Servo Controller

Comments

• Palmer Posts: 11

  2006-10-21 01:52 edited 2006-10-21 01:52

  I believe the continuous rotation servo won't hold a load other than with the mechanical resistance in the gear reduction at a specific static position because you can't stop it and hold at a specific location other than center (you can try to make an equation relating time, and your duty cycle to stop it at a specific location but it would be pretty tough without a dynamics course under your belt). I don't think even at the center position it won't hold a load there because the feedback loop has been cut and it doesn't know to go back if you physically move the horn. All you can do is rotate for a specified amount of time cck-wise or clk-wise with a specified speed (up to what the servo can spin at base on the gear reduction). I'm 95% sure this is the case.
• SouLJah Posts: 35

  2006-10-21 02:16 edited 2006-10-21 02:16

  The information I want is really necessary so I could relate the speed and/or torque of the servo for a given load, if the servo is tugging·.25 pounds it will move slower tuggin .50 lbs.
• Palmer Posts: 11

  2006-10-22 15:49 edited 2006-10-22 15:49

  You can easily change the speed that a servo moves by changing the amount of time you pause between pulses. More pulses per second = faster rotation. However with a continuous rotation servo you have to be careful if you go too slow because the servo will not resist force against the direction of rotation between pulses. A regular servo will hold its position because the pot inside will continually adjusts the position to match the position you last told it to be at.
  I'm not sure if you ment "will it move slower..." but if you did then it depends on the max torque of the servo. You probably won't see a difference in a really strong servo in relation to a light load but one where your load is close to the max torque it will strain the motor and slow it down, in which case you can up the speed to a limit by adding more pulses per second. You'd need some feedback as to how fast the servo is actually rotating though--an encoder or a through beam sensor or contact switch, etc...
  Are you trying to maintain a constant speed with varing loads? The data sheets for most motors (not sure about servos) will have graphs of torque and speed with some other information there too like amps, voltage, ect...it might be worth looking for the data sheet from the manufacturer. The relationship is usually already there but only graphically, no equations are provided.
  Just ask if you need more specifics on any of this, I'll try to help.
• SouLJah Posts: 35

  2006-10-22 20:10 edited 2006-10-22 20:10

  Hey Palmer, I appreciate all the help you have given to me.· Is there a complete data sheet available?· Because once I have that I'm in buisness
• Tommy Bot Posts: 60

  2006-10-22 20:35 edited 2006-10-22 20:35

  SouLJah,
  
  Take a look at the spec sheet:
  
  Technical Specifications
  > Power 6vdc max
  > Average Speed 60 rpm
  Note: with 5vdc and no torque
  > Weight 45.0 grams/1.59oz
  > Torque 3.40 kg-cm/47oz-in
  > Size mm (L x W x H)
  40.5x20.0x38.0
  > Size in (L x W x H)
  1.60x.79x1.50
  
  
  I blieve·this·means that·47oz-in (inch ounces) of torque will "stall" the motor.
  This is its "workload" if you will. I have no idea how to convert this to "towable" power. Friction in your drive system plays a part.
  
  Maybe a reason for an experiment... Incrementally stack wight on your Bot and measure run speeds at various servo speeds...
  
  ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
  (Frequently heard from other's)
  
  Tommy, I know it wasn't designed to·x, but can you make it·do x·anyway?
  
  ·
• Palmer Posts: 11

  2006-10-22 23:07 edited 2006-10-22 23:07

  I looked on Futaba's website (I'm assuming you're using the continuous rotation servo from parallax) to try and find spec sheets. I didn't see any spec sheets with info you were looking for. You can always email their tech support and ask if they can provide the current-torque and speed-torque graphs. But like I said before I don't even know if they make those for servos. They almost always do for DC motors though which is what's in there driving the servo. Sometimes its just easier to pick up the phone and talk to them rather than email (you may not hear back by email). If you need more help just ask.
  
  Palmer