Nyboard v0 motor driver questions
It's probably in the documentation somewhere but could you save some searching and outline the specs on the nyboard for driving motors? i.e. how many motors can be controlled? are they all pwm? how much power output is there and how many say mg92 motors can be directly powered by the board? Can bigger motors be used if powered separately (that's beyond me at this point but one can grow into it)? Can it be supplemented with another motor driver board if one want to make like a 12 legged cat or something?
Thanks!
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@zetathix
The powering chip for servos is rated at 5A. The actual limit is always smaller due to barrel effect (the constant discharging ability/overcurrent protection of batteries, EM interference in the circuit, etc).
The peak current draw I observed was 4.2A with 16 x mg90d, that's the knee servo of Nybble, slightly weaker than mg92b on the shoulder. Nybble uses only 8 servos (4x mg90d, 4x mg92b) for walking, and the max number of servos for walking should be 12.
Decreasing the voltage to about 5.5V will allow larger current from the batteries, because
P = U x I
where P is the maximum power capability of batteries, U is the voltage, and I is the current.
Using better batteries should increase the limit towards 5A. But that may also increase EM interference and make the board unstable and reset. So NyBoard V0 is better for programming rather than racing. I'm doing more experiments to improve its performance. Some can be done by adding capacitors or jumper wires, some has to be applied on the next version.
Note that the test I made was driving all 16 servos with the same sinusoid signal. In practical walking there will usually be some phase shift, like sin(t) and sin(t+ Pi/2). It will distribute the current draw evenly over a period and reduce the peak current.
The left plot shows the current draw from individual servos, the right one shows their total current. The blue curves have larger phase shifts, and simulate the actual cases.