polarity switch for external power supply.

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polarity switch for external power supply.

Postby Rickz2020 » Sun Jul 03, 2011 5:27 pm

Hi all,

Ok, I have my NXT brick which can supply voltage from the motor ports in either polarity...But I want to use an external battery as a power source for the motors.
Getting the motors to go in one direction is easy - just use a relay. But, what if I want to be able to reverse the direction of the motors ( swap the polarity of the voltage supplied to them)?

I need to basically swap the wires going from the external battery to the motor, using the motor port on the NXT brick. Any ideas?

If you need more info just say so.

Rich.
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Re: polarity switch for external power supply.

Postby TechnoX » Sun Jul 03, 2011 10:55 pm

Maybe you could use an http://www.peeron.com/inv/sets/5120-1 ?? You can buy them on Bricklink :)

I don't really remember how it's work anymore, but if I remember it correct you can turn the motor on in either direction and turn it off.

It's for the old RCX connectors, but you can use a converter or build your own ;)
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Re: polarity switch for external power supply.

Postby Rickz2020 » Sun Jul 03, 2011 11:48 pm

Thanks for the reply but I'm not sure if it will do what I need. I don't want a switch in the sense that you need to physically press it - I need on that will change based on the polarity from the NXT motor port.

I have made a little drawing to illustrate my problem a little better.

Image

Obviously, I will be controlling the polarity of the motor port with code such as Motor.A.forward(); or Motor.A.backward();

Rich.
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Re: polarity switch for external power supply.

Postby TechnoX » Mon Jul 04, 2011 12:02 am

The brick I linked to can be controlled by a normal lego motor. It has a + hole in the center of its switch-arm. If you use an white gear with friction you can just start the motor and keep it spinning to the left.
But it works w/o a friction gear too :)

So you control your external motor with an normal lego motor connected to the NXT :)
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Re: polarity switch for external power supply.

Postby Rickz2020 » Mon Jul 04, 2011 12:09 am

Thanks, but do you know of any component that I can use that will accomplish the same task? I don't want to have to use a lego motor to control another motor. I just want an electronic switch that will switch the polarity depending on the polarity from the NXT brick :)
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Re: polarity switch for external power supply.

Postby Aswin » Mon Jul 04, 2011 6:07 am

Hi,

Maybe you can use the Mindsensors motor mux. This uses an external power source for the motors (and gives you the option of using more than three motors).
My NXT blog: http://nxttime.wordpress.com/
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Re: polarity switch for external power supply.

Postby s.frings » Mon Jul 04, 2011 12:40 pm

Code: Select all
+ Battery  -
 o          o
 |          |
 +---+  +---+
 |   |  |   |
 |   o  o   |
 |     /    |        Relaise 1
 |    o     |    +----XXXXX--------|>|----+
 |    |     |    |                        |
 |    |     |    |                        |
 |    o     |    |                        |
 |  Motor   |    o NXT Pin 1    NXT Pin 2 o
 |    o     |    |                        |
 |    |     |    |                        |
 |    |     |    |                        |
 |    o     |    +----XXXXX--------|<|----+
 |     \    |        Relaise 2
 |   o  o   |
 |   |  |   |
 +---+  +---+


This ciquit supports three of the four operation modes:

- Forward
- Reverse
- Break

But not supported are:
- Coast
- Speed/Power control

Use 6V relaises and configure the program on the next to send 90% power to the relaises, which should work fine with both alcaline and rechargeable batteries. For the diodes, I would use 1N4001.

There are small and compact dual relaises for motor control available on the market. My car has such relaises in the electric door locks and windows.
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