The BrickPi+ uses a power scale of 0-255, so 75 is only about 30%. If your batteries are only at e.g. 7.2v (nominal voltage for 6 AA rechargeable cells), that’s an average of only abou 2.1 volts. This seems reasonable. BrickPi3 uses a power scale of 0-100 (percentage).
The BrickPi+ uses a low PWM frequency (490Hz if I remember correctly); certainly within hearing range (which is why you can hear them hum). BrickPi3 uses a PWM frequency of 20kHz, which is more like the NXT or EV3 (you can’t hear the PWM hum).
I’m powering the motors over a 9V 4A power adapter, so there should be enough voltage. AND the motors really sound fine when being used with a NXT, so I don’t think it’s due to the motors.
Is there a way to patch the firmware to use the frequency of a BrickPi3? From what I understand the BrickPi is basically two Arduinos and H-Bridges ontop of the Raspberry Pi, so this should be possible. Otherwise I think I’ll just write my own firmware (since I use no sensors this shouldn’t be that complicated), is there a guide on BrickPi hacking or do I have to figure everything out myself (speaking of, is this about the BrickPi+ or the BrickPi3)?
I’m powering the motors over a 9V 4A power adapter, so there should be enough voltage. AND the motors really sound fine when being used with a NXT, so I don’t think it’s due to the motors.
Is there a way to patch the firmware to use the frequency of a BrickPi3? From what I understand the BrickPi is basically two Arduinos and H-Bridges ontop of the Raspberry Pi, so this should be possible. Otherwise I think I’ll just write my own firmware (since I use no sensors this shouldn’t be that complicated), is there a guide on BrickPi hacking or do I have to figure everything out myself (speaking of, is this about the BrickPi+ or the BrickPi3)?
actually each single EV3 motor draws 600mA at free-wheel and up to 2A each under heavy load and especially when stalling. So given you are running 4 motors simultaneously under load, then up to 8A may be possible and your 4A power supply might become overloaded.Admittedly, for just 1 motor at 75/255 pwm that should be no issue IMO .
OTOH, the noise thing can be unpleasant even if it’s not supposed to cause severe issues. But IIRC, the BrickPi+ is controlled via UART by the Pi, not sure about pwm generation source though.
(hell, this editor is really annoying…)
The PWM base frequencies are indeed about 31kHz and 62kHz, but the default divisors set the PWM frequencies to 490.2 and 976.5625. The clocks are used by more than just PWM, so things like millis, delay, servo, tone, etc. might stop working as expected if you change the divisors. See here for more details.
I’m just writing my own firmware and changing the pwm solved the problem. I changed the frequency and now the motors sound better and I’m able to run them with a speed of 20 in idle. (Although senors don’t work anymore, but I don’t need them…)