Rule states custom circuits are expressly prohibited…, such as directly powering a motor. Can is use some simple electronics (diodes, resistor and MOSFETs) to build a H-Bridge circuit that CONTROLS (not powers) the direction of motor rotation based on the stae of an input signal? Any guidance would be appreciated.
No, as the rule states, no custom circuit can be placed between a speed controller and a motor. In effect any custom circuit may only modify the speed of a motor through software in the Crio. Ideally, this method would perform the same actions you are suggesting with the use of a custom circuit.
The intent would not to be to place the circuit between a speed controller and a motor. Rather, it would only reverse the effective battery polarity to a motor. Our intent is to build a telescopic arm to hook the bar so we can winch ourselves up. In order to do so, I need to spin a motor in one direction to extend and then reverse the polarity to retract it. The motor wouldn’t even be connected to a speed controller. In this case, if the answer is still NO, can this functionality be accomplished with simple 12V relays?
No worries. The standard IFI Spike relay provides the forward-off-reverse control you’re looking for. You need to hook it up to two of the Relay outputs on the difital breakout board.
A Spike relay module will work fine up to 20A (keep in mind that it has a fuse, and if you blow it, then you’re out for the game). A Victor or a Jaguar handle 40A, and will work just fine for your purpose as well. It adds no complexity to the overall programming or design of your robot.
It only takes one output. Each relay connection on the digital sidecar has the two required signals for controlling the Spike exactly as hcarry wants.
H,
I have to ask why you don’t want to use the speed controllers which are designed for exactly your purpose. If it is your intent to make the lift automatic you can easily write forward and reverse commands into your code. Depending on the motor you choose, the rules have specific requirements as to which device can be used to control the motor.
<R55> All electrical loads (motors, actuators, compressors) must be supplied by an approved power regulating device (speed controller, relay module, or Digital Sidecar PWM port) that is controlled by the cRIO-FRC on the ROBOT.
A. Each CIM motor and Fisher-Price motor must be connected to one and only one approved speed controller. These motors must not be connected to relay modules.
B. Servos must be directly connected to the PWM ports on the Digital Sidecar. They must not be connected to speed controllers or relay modules.
C. If used, the compressor must be connected to one and only one Spike relay module.
D. Each other electrical load (motor or actuator) must be supplied by one and only one approved speed controller, or one and only one relay module.
Hope this helps.
The fuse can be replaced with a 20A circuit breaker, even if it is not for the compressor, as per
The control system is designed to allow wireless control of the ROBOTS. The Classmate PC, FirstTouch I/O module, cRIO-FRC, speed controllers, relay modules, wireless bridge, batteries, and battery charger shall not be tampered with, modified, or adjusted in any way (tampering includes drilling, cutting, machining, gluing, rewiring, disassembling, etc.), with the following exceptions:
<snip>
F. The fuse on the Spike relays may be replaced with a 20 Amp Snap-Action circuit breaker.
That would be illegal. Per the rules, ALL motors must be driven through an approved motor controller (victor, jaguar, spike, or digital sidecar PWM outs for servo’s). See .
The motor you use and the power requirements will determine what motor controller you need to use. If it’ll draw under 20 Amps (which is possible for an arm if the winch that holds the robot’s weight is separate), use a Spike relay - that will do exactly what you want. If it’s over 20 Amps (for example the motor is part of the winch that holds the robot up as well), then you’ll have to use a Victor or Jaguar, as the Spikes are only rated to 20 Amps.
Eagle,
Just for understanding, the rule cited in my post above does apply to all motors. Even if you have loaded a CIM so that it only needs 2 amps to run, it still needs to be connected to a speed controller and not a spike.
My fault for not specifying Al… We always have, and always will be hooking up CIM’s to victors or Jaguars (or whatever FIRST may replace them with in future years). I was referring more to all the other motors in the KoP with my post. 
Eagle,
Just trying to keep things clear. I knew what you meant but…
I will be in Minnesota so I will try to come your pit and say hi.
The Fisher Price motors must also be connected to speed controllers per <R55-A>
A. Each CIM motor and Fisher-Price motor must be connected to one and only one approved speed controller. These motors must not be connected to relay modules.