Run brushless motors from brushed AlienWii FC

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Run brushless motors from brushed AlienWii FC

Postby Pedro14755 » Sat Sep 03, 2016 10:02 am

Hello,
I am trying to work out how I can convert an AlienWii Classic Narrow FC to run ESC's and brushless motors. I have removed the FET's and 10K pull-up resistors from the motor output pins and along with an appropriate GND connected these two to the PWM signal in and GND of an KISS 18A ESC. A separate 2S battery is powering the ESC/ Motor combination. The ESC's do not appear to be getting a valid PWM input signal from the FC but the FC was functional for brushed motors prior to me removing the FET's and pull-up resistors, so I know the the board is sound. This Atmega32U4 on the AlienWii is running at 16mHz at 3.3v which I am told puts it into an overclocked situation but the FC running brushed motors works perfectly as this is the default operational model.

I have a later AlienFlight FC that is exactly the same circuit except for the fact that the Atmega32U4 on this runs at 16Mhz but at 5v instead of 3.3v. This FC works perfectly in a brushless set up. I have tried the same code that I successfully used on the AlienFlight FC, on the AlienWii FC but the ESC LED comes on when the 2S battery is first connected but then goes straight out, indicating that there is not a valid PWM signal being detected. I have looked at trying to change to operational voltage of the Atmega up to 5v but seeing as the MPU6050 gyro will only run on a maximum of 3.3v this is not feasible without doing a whole new board design with both a 3.3v and a 5v buck boost regulator. It was also suggested to me that if I incorporated some level shifting circuitry into the PWM lines to the ESC's that this may provide the correct PWM signal to power the ESC's.

Can anyone offer any suggestions as to how I might proceed please
Last edited by Pedro14755 on Mon Oct 16, 2017 4:36 am, edited 1 time in total.
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Re: Run brushless motors from brushed AlienWii FC

Postby Cereal_Killer » Tue Sep 06, 2016 2:07 pm

Pedro14755 wrote:The ESC's do not appear to be getting a valid PWM input signal from the FC but the FC was functional for brushed motors prior to me removing the FET's and pull-up resistors, so I know the the board is sound.

Well the good news is you're correct it's not receiving the correct type of signal. FET's on the brushed controller are ran by a varying duty-cycle signal of 0-100%, a PWM value. Brushless ESC's are ran by a ppm signal (pulse position modulation) that's 1000-2000uS. Not compatible AT ALL!!

Depending on the ESC (and what version of blheli) it may have a setting to accept ppm input but idk how well that does or doesn't work, never seen a single person running it like that.

Your cheapest (and best) option will be to get a $12 naze32 board...


Also you should be able to set multiwii to do the correct output (actually multiwii has to be set to do pwm output for brushed motors so you should be able to disable that option to go back to a standard ppm based output.


Note don't confuse ppm timing signals with the "ppm receiver signals" some receivers use. Different things totally...
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Re: Run brushless motors from brushed AlienWii FC

Postby Pedro14755 » Mon Oct 16, 2017 4:58 am

Thanks for your insightful reply Cereal_Killer. Sorry that my reply comes 13 months after yours :) but I obviously forgot to turn on email notifications for this post.

I have never heard anyone else explain the difference in signals as well as you have here and I thank you sincerely.

I ended up doing a total new board design with both 3.3v for the gyro and 5v for the Atmega and it works a treat :)
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