Mindboards

Hi, I am on a team right now that is building a robot for a school project and we are using the NXT brain in order to drive our robot autonomously. Is there a way to have the nxt control a dc brushed motor (forward and reverse) and hook it up to an external power source such as a regular 12 volt wheelchair type battery that just sends power to the motor. The motors we have are off of a power wheels barbie jeeb setup. These motors supposedly draw about 1.6 amps of current on 12volts.

I know the motor ports on the nxt only put out about 3 volts but I would like to know if there is a way it can power these bigger more voltage motors. We need to do this so we can write a program to tell the motor to spin either forward or backwards like a regular nxt motor.


Can anyone help me out?

There are two ways (that I'm aware of). the simplest is to use a relay (http://en.wikipedia.org/wiki/Relay), but these can only control the motors in one direction, at the same speed (using a simple circuit and two relays, it is possible to control direction). If you need speed control, you could also use a MOSFET transistor (http://en.wikipedia.org/wiki/MOSFET), but once again you have to do some extra soldering to get directional control.
See the book Extreme NXT by Philippe Hurbain for good (*great*) instructions on how to use these.

Also the NXT can output 9v (battery voltage) to the motor ports, however, the current is the biggest limit, being 1A max. MOSFETs are indeed the way to go.

Do you still have the motor control from the Barbie jeep? If so, perhap a NXT motor could simply operate that control.

I think that typically, there is no speed control, or opposite direction allowed with the original controls, so that would probably not end up working for a robot, not to mention all the work that would go into making it connect mechanically.

Look for an I2C controllable motor controller, you could control them using the NXT.

How about using this

http://www.mindsensors.com/index.php?mo ... PAGE_id=58

where it says
If you wish to connect regular DC motors to this -
Connect DC motors to NXT
You can connect regular DC motors (max 35 volts, 500 mA) to this MTRMX-Nx by attaching motor pins to the holes shown in adjacent picture. Connect your power supplied expected by DC motors to the power pins on MTRMX-Nx. The controller will provide same forward/reverse rotation with speed control as it would for RCX motors.


There is also this solution (read post from Brian Davis) here: http://thenxtstep.blogspot.com/2009/01/ ... chnic.html

Hope that helps

The OP's motors draw1.6 ampers at 12V. The MTRMX-Nx only supports 500mlMa. I have two of these myself and once you run it on more than 9v, it can get hot even just running Nxt motors, I have test it on SHORT runs of 15v, and heat was a issue.

HiTechnic DC Motor Controller for TETRIX, is out of stock at Lego ED and no details on its spec there. At Hytechnic they dont list ? Those this may work it is intended for the tetrix motors.

The OP wants to run a much larger motor from a "barby Jeep motor".http://www.alibaba.com/product-gs/35649 ... power.html

I see a lot of issues here

Model No. RS-550SHFT-7028RB
Rated voltage 12VDC
No Load Speed(RPM) 16000 THis is ALOT of RPM guys lego has no bushings or bearing, i can see axles twisting and melting
Current(A) 0.95 < No load draw
At Max Efficiency Speed(RPM) 14391
Current(A) 8.5
Torque(mNm) 44.4
Output(W) 66.88
Eff.(%) 65.6
At stall Torque(mNm) 441.3
Current(A) 76 WOW loaded draw man thats alot of amps

the motor multiplexers of Tetrix are supposed to have NXT-G control blocks as this kit is used by the FTL (only NXT-G and RobotC are allowed as programming languages).
I own one of them, the Tetrix DC motors are really powerful, and they have an optional motor encoder unit which can be attached to it - but unfortunately there's no NXC driver available yet.

The Mindsensors mux also works fine (I got one too) but supports no encoders (but for this issue a rcx rotation sensor can be used).

edit: if you have real heavy duty industry motors (something kind of car wiper motors - I used 2 of them for a lawn mower drive: 12V 30A DC each) you can use relais or industry H-Bridges.