. Where can I buy it with low price? I checked the price in

http://www.harmonicdrive.net/

, but the prices were very expensive.

 

[medo79]

@spigor
what do you mwan with "I have a prototype of such a drive sitting on my shelf"? I don't get what do u mean?

 

[drawoh]

medo79,

When you drive anything through a gearbox, the inertia of the load is multiplied by the square of the gear ratio. In your case, it is multiplied by 10,000. You will notice this.

My understanding is that harmonic drive has a fixed friction torque. It is about 90% efficient at maximum torque. It is less efficient at lower torques.

Harmonic drive is not cheap. Rather than buy a packaged gear reducer, you might want to buy just the gearset, so that you can integrate it with your system. You can wind up with a really cool design.

If you want dirt cheap, buy some worm gears, and forget about backdriving and efficiency.

JHG

 

[medo79]

Is the dynamic mathematical model for harmonic drive is similar to any gearbox? Or it is different.

 

[spigor]

medo79, I mean I have practical experience in developing of such gears, and I have one of them available physicly, e.g. for testing purposes. Should probably only be downsized to fit your application, but that's not a problem.

 

[drawoh]

Is the dynamic mathematical model for harmonic drive is similar to any gearbox? Or it is different.

What do you mean?

The output speed is an exact multiple of input speed, just the same as a gear drive. There is no backlash in a standard harmonic drive gear set, but there is a little bit of elastic wind-up.

The catalogues are very good. Read them.

JHG

 

[medo79]

Where could I find the harmonic drive catalogue?

 

[drawoh]

medo79,

Google.

JHG