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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Radio emitter/receiver are only able to communicate, they don't know their position... For that you'd need a gps module (or in your case, several, but you need really accurate ones if you want two on you... and i'm not sure you can find that)

That's not exactly correct I'm afraid; there are several methods for determining direction and/or position using various radio transmitter/receiver combinations.
The two main ones that come to mind are:
• Scanning and triangulating using directional antennae (1 transmitter and 2 receivers, or 2 transmitters and 1 receiver)
• Triangulating by measuring varied signal strength (1 transmitter and 2 receivers, unless you use mutiple frequencies)

Unfortunately the second option is almost totally impractical at such small scales... and to be honest I don't see the first option as being too great either. In order to get any kind of usable accuracy from the sensors you'd need to have the 2 transmitters or the 2 receivers a decent distance apart, and making directional antenna at a small scale would be a right pain as well.

Sorry for the mistake, and thanks for the correction!

Many thanks.
But is there not a way you could send and receive a signal and measure the time lapse to evaluate the distance ? Or would this need real specialist equipment ?



i think that that has a too short range for what he plans to build. 

hum, looks like it has a 4 meters range...

But maybe i'm wrong, again! -_-v

sorry, you are right, i never got my ping to work at those ranges though...

I don't think anything like that has ever been tried here on LMR, so i really don't know the answer. But personally i don't think you can do that with the equipment we use, you know...the difference in reception is going to be very very very small...

You could try to see if google has  something about specialist equipment, or else you could go for the gps, which sounds much easier and more effective i'd say. 

Let's do some rough calculations to check the viability of this concept:
• Speed of radio waves: C = 300,000,000 m/s (give or take)
• Optimal distance between transmitter and receiver: l = 3m (from target to robot)
• Minimum time between sensor readings: 0.2μs (this is one instruction cycle for a PIC using a 20MHz clock)

The time it takes for the signal to travel from the transmitter to the receiver is 3m/(300,000,000m/s)=0.01μs. In other words, even quite a fast processor with flawless sensors and programming would still be 20 times too slow to catch the delay from transmitting to receiving.
This idea works for GPS because the satellites are very far away from the receiver and each other, but it just doesn't scale well to the kind of dimensions humans are used to.