How to model a worm gear

[JohnnyMudcrab]

Hey

i need to model a worm gear, so that i can move the joint but it can't be moved from external forces or torques due to the self-locking of the gear. I'am pretty sure it won't be a good idea to model the mechanic of a worm gear, since it relies on a complex geometry which i can't model with primitives. I can use convex shapes but i can imaging it won't be very stable.

Is there a reasonable way/trick to simulate the behaviors of worm gears in V-REP?

[coppelia]

Hello,

a worm gear is tricky. But it depends on what you really want to do.

you have several possibilities:

• have an output joint that simply works in position control, and you would programmatically control it
• have 2 joints: output joint, in position control as above. Then you would use the input joint, also in position control, but with a limited torque, that you could dynamically adjust depending on the load on the output joint. And link the input joint to the output joint programmatically

But you will have to try it out to see if that fits your needs.

Cheers

[JohnnyMudcrab]

Hey,

thanks a lot for the reply. This is exactly how i do it at the moment, but its not ideal.
The problem is that by dynamically adjusting the torque in order to lock it, you will also change the torque the worm gear is able to apply. Maybe it is possible, if you make it depend on the current rotational movement direction of the gear. I will try that! However, maybe it would be nice to be able to restrict the movement direction of joints for future releases. That would make it very easy to model a worm gear.

[JohnnyMudcrab]

Hello,

i found a good solution. In my case the movement direction of the gear and the direction the external forces want to move the gear are reverse. Therefore i can just change the joint interval so that the minimum joint position follows the gear movement. That makes sure that the joint can't be moved back once it reached a certain position. It is however important to reset the joint so that the changed parameters will be applied while simulating.

cheers

[coppelia]

Yes, that's a good approach. The pity is that you have to reset the joint everytime for the changes to take effect.

Maybe you could reach a similar behaviour by having two joints built on top of each other (with an intermediate mass in-between), and do some regulation between both? (both would be position controlled, but the base joint would have a stronger torque but wouldn't have any limit)
In any case, it would indeed be useful to be able to adjust the limits without having the reset the joint.

Cheers