Does anyone have a definative reference for how the “backup power” circuit runs through the RC unit to the perhiperal devices (PWM, RELAY etc.)?
The “standard description” of how this works seems to be that the 7.2v battery is used to deal with sags in the main 12V supply, but that doesn’t seem to be the case.
I’ve noticed that when I power the CMUCam off a PWM output (as recommended), after a moderate time of camera testing (with no other major loads) the camera stops communicating until I replace the backup battery with a fresh one.
I would have expected the RC to be powered by either the 12V or the 7.2V via diodes. So if the 12V is good, the 7.2V battery won’t get drained… but that does not seem to be the case.
Unless this is just a matter of me using an incorrect output to power the camera, this is pretty annoying, since the rules don’t seem to permit me to substitue the old-style AA NiCds with NiMH barteries that would give me better camera life.
I’m just trying to find a reliable way to ensure that the camera keeps running as long as the RC runs.
Is there a better “legal” way to power the camera? maybe run the camera off the 12V supply directly. Is it just as simple as me installing my own 5V regulator?
The backup battery is being drained because the servos are powered off of the backup battery. The standard acceptable voltages for servos are 4V to 9V (If I recall correctly), hence they are powered via the backup battery and not the main 12V battery.
I’m not using servos on the CMUCam board, or the RC itself. In fact we didn’t have any servos…
But are you saying that the +V pin on a PWM output is the unregulated 7.2backup supply?
I thought that these were +5v pins (but never actually mesured one).
So… is there an output from the RC that does send out regulated +5V that can be used by the CMUCam? Is there a Schematic anywhere that shows the power circuit?
The digital ouputs do provide +5, however the camera has its own regulator and requires an input of +6.25 volts to function correctly. The only pins on the RC that output +6.25 volts or greater are the PWM outs.
<R56> The 7.2v backup battery may be charged on or off the ROBOT. When off the ROBOT, the battery is to be charged with the provided 7.2V backup battery charger. When mounted on the ROBOT, the backup battery may be charged from the 12VDC primary battery by using the custom charging circuit available from Innovation First Inc. (note: IFI will provide the design for this circuit on the IFI website, however teams must obtain the parts for this circuit and assemble it themselves). The use of this circuit is strongly encouraged.
Actually the spec for the CMU cam is 5.2v to 8.6v. You can run the camera off the Digital Inputs, or Analog Inputs and it will run off the 12v battery instead of the backup battery. If you use any servos you should definitely build a changing circuit. Hope that helps.
Team 40 Runs a TTL cable directly from the RC to the TTL port on the camera. The camera gets powered by the RC and only requires one cable. If you go over 2ft of cable you should use a shielded cable.
You want to power the camera as intended so that it is up and running when the match starts including the servos. The camera derives it’s power from the backup battery as that battery is the only source of power for the PWM outputs on the RC. An alternative is to use a larger capacity backup battery pack. You can specify a battery pack of your choice from Digikey and they will build whatever you need.
NO !!
The nicad battery pack has to be the same pack in the kit, or another of the same part number. Building a larger pack increases the amount of stored energy and is disallowed.
The correct was is to build the IFI charger circuit.
we built a circuit last year that was similiar that provided a 6 volt bus that was regulated down for the 12v bus. We ran the servos and cameras off the 6 volt bus.
**8.3.7 - Control System Rules
**<R73>
… As a replacement for the FIRST supplied battery, any other
commercially available 7.2V NiCad battery pack may be used.
I also questioned this interpretation, since the rules specify the voltage and material, but not the capacity. NiMH are out (bummer) but not a 7.2V C cell NiCD pack (as Mark pointed out)
I also wondered about this… R63 would seem to indicate that a 6V regulator is an acceptable “Custom Circuit” as long as it it not connected to an output device. To me, this would make the CMUCam OK, but not a Servo. Hmmm…
My reasonning… Since a Servo contains a motor, and is covered by various motor limitations rules, and R63 says that a custom circuit cannot power a motor directly… so… wouldn’t it be excluded?
Phil,
NiMH batteries are not allowed due to their unusual reaction when exposed to air. Regulators on custom circuits are allowed but they may not be used to power servos or other motors on the robot. They may (as interpretted in the past) supply power to sensors used in conjunction with the custom circuit. All control initiated by the custom circuit must be passed through the RC to control motors, lights, servos, pump, etc.
