Getting the Lego NXT to run larger brushed DC motors???

[davidgeorge212]

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?

[helumpago]

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.

[mattallen37]

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.

[dad-and-adam]

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

[mattallen37]

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.

[schodet]

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

[bazmati]

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

[doc222]

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

[HaWe]

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.