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robot wheels

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Makaram

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hey guys?
why use a full rotation servo over a motor and a hbridge?
im using a basic stamp to control 2 servos acting as wheels. just wondering why people opt for servos instead of standard motors with an hbridge
 
Servos are easy to use because they have sensors, control electronics, gears.. all build in. And the interface is good for microcontrollers. For small and slow robots they are good option.
 
Yes it is all built in. Standard motors go too fast and have to be geared down.
 
Yes it is all built in. Standard motors go too fast and have to be geared down.

Sometimes you can control the speed without resorting to gears.
 
Sometimes you can control the speed without resorting to gears.

Gearing is mainly used to increase the torque; something that PWM can't control.

Servos that have been converted to continuous rotation (and thus aren't servos any longer - at least by standard definition) combine an h-bridge and a gearmotor into a single small package that is easy to interface with. They are ideal for small desktop roverbots and the like. The downsides of servos used in such a manner are mainly on the "robustness" of the servos; unless you purchase the more expensive dual-ball bearing servos with metal gears, and depending on the size/weight of the robot - the servos just aren't designed for use in such a manner over long periods of time (though generally, this means a much longer period than what you are likely to use the robot for, I will grant).

They are much cheaper and easier to work with than a standard gearmotor and custom h-bridge design; such designs are generally only needed in one of two scenarios: Larger robots that go beyond "desktop" size, and extremely small robots (microbots), in which you need to use very small motors and custom SMT h-bridges and such, just to conserve space. More hobbyists explore the former machines than the latter (I've often thought about building a microbot just to do it - but I'm not sure my eyesight or hands are steady enough anymore - heh).

:)
 
a DC motor is running at 3000rpm. if you connect a wheel of 2cm diameter you will run at 1000km/h :D so you need motoreducer in order to slow down the speed of the motor and increasing torque! (at 3000rpm your motor isn't able to move heavy charge).
So if at 3000rpm the motor has a torque of 10g/cm if you reduce the speed of 100times by using gears, the motor gets a torque of 1kg/cm!

With PWM you can control the speed but not the torque that is always less than the maximum.

So servos are practical, with gears inside and have just one pin for control (with H Bridge you need 2 pins and it needs space).. in anyway i prefer using DC motors and H bridge, maybe with encoders.

Regards.
 
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