Subject:
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Re: Encoder Implemenation questions
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 12 Jan 2001 03:32:22 GMT
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Viewed:
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1340 times
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> My question is: how can I accurately get a wheel to stop after any number of
> ticks? I coded a routine to count up to 24 and stop. Its obvious from watching
> the wheel that once it turns off it continues to rotate about 3 to 5 more ticks
> which is over 1"! Not good.
I would suggest shutting it down early (say 5 ticks early) and using a
"jog" mode whereby brief pulses are sent to the motor to move it the
remaining distance.
Lets say you shut it off at 19 (targeting 24) and the motor/load's
momentum carries it to 23. You simply jog it to 24. You won't get up
enough speed to pass your target during the last count (or two).
Of course, you didn't tell us what the application was, so I don't
know if a jog function is appropriate (it slows the positioning time).
You also don't indicate if the load is variable. If the load *is*
variable, you could try a simple software workaround by having the
software learn about the momentum characteristics of the load. Simply
shut the motor down and count the number of ticks until it stops.
We'll call this the "momentum number", You can then use the momentum
number to deduct from the number of desired ticks to determine when
the motor should be shut down early.
If the load test tells the program that it takes the load 6 ticks to
stop - set the momentum number to 6 and stop the motor 6 ticks early.
If the load changes and it now takes 3 ticks to stop, set the momentum
number to 3 and shut it down 3 ticks early.
Use the jog function to compensate for any error and increase or
decrease the momentum number accordingly.
Matthias Jetleb
VA3-MWJ
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Message is in Reply To:
 | | Encoder Implemenation questions
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| I have contructed a robot that I want to be able to move and position itself accurately. I have encoders (the Hamamatsu P5587) attached to analog inputs 4 & 5 using sencdr4 & 5. I have 24 segment encoders that should give me a resolution of about (...) (24 years ago, 11-Jan-01, to lugnet.robotics.handyboard)
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