Oct 9, 2006

HiTechnic Compass sensor available

HiTechnic will start taking orders for the NXT compass online today. It will begin shipping on Tuesday, October 10. Cost is US$46.00 + shipping costs ($7.50 US and $18.95 International)

From the HiTechnic website, some guidelines/rules to remember:

The HiTechnic compass sensor will only operate correctly in a horizontal plane so you must keep the compass level for it to read correctly. This is very important so remember this when you build it into your robot.

NXT Firmware version 1.03 must be loaded in the NXT for the compass to operate correctly. You can check the firmware version by displaying the NXT Window in the Mindstorms software.

It is highly desirable to mount the compass at least 6 inches (15 cm) away from the motors and 4 inches (10cm) away from the NXT brick itself.

Try to make sure it is firmly mounted, if it bounces around, the readings may bounce around too.


Maniac000 said...

I'm still curiose about everybody's take on whether or not FLL will allow these in competition. I'm under the impresion that since they are being sold through LEGO, they count as an official LEGO product and don't violate any of those rules. But I think that they will not be allowed for a while yet, at least not until the NXT is the prominent figure in competiotion. Having a compass sensor would be a huge advantage, and since there is only one for the NXT (being sold through LEGO that is) RCX users would be out of luck. What does everyone think?

Jim Kelly said...

I'm sure it won't be allowed this year... maybe never. While I love the sensor, there are plenty of methods out there for navigating the playing field that don't require Compass headings. I'm not saying it can't be done, just that software could handle the movement options and free up the port that the compass would use.

I think the Compass sensor will find its own niche among those of us who like designing robots that roam and discover... I want to pair it with my Wireless Camera and have it provide feedback to another Brick (or BT-device) about position...


Maniac000 said...

Location sensor...

I think there could be a way to connect my GPS with the NXT. Now that would be cool, haveing it send info to my comp via BT so that I can know exaclty where it is at all times. Except that the reange of the BT would prevent it from getting out of site outdoors, and my GPS wouldn't work indoors. Drat.

Brian Davis said...

Several of us have wanted to use BT GPS units to allow the NXT to locate itself. The only big problem right now is getting the NXT to read the BT messages that a GPS unit can send - NXT-G can't seem to do it, and I don't remember if this is a problem that can be solved on top of the standard firmware, or needs a firmware replacement (which we don't have... yet. RobotC doesn't yet support BT, IMS).

As to compass sensors in FLL. They would be neat. But are they needed? I don't think so. And the only way they should be allowed is if *every* team has equal access to them. I'm not sure if Hitechnic could supply all the FLL teams by next year, but I'm reasonably certain that they can't this year.

Brian Davis

David Levy said...

To what degree of accuracy would the GPS be anyway?

Brian Davis said...

Perhaps this could use it's own thread at some point, but... with selective availability turned off, it's pretty good, and for outdoor navigation, positioning within 30 cm isn't too bad (i.e., could be useful). With *two* GPS-equiped NXTs playing "leapfrog", I can't see a fundamental reason why differential GPS can't provide centimeter-scale accuracy (obviously not really fast, on-the-fly, but still very useful for outdoor navigation). I'm thinking about the SRS Magellen:


This plus RFID tag reading are still very high on my list... I've been thinking about them for the NXT since long before the official announcement that the NXT was even going to be produced.

Brian Davis

Maniac (no 000 any more) said...

I don't know if your average GPS can is acurate enough for this kind of application. Mine would not work as it only has an acuracy of 10" in good conditions. With such a small robot (or perhaps some really neat sumo contests) you would want it to be much more acurate. Millitary.

Brian Davis said...

With selective avalibility turned off, military is civilian... and with a technique called differential GPS, even with the selective avalibility "degraded" signal, you could get to an accuracy of a centimeter or so (I've used this for locating cave entrances - two hours babysitting a couple of laptops with GPS units, or ten hours of fighting through tick-infested backwoods with a compass and clino. i'll take GPS).

Brian Davis

Tony Naggs said...

Hi Brian

If you were using a Bluetooth GPS I hope you were also packing a spare battery. When I recently used a BT GPS with my mobile phone the batteries in both ran down quite quickly.

Regarding NXT & BT GPS comms - I think this would require custom firmware. Possibly requiring customising the code running on the Bluetooth subsystem - in order to cope with a continuous connection, rather than the NXT's packet oriented system.

Probably not too difficult - at least both devices present a serial port over Bluetooth interface.


Brian Davis said...

I think it might require seperate batteries, but not too much. For most applications, you probably don't *want* continuous BT GPS data transmitted. What you'd like is for the NXT to be able to send a message to the GPS *requesting* a position update, and then the GPS unit sending back just that update. Yep, continuous BT pinging will eat in to the battery (I use it in my remote control schemes), but even that isn't needed for most applications.

The point about needing custom firmware is a good one, and one I mentioned in passing in an early comment here. I strongly suspect it will need a different firmware, but until I've really poked around in there I'm not going to swear it's dependant on that. I'm still learning new stuff about NXT-G all the time.

Brian Davis

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