Speed Controllers

The Unnamed will be powered by 2 Gimson GR02s which drive a wheel and a pulley each, which turn another wheel and pulley combo. This gives me four wheeled drive which helps with acceleration and manoeuvrability. However I need something to take the servo signals (a period of 20 milliseconds with a high pulse between 1 millisecond to 2 milliseconds to determine speed and direction) and convert them into motor signals.

A GR02 will, when stalled, pull approximately 61.6 Amps according to the manufacturer. This means I need to find something that can withstand that much current for short moments of time. The best way to do this is to do some research and build up a table of options.

	RageBridge	BB TZ-85A	TZ-85A	Sabertooth 2x25A
Channels	2	1	1	2
Continuous Current	30 Amps	85 Amps	85 Amps	25 Amps
Peak Current	90 Amps	100 Amps	100 Amps	50 Amps
Min Voltage	12 Volts	7.4 Volts	7.4 Volts	6 Volts
Max Voltage	36 Volts	25.2 Volts	25.2 Volts	30 Volts
Dimensions	?	?	?	?
Weight	99.2 Grams	89 Grams	89 Grams	90 Grams
Price	£    116.16	£    43.94	£   28.22	£      78.48

One thing to note about this comparison is that the TZ-85As are only single channel, I will need two to drive both my motors. I'm also not confident that they will withstand 85 Amps continuously. However there have been widely used without complaints in the Australian robot combat leagues. I've included the pre-programmed ones sold by BotBitz as well as un-programmed ones directly from HobbyKing.

Looking at that table the TZ-85As seem to be the best for current handling capabilities and their maximum voltage is greater than the motor can handle. They are also quite compact and if I buy them from HobbyKing and re-program them myself they work out to be much cheaper. The lower cost also means that I feel a lot better about modifying them as having spares around will not be expensive.