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M.L. Toys
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Gruber
HobbyMasters
M.L. Toys
KidsWheels
HobbyMasters M.L. Toys
Gruber
KidsWheels
Need new batteries? Going from 12V to 18V or 6V to 12V? Wiring Questions?
User avatar
By Hackish
#147432
With all the historical discussion of broken gears, I was wondering if anyone had ever thought of gutting the gearbox and swapping for a flat belt - v-belt or ribbed? With the fact you can even use 3D printers in libraries these days, I assume this should be pretty simple to produce. I might be tempted to wander around the local u-pick scrapyard and harvest some balance shaft belts from a few car engines. They usually come with nice cast aluminum pulleys.
User avatar
By Hammer-fm
#147445
The big problem with that strategy with trying to reuse the factory motors/gearbox (or similar) is that you need pretty massive amounts of reduction to get the right speed & torque. The 16T/19T boxes are in the 120-150:1 range. A typical pulley arrangement would require 3 stages of reduction minimum to get there (at 5-6:1 each). 10mph on the average power wheels (13-14" tires) is going to be 250rpm. Most people that go to a "non-plastic-gearbox" are using larger scooter motors with 2500-3500 RPM no-load speeds and then a ~8:1 speed reduction (and are shooting for slightly correspondingly higher speeds).

You can buy lower-speed motors, but I haven't seen any in the standard footprints (550/775) that run at 3500RPM AND put out 5x the torque of the 15k RPM ones -- they're always lower power and not very well suited to that type of application.

I think you could build a 2-stage metal gear gearbox with some of the parts they sell for the competition robots, but you're talking about some fabrication. If I had a lot more time, 48-60V into 3 or 4 RS775 motors per gearbox, driving a 42:1 reduction would net a good 2-3HP per side (with appropriate batteries, of course) at 15-20mph, but at that point you really want a chassis that could keep up. And the only reason to do that is if you have a lot of cheap 775s (which I do...) -- otherwise, just get a scooter/winch/other large DC motor.
User avatar
By Hackish
#147465
Interesting, I didn't realize there was such a big reduction, but it make sense. I'm coming from the industrial end where servo motors are 1000w+ and drive on 220v. These things cost thousands of dollars but can give huge torque output at low RPM. Maybe there is a gearhead motor that could fit the bill. The "jeep" I have is made by AMAV so it isn't the standard PW stuff. As a result, I haven't torn any of the parts down to look at them closely.

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