PWM Ouput

What kind of PWM signal does the Robot Controller output?

**They are not regular duty-cycle PWM signals.

They are the same type of PWM signals output by hobby radio-control receivers and read by hobby servos. The output is a pulse whose width varies from about 1ms to 2ms. In the Robot Controller program, a value of 0 corresponds to a 1ms pulse. A 1.5ms pulse means neutral, or a value of 127, while a 254 corresponds to a 2ms pulse.

By default this pulse is repeated every 17ms (in the EDU Robot Controller, similar to hobby R/C equipment) or 25ms (in the full-size Robot Controller). This rate can be changed by changing the PWM control to the User processor and calling the Generate_PWMs() function more or less frequently, as described in the 2004 Programming Reference Guide. Be careful when doing this, however, as not all equipment can handle a non-standard signal.

How much current can be supplied from the +7.2V pins on the PWM OUTPUTS headers?

The total combined current that can be supplied from all 16 PWM Output +7.2V header pins is 4 Amp. This current is supplied from the Backup Battery.

How many Victor 883’s can we connect to one PWM output?

You can safely connect two speed controllers to one output on the Full-Size RC using a PWM Y-cable. Three is pushing it. Finally, you do not want a servo and a either type of Victor to share the same output.

After connecting both the 12V and 7.2V supplies to the RC, we can’t detect any voltage on the pins labeled “7.2V” on the PWM outputs. In addition, there are no PWM output signals (with a period of 17ms), and the Backup Battery LED is solid red on the RC section of the OI, indicating that there is less than 6V being supplied. Could there be any reasonable explanation of this? The 7.2V battery was measured to be around 8V, while connected. The RC is receiving information from the OI, and the OI is receiving feedback from the RC (the PWM LED’s in the Robot Feedback section are blinking as the joysticks are moved, as expected), but there’s no supply voltage going to the PWM outputs on the RC.

After working with the customer, it was found that a “short” was on the board. The customer replied: “Apparently, the 7.2V and GND pins were bridged".