Hi, I would like to make a diy drone using the motors from my old Syma X8W. They are brush motors and I would like to control their speed. I've read about MOSFETs on the wiki,and it said they are good for projects where fast changes are used. Is it correct to use them in this case as well? Which MOSFETs would you recommend for my motors (5V; 400mA at start-up, than 300mA)?
I tried to understand the parameters and found the IRLZ44N or IRF520N could be a good choice. Am I right? I also looked at the MOSFETs on the Syma X8W board and they are 30H80A. Which option is better?
This looks like a good choice.
Look for a LOW Rds(on), if it is to be driven by logic levels, select one of this type.
I'm sorry, but I'm new to all this. Why is it better to have the Rds(on) lower?
Lower Rds(on) means less dropout voltage across the mosfet and a higher voltage for the motor.
Forget about the IRF520.
It's not logic level, so a poor choice for any MCU.
Leo..
Thanks for your explanation. I found two more MOSFETs, that I can easily buy in my country and I think, they would work too. It's FQP30N06 and FQP50N06. What do you say?
If the data sheets say they are "logic level", then they should be OK.
Look for Vgs(th) less than about 3V. For the FQP30N06L (note the "L") it is 2.5V.
So lower Vgs gives me bigger scale of values to use? Or what's the advantage to have 2.5V instead of 4v?
The transistor won't even begin to turn on at 3V, if Vgs(th) is 4V.
It should be clear that if you are using 3.3V logic, you don't have a choice between those two options.
Okay, i think I understand it. Thanks for your help.
A MOSFET is not half the way if you want to control motor speed. Since the motor speed is related to many parameters you also need a rotary encoder for speed feedback and a (PID...) regulator in code. That's why nowadays drones use BLDC motors with immanent direct speed control.
Well, using the PID was sure thing for me. I think it could work even with my current setup, but it's possible, that I will upgrade to BLDC motors later.
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