Post by thread:Controlling Brushless DC motors

Has anyone tried to use a PIC to control a brushless DC motor? I have worked with controlling brush type DC motors using encoders, pwm, and a driver chip. However, a brushless motor seems to be quite a bit more complex. Has anyone tried this? Can you point me to any code or references? Is there a way to implement a feedback control loop on these without using encoders? Paul

>complex. Has anyone tried this? Can you point me to any code or >references? Yes, several have, but they're all commercial (aveox.com, maxcim.com and others) and I doubt they would share their code. The simple method (no great tough stuff) is to use the encoder outputs as the index into a lookup table, the entries in the table consisting of the bits to write to the ports controlling the FETs. You can still use the PWM hardware to control the RPM with a little extra circuitry. >Is there a way to implement a feedback control loop on these without using >encoders? Yes, but it requires that you either a) Monitor the currents into the FET gates (this is being done in some hobby-oriented controllers) OR b) Push the motor at a constant RPM (only good for low-load motors) by commutating based upon a timer. Andy ================================================================== Eternity is only a heartbeat away - are you ready? Ask me how! ------------------------------------------------------------------ spam_OUTandyTakeThisOuTrc-hydros.com http://www.rc-hydros.com - Race Boats .....andyKILLspam@spam@montanadesign.com http://www.montanadesign.com - Electronics ==================================================================

The basic idea behind a brushless dc motor is that it regulates its own speed. Trying to control the speed externally without messing w/ the electronics inside is not going to give you a very good/nice range. The motor already has feedback, usually in the form of a hall effect chip which senses how fast the rotor is going, and when it is in a certian position. The rest of the circuitry then sends appropiate currents through the coils to make it spin. Some fans (notably processor fans such as the Pentium II and III) have a third wire which either 1) sends out a pulse every revolution (generated by the sensor) or 2) is in a certian state (high or low) when the fan is operating correctly, and switches state when there is a fault which may cause the fan to stop moving. -Adam Paul Brown wrote: {Quote hidden}> > Has anyone tried to use a PIC to control a brushless DC motor? I have > worked with controlling brush type DC motors using encoders, pwm, and a > driver chip. However, a brushless motor seems to be quite a bit more > complex. Has anyone tried this? Can you point me to any code or > references? > > Is there a way to implement a feedback control loop on these without using > encoders? > > Paul

At 07:29 AM 9/23/99 -0400, you wrote: >The basic idea behind a brushless dc motor is that it regulates its own >speed. Trying to control the speed externally without messing w/ the >electronics inside is not going to give you a very good/nice range. Not all brushless motors have the controller internal. From his questions, I believe he was talking about controlling a brushless motor with external electronics. To see what I mean, visit these sites: http://www.maxcim.com http://www.aveox.com These motors are quite a bit more powerful than your Pentium fans <G>. Several of the controllers available for the above motors use PICs. Maxcim has "sensorless" controllers in development, if not already deployed. Andy ================================================================== Eternity is only a heartbeat away - are you ready? Ask me how! ------------------------------------------------------------------ andyKILLspamrc-hydros.com http://www.rc-hydros.com - Race Boats .....andyKILLspam.....montanadesign.com http://www.montanadesign.com - Electronics ==================================================================

> Not all brushless motors have the controller internal. I'd also like to add that not all brushless motors have controllers, period. Your typical cheap brushless DC computer fan has 1 hall-effect sensor, 2 NPN transistors and 3 resistors. The fancy ones may have a decoupling cap. Brushless motors don't need to be rocket science if you don't need to go into space :-) Cheers, Bob

Actually, cost is no object. The problem is space. I think the problem can be handled using the feedback from the hall effect sensors in the motor and a lookup table. The disadvantage is that the position resolution is only 1/6 of a revolution. Paul A. Brown