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using different servos? — Parallax Forums

using different servos?

blink13blink13 Posts: 65
edited 2005-10-24 20:26 in BASIC Stamp
ive jus used some of the code from the What's a Microcontoller book·to make a servo rotate in using a variable resistor, and i was wondering if i were to change to a more powerfull servo would i have to alter my code?
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Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-10-23 04:53
    Hello,

    ·· You should if the servo is the same type, i.e. a standard unmodified hobby servo.· Most have the same general range of PULSOUT values for control.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • bulkheadbulkhead Posts: 405
    edited 2005-10-23 05:44
    If you are looking for cheap high torque servos, check out www.slickzero.com. High torque servos for $15.75 with $.95 shipping. Add $6 for the metal geared version (impossible to metal strip gears, although plastic gears are usually tough enough for most applications). I ordered the "BMS-620MG" and it worked great, at about half the price of comparable servos.
  • blink13blink13 Posts: 65
    edited 2005-10-23 16:11
    i need the servo to rotat around 5 pound object(the last time i did this i melted the servo), will these be strong enough?
  • allanlane5allanlane5 Posts: 3,815
    edited 2005-10-24 14:49
    A servo should only be driven with 5 to 6 volts. Any more than that, and they will melt, regardless of the load.

    Most servo's use the "1 mSec pulse full left, 2 mSec pulse full right, 1.5 mSec pulse center" and "Repeat pulse every 20 to 50 mSec" control algorithm. This means you don't need to change your code when you change a servo.

    "rotate a 5 pound object" believe it or not is a vague statement. What you need to do is determine the amount of torque you require to rotate the object. Servo's are rated in the amount of torque they can put out.

    Torque is force times displacement. If your 5-pound object were balanced in the middle of a plate, on mostly frictionless bearings, and your servo was connected to the middle of the plate, it would take very little torque to rotate it. This would be because the displacement of the mass from the center of rotation would be effectively zero.
  • houbahouba Posts: 3
    edited 2005-10-24 19:11
    Most of the servos you can find on the Hobby markets are going to be compatible. For remoted controlled aircraft used in competition you can find servos with a very high torque. Futaba for example offers a servo with 18 pounds torque (FUTM0051)
  • allanlane5allanlane5 Posts: 3,815
    edited 2005-10-24 20:26
    Well, from http://www2.omnimodels.com/cgi-bin/woi0001p?&I=FUTM0051&P=O

    Torque: 233 oz-in @ 4.8V - 292 oz-in @ 6V

    Now, Torque is Force X Displacement.

    292 oz-in == 18.25 Lb-inch. So, if you had a 1-inch pully, this servo could in fact lift 18 pounds (slowly) with LOTS of current (somehow, they don't list full load current, go figure) at 6 volts.
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