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Tech Notes on Speed Controllers

IBC Related Notes

Voltage doesnt bother the IBC at all, it will happily run 5v motors or 35v motors. its *current* that gets things warm.

The Fets have an internal resistance (a very small one - .005ohms). if you suck lots of current through that resistance, a small voltage drop develops across it and the power that the heatsink needs to dissapate is that voltage drop multiplied by the current. so effectively Power dissipation goes up as the square of the current, or P =Isquared *R.

If you are using RC car type motors, they are designed to run at low-voltages (7.2-9.6v) but at very high currents, which will make the IBC work much harder than getting an equivalent amount of power out of a higher voltage (12 or 24v) system.

To get a 200watt drive from a 24v drill motor, you only need to feed it 8.3 amps, which means the IBC only has to dissipate .345 of a watt per Fet (2 per motor).

To get the same power (200 watts) from a 7.2v (less than 1/3 of 24 volts) motor you need to feed it 27.7 amps (3.3 times as much current), and as the power dissipation goes up as the *square* of the current, the IBC now needs to radiate 3.85 watts per Fet or more than *11* times as much heat for the exactly the same output power. No wonder it gets hot..

What all this means is trying to get the same power out of high current low voltage motors stresses the controller a hell of a lot more than getting the same power out of a higher voltage lower current motor does. If you are running 4 of these low voltage motors, you are working it *hard*.

We have 4WD 4 x Drill Motor powered 12Kg (twice your weight) robots running on 24v with the IBC in a sealed, unventilated box without a problem. They get warm, but they handle it ok, provided they dont have to maintain a stall.. so higher voltage and lower current draw motors is definitely the better direction to go.

Failing that, give it a Fan. The IBC's heatsink is designed to absorb surges of power with high thermal mass, but doesnt have much surafce area to radiate sustained power input away into space (we didnt want to have big finned heatsinks hanging off it), so if you are constantly drawing high currents through it, some cool airflow across it will really help)


IBC Flip/Aux Functions

http://www.robowars.org/forum/viewtopic.php?p=1695#1695
(lots more info on controller tips in that thread, worth browsing through)

To easily use the invert/flip function, (if you arent using the third radio channel), just hook up the third channel to your receiver, and connect either the aux-hi and/or the aux-low output pin straight back to the Flip input pin..

voila. radio-controlled flip. move the third channel (whatever it may be on your controller) into the auxillary activation zone, and the aux-output will activate the flip input, and you are driving backwards.

If you are already using the 3rd channel for your weapon, you can use the "other side" of the aux (aux-hi if you are using aux-low for your weapon, or vice-versa) to still activate flip using just 3 channels, but you wonbt be able to activate your weapon AND flip at the same time, so no firing the weapon while upside down and continuing to drive backwards. only 1 auxillary output can be on at a time.

If you need bi direction weapon capability (ie, you are already using both aux-hi and aux-low), or you need to be able to fire and drive inverted simulataneously, then you will need to either 1, get a 4th radio channel and switch decoder (available from hobby shops), *or* 2. fit a manual flip-sensor to your robot like a tilt-switch that automatically activates the flip input whenever you are upside down.

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