Lego Mindstorms sensors

[implosionprez]

We have been testing our minibot with a plywood cap on the pole, and we now realized that the cap on the pole in the competition will be polycarbonate. Will any of the mindstorms sensors (ultrasonic, color, light) "see" the polycarbonate cap, rather than just seeing through it?

[implosionprez]

Oh, and we don't have a infrared sensor.

[Techhexium]

I think the ultrasonic sensor should "see" the polycarbonate because the sound wave the sensor sends in should bounce from the polycarbonate and back to the sensor, giving you the distance between the sensor and whatever it is in front or below of.

HiTechnic, a company that makes certified LEGO sensors, sells a Infrared Seeker for the NXT that seeks infrared signals. It is not a very powerful sensor however. Any FTC team should have a Infrared Seeker.

[DonRotolo]

Are Mindstorms sensors legal on a minibot? I don't see that in <R92>

[Techhexium]

R92-BB applies here. Yes they are legal. Lego Technic beams and pins used in conjunction with the TETRIX system are also legal (http://forums.usfirst.org/showthread.php?t=17048). I would assume LEGO certified sensors are allowed (HiTechnic Sensors)

BB. NXT compatible sensors and related connectors/cables

[StevenB]

Yes, the ultrasonic sensor will work with polycarbonate. But I would be concerned about other sources of interference - the high-noise and high-vibration environment, or possibly the pole itself. The ultrasonic sensor has a rather wide beam, so it's possible to see things that aren't straight ahead.

I'm sure you have reasons for considering some kind of proximity device, but I think your best bet would be a touch sensor. ;)

[implosionprez]

Yeah, a touch sensor would probably be most reliable, but we can't figure out a good way to get the touch sensor button pushed, without it taking all, or a good part of the force of hitting the top of the tower. We don't want to obliterate a touch sensor each match. That could get expensive. Any Ideas on how to push the touch sensor but let the bot take the force?

[StevenB]

What I remember doing in my FLL days (before the NXT!) was building up the area around the sensor with other bricks to make a large flush plate. The sensor is designed to be pushed all the way into the housing without damage, and the surrounding support helps take the load off the sensor casing.

But even better would be to device a system where the sensor is normally pushed, and impact causes it to be released. I could see you doing this by some kind of lever, where pushing down on the lever causes the end on the sensor to go up. You could also point the sensor downwards and have a link that gets pushed down, releasing the sensor.

[cgmv123]

If you want, you can build some kind of mechanism (lever?) that reduces the force. I used the touch sensor a lot when I was in Lego League and can attest to the fact that it is more resilient than it looks. It shouldn't blow up as long the motors reverse right away.