I just thought I’d pass on the method that we just discovered for increasing the speed of the Globe Motor.
There have been several discussions about removing one of the stages of planetary gearing from the Globe Gearbox, but so far they have all required machining of the housing or a special spacer.
Last night we pulled one apart, and came up with a really simple way.
The trick is to remove the function of the second stage of the planetary gear.
We did this by removing the 3 gears around the perimiter of the second stage, and then epoxing the second stage plate to the back of the first stage.
This has the effect of making the first plate, drive the third stage directly.
To keep the second stage parrallel during the gluing process we used three nylon spacers (from this year’s FTC kit) in place of the the gears that we removed. First the spacers were glued in place, and then the two plates were glued together. As the glue was curing, we inserted the assembly back into the housing to help with allignment.
For our test we used regular 5 min epoxy, but for production we will probably go with a high PSI epoxy. We used it to run out turret last night, and it ran really fast (too fast :). We did prep the metal before gluing by cleaning and then scoring, but the pins and 1st stage gear are very irregular so the bond seems pretty good.
We won’t use this for a high load application… All in all a very easy modification. (Plus the kids came up with the gluing idea)
We did something along these lines to help out a rookie team with a too slow globe for steering last year. Our solution was to clean and degrease the second stage, then take it over to the machine shop to have them weld the planets in place. After that was a trip to the grinder to remove all the teeth that would have engaged with the ring gear, and you’re done. It’s somewhere between straight epoxy and lathing down the ring gear in complexity and strength. I did work remarkably well, however. And was quicker than having the ring gear lathed, as the welder wasn’t nearly as busy as the machinist.
For epoxying, you might consider a similar solution of leaving the planets in place and grinding off the outer teeth. You could actually slather it with epoxy, reassemble to let the epoxy cure with everything tightly aligned and engaged, and then pull it apart to do the grinding. If the sun and planets are reasonably engaged, it should spread the load much better and result in a much higher strength.
Granted, method B requires a Dremel, and method A requires a Dremel and welder… But most teams should have a Dremel hanging around somewhere. After all, Dremels are the Leathermans of the power tool world. They do just about everything as long as you’re willing to pay for the options and put up with somewhat reduced quality.
How do you get the gearbox off - drill out the 3 little roll pins?
You press them out. You need them to reassemble the gearbox so drilling them out may not be the best plan.
For the uninitiated in globe motor deconstruction, you get a punch and press the roll pins into the gearbox. Then the geabox slips off and you retrieve the roll pins from inside it, as you’ll need them to reassemble it later.
Any rough guess as to the RPM?
I’ve heard 4-500 rpms is the output after modification. We just took out the second stage and threw a few washers in it. Took all of 3 minutes and works like a charm. It does shorten the output shaft but we can live with it
Great idea, thanks. I shortened one as a test, but I like this idea better.
What we usually did was remove the second stage and machine the gearbox casing to account for the different height, but your solution seemed clever, so we came up with this:
We machined the aluminum spacer (3mm, ~1/8") on our home-made CNC mill, but just because we’re lazy - that part could’ve easily been made with simple tools. The hole is somewhat smaller than the gear’s outside diameter so it gives a pretty tight press fit (squeezed the harder steel and aluminum together in the vise so that the spacer deforms into the shape of the gear).
Thanks for sharing this and we hope our solution helps someone.
Thanks again for the tip. I modified ours, but instead of washers, used a 3/8" bronze bushing, cut to .25 inch long.
Thanks for the help. We just modified two of ours. We tacked the 2nd stage gears onto the plate and ground down the outside teeth. Worked great.
We reduced a second gearbox by drilling small holes in the gears and plate and inserting pins. This also seems to work great if you have the machining capabilities.
My team was looking into this…but…is it legal? I’m pretty sure it isn’t…even though the inspectors might never notice…
It’s legal. The Globe gearbox isn’t considered integral under <R53>.
And the inspectors would notice, most likely. I’ve heard of one of the Championship ones catching someone using an illegal motor just by the motor number. Not sure who, but it’s happened.
Instead of using epoxy, I would suggest J-B Weld. It’s very similar to epoxy in usage and waiting time (regular epoxy, not instant, it’s about 6 hours to handling time, and 15 to full cure). It’s basically a specialized epoxy for metal, which both chemically bonds any kind of metal (similar to Loctite threadlocker) and hardens into something similar to ceramic. It will probably hold better than epoxy. We used it to convert a 125:1 BB gearbox into a 25:1 and it worked great. You clean off the grease between the two plate’s your welding, mix a little of the two compounds (and I do mean a little, doesn’t take much. Make sure everything is well covered, but you don’t need to slather it on), apply it to all of the gears, top, bottom, and between all of the teeth meshings, wait 15 hours for it to cure (a small heat source like a light bulb, heat lamp, or space heater decreases waiting time), and grind off the teeth of that stage. Probably the best combination of simplicity and strength. Not to mention, the J-B Weld doesn’t harden in its container like epoxy does. J-B Weld can be bought at places like Home Depot for about $5, which is about as economical as epoxy, because you don’t use as much.
I meant 400 to 500 rpms, I think I heard around 486 somewhere? For me, that rpm range is good enough to design with. Good luck.
you don’t even need a special spacer, last year 612 just used a bunch of washers. Motors held up for 2 regionals, championship, couple off seasons, and are still going.