[Al Skierkiewicz]

General,
There are diodes built into the MOSFETs that are used in the Victor output stages. Don't add any diodes externally. If it helps, the Victor acts more like four switches. If you can visualize the letter H the four switches are the vertical lines above and below the horizontal line. If a motor is inserted in place of the horizontal line and the top of the "H" is tied to plus power supply and the bottom to negative power supply then the four switches can control the motor. For one direction, two diagonally opposed switches close and current flows through the motor in one direction. (i.e. from top left to bottom right) For direction reversal, close the other two switches instead (i.e. from top right to bottom left) and the motor current is reversed. Open all switches and the motor coasts and close just the bottom switches and the motor is attached to a dead short or is in brake. What takes place during operation is the switches for a particular direction are turned on and off at the duty cycle for less than full on. The switching frequency of the Victor is about 120Hz. IFI has programmed the Victor to convert the input 0-254 steps to 94 distinct steps plus direction between zero and full on. The brake selection determines the action of the output when the joystick input is at zero (the deadband or 127 +/- 10).
Onto your original question, rarely will designers use a motor speed controller to operate solenoids. Since solenoids generally just turn on or off, the designer will use a simple switching device to energize the solenoid. Since the current flows in only one direction (for DC solenoids, diodes are not used on AC devices) to actuate the solenoid, the collapsing field causes a current to flow opposite the actuating current. It is this current that the diodes will clamp when used. They are always wired to conduct when the energizing current is removed. (i.e. cathode to the more positive terminal of the solenoid.)
Now, I know what you're thinking, motors act like solenoids don't they? And the answer is Yes. But we still need the motors for our design so we put up with the arcing caused by the generated EMF. It is the current generated by the rapidly collapsing field that causes the arc you see at the brushes in a motor. When the arc produces problems (like generated electrical noise and RF interference) then designers use capacitors to try and squash the generated pulses. FIRST allowed caps for the first time this year to be placed across the motor leads. Some motors caused some significant problems in the servo PWM feeds to cameras. The caps were allowed to try and solve that problem. I have not received any reports but one team that used this approach and it was not conclusive.