Subject:
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Re: Using the Differential to drive straight.
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 11 Jan 2002 20:47:56 GMT
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Viewed:
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867 times
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In lugnet.robotics, Dave Chen writes:
> I've been playing with the following design to try to overcome the
> problems with getting the robot to drive straight while using an A B
> Differential drive train (ie left side wheels driven by motor A, right
> side by motor B) and to get consistent turning.
I suspect there are two different issues being discussed here.
One is to be able to go straight in some known direction.
The other is be able to go straight.
If you have a direction to go in, because you have a light beacon or a
compass or a line to follow, then you can usually find a way to create a
closed loop around whatever your sensor system is and correct for steering
errors like that. This scheme is ultimately the only one that works on
unknown terrain with all sorts of nasty variables at work like changing
battery voltage, changing inclination of the driving surface and changing
conditions of both the driving surface and the wheels/tracks surfaces.
If you want to go straight, within the limitations of slippage etc I have
found by far and away the best answer is to under-utilize motor power and
match the motors. If the left and right side motors are matched to within
one or two rpm and are lightly enough loaded so that they run close to their
off-load speed when driving the platform, then the platform will run
straight within the limitations of the driving surface. (I sometimes use two
(or more ;)motors per side to keep the individual motor shaft load down.)
I made a simple test fixture with a Lego speed computer driven by a 1:5
speed up from the motor. (40 tooth gear to an 8 tooth gear.) I drive the
motor from a lab supply set to 9.00 volts. All my motors have their 9 volt
clockwise rpms written on the underneath (on the curved area) in indellible
marker. It is then quite easy to look in the little tupperware tub for a
matched set when required if they are all stored upside down.
And the resulting (usually tracked) platform normally goes pretty well
straight afterwards.
JB
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Message is in Reply To:
 | | Using the Differential to drive straight.
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| I've been playing with the following design to try to overcome the problems with getting the robot to drive straight while using an A B Differential drive train (ie left side wheels driven by motor A, right side by motor B) and to get consistent (...) (23 years ago, 11-Jan-02, to lugnet.robotics)
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