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  Robotic Madness
  DC Motors and Servos

DC Motors and Servos that I use


Here are a number of different servos I That I use in my robotics.

Tower Pro mg995
all metal gears and BB very rugged for drive servos.

Parallax's STD BB HS
continuous rotation servo used for drive setup.

E-Sky mini ES070A Handy for Pan/Tilt WI-FI camera setup and any small sensors.

Modified for continuous rotation drive units.

LEGO NXT servo motors, These have a lot of use in my robotics.

Converting the RC Servos to Continuous Rotation

Rotation Overview

Modification For Continuous Rotation

One popular modification to RC servos sets them up for "continuous rotation". Instead of moving through a range of about 90 degrees, a modified servo spins around and around. This modification is often used by those building their own miniature robots: the servo is turned into a combination motor, gearbox, speed control, and reversing switch.

I won't go into details of how this is done, but I will outline the general principle.

  • A normal servo uses feedback to determine where the current angle is, as opposed to where the pulse train says it should be.
  • The feedback comes from a potentiometer attached to the output shaft. The potentiometer is used in a voltage divider that produces a voltage proportional to the current angle.
  • The incoming pulse train is measured, producing a voltage proportional to the desired angle.
  • The one voltage is subtracted from the other.
  • This difference drives the motor. Big differences drive the motor rapidly. Small differences drive it slowly.
  • The modification removes the feedback and substitutes a fixed voltage divider set for 50%. [It also removes any mechanical "stops" used to prevent 360-degree rotation.]
  • Now, the speed and direction of the motor is relative to a fixed voltage, not the current position. Pulses of medium width produce 50% voltage, no difference, no movement. Slightly longer pulses move the motor slowly. Longer pulses move the motor faster. Pulses shorter than the medium width cause the motor to spin in the opposite direction.
You can see how handy this is to robot builders. Just bolt a couple of modified servos to the bottom of the robot, and put tires on the output shafts. Then just generate a stream of pulses to control speed and direction.

Different servo lead pinouts

brand universal positive wire negative wire signal wire
KO Propo NO Red, outside pin Black, middle pin Blue or White, inside pin
NO Red Black, middle pin Black, White, or Blue
Airtronics/Sanwa T
NO Red, outside pin Black, middle pin White or Yellow, inside pin
Airtronics/Sanwa Z YES Red, middle pin Black, outside pin Blue or Yellow, inside pin
Futaba J NO Red, middle pin Black, outside pin White, inside pin
Hitec S YES Red, middle pin Black, outside pin Yellow, inside pin
Japan Radio (JR) YES Red, middle pin Brown, outside pin Orange, inside pin
Tower Hobbies YES Red, middle pin Black, outside pin White, inside pin
Futaba G
Kyosho/Pulsar ? Red Black Yellow

Motors I use in my robotics

These Como Drills planetary geared motors are great for drive and body rotation, They run on 3v, 6v, 9v, 12v, 15v and can have up to six stackable gear box's.

These were discarded from my RSV2 when I did a mod for my Robotic generic base, They may be used in the future for some project. They are very power full. 9v but will happily run between 6-12v.

These Technics two speed gear box motors run slightly fast for robotics but could be fun. The two red output shafts can be seen. 6-9v.

Light weight 1/8 th shaft DC motors 6v

These CD Rom motors come in handy from time to time, they definately have there uses.

These are Sagem 12-24v double ended BB motors with a stall of 10amps, I acquired 20 of these from a friend from discarded Printers a few years ago. They have an 8mm shaft with nice shaft encoders.

Some my collection of small to medium DC motors and servos.

2007 © Robosapienv2-4mem8
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