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# School Project Need Help

I am coaching a Science Olympiad Team in Michigan and my students are building a robot for the Robo Cross event. They have built a mini tank that is using the Tamiya double gearbox (58:1 gear ratio) running on two batteries (3 volts). The tank moves okay but kind of slow. The question my kids are wondering is the description on the gearbox on the website says the gearbox can run on 3 to 6 volts . . . however the individual motor specs say each motor only takes up to 3 volts.

My kids and I are wondering if they add more voltage . . . to increase speed, say up to 6 volts will that burn up the motors? If each motor (there are two in the gearbox) runs up to 3 volts is the dual motors drawing 3 volts each . . .

Any help would be greatly appreciated!

Jeff

Hello,

The motors will run faster but have a shorter life if you raise the voltage. Since these are toy motors, we don’t have any reliability or lifetime numbers even at 3V, so we can’t say how much life you’re losing with a higher voltage. In my experience, they haven’t died right away at 6 V.

I think your second question is a series/parallel question. You should connect your motors in parallel, meaning that each one has an independent connection to your power source. Both motors should run as fast as just one motor; if you see the speed go down a lot for both motors, you probably have them hooked up the wrong way (in series). Provided your battery can supply the current, each motor will have the full battery voltage on it, not the battery voltage divided by number of motors.

If you want more speed, you might consider a different gear ratio, which you could get with the double gearbox, which we like more than the twin-motor gearbox.

- Jan

Thanks for reminding me Jeff. I have a bunch of the small Tamiya motors left over from a project, and I’ve been meaning to test them, to see how they perform at higher voltages (and for how long). I’ve started another topic with my data so far here.

-Adam