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Continuous Rotation Servo — Parallax Forums

Continuous Rotation Servo

DominoDomino Posts: 2
edited 2007-07-30 04:09 in Learn with BlocklyProp
Hi,

I'm new in this Forum. I have·a Continuous Rotation Servo·and a·Parallax Servo Controller (#28023) - Rev B.
Is it possible to change the rotation speed of the servo with this board. Till now, I only can change the direction of the servo.

Dominik···· ·turn.gif

Comments

  • allanlane5allanlane5 Posts: 3,815
    edited 2007-07-20 15:07
    You CAN change the rotation speed, but not by a lot. The rotation speed is controlled by how far away from a 1.5 mSec pulse your PULSOUT is. However, it's not very linear, I believe between a count of 750 (1.5 mSec, stopped) and 800 (1.6 mSec) you get most of your speed control. 800 and above is probably "full on".

    On, and this 'speed curve' probably varies quite a lot between different servo's.
  • DominoDomino Posts: 2
    edited 2007-07-21 07:31
    Thank you for this quick answer.
    I think, this servos are not the best choice for a mobile platform. Because·I want to control the drive!

    smile.gif·Dominik
  • FranklinFranklin Posts: 4,747
    edited 2007-07-21 14:07
    The BOEBOT uses servos and it can do a lot. Take a look at the documentation if you are having trouble, there are step by step instructions on setting and adjusting servos for drive motors.

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    - Stephen
  • allanlane5allanlane5 Posts: 3,815
    edited 2007-07-23 14:13
    True, modified servo's have some drawbacks. Their chief advantages are that they are very inexpensive compared to any alternative, that they DO have some speed control, that they can do forward, stop, and reverse with a single I/O pin, and that their control signal allows the BS2 to remain a 'single-tasking' processor while still controlling multiple servo's.

    In all fairness, wheel-slip makes dead-reckoning by speed not very accurate, no matter WHAT motor you put on a wheel.
  • MightorMightor Posts: 338
    edited 2007-07-30 04:09
    The great thing about servos is that you don't need any special extra hardware to make it work. For a normal DC motor, you'll need to fabricate a double H bridge per motor. These can be bought in a pre-made package or you can put it together yourself. Never attach a motor directly to your microconroller or you'll kill it. With PWM you can control their speed.

    As for positioning, I've used the encoders on the Boe-Bot and they're accurate to about 10 brads per encoder pulse so you will need to make course corrections all the time or put up with the inaccuracy. You can get more accurate encoders (the wheels I have only generate 16 EPs per revolution) but then you risk the chance of missing a pulse if your controller is busy doing other things. Some inventive folks have used an optical mouse sensor to detect and calculate changes in direction. Perhaps you could search these forums for some more info on how to accomplish that. I've never done that myself, tbh.

    Gr,
    Mightor

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