Added a Globe with sched 25 sprockets and chain. Hope to get some test results soon. Expecting quite a bit of torque, maybe 500 lbf-in at 2 rev/min with about 2 Ampere current draw. Should make a nice elbow joint or winch drive.
Looks nice. What is the weight of the device? I am also very curious to see how much output force you will have. I would also like to know how well it holds up.
Nice work, keep us updated on your progress.
What is jabba the hut’s role in this?
Silly me, I left out the most important data! Weight including the torque multiplier, the Globe and its mounting system, sprockets and chain, and a 3/4" socket is 4.2 lb.
I am also very curious to see how much output force you will have. I would also like to know how well it holds up.
Nice work, keep us updated on your progress.
Thanks, I’ll post some results when I get chance to test it.
What is jabba the hut’s role in this?
Jabba is using his head.
Jabba is giving the project his full support!
He must be using his mucas slug slime to lubricate the system
This is a simple and elegant application.
At this ratio, a 90 degree arm movement would take about 8 seconds. If the torque was cut in half and the speed doubled, then a 90 degree motion would take 4 seconds. This faster speed is probably more in comparable with arm movements during recent FIRST games (04, 05).
If I recall correctly, the 2005 TechnoKat robot’s arm (along with many of the winning teams) had about 120 degrees of movement in under 2 seconds.
Andy B.
This would have been nice for our winch in 2004. We most likely wouldn’t have had any slippage issues. We fixed that pretty easily, though.
Thanks, Andy. You make an important point that faster action might well be needed; such a requirement might push beyond the power range in which a Globe can be effective. I was thinking about possible heavy lifting or short-throw, high-load applications.
When the throw is longer and the load is lighter, a modified Globe with about 450 RPM free speed might work well in a similar configuration – possibly using plastic sprockets and chain. In applications requiring both longer throw and high loads (such as the 2005 arm) someone might use a FP/NBD or FP/BaneBots gear-motor solution instead of the Globe. Or they might use a CIM motor fitted to an AndyMark planetary. Or if space permits they might use a pneumatic cylinder.
Of course FRC teams have used many other stock and custom gear-motor solutions. And if FIRST stays true to form, there will be even more options next year.
Richard,
I’m looking at your very well crafted assembly, and can’t help but wonder if there’s a way to directly link the Globe output shaft to the input shaft of the torque multiplier. Have you opened up the gearbox (via the 4 screws) and looked at the input shaft? Can that square socket attachment be machined down to fit a collar over both it and the globe output? Any further details would be greatly appreciated. Thanks!
BEN
I did open the torque multiplier and just posted an image. It might be possible to modify the input shaft to accept an in-line coupling to the Globe; however, I wanted to preserve the option of re-using the torque multiplier later on. I also wanted to minimize machining. So far I’ve only turned some brass spacers, broached a square hole, drilled and tapped in two places in the torque multiplier arm, and laser-cut a motor mounting plate. Still need to laser-cut a stack of double-D adapters which I can bolt onto the (faced-down) drive sprocket to make it suit the Globe shaft. I also plan to run a die onto the 1/4" stub of the Globe shaft so a jam nut can be used to keep the drive sprocket on. Power take-off will be via a standard 3/4" socket driving a piece of hex stock, which I’ll turn down to fit in standard pillow-blocks. The same hex will be used to drive the arm.
Sorry for the cryptic description – I’ll post some more pictures when I get this built.
They use globe motors and have a high reduction. They were originally used for satellite dish positioning. They are pretty heavy, but we took one apart and were able to take the weight down. I apologize I don’t have any exact figures for that.
They do provide really nice mounting options, and the decent sized through hole offers some unique possibilities 
I remember finding them for cheaper, but a google search turned this site up:
http://www.skycraftsurplus.com/index.asp?PageAction=VIEWPROD&ProdID=1016
So, the current BaneBots backorder got me thinking about this thing again. So, I went and picked one up today. This thing is really neat, and particularly easy on the wallet ($16 with 20% off coupon). Oddly, mine came pretty much ungreased, which was actually a good thing. I first opened it up and filled it with abrasive rubbing compound, and ran it for maybe 15 seconds each direction on high speed from a cordless drill to wear it in, and then I flushed it out with solvent, and packed it with EP wheel bearing grease with moly. It spins pretty nice and smooth now. I noticed the outputs shafts are rather sloppy in the bushings which is somewhat unfortunate. Maybe about 20 thou under size, but that didn’t affect its operation much. I tested putting 50 ft-lbs back-driving into the output (with no additional support on the shaft) and it held fine. It seems to be just on the verge of being able to backdrive. With any sort of other gearing coupled to the input, I doubt it would backdrive. Anyhow, I mounted the thing in a bench vise, rigged up a pipe and mass which put about 25 ft-lbs on the output shaft (again, no additional support) and I coupled a Ryobi 18V a cordless drill to the input shaft. Worked fine in both high and low gears. I noticed when powering the motor for the arm to go down, the motion is a little bit jerky, but it still works just fine.
I personally wouldn’t use this thing as the final stage of gearing in an arm, but it seems like you most certainly could.
If somebody is struggling to get a gear reduction for an arm and you’re out of money, this thing may be worth a try if you have the machining capability to adapt to its square shafts. And the input shaft is not a standard 1/2" square, it is larger.
