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Topic: Arduino Fio - increasing output PWM resolution (Read 2 times) previous topic - next topic

MercerProject

Feb 07, 2011, 06:20 pm Last Edit: Feb 07, 2011, 08:47 pm by MercerProject Reason: 1
Hello people,

 So we're currently working on an Arduino project and need more resolution to get better control of our motors.  Currently, our motor drivers only respond to a PWM duty cycle between 20% - 60% duty cycle which only allows us to use 40% of the overall 255 resolution of the Arduino Fio's PWM output (approximately 102 levels).  This brings me to my primary question:

 Is it possible to increase the Arduino Fio's resolution output PWM resolution from 255 to something greater (perhaps 65k?) and if so how?

 Also, if there are ways to allow for the motor drivers to respond to a broader spectrum of the Fio's resolution that would work also.  We're open to all practical ideas.

 Thanks for the read!

*Edit - fixed typo.
*Edit - changed PWM range from 20% - 50% to 20% - 60% which gives 40% of the overall PWM range and 102 levels from 76 levels.


Grumpy_Mike

Quote
Currently, our motor drivers only respond to a PWM duty cycle between 20% - 50% duty cycle


What do you mean by respond?

If you mean that greater than 50% it gets no faster then remember that PWM only works on a fully loaded motor. On a lightly loaded motor it simply coasts during the unpowered part of the cycle.

Also do you mean that lower than 20% it stops, then yes it might very well do, again it depends on the load.

MercerProject

By respond I mean...

  When we programmed the motor drivers (sent PWM signal with a particular duty cycle, then hooked up the battery and waited for audio confirmation) we only heard confirmation tones for duty cycles between 20% and 60% duty cycles.

  Thus we continued testing until we found our maximum spectrum/range of duty cycles which the motor drivers would send a confirmation audio beep.  This range was experimentally determined to be 20% - 60%.  Accordingly, our 20% duty cycle was mapped to "no throttle" and 60% duty cycle was mapped to "full throttle." 

  So yes, at 20% duty cycle the motors are stopped and 50% (or perhaps 60%) duty cycle we can only imagine how much louder it will get (we've only tested up to 35% duty cycle as it gets scary loud and atm have no way to recharge our battery thus we've be restricted to limited testing).

MercerProject

We have successfully performed the power-up calibration sequence (to the best of our knowledge). 

We initialize the motor drivers for our batteries and received a confirmation tone afterwards.  After initializing our motor drivers we were able to step up the pwm one level at a time (starting at 20% duty cycle and we've tested up to 35% whereas we should be able to reach 60% as a maximum theoretically) and the motors have responded by increasing rpm (noticeable by a louder buzzing sound) at each level.

The load on the motors is a plastic propeller.  The motor itself is clamped to a table rendering it unable to move.  The propeller is:
GWS 3-Blade 9x5 Prop, Black, Reverse Rotation
http://www.rcdude.com/servlet/the-838/GWS-3-dsh-Blade--9x5/Detail

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