Chief Delphi - Worm gears

Chief Delphi (http://www.chiefdelphi.com/forums/index.php)

- Technical Discussion (http://www.chiefdelphi.com/forums/forumdisplay.php?f=22)

- - Worm gears (http://www.chiefdelphi.com/forums/showthread.php?t=80596)

Our team used a McMaster-Carr steel and cast iron worm gear set on last year's robot arm. We used one of AndyMark's nanobox's and a CIM to drive it. This drove a bicycle sprocket and chain to another larger sprocket mounted directly to the arm. Our worm gear set alone did not backdrive and with all the reduction we had very good control and speed, plus plenty of power. The system gave us no problems at all and we didn't even give a thought to efficiency since we had more than enough torque

We did notice some severe action when going from full up to full down, so we spring loaded the arm to reduce the "slam" factor. The arm was balanced by the springs when horizontal, so we actually drove the arm both up and down from horizontal. It worked quite well, and our rookie team was able to hang more than its share of tubes.

Though the weight of the steel.cast iron gears is greater than the plastic, I think I would go with them again, particularly on a drive system. I know the plastic gears work well in the garage door application, but I want to see some data on durability in our robot applications.

Dr. Bob

294 used a 20:1 single threaded bronze gear/steel worm combination made by Boston Gear in both 2010 (for our kicker pullback) and 2011 (for our lift winch).

In 2011 we made the mistake of going with a cast iron worm gear (for cost reasons) on our practice robot; turns out we were operating with too high of a torque for cast iron and shredded the gear; cast iron is only rated at something like 25-50% of bronze, and our practice robot telescope wasn't as smoothly operating so it put more load on the gear. We never had an issue with it on our competition robot (as it had a bronze gear).

I'll post pictures/CAD of our 2011 gearbox if anyone is interested in more details. We used two banebots into a ~4:1 pinion/spur reduction, and a 20:1 worm reduction directly driving our 4" diameter drum. Good speed and absolutely no backdrive (we notched a slot in the end of the worm shaft so a power screwdriver could be used to manually raise/lower if necessary).