I take it you've seen the videos on the web of the similar flying wing from Stanford, maybe 10 years ago? They had to build custom servos because the rates required were so high; the thing looked like it was flapping its ailerons for propulsion, they were so fast. I digress... Thanks, I check out the other classes of PICs. My bot is 24' stem-to-stern so my plan was to keep cost and complexity low by running only DC power and serial comm lines to the extremities of the boat, with several generic/"general purpose" microcontroller modules living next to the distributed pockets of sensors or actuators. Ergo I chose the biggest, mos= t feature-packed PIC I could find for the generic modules, hoping that it'd b= e adequate for the various applications. Generally the 16F747 has enough toys, though obviously this particular problem is a little tricky. I have no answer as to why I didn't look outside the 16F lineup; tradition I suppose. Drew On Thu, Jul 29, 2010 at 5:18 AM, Olin Lathrop wr= ote: > > Usualy, the standard PWM module(s) are not particular good at > > generating a standard 1.5 +/- 0.5 ms servo signal. And in > > many cases you have not a single servo anyway. > > I've got a side project (active control of a inherently unstable flying > wing) that drives 4 hobby servos directly from a 24HJ32GP302. The dsPIC > class PWM modules have wide enough period counters that you can do 500us = to > 2.5ms every 20ms with sufficient resolution in fire and forget hardware. > > With a PIC 18 or something I would look into multiplexing the output of a > single PWM module. The important observation is that you can fit a numbe= r > of 1-2 ms pulses in the 20ms repetition period. You do the pulse for eac= h > channel successively. The multiplexer can be as easy as a AND gate per > servo output. Now the PWM hardware only needs a period a bit more than > 2ms, > so you should have enough resolution for the varying pulse width. > > > ******************************************************************** > Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products > (978) 742-9014. Gold level PIC consultants since 2000. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .