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I'm trying to synchronize 4 brushless motors' speeds to, eventually, fly a drone. I chose every electronic component and it's starting to look like something.

I control my motors with the pigpio library on a Raspberry Pi. I communicate with the Pi via a small Qt Software I made, and they are linked via Wifi (5-10ms latency).

My problem is : I calibrated each of my ESCs to the same PPM range (1ms as min pulse width, 2ms as max). However, my motors are not reacting the same way : for a same command, one is starting at ~1050, 2 others at ~1100 and the last at 1125.

I could simply use an offset or something, but I have no tachymeter to measure their respective speeds, hence I can't force my motors at the same speed since I'm not sure if they have the same response on the range. Are they even linear, can they all reach their top speeds? How can I study my motors to synchronize them?

Thanks for your help.

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    \$\begingroup\$ "I'm trying to synchronize 4 brushless motors' speeds" - that's not how quadcopters stay stable, there's no need for them to be in sync. You absolutely need a three-axis angular rate sensor (also known as a gyroscope) which senses the attitude, and a control system which adjusts motor power settings individually in order to counter any deviations of the attitude from the desired attitude. \$\endgroup\$ – jms May 25 '18 at 17:44
  • \$\begingroup\$ Well, I deduced that because on the first flight test, it flipped over the one that turns on last ! How may I stabilize it then? \$\endgroup\$ – Gueg May 25 '18 at 17:44
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    \$\begingroup\$ It won't flip over when it has sensors to detect that it's flipping over (gyro), and a properly tuned control system which reacts within a millisecond by reducing motor power on one side and increasing on the opposite side. Quadcopters are fundamentally unstable, every "drone" you see is only able to fly because a computer is constantly wrestling for control. Ever wondered why quadcopters were almost unheard of 10 years ago? Cheap MEMS gyroscopes, needed for the flight controller, didn't exist yet. \$\endgroup\$ – jms May 25 '18 at 17:46
  • \$\begingroup\$ I wanted to add a corrector later on, but I guess it's time! Thank you \$\endgroup\$ – Gueg May 25 '18 at 17:54

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