Worm gears

[Craig]

We used that exact gear set for our winch in 2004 (Frenzy)

We were very pleased with the results. Lasted 2 regionals with no significant wear.

If it is possible to back-drive it, one robot is not nearly enough force to do it in our experience. If you were lifting 2 or 3 I suppose you'd have to try it to find out.

[Joe Johnson]

Worm gears are fraught with peril for FIRST teams.

Well, actually, they are fraught with peril for any application, but some times you need to face your demons!

In one off applications like FIRST robots, you really need to know what you are doing to use a worm gear (other than the one in the window motors of course).

Getting the center distances right is a harder task, managing the thrust loads, etc. etc. And don't get me STARTED on efficiency (you flush half to 2 thirds of your power right down the drain -- and that is if you do things right you can waste 90% easily without even trying! But... that is is why they are not backdrivable - so that can be a plus but...)

My advice: find another way if you can.

As for me and my house... ...I am thinking this is a job for NBD -- Nothing but Dewalts -- Worked for me and Chief Delphi in Raising the Bar, I don't see why it shouldn't work for Breakaway

Joe J.

[MrForbes]

Originally Posted by Joe Johnson

And don't get me STARTED on efficiency (you flush half to 2 thirds of your power right down the drain -- and that is if you do things right you can waste 90% easily without even trying! But... that is is why they are not backdrivable - so that can be a plus but...)

It appears the door opener gears probably have better efficiency than most worm gears, because they don't have a very steep ratio, and apparently are backdriveable. The sliding tooth contact is not as efficient as the mostly direct contact of spur gears, so the efficiency must be less, thanks for pointing that out.

As for me and my house... ...I am thinking this is a job for NBD

We had some fun with DeWalts our rookie year, and are a bit leary of them. I suppose if you are good at machining an 8mm hole in a pressed metal gear that has a 9mm minor diameter, then can get the gears pressed on the shafts (and have it survive a few regionals) without breaking they are OK, but that shaft to gear coupling problem makes me shy away from them for use with a CIM. A FP driving them should not be so bad.

Thanks for the comments!

[Chris is me]

Originally Posted by Joe Johnson

As for me and my house... ...I am thinking this is a job for NBD -- Nothing but Dewalts -- Worked for me and Chief Delphi in Raising the Bar, I don't see why it shouldn't work for Breakaway

I don't know much of anything about this kind of thing, but a DeWalt was one of my initial thoughts this year for hanging. It's not too heavy either, and it's stood the test of 2004. Once I figure out the easiest way to get my hands on them...

[Retired Starman]

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

[Peter Johnson]

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).

[Aren_Hill]

Originally Posted by squirrel

Or a socket wrench ratchet?

We used and box end ratchet wrench in 2007 to make our lift winch non-backdrivable.

All it required was a hex of the appropriate size welded to the winch shaft, and then prodding the pawl with an allen wrench to let it back down.

worked like a charm

[lemiant]

reported ^