Subject:
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Re: Adder/Subtractor revisited
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 7 Feb 1999 07:30:52 GMT
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Viewed:
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1090 times
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> Anyway, the challenge is to build something that can run the straight
> sections very fast, while optically following the tape. The problem I
> encounter when trying to build a really high-speed robot is that there's
> no good way to control the speed of the motors; they're either on, or
> off. etc..
>
> Unfortunately, if the robot is geared for high running speed, even a
> very brief stoppage to left or right drive power causes the robot to
> jerk much too strongly to left or right,
Here's what I do and it works quite well. I have added a "partial duty cycle"
mode to my motor control system. Basically I intermitantly turn off the motor
for a very small increment of time. The time-average of a properly synchronized
sequence on off-on cycles yields an effective reduction in the duty cycle of
the motor, reducing its effective power output. For example, a 100 msec off
cycle followed by a 100 msec on cycle yields an effective duty cycle of 50%;
100 msec off followed by 300 msec on yields 25% duty cycle, etc. A little
experimentation will yield an ideal duty cycle to effect gentle course
corrections for a particular motor power setting and gear arrangement. Since I
have separate tasks for each motor, the coding is quite simple:
while(true)
{
freewheel motor
sleep(100 msec)
on motor
sleep(100 msec) /* for 50% duty cycle */
}
OH! one very important point: as in the above, rather than turn OFF the motor,
FREEWHEEL it! This prevents the a jerking motion, resulting in the veering
behaviour that you experience.
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Message has 2 Replies:
 | | Re: Adder/Subtractor revisited
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| A nit, but you meant 75% duty cycle, no (or reversed your terms) ? -- SeeYa ! ---...--- Jim ---...--- Hello... Is this thing on ? David Harry wrote in message ... (...) (25 years ago, 7-Feb-99, to lugnet.robotics)
| | | Re: Adder/Subtractor revisited
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| (...) [snip] (...) I actually had already tried that, and couldn't get to work in these particular circumstances. I couldn't get the robot to turn off the motor for any period briefer than 50 ms, and even that short a period (coupled with setting (...) (25 years ago, 7-Feb-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: Adder/Subtractor revisited
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| (...) Actually, I've had pretty good luck with independently driven left and right drive trains; I haven't had a lot of problems with robots curving when I want them to go straight. I find the adder/subtracter useful for a different reason: it makes (...) (25 years ago, 6-Feb-99, to lugnet.robotics)
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