Electrical – Quadcopter balance with MPU-6050

accelerometerbalancingdronegyroscopequad-copter

It is not uncommon to see people asking about how to balance a quadricopter using MPU-6050. It's also common to see people answering that a PID controller is needed. However, people doesn't say how.

In my case, I've already managed to combine data of accelerometer and gyroscope with a complementary filter. Also, I've already studied about PID in college. What I don't get is:

The input is voltage signal to the motors, the output is quadricopter's tilt angle and the setpoint is 0 (no tilt angle), right? The error operated by the PID is the difference between setpoint and output. So, how will my system know how to operate in the motor in order to make tilt angle closer to zero? I guess I have to implement my own logic to speed up some motors and slow down others, according to the error. But, if I have to do so, I don't see why PID is necessary. If I haven't, I don't get how motor is balanced according to the error. Could someone clarify how PID could work or share another solutions?

Best Answer

There are tho worlds in controll theory: open-loop (ger. Steuerung), closed loop (ger. Regelung). These two worlds can be joint together with addition.

The picture above is a depiction where open and closed loop are binded together. A PI controller only adds some correction to the setpooint derived from LUT (static characteristics) aka feedforward compensation. The stability of closed loop isn't affected, because the feedforward component is open loop - You must take care that you don't make an accidental loop from PV.

Related Solutions

Electronic – Reducing jitter and improving speed of accelerometer output

It sounds like the display response time you need is fairly and squarely coincident with some of the dominant vibration frequencies seen on the tractor's front loader and this could be a right royal b*tch to solve. In my opinion you do need to sample at a much higher rate to prevent aliasing - this is high frequency vibrations becoming aliased down to lower frequencies due to inadequate sampling rate. This may be enough to overcome your problem. Next is higher order low pass filtering like 2nd order of third/fourth order. It seems, in your question you have implemented a 1st order filter but this could produce much better results at a higher order BUT, you're running out of CPU speed.

OK, as a definite must-do thing, you must remove frequencies that can cause aliasing at your sample rate and maybe consider a fourth order analogue low-pass filter by cascading two sallen-key filter stages. Here is a calculator that you can set for a low pass frequency of 2Hz (the best you're going to get with 10Hz sampling and lots of nasty high frequency stuff.

Good luck - I'm not going to say you will be successful without some form of mechanical dampening and a high order analogue LPF at the front-end.

Electronic – Reading MPU-6050 with MSP430g2553 using I2C

You might not be waiting properly for the rx buffer to fill. In your Receive function, after your line:

while (UCB0CTL1 & UCTXSTT);             // Start condition sent? RXBuffer full?

try adding a:

while(UCB0RXIFG != (IFG2 & UCB0RXIFG)); //keep checking for recv ready flag

Or some variation of that, and see if it helps.

Best Answer

Related Solutions

Electronic – Reducing jitter and improving speed of accelerometer output

Electronic – Reading MPU-6050 with MSP430g2553 using I2C

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