pic: Concept 6x rs545 planetary gearbox

[nate12345678]

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[BBray_T1296]

Originally Posted by nate12345678

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I think the electronic component of this gearbox (cost/footprint of 6 motorcontrollers/relays) would be prohibitive in FRC applications. But it is very nifty!

[sportzkrazzy]

Nice first attempt we all have to get started someplace =). It looks like you are shooting for a planetary gearbox but its hard to tell based on the view. Planetary gearboxes are good for high reduction in tight spaces at the coast of efficiency. The ones we see in FRC most of the time have a locked Outer ring-gear, planet gears and sun gears. They receive an input from the motor that spins the sun gear. This rotation is spread though through the sun gear too the planet gears that revolve around it because the outer ring gear is locked achieving the reduction desired between those two interfaces. The rate at which the cluster of sun gears is rotating around you motors axis is your new rotation speed. These stages can be stacked by transferring the rotation rate of the planet gears down the line to another sun-gears input. With each additional stage come a reduction in efficiency.

A good place to start on planetary gear boxes would be to look at whats already offered. Vex robotics makes great planetary gearboxes that are stack-able. They have step files of the cad online that you should take a look at so you can better understand how they work. http://www.vexrobotics.com/vexpro/mo...planetary.html

That being said If I was starting out I think my first goal would be to make a spur gearbox. It is much more in line with what your team is capable of making. A lot of times planetary gearboxes will require special tooling to make. The plates for a spur gearbox could be done on one of CATs water-jets in less that 30 min. You can typically make them more efficient than the planetary ones but you do sacrifice a little space. If you need any help pm me and let me know.

Just food for thought

Edit- I understand now. I couldnt tell at first because everything was the same color.

How much does it weigh Including wire and motor controllers?

[nate12345678]

I couldn't tell you how much the electrical weighs, but with an aluminum body and steel gears, about 3.3lbs. Also, this was just the first stage. I plan on following this up with a smaller gearbox. Also, it's output shift is the same size as a cim, so any gearbox for that does fit.

[sportzkrazzy]

Looks like a fun project but in a FRC situation you would probably use a mini-Cim. They put out 2/3 the power of a Cim (around 1.4 nm at 6,200) and only weigh 2.16 lbs. Plus they have the added benefit of only needing one motor controller, wire run, and Pwm slot. Although on the other set up you could run CAN to minimize the signal wire runs and clean it up a bit.

Sometimes even If you have the motors laying around it makes more sense to buy what you need. In this case 25 bucks would save you machine time, the price of the stock and the price of the gears and pinions. It would probably actually save you money and time in the long run to be honest.

[GeeTwo]

As hinted above, this isn't a planetary gearbox, but simply a multi-motor single stage gearbox. Using this design to stack up 6 small motors is probably a waste of resources (easier and cheaper to do with a single larger motor), but with a bit of scaling up and a larger output shaft, this would be an elegant way to feed 6 CIMs into a single PTO drive train. You could get the output stall torque of two CIMs while drawing ~23A per CIM (assuming a 95% efficiency) - and achieve output speeds at that torque of around 2000 rpm.

Anyone know off the top of your head how long you can pull 130A (guessing 15A hotel load) from an FRC battery before you hit roboRIO brownout?

[JesseK]

Toughest part about this particular design for me is the assembly & maintenance. Presumably the motor would be mounted, and then the motor pinions pressed on. It'd take a pretty specific press setup to do this successfully without damage to any other mounted motor. Then if a motor burned out, figuring out which one to replace is tough. After that, replacing the motor is equally tough since it doesn't appear that a gear puller could get in there well enough.

All of these can be alleviated to an extent via design considerations, so I'd be interested to see what you come up with. At the same time, if 1 motor fails there are 5 more to keep something running - this redundancy is really nice for open-air motors. The dead motor provides little resistance in the form of friction or back-emf, so it's a decent redundant setup.

As for utility of this design - finding a way to use cheap motors is always a plus to me. We can get away with splitting wires off of a controller in the 'real world'. This message board seems to forget that nifty/niche designs usually have more use outside of FRC than the typical FRC design

[mastachyra]

Originally Posted by GeeTwo

As hinted above, this isn't a planetary gearbox, but simply a multi-motor single stage gearbox. Using this design to stack up 6 small motors is probably a waste of resources (easier and cheaper to do with a single larger motor), but with a bit of scaling up and a larger output shaft, this would be an elegant way to feed 6 CIMs into a single PTO drive train. You could get the output stall torque of two CIMs while drawing ~23A per CIM (assuming a 95% efficiency) - and achieve output speeds at that torque of around 2000 rpm.

Anyone know off the top of your head how long you can pull 130A (guessing 15A hotel load) from an FRC battery before you hit roboRIO brownout?

I like this idea. Maybe you could use this to design an electric lawn mower. Depending on the answer to the final question, you'd have to sap batteries out quite often.