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Predicting the time it takes PSC to finish a servo command — Parallax Forums

Predicting the time it takes PSC to finish a servo command

FleurDeLisFleurDeLis Posts: 2
edited 2005-07-07 14:59 in BASIC Stamp
How does one predict the time it will take for a motion to complete?

It would be great if I could consult a chart or use an equasion to predict what the combination of "rate" and "position" would equal in "time".

guessing and trail and error are too long of a process...any help?

keith rowell

http://knewt.blogspot.com/

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-07 03:29
    Keith,

    ·· Under ideal circumstances this would seem to be easy.· But it's not an exact science as there are more factors than just the motion/speed of the servo.· As batteries weaken speeds change.· As servos are put under load or stall, these parameters would also change.· Even the position of a servo can affect it's speed.· For example, consider a servo moving an arm.· Going down might go quickly, whereas going up the servo works harder, so it would take longer.· Just some things to consider.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • FleurDeLisFleurDeLis Posts: 2
    edited 2005-07-07 13:27
    I agree that the response of the motor can vary. It should be possible to predict the timing of the commands that are being sent to the servo though. Like a chart or equasion. The documentaton for the serial servo controller mentions that a rate setting of 63 can take 45 seconds to complete a 1500 increment motion. The documentation for the USB servo controller gives a different number. I'ld just like the accurate values for rate / distance travelled in milliseconds...

    keith rowell

    http://knewt.blogspot.com/
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-07 14:11
    Keith,

    ·· The best way to go about that would be to chart them on your servos, at the voltage you're running them at.· We could give you fully accurate specs based on a test model here, and it may be off from your setup there, even just due to slight differences in the servo itself, as well as the batteries or power supply.· Good luck.


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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Don BuczynskiDon Buczynski Posts: 31
    edited 2005-07-07 14:47
    I think it would also depend on how the servo is being driven. Given that the servo is receiving a periodic pulse for its current position, how many pulse steps are used to move to the new position? For a large pulse width change in just a few steps, the slew rate of the servo and its load would have a significant effect and be hard to predict consistently. For a large pulse width change using very many·short·steps, the step repetition rate would have more of an effect. Since the repetition rate is controlled by the BS2 code,·the move time could be calculated fairly accurately as long at the step rate does not exceed the servo slew rate.

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    Don Buczynski

    http://www.buczynski.com
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-07 14:59
    Don,

    ·· You bring up some good points.· My main point to Keith was that you can take two identical setups, and the same code, and get somewhat different results on the values he was looking for in values for rate / distance travelled in milliseconds.· It would be fun to work on though!·

    Keith,

    ·· If you can come up with some sort of table for the values and rates for the ramping, it might be worth some Parallax Hardware.· =)

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
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