Full Motion Flight Simulator: P6 Mods

Full Motion Flight Simulator
P6 Mods - Power

The DOFReality P6 control boxes have three power supplies [1] (one for each motor), that supply the motors via three MD13S [2] drivers. After switching from the original to the SFU gears, my platform showed a strange behavior. When a motor moved down and then up again, at the lowest point of the movement it appeared as if it shortly lost power and made a "dip", which immediately broke immersion. The following video was taken running the SMC3 utility in "Motion" mode:

The oscilloscope displays the voltage between the two motor wires. Note how in the beginning the arm moves smoothly and the voltage switches between +/-24V and does PWM. At about 17 seconds the first "dip" occurs, which also can be heard (the motor sounds differently for a moment and the whole platform makes a bang).

My first idea was that perhaps the power supply is too weak and can't support the sudden change of direction. But after some further investigation I stumbled across one feature of the MD13S drivers: "Regenerative Braking". This means that when the motor is driven by an external force, it works as a generator and delivers power back to the power supply. And as soon as that power exceeds 24V, the switching power supply tries to keep the voltage stable and regulates itself down, which results in the "dip".

To fix this, I added three Schottky diodes (30A 50V) [3] between the power supplies and the driver.

CAUTION: Make sure the control boxes are disconnected from main power before opening them!

The original wiring of the motor drivers.

The Schottky diodes go between the red wire and the green connector block.

Note that the ring (indicating the cathode) must point towards the green connector. I used WAGO clamps [4] to connect the red wire to the anode of the diode, but any other method of making a secure connection will do as well.

This is the voltage measured over the Schottky diode. At the times where the curve is almost zero, power runs normally from the power supply to the motor. When the curve goes negative, this means that power from the motor (now acting as a generator) would flow back to the power supply, but since the diode prevents current from flowing in that direction, the voltage can be measured over the diode.

With this modification (applied to both control boxes), the "dipping" is gone and the platform runs smoothly again.

Mark Scheierman made a video [5] that shows in detail how to implement this fix:

[1] https://www.amazon.de/Meanwell-Biltron-Schaltnetzteil-geschlossene-Struktur/dp/B07SVH2H3G
[2] https://www.cytron.io/p-13amp-6v-30v-dc-motor-driver
[3] https://www.amazon.de/dp/B09Z21NZW3
[4] https://www.amazon.de/dp/B00JB3U7Y6
[5] https://youtu.be/ZpWa3DVayv8