Subject:
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Re: Detecting tilt with an Accelerometer.
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 22 Oct 2002 03:21:21 GMT
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Viewed:
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674 times
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> For a thought experiment, I'd propose a robot with two big wheels
> attached to two motors, and 3 linear accelerometers set at right
> angles. That's five elements of interest, with 1-dimensional
> data from each.
>
> To start with, I'd use the prior accelerometer readings and motor
> outputs over a time span sufficient to account for sensor lag and
> transient motor startup/slowdown effects (plus any applicable gear
> lash) as the inputs to the simulation. Measurments every 5ms over
> a period of about a second is probably sufficient... for a total
> of about 1000 inputs to a closed-form inputs-to-attitude function.
> If the robot is actively trying to maintain a vertical attitude,
> then much of the domain of the function will never be used...
> This can probably be significantly simplified by finding patterns
> in the data, but that sort of analysis I leave until after I've
> moved beyond the thought-experiment stage.
>
> - Alex
Alex,
I think that you would only require two accelerometers, one positioned low
near the wheels, the other near the top. Both should be oriented to measure
accelerations along the direction of travel.
Using two accelerometers gives you a frame of reference with which to
evaluate the meaning of the acceleration feedbacks. If the vehicle was
tilting, the angular acceleration will generate different linear
accelerations for each accelerometer. You could write an algorithm to
accelerate the vehicle to drive the difference to zero.
The problem is that now you have a runaway condition. As long as the
vehicle is tipped, it has to continue accelerating to keep the angular
acceleration at zero. I think some sort of washout algorithm would be
reqired to return it to an upright position. This might be as simple as
having a seperate control loop that tries to drive the accelerometer
readings to zero. This second loop would have less authority than the
angular accel compensator, but would be the main source of control under
normal operating conditions.
What do you think?
Dean
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Message has 1 Reply:
 | | Re: Detecting tilt with an Accelerometer.
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| (...) Yes, this would be a simpler solution. Using the difference and the sum of the two accelerometers as two inputs would likely make the driver logic very neat and clean. In addition, it could be useful to have two (much more sensitive) (...) (22 years ago, 22-Oct-02, to lugnet.robotics)
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Message is in Reply To:
| | Re: Detecting tilt with an Accelerometer.
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| (...) Do you have some concrete reasons why it won't work, to go along with your assertion (for those of us just now joining the conversation)? I suspect that it could be made to work (in conjunction with other data like what the motor output is, (...) (22 years ago, 21-Oct-02, to lugnet.robotics)
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