Torsional Spring in Two-mass System

Hello!

I need a spring that can connect shafts of two motors. One of the motors is controlled by a motion controller, while another one serves as a load:

I***********I I****************I
I**Motor 1**I----||---I*Motor 2 (load)*I
I***********I / I****************I
Spring

This setup is used to demonstrate how to control a two-mass system where the masses are not rigidly connected.

Unfortunately, I cannot find such a spring coupler. There are a lot of spring couplers on the market which are used to compensate for misalignments of motor shafts. However, in my case I need the spring coupler that would introduce torsional axial flexibility in the system. This is pretty unusual for couplers or muffs...

I would be very grateful if anybody could point me where I can order or buy such product.

Thanks.

Aleksej