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.

[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

[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!

[Joe Johnson]

Originally Posted by squirrel

<snip

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!

My experience is nearly universally positive. The shifters have had some problems (mostly due to programming issues that put them out of gear in autonomous) but other than that, I have been very happy with them.

Of course, I have always had access to either a good wire EDM source or a retired tool & die maker that made jewelry (figuratively) so getting things made were never an issue.

AndyMark (and to a lesser extent Banebots) has pretty much put me out of the NBD business, BUT... ...for an efficient high ratio (roughly 50:1) with a non backdriveable output, it is tough to beat it. imho.

Joe J.

[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...

[MrForbes]

Very interesting....

http://www.andymark.com/product-p/am-0917.htm

[Jared Russell]

Originally Posted by squirrel

Very interesting....

http://www.andymark.com/product-p/am-0917.htm

These were available to play with at IRI - very cool!

Just a note to those who may be wondering - these gearboxes are indeed backdriveable (I backdrove one by hand). Design accordingly

[Teched3]

Just another thought to consider with garage door gear strength is the fact that garage doors are counterbalanced with either coil or torsion springs, so the opener is not lifting as much weight as you might think. Backdriving can be eliminated with a ratchet/pawl operated by a servo to lock the transmission in position(s).

[Andy Baker]

Good find, Jim! And, thank you for starting this thread.

I must say that a couple of things inspired this design. One was this thread, and another was the failure of my home's garage door opener this past spring. After replacing the gears in my own garage door open twice, I figured that these gears may be good to try on a FIRST robot.

Also, I recall that there was an FRC team in St. Louis who used these same gears in their drive train this year. I forget who it was.

We did some testing on these gearboxes, and found that it takes about 85-90 ft-lbs of torque to strip the plastic teeth. We actually broke the large gear hub with a previous design at 60 ft-lbs, but then we beefed up the support around the hub so that the weak link in the design was indeed the gear teeth.

We have found a few things about this design that we like:

1. It is lightweight. The entire gearbox weighs 1.1 pounds.
2. The gearbox is quiet.
3. The CIM motors are out of the way, leaving the center of the robot with plenty of room for game object pickup (if needed)

Here is a video of a 4wd mecanum system using these gearboxes.

Sincerely,
Andy B.

[Gary Dillard]

Andy - did you measure an efficiency?

[MrForbes]

Neat!

It appears to me that the common failure mode in garage door openers is wear due to lack of lubrication. So make sure you provide plenty of grease, and instructions to use plenty of it, with the gearboxes.

[DavidGitz]

Originally Posted by Andy Baker

1. It is lightweight. The entire gearbox weighs 1.1 pounds.
2. The gearbox is quiet.
3. The CIM motors are out of the way, leaving the center of the robot with plenty of room for game object pickup (if needed)

Andy - We like these a lot and plan on getting some in the next month or so. Are you planning on releasing a CAD file of this at some point?

[Chris is me]

Guess who's making this into an arm gearbox?

With some earlier reduction (say, an RS-775 into a CIM-U-LATOR and AM Planetary), you can easily get your robot down to arm speed.

[Cyberphil]

Awesome.

103 used a worm gearbox this past year for the tower (though it was not designed by us). It worked really well and the only thing that had problems were the spur gears driving the shaft that the worm was on.