Subject:
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Re: Different motor speeds?
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 28 Dec 2000 20:40:20 GMT
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Original-From:
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Steve Baker <sjbaker1@airmail.#nospam#net>
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Reply-To:
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SJBAKER1@AIRMAIL.NETsaynotospam
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Viewed:
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462 times
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Doc Kinne wrote:
> I've build a very (VERY) simple robot that basically consists
> of two medium sized wheels coupled directly to the motors so I could
> begin to play around with the programing. I've noticed that one
> motor seems to go ever so slightly faster than the other even with
> the power setting to the motors A and C set identically. This
> causes my little 'bot to go in a wide circle when it is supposed
> to be going straight.
>
> Is this a fault in one of my motors or is it a basic flaw of
> design I can fix by using gears to couple the wheels to the motors or
> something?
Well, we've talked a bout this quite a lot over the past month or so -
and as I'm sure others will say - you can't guarantee that all motors
have identical speeds - and it's known that the motors spin slightly
faster "forwards" than "backwards".
All of this means that you have to work hard to get the robot to go
in a straight line.
Either:
1) Use some kind of a mechanism where one motor drives the robot
forwards - and the other steers.
Or:
2) Get a rotation sensor and use it to measure the relative speeds
of the two motors using a differential - then in software, 'Float'
whichever motor is going faster until the rotation sensor tells you
you are pointing in the right direction.
Or:
3) Get TWO rotation sensors and measure the total rotation of each wheel.
That allows you to measure how much you've turned as well as the
speed of the robot. Once again, 'Float' the motor that's going too
fast whenever one rotation sensor reads higher than the other and you'll
go straight.
Or:
4) Use some kind of external landmark to guide the robot - aim towards
a bright light - follow a line on the ground, etc.
In the end, because wheels slip and have slightly different radii, even mechanisms
(1), (2) and (3) won't get you a *perfectly* straight line - you'll have to use (4)
if you need precision navigation.
If you want to go with (2) or (3) but don't have a rotation sensor, you
can use a light sensor and a rotating black and white disk instead.
--
Steve Baker HomeEmail: <sjbaker1@airmail.net>
WorkEmail: <sjbaker@link.com>
HomePage : http://web2.airmail.net/sjbaker1
Projects : http://plib.sourceforge.net
http://tuxaqfh.sourceforge.net
http://tuxkart.sourceforge.net
http://prettypoly.sourceforge.net
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Message is in Reply To:
 | | Different motor speeds?
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| Folks: 1040EST 363-2000 Now that I'm "off and running" with regard to emailing to the list I thought I'd ask a question that's been going through my mind. I've build a very (VERY) simple robot that basically consists of two medium sized wheels (...) (24 years ago, 28-Dec-00, to lugnet.robotics)
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