power available from BASIC stamp 2

[dmehling]

I am making decisions about what microcontroller to use for my robot, and I have basically settled on the basic stamp 2 with the super carrier developmental board.  I am needing to know if this will have adequate power for my robot.  I will be using a 12 V, 1 amp power supply.  My robot will use about eight motors, including both servos and DC motors ranging in power from 3-6 VDC.  I will probably need to use an additional motor controller connected to the stamp in order to control that many motors.  Will the developmental board I have chosen be able to power that many motors?  Not only that, but I'll need to have a least two, possibly three of those motors rotating simultaneously for limited periods of time.  I'm really confused about these matters since I don't know the difference between voltage, amperage, and current.

[Steve Joblin]

what you need to do is understand what the maximum current draw is for the motors and/or servos.  Usually, they draw the most current when they are stalled.  Once you find this out, it is a simple analysis to see if your power supply to the motors will provide the current needed or not.  for example, if each motor draw 2 amps when stalled, and you have two motors, then a power supply that can only provide 1 amp max is not going to cut it.

[dmehling]

What exactly determines whether a motor is stalled?  I don't expect the motors to encounter much resistance as they are rotating.  Also, how many amps would those motors be drawing on a regular basis?

[Steve Joblin]

when the motor shaft is held with enough force, the motor won't be able to spin.  The amount of torque (or twisting force) tells you how easy (or hard) it will be to stall the motor.  For example, if you hold the wheel of a toy car, you can easily stall the motor... now try doing the same thing with a good power drill.

As for how many amps they normally draw... I can't say without knowing anything about the motor.  Like most items, it should have a part number or manufacturer.  You can use this to look it up on-line and find a spec sheet.  If there are no markings and/or you are not able to find a spec sheet, hook it up to your mulit-meter and measure it.

[Kohanbash]

Its usually a good idea not to provide current from the controler. It is better to use the micro as the ground.
Again make sure to check the data sheets for your controller.

[Robotboy86]

Ya I agree, powering something from your stamp can lead to microcontroller resets at times even.  As such, I recommend that you perhaps use an external power source or a controller. 

[dmehling]

So are you saying that the power supply that is designed for my particular developmental board is only intended to power my microcontroller?  If I add an additional motor controller to my developmental board, do I just wire it up directly to an additional power supply?

[Steve Joblin]

What motor controller are you planning on using?  What we are saying is that "good practice" is to use one power source for the digital electronics and one power source for those things that can consume lots of power (like motors).  It is very important that you tie all the grounds together!  Of course, this is "good practice" and may not be "required".  The BOE-bot, for example, uses one power supply for both the Stamp and for the two servos.  to help ensure that the servos current draw doesn't reset the stamp, they added capacitors to the BOE-bot board.

[Kohanbash]

Also if you are only using one power supply, and you have enough power. It is better to run you electronics from the power source directly than to do it through the micro.

[Robotboy86]

The thing is that even though the Basic is designed to run great while using X amount of power to power servo's/motors, it does not mean you should.  DC motors can send spikes back through the system, and learning to power it externally is really worth it.. I am going through that right now, I have found it to be VERY enlightening.  While yes your controller can indeed power a normal servo..   what if you build it, and suddenly want to increase it?  Guess what:

Gotta redo the whole thing..  change the programming, your setup, etc etc.

Thats why its good practice to let the MCU do what it is designed to do:

Control!