Servo motor from 9398 4x4 Crawler

[tabbycatrobots]

Has anyone tried the Power Functions servo motor from the 9398, with the NXT controller? I just
finished building the main model - some good ideas and parts for a robot dump truck I plan to
build. Before tearing the model apart and experimenting with the servo motor, I thought I'd ask if
anyone here had tried this motor connected to an NXT. (Why reinvent the wheel?) Thanks for any
info.

[mattallen37]

See here for related information.

[jwiger]

It will work, just a matter of having the cables to do it. And using the power level to control its position.

[tabbycatrobots]

Thanks for the pointers to the details. Interesting that it can turn to intermediate
positions, not just 90 deg left or right.
Yes, I have some adapter cables from LEGO Education that I think will work.
Thanks.

[hassenplug]

I'm not sure the regular adapter cables will work. I don't know if it says anything on Philo's page, but I suspect the servos require both the +v and the variable voltage, but the NXT->9v cables will only pass the variable voltage.

My guess is that you could make a custom cable that may allow you to run them from an NXT.

Steve

[jwiger]

Oooh, that's a good point. I was just wondering how it would get enough power to provide good torque at low duty cycle PWM.

[tabbycatrobots]

I've been studying Philo's page, particularly the NXC code and it looks like he is using
NXT port A for the 9v and NXT port B for the control. I can imagine what the cable may
look like, but didn't see a diagram on his web pages. I did post a question on his page,
asking if he could post a diagram of the cable he used. I also proved to myself that the
LEGO adapter cables don't work, but don't harm the motor. It still does work, and
quite well with the train RC 8879. Controlling the 9398 with the 8879, allows good
speed and steering control.
But having to use 2 motor ports to control the servo motor negates its pluses. Maybe the
next Mindstorms will interface nicer to PF.

[mattallen37]

See this page for a diagram of how the wiring works. The PF-S get's it's power through 0V and 9V, and it's control through C1 and C2. In order to power it through port A, and control it through port B, you would need to connect PF-S 0V and 9V to port A (pins 1 and 2), and PF-S C1 and C2 to port B (pins 1 and 2). Just be sure the supply polarity is correct; I would use a diode to be sure I didn't burn out the PF-S.

[jwiger]

...The PF-S get's it's power through...

For a moment I thought there was a "PF-Small" I haven't heard of yet. If we start calling the servo PF-S what would we call a small motor? It can't be "Little" or "Mini" (PF-L and PF-M are taken).

Here's some ideas http://thesaurus.com/browse/small?s=t

Sorry for the tangent.

[mattallen37]

I'm quite sure I didn't make up "PF-S" to mean servo. I remember thinking the same thing when I first saw it (which was probably on the TechnicBRICKs blog).

Perhaps "Tiny"? Or for the fun of it, "Diminutive" would also work.