NXT-G Blocks for dGPS

LEGO Mindstorms Navigation Sensors for LEGO
1

Where can i download the NXT-G Blocks for dGPS ? All links I have seen are broken (404 Not Found).

2

I think they missed our big move of the website. We’ll work on getting the links up in the manual asap.

In the meantime, I’ll post them up here.

These are just temporarily on Google Drive. When we switch back, we’ll change the link again. Thanks for your patience!

3

Thank you for the blocks John, they fit into the program well. We do have another question, actually two:

1 - You sent a block called GPS Angle of Travel, but that is not in the SARG program you provided, is this for the new dGPS vs the old and we need to incorporate it into the program.

2 - When we run the program as is, the ‘robot’ runs in a circle and does not go to the destination. When we carry it though, the display shows the correct results it appears and the unit will shut off when we get to the destination. To clarify, it actually goes in circles south of the destination and just continuous to hunt back and forth north of the destination point and continuous north.

Any help would be appreciated.

Thanks,

Doug

4

Hey Doug,

The GPS Angle of Travel is, if I remember correctly, a bit of a hack. A gps sensor won’t give you the angle you’re pointed (like a compass does). However, if you travel over a long enough distance (say 10 meters or so), you can take the two gps points, and calculate what azimuth you just travelled along. We meant this as sort of a hack to get around not having a compass. To be honest, the math is perfect, the application though is not.

One thing I would check in real-time is the value of the compass. The magnetic compass can be disturbed by the motors, and this might be causing it to mis-direct. Another thing off the top of my head is to reverse your motors. The feedback might be reversed, causing it to just run in circles.

Thanks Doug, please let us know how it goes!

5

John,

We have narrowed it down, we are not getting an output from the navigation block for the “angle to destination”. Any thoughts?

Thanks Doug

6

Hey Doug, if I remember correctly, the Angle to Destination reports back the azimuth to the destination set of coordinates.

So, you’re saying it’s not working. Can you show me (maybe pictures or something) about how you’re not getting any output from the block?

7

John,

Here is a quick video of the screen:

Line 1 is Distance to Lat and Long Coordinates, Works, the bot stops if you walk it there.

Line 2 is the Absolute Heading from the compass. Works, we calibrated and verified and it changes as you rotate the bot when running.

Line 3 is the Angle to Coordinates. This for some reason stays constant even when you rotate the bot or walk around with it.

Line 4 is the difference used to steer the motors, it subtracts the difference and is working.

We went through and added a line to view the Heading from the GPS and this also is not changing even when you move the bot or spin with it.

Do you have any thoughts as to why the Angle to coordinates is not changing? Without that information from the GPS, we can not steer?

Thanks for your help.

Doug

8

John, another question also, is there a way to get an electronic copy of the NXT GPS Workbook? It has been out of print for some time I think, but it may be a big help to us.

Thanks

9

If I understand correctly, you’re concerned that you’re rotating the NXT and line 3, the angle to destination is not changing. Is that correct?

The Angle to Coordinates is really the azimuth to coordinates. It’s the compass direction you need to point towards to head towards the destination. So that will not change dramatically unless you radically change your relative angle to the destination. If you want to test it, I would go outside with a GPS coordinate preprogrammed, and walk 50 feet away from the destination coordinate. Check the angle. Then walk 50 feet to the other side of the destination coordinate. This should give you the exact opposite angle.

Does this make sense?

It’s really important to realize that the angle to destination function is an azimuth to destination. It’s the compass angle you head along to hit the destination.

10

Also, anyone else looking at this: we’ve added the dGPS NXT Blocks into a new github repo here:

They’re all zipped up. I’m removing them from the forums above so we can reduce our own server load.

11

Dear JohnC

if I understand correctly, the “angle to destination” output from the “navigation block” is the course to go from origin to destination. In other words, to go from origin to destination a compass should display the value from the “angle to destination”.
Its OK?

Best regards,

Ernesto

12

Hey Ernesto, that’s correct. “Angle to Destination” is the compass angle or the azimuth you need to travel to the destination you’re seeking.