Simulating GPS

is there a way to simulate the function of a gps using a high resolution magnetic sensors? or is the change in the earth’s magnetic field to small?

Encoders, gyros, and/or ultrasonic sensors are your best bet when it comes to detecting positions on the field.

Simulate GPS? How about this:


I’m just going to assume that this isn’t less than $400 :open_mouth:

The earth’s magnetic field varies from place to place, but it isn’t a simple predictable function you can use directly to navigate. It is affected by topography, lithology (e.g. ores), and even what general direction the earth’s magnetic field was pointing back when the local rocks cooled.

Check out how they do the RG3:

Last time i check a compass measures magnetic fields.

On a robot you will need to keep it mounted away from large motors and wires and calibrate it.

Oh, a question I can field with knowledge from a non engineering course! :stuck_out_tongue:

GPS usually has a high DOP (Dilution of precision), (in layman’s terms; accuracy), for handheld recievers, especially roving recievers without some specilized setups with base stations and (you guessed it) radio transmissions in order to solve for position in real-ish time. And of course a GPS reciever needs line of sight to at least 4 satellites for trilaterlization, a WAAS satellite probably wouldn’t hurt either… but you wanted to simulate, so let’s ignore the can of worms that is accuracy levels.

Your question sounds as if you want to use magnetic north as a reference for determining an azimuth angle (alpha).

Delta alpha will be in the order of hundredths of arcseconds across the field (if not smaller, this is a dead reckon). Any change that small cannot be consistantly measured with sub $400 equipment. Any signal noise would probally destrou you confidence in that change in alpha accross the field.

This model is also assuming you have another angle to work with as you cannot solve for position with an angle alone. (Remember ASA and SAS from geometry?) Additional assumptions include working on a flat plane, which unless physics changed, The Earth is not flat. Not to mention interferace and sensor lag.

So, you arn’t really simulating a GPS system as you are trying to solve for distance using an measurment of delta alpha. Do as the others have said and use a gyroscope and some encoders. There is no real need to know absolute coordinates of your robot on the earths surface unless you are calling in an airstrike on the other robots. You only need be concerened with reletive coordinates to the field.

Hope I answered your question in far more detail than was necessary, :smiley:
Skye Leake

I’ve heard mixed results from teams using a compass/magnetometer to get orientation. They’re reasonable accurate, unless there are large electric currents nearby. I know of teams who had issues on a practice field due to the power feed cables for the pits running right next to the field.

Assuming by “GPS” functionality you’re referring to measuring your absolute position on the field, I don’t know of anyone who’s been able to use magnetic sensors to do that. The most successful strategies i’ve seen involve using a lidar or ultrasonic sensor to measure distance to a known object.

Try something more like > $250k. :slight_smile:

You can get 'em on eBay for $249,995.89

Just imagine if you were able to deploy flashing infrared beacons at certain points around the field, and had a sensor array on the robot that could see those beacons. Hmm, what could that do :confused:

I"m having an IR flashback to Overdrive Hybrid Mode.

gyros, ultrasonic sensors are one of the best for the geo-positioning sensors. You can use them!

Or the IR beacon you had to have on your robot for automatic lap counting. Did that ever work, or were refs just using manual lap counters?

No, it is not possible. One of the many problems faced is that there isn’t much difference between the magnetic field of the Earth on different sides of the field.

Even using compasses for determining direction is theoretically possible, but usually doesn’t work well because of all the magnetic noise from motors.

For the general problem of determining where you are at on the field, the key word generally used is “localization”. When googling it, include “robot” in the search term, because that word is also used to describe the process of making software user interfaces adapt to different user languages/locations.

For people interested in such topics, I have taken classes in robotics at Edx and Coursera, and localization is always covered in the coursework. Be prepared to do math.

It should be noted, if you did have a real GPS system, it would be in violation of R68 for communicating with satellites.

While you receive signals from GPS satellites you don’t transmit to them… Not sure how you would rule on this as I don’t consider this as communication. I would figure using a gps signal could be similar to reading a compass for heading.

Sent from my XT1254 using Tapatalk

Looking at the rule, it seems you’re right based on the blue box. (assuming the GPS satellites aren’t manually operated for some reason)

The blue box says

non-RF sensors that don’t receive human-originated commands aren’t wireless communication devices and thus R68 doesn’t apply.

(Emphasis mine)
Which, from my understanding of how GPS works, rules it out because it uses RF, even though it is automated.

You could also potentially use RTK with a phone or GPSr for you.