[Zoidberg]

I made a drawing and realized that the worms would need to rotate in the same direction in this configuration :P

The dual servo version seems more and more appealing!

[BobWarfield]

There are a lot of commercially available low backlash drives on eBay. Search for "harmonic drive" or "bayside drive". One of those sure will least trouble and expense.

Another possibility is to preload the heck out of your rotab drive with another gear and some bellvues. Not sure how much torque you plan to put on it though.

People also run 2 of the main circular gears spring loaded to spread the teeth just enough to get rid of the backlash. In this case, you'd make the spread adjustable with a threaded screw.

These last two solutions seem prone to binding and wear.

I would be tempted to also consider a big timing belt drive. properly set up, you'll get minimal backlash. People are even using these for linear motion with good success.

For really high torque situations, you might still find a brake is useful. Slew the 4th axis to the desired position, send an M-code to lock the brake, cut, and unlock. Small disk brakes from everything from mini-bikes to lawn tractors are readily available and work with an air over hydraulic and solenoid valve.

Cheers,

BW

[petecul]

I made a drawing and realized that the worms would need to rotate in the same direction in this configuration :P

The dual servo version seems more and more appealing!

You could use a right and left threaded worn screw but in your desing, backalsh is transfered to the bevel gears!!

Keep going on design, i am also interested in a rotary axe.

thanks
petecul