1.5 KiB
The servo used in the Payloadbay behaves quite weirdly. Currently we use the standard PWM signal at 50Hz with a on-period between 800-2200 microseconds. As is visible in the scope-shot below.
!
Whenever there is a load on the servo it becomes acoustically very noisy and the current draw goes up significantly, which makes sense. But even if I stop the servo at a certain location the noise continues. In the scope on the signal line you can clearly see spikes at roughly every 2.7 milliseconds.
!
Experiments
Current draw
When making the sound the servo draws roughly 0.5A.
Voltage Drop of the Supply
In purple we measured the power supply of the servo, while it was making the sound and in yellow the signal. We can observe a voltage drop of roughly 0.5V in the power supply at roughly 370 Hz.
!
!
Since both the power supply and the signal are affected it can also be the ground reference that has changed, even though the voltage drop is smaller in the signal than in the power supply.
Possible solutions
- just turn the servo off
- program the servo (torque limit, PID-values)
- a flyback diode across vcc and gnd
- a large capacitor across vcc and gnd
- power supply that is not powerful enough.
- use the commanded signal to overshoot quickly (to pull it further) and then back to the desired value. This would help to imitate a larger P value to overcome the friction.
- use feedback signal (ideally from the servo itself, or from an additional sensor)