I will be getting my V5 soon, and was wondering how best to use my current 393 motors with it. Official sources say just to use an mc29 off the 3-wire port, but @Got_a_Screw_Loose told me to use a power expander off the three-wire ports. I know it isn’t competition legal (using 393s), but would it work? Is it possible to use a NiMH battery on a power expander off of the V5 3-wire ports?
It should be. I don’t see any reason why it wouldn’t work.
To expand on what @sazrocks said, the PWM control on the V5 legacy ports should be no different than that on the Cortex motor ports. The only change is the voltage across the power pins.
As such, the power expander, which directly passes through the PWM control signal but replaces the power pins with its own (from the additional battery), should work just fine.
Would a power expander make the motors run at 7.2 volts instead of 5?
Yes. They would run at whatever voltage the battery connected to the power expander is at.
For the “experts”: what exactly would the risk factor be of running the motors without a power expander? I would think they would not only run at a slower speed with less torque (lower voltage), but would also risk “blowing a port.” Am I correct in this assumption? Or is there a ptc in the 3 wire ports capable of handling a motor?
Just trying to get Taran the best information, because I am admittedly no expert.
current is limited to 2A. Voltage is 5V. There is no PTC, the voltage regulator chip will shutdown if too much current is pulled. The VCS/VEXcode motor29 class has some slew rate code to help with current transients, the motor_victor and pwm_out classes drive without that. The V5 supports the old motors primarily for classroom use with lights loads.
So is it safe to the brain to use?
I gather yes, but it won’t be as powerful. If you have them, I’d use a power expander.
I’ve never heard of anyone damaging a V5 using old motors. If you have a power expander and 7.2V batteries then use them in the short term until you can buy more V5 motors.
One other thing to add. Motors on the legacy port do not shutdown when the robot is disabled by the competition switch. They are not competition legal, so we didn’t see the need to do that.
Okay. Thanks for the help. I don’t have a power expander on me, but I think I will see if I can borrow one from my coach. He won’t need them anymore (we have V5). This is for a personal project, and I’m only gonna have 5 V5 motors.