p.p.m to p.w.m conversion

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toejam
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p.p.m to p.w.m conversion

Post by toejam » Sat Dec 15, 2001 4:28 am

hi,
T'm looking for a way to convert the servo output of an r.c. reciever to p.w.m to control the foward and reverse speed of a motor.Instead of using an h bridge i want to use a relay to reverse the motor. The speed must be ramped up with an adjustable rate.I think a pic would handle this but am lacking in this area thanks, jim

Isenbergdoug
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Re: p.p.m to p.w.m conversion

Post by Isenbergdoug » Sat Dec 15, 2001 5:46 pm

I tried to do the same thing this past summer, but didn't advance far enough on it to actually get something working. If you find anything out, please post it, I'd be interested. <p>Douglas Isenberg

russlk
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Re: p.p.m to p.w.m conversion

Post by russlk » Sun Dec 16, 2001 5:00 pm

Not being familiar with radio control, I have to ask: How does the H-bridge know when to reverse the direction of the motor? Seems to me that the same thing could operate the relay. For instance, use a latching relay and connect it to the H-bridge in place of the motor. To convert PPM to PWM, filter the PPM to DC and use the DC to drive a PWM circuit. A switching requlator with input to the error summing point can do that.

toejam
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Re: p.p.m to p.w.m conversion

Post by toejam » Mon Dec 17, 2001 5:10 am

basically,the h bridge gets switched by a signal that changes when the pulse is positioned past the the center of the of the timing cycle.This signal can be used to switch e relay.I think the best way to do this is to create a counter that counts how long it takes for the pulse to happen and convert the amount of time into a number which can be converted to a speed command signal.The ramp up stuff is a problem though.Thanks for your input.
tj

bdickens
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Re: p.p.m to p.w.m conversion

Post by bdickens » Thu Jan 10, 2002 9:04 am

I asked a similar question around OOPIC processing not long ago. I ended up using a PAK-VII pulse input coprocessor ( Al Williams)<p>My intent was to read a servo and convert to something I could manipulate using the oopic and send it on to the servo. Seems to work on my test bed and the instructions that come with the chip are pretty good ( even for me)

hlreed
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Re: p.p.m to p.w.m conversion

Post by hlreed » Fri Jan 11, 2002 9:01 am

The output from the receiver to the servo is a 2 millisecond pulse repeated every 20 milliseconds.
Within the two millisecond pulse, 1.5 ms is center, 1 ms is ccw and 2 ms is cw.
With a PIC program you would need to time the pulse and create the equivalent integer. Then you can send that out to an H bridge to create speed and direction.
I have a motor controller that converts an integer into motor speed and direction.
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Harold L. Reed
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