Let's Make Robots!

Radio emitter and receiver query

Hi all..

I'm new here so hello and be gentle!

I am looking into developing a small bot that could follow me around at a set distance (approx 3m) behind me. Ideally I would like to find a cheap pair of radio emitters and receivers that I could use to measure distance (2 small emitters placed on me and the receivers on the bot) This way I could separate the receivers on the bot to triangulate the position of me relative to the bot, this being used to guide the bot in my direction.
Are such things available as I can’t seem to find anything anywhere.

Has anybody done anything similar to this who could share some of their ideas or findings. I have an alternative idea as follows but it’s not as solid. Comments on potential issues would be greatly appreciated.

Use an ultrasonic range finder mounted on a servo or stepper that scans left to right until it finds a target (me) and returns the distance and angle so as to guide the robot. It is then continually scanning left and right at the target until it passes the target and then reverses direction and so on – this would give an angle range of the target with the direction being between the 2 extremes.

Thanks again for any help.

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If you plan on going this way you could use LED strips, maybe tape them to a waist. If needed you could lens them to output a narrower beam. (i do that for my lasertag project so if you need help just ask)

The project is an interesting one, it makes it easy to want to contribute =D

BTW Totoro, I almost suggested using an IR beacon + a pair of receivers too. You could modulate the IR signal to provide good sunlight immunity, but the main problem I thought of (just before I posted) was that it would be hard to get the bot to see you from all directions, unless you had several IR emitters over your body... I don't think it would really work from an aesthetic perspective...

As mentioned before, you could use a grouping of 5 with one central and the other surrounding emmiters flowering out. this would give a slightly wider coverage.  Since the design is to follow you, I would imagine that one direction should be good, maybe with a 3pack of emmiters to cover the sides just in case. As far as the following part, 3 sensors would give  low resolution, but it really depends on what you are looking for. 5 would give you some pretty decent resolution as well as giving a bit more coverage.


just my 2 Cents...

Hmm, the problem with your typical reflective ultrasound is that there's no real way to tell which object is your intended target. Has anyone ever tried using a discrete transmitter and receiver pair? The target could have an ultrasonic transmitter in their pocket, and the bot would then 'home in' on the broadcast signal using a sweeping ultrasonic scanner, or a pair/cluster of receivers. You could even encode a password into the broadcast signal as some sort of basic ID check.
Theoretically you'd also get twice the maximum distance from the usual hardware, since the ultrasonic pulse only has to travel one way, not to the target and back again.

Thanks all for the comments..
Much appreciated. !
I like the idea of ultrasound, i will research this a little and see what comes up.
Again many thanks!

I can see how your (second) idea might work, but I see many obstacles. The main problem is that you (your legs presumably) are not big flat square hard surfaces. And your environment (unless your are playing around in an empty parking lot) probably is full of such objects.

That's why the ultrasnound distance ranger is so effective as an obstacle avoiding sensor in household environments.

I like your first idea better. It has been discussed here before. People just want to build robot puppies, I guess. Forget about accurate distance measuring. Just try to get your bot to see which direction to find the transmitter (in your shoe?). And maybe you can have the receiver measure the signal strength. Make it stop when the signal gets too strong. Say at 3 meters distance.

about the second idea... i have an idea into mind but i don't know it it can be made. Something like: placing a tube in front of the receiver which grounds all incoming transmissions, basically this would let the sensor receive data only if directly facing the transmitter. Could this be done? I am afraid that data might be grounded even if they are directly facing each other (tx and receiver).

With a single transmitter and a sweeping, highly directional antenna it might be possible to pull this off. The angle of the servo when the signal reaches maximum strength would give you the relative angle from bot to target, and thanks to the inverse square law you can use the reception strength to estimate the distance.

Now we're getting somewhere (well you lot are), i like the idea of this - any thoughts of where it would be possible to find a directional antenna ? Cheers.
You might find it's easier to just make one from some schematics on the net. They use them in 'Amateur Radio Direction Finding' events and for tracking tagged wildlife etc.