In looking at issues seen up to and including the Rev 4.9 controller boards we have identified and addressed in our now in production verstion 5.0 board two things that are designed to solve the issues seen on some field units where motor power is lost.
(There is another issue related to not having a battery in the back of the board that leads to motors stopping but in that case there WOULD still be 24V so I restrict the discussion to just the hardware loss of 24V)
The ‘short’ answer is we are aggressively addressing and fixing this issue in our rev 5.0 boards now in production. It is not easy to fix this on rev 4.9 boards in the field but we here can fix it if required and it is arranged.
Here is the ‘long answer’
The main issue is that through a mistake in parts procurement and us not catching it the chip that does power protection for battery low, battery high or overcurrent (short protection) ‘latches’ and once triggered it remains totally off until a full power cycle. A second issue is that the current sense was set too low so that if the motors are made to jerk in a very strong way it would trigger the protection circuit.
So our fix is to use a motor protection circuit that once triggered will after a fraction of a second re-try and keep doing that till the fault is removed. This then allows an accidental short or a strong surge in the motor current to NOT keep the motor power off.
We also have put in an LED that if the motor power gets cut off for whatever reason it will turn off. We also are adding other logic so the high level Linux based code can know if motor power has been lost either from the red switch being off or any other reason.
In the case of returned rev 4.9 boards we can replace a part to avoid the power staying off but it is a very fine pitch part and should not be tried to be fixed without experienced surface mount soldering technician help with proper gear (very tricky work).