Adjusting motor speed with battery charge

During regionals, our encoders fried due to them not being able to handle the speed of our throwing wheels.
In lieu of encoders, is there a way to adjust the speed of a motor from the battery voltage so the motor spins at the same general speed, even if the battery is low?

If you are using Jaguar speed controllers via CAN bus, you can use Voltage mode command. The Jag will automatically adjust its PWM output to the motor to to provide the commanded voltage (unless of course the available voltage drops below the command).

If you’re not using CAN bus, you can read the battery voltage and adjust your command accordingly.

Does this help? http://www.chiefdelphi.com/forums/showpost.php?p=1137469&postcount=17

However, in general, if you want to control something (like the speed of a motor) you would use a sensor to measure that something.