Wireless problem - losing communication

[EricVanWyk]

Please verify that the bridge and cRIO are plugged into their dedicated connectors on the PD, and that nothing else is sharing their power.

If the bridge isn't powered by its dedicated power supply, it can drop out and create a situation like the one you described. Next time this happens, watch the lights on the bridge. If it goes through the same sequence as it does during power on, you have verified that the bridge isn't getting good enough power.

* Below this point is a ramble. Ignore or Enjoy at your leisure. *


Slamming the motors from one direction to the other draws a *lot* of current, and can be the hardest thing for the battery. The peak draw can approach twice the stall current of the motor in the worst case scenario.

Lets simplify to a perfect battery driving a motor that is a resistor and a back emf in series - ignore the series inductance for a moment. At full speed forward at steady state, the motor will have a back-emf that is equal to the battery voltage: No torque is being applied. When you suddenly slam the motor in reverse, this back-emf now adds with the applied voltage. For a brief moment, it is almost like driving the motor with a 24V battery. In this idealized case, the peak current is exactly 2x the 12V stall current.

When you go non-ideal, several things reduce this current. For one, the losses in your drive train will force the motor to apply torque to keep at steady state. This torque translates to a current, which translates to a voltage that develops across all of the resistances in the circuit. This reduces peak back-emf. Additionally, the inductance we previously ignored won't allow the current to instantaneously change, which will further reduce the peak.

In either case, this massive current slug is relatively quick - it only lasts as long as the motor is still spinning the wrong way, and the motors are being given a lot of power to convince them to spin the other way. This is therefore a quick but serious event that can easily offend the delicate sensibilities of the bridge.

The boost supplies on the PD are designed to handle this sort of thing and should be just fine.