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sinusoid code? 
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Joined: Wed Apr 21, 2010 3:26 pm
Posts: 1
Post sinusoid code?
Hi all,
I'm new to robotics and C. I'm trying to drive my vex servo sinusoidally with the pic18F8520 vex microcontroller - from what i've seen so far online and in the help topics, it doesn't look like there is a function for this in robotC for ifi, but i thought i'd post to the forum and see if anyone had any experience or advice on how to write code which would drive the servo in a sine function, or just vary velocity over time smoothly. Any advice would be appreciated, thanks!

Wed Apr 21, 2010 3:39 pm

Joined: Sat Nov 22, 2008 8:06 pm
Posts: 48
Post Re: sinusoid code?
It can be done, but it would be manually. If it didn't have to be sinusoidal and you just wanted it smooth, you could just average the old and new motor speed values. I would suggest about 3 to 1 average, old value to new, such that you would have code like this.

motor[leftMotor] = (int)(3*oldMVal+motorVal)/4;
oldMval = (int)(3*oldMVal+motorVal)/4;

oldMVal would and motorVal would just be standard character variables. You would change motorVal in your code to run the motor smoothly. I think the (int)s would be required to keep the values from overflowing.

Anyhow, this would do it, with just a short pause between loops. Maybe like 50 milliseconds. More if you want it even smoother.

If you really want perfect sinusoidal control, well, RobotC does have some built in trig commands.

Thu Apr 22, 2010 12:34 am
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Location: Rotterdam, The Netherlands
Post Re: sinusoid code?
Using trig functions might use unnecessary amounts of processing time. Does it really need to be sinusoidal or does it just need to be smooth? I would go with Bluesaberist's solution. Remember, K.I.S.S.


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Thu Apr 22, 2010 1:36 am
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