building a drum spinner

No as the voltage regulator would have to handle huge current surges. The simplest way to do it is to set the travel on your transmitter to 50% on the two channels that are used for drive. This way the motor only ever effectively sees 12v. What transmitter are you using?

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Originally Posted by typhoon_driver

No as the voltage regulator would have to handle huge current surges. The simplest way to do it is to set the travel on your transmitter to 50% on the two channels that are used for drive. This way the motor only ever effectively sees 12v. What transmitter are you using?

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i am using a dx6i transmitter, and i thought that the speed controler varied the current not the voltage to change the speed but i could be wrong? could i use a transformer imbetween the battries and the speed controler to turn the 24v into 18v? does this kind of transformer exist and would it be to heavy?

all the speed controller does is turn on and off very quickly to control the motor.

http://www.4qdtec.com/pwm-01.html

To put it simply, no, no it doesn't exist. Hook up the speed controller to your batteries. Change the travel adjust on the transmitter to 50 percent for the two channels you use for drive on the transmitter and the motors will only effectively see an average voltage of 12v.

Please note, that you should still respect the maximum limits that the sabretooth states overall.

This is the simplest method to run your motors on a lower voltage by tricking them into seeing the lower voltage. I have used this method several times myself and it doesn't require additional weight or parts in the robot.

How do I limit the travel of the gimbals on the transmitter

You don't. Check the manual for the transmitter and read the section on travel adjustment

How flat is the robo-challenge arena? Will 2-3mm ground clearance be enough? And how much do you think my new robo-challenge blue wheels will wear down?

The RC arena floor is pretty damn flat, so much so that ground-scraping wedges or flipper blades very rarely get stuck on the joins. 2mm-3mm should be fine (particularly if your robot is 4WD, but 2WD will still cope comfortably).

The blue wheels are pretty tough too. They will wear down over time (and by how much depends on how much pushing your robot does and how often it runs) but you could be looking at as much as a couple of years use, if not more, before they get so worn down that your ground clearance becomes an issue.

Where did you get the speed 900?

I got mine from Cornwall model boats

you can get them from smc