NXT motor: use as an encoder with removed motor?

[HaWe]

hi,
using the NXT motor passively driven just as an encoder is giving a high drive resistance
- anyway, the advantage doing this is having a very quick encoder without losing a sensor port for each motor encoder.

Has anyone tried to remove the motor out of the housing so that the encoder can be driven with a with a lower driving resistance?

[h-g-t]

Nope, but from Philos page (http://www.philohome.com/nxtmotor/nxtmotor.htm) it looks like the encoder is on a separate axle which is driven by a gear on the motor axle. You would have to provide a new axle and supports. bearings, etc.

[HaWe]

yes, of course I already read this page ;)
But I'm curious if anyone already tried it out removing the motor for having a fast encoder sensor at a MOTOR port... ^^

[mattallen37]

Can't you use a non-NXT encoder? I know I have seen where someone did this. If it is for your tetrix stuff, those encoders should work I think. Do you know the precision? The only issues I foresee is that they could pulse too fast for the NXT to read, but I don't think that will be a problem, and the other, is that the ~4.3v might be too low (they are probably rated 5v). I am quite sure they are quadrature encoders, same as the NXT.

[HaWe]

hi matt,
the disadvantages in this case are
1) I have to buy two of them although I got lots of NXT motors, and
2) I have a big lack of sensor ports: I already need 1 for the Tetrix controller, and now even 2 more for each encoder - then only 1 is left, but I need 1 for the nxtCam, 2 for USsensors and actually even 1 more for a touch multiplexer - I don't see how to manage it all. So what I need are encoder senors for the motor ports!

[philoo]

If you dare to do some electronics tinkering, here is an old attempt I did, that worked fairly well (but I never wrote up about it). It uses ball mouse encoder components and a LEGO wedge belt wheel. The schematics is more or less the same as NXT internal motor encoder. A Y split cable allows to use an unencoded motor at the same time as the encoder.

[philoo]

The final image...

One drawback of this setting is that the open frame construction makes it somewhat sensitive to ambient light. The resolution is also limited, to 12 ticks per turn.

[mattallen37]

...2) I have a big lack of sensor ports: I already need 1 for the Tetrix controller, and now even 2 more for each encoder - then only 1 is left, but I need 1 for the nxtCam, 2 for USsensors and actually even 1 more for a touch multiplexer - I don't see how to manage it all. So what I need are encoder senors for the motor ports!

You would use it in the motor port, not the sensor port. You would use it exactly as you would an NXT motor without the motor itself.

I thought you said you have something like three NXTs on the robot, that should mean 12 sensor ports, even though my suggestion wouldn't require a sensor port.

@Philo, thanks for sharing, I like the concept.

[HaWe]

matt,
if the encoders you meant can be attached to the motor ports it would be fine - do you have a link (or did I miss it?)
(BTW over all I have 10 motors and more than 20 sensors to be attached...)

[mattallen37]

I was speaking of the tetrix encoders. Isn't that what you want?