Dynamic measurement of robot's distance from fixed point


I am interested in wirelessly and dynamically/continuously measuring the distance between my slowly moving robot and a fixed point. The robot will act in a space which will never be more than 5ft from the fixed point. Is this possible??

Thank you very much.


It is possible.
It is possible.

I agree
It is possible.

This actually sounds a bit
This actually sounds a bit complicated. You need a way to ping the object or have the object send out a signal. I think the posts above were referring to keeping the bot no father away that 5feet of ANY object, but no farther than 5 feet of a specific object requires overcoming the hurdle of how to know exactly where that object is when you arent looking at it and how it recognizes THAT object and not another.

I’d say, it sounds like

I’d say, it sounds like preventing robotic vehicle from running away too far from the remote control by accident, when running it in the open space.

I believe the range of all those RF links out there depends on the voltage power supply, so you probably can measure the distance. However, I hardly can see, how you can determine direction where you should go to return to your remote… unless you build some kind of radar?


Thank you for responses


Thank you for your comments. The idea isnt to keep the robot from moving too far away from a point or trying to control its range of motion; I just want to be able to visually display how far the object is at any given moment from the fixed point. An operator will be controlling the robots motions and it will only be acting in a small area (appx 5’ in diameter) - Im just wondering how this can be accomplished wirelessly and dynamically.

Thanks again.

The first idea I came up

The first idea I came up with is to have the object send out some sort of ping signal that is weak enough to only be heard from 5feet or slightly more away. Once the signal gets weak enough the bot moves until it gets strong enough. I’m sure there is a better way, but thats all I got :wink:

You could use an audible sound and use a microphone on the bot to detect the volume of the sound (not really accurate if 5 feet needs to be kept exactly). I’m sure others have better ideas.

visually display huh?

An overhead camera should do the trick.

Or take a leaf from BaseOverApex’s book (which he ripped from bomber wallace): https://www.robotshop.com/letsmakerobots/node/1797#comment-5529 and create two or more crossing lightbeams.

Either measure the distance between de projected lightspots (focussed beams) on the wall, or the intensity of the resulting spot where the (soft-focussed) beams collide.

Of course, this will give you only a one dimensional distance reading.


The problem with a camera is
The problem with a camera is how to detect a specific item. I suppose it could be done easily in a white room with 1 black object, but if you have a lot of object and you need to detect a specific one thats a bit tricky. Add in the fact that at various distances and angles the object will look different and you have a big hurdle. Not impossible, but it may require more code that a PIC can handle.

display is display

Noone asked about automated interpretation of the produced images. Just show them on your operator console. Let him worry which is which.



I was assuming the robot
I was assuming the robot couldn’t move outside of the 5 foot circle (and it made sure of that itself) and the camera was to help it do that. I guess the operator could always see what the camera picks up and determine not to drive it too far away.


Ultrasonic is perfect for this. The sensors typically used on robots at LMR might not be suitable - they’re good at detecting a large flat surface, but not a small object.

You might consider an untrasonic transmitter as your fised point. It would send out a ping. Your “robot” would contain a U/S receiver. When it received the ping, it would transmit a ping back to the “fixed point”. The fixed point receiver would pick it up and calculate the travel time for the conversation.

This gives me an idea. You could have two fixed points. One transmitting a single ping and the other transmitting a double ping. The robot would echo them both. Using this technique, you could establish the rbotos position from two fixed points and thereby trianglate its position in 2D space.

An alternative I’ve seen used is a ring of (appx 12) I/R transceivers around the top of your robot. They all fire in a cyclic sequence. Two fixed points with transcievers detect when the signal is strongest and therefore the angle between the bot and the fixed points. From this the distance can be calcualted.

This post is a little disjointed, but if it doesn’t give you something to work on, ask me. I know what I mean!

Sensors on the point?
Perhaps a ring of sensors on the fixed point can tell you how far the robot is at any given time. The 5 feet range may be a bit much for the typical Sharp IRs, so a ring of sonars could be good. Just difficult if there are any other obstacles in between. It might be done with as few as 3 or 4 sonars, depending on the type of sensor, and the size of the robot being detected. Alternatively you could try something really strange that I’d thought of : direct a single sonar up (or down) into an omni-directional reflector, which sends the pulses out radially in all directions, and would catch returns to have them be detected. It would seem this would only work with single transducer sensors, like the Maxbotix ones or the Sensecomp devices, if it worked at all.

if it only needs to sense

if it only needs to sense the distance from a central point, you could use the easy radio device

https://www.robotshop.com/letsmakerobots/node/77 and use the analogue signal strength output to gauge distance…

not so good for 2D locations though.

While reading the above

While reading the above posts I was thinking about an idea similar to yours BOA.

With the fixed position, you could have the ping sensor and an ir emitter(array)/detector.

On the mobile unit, you could use just the ir emitter/detector

Both units could keep track of each others location based on the ir emmision as a fixed point to align to.

The bot would also have a small flat surface that would be perpendiculer to the ir transmission.I would guess it would have to be flat black so as not to bounce the fixed point ir signal(false readings). It wouldneed to be big enough so that the pinger could get a reading off of it…maybe a 2x2 piece of plastic or something…

Not sure if you’d need an emmiter array as to keep better track of bot/fixed point but it might help.


I knew of TV-remotes that
I knew of TV-remotes that actually used dual-tones (in ultra sound)… I am petty sure!

Or if you wanted to keep it
Or if you wanted to keep it super simple just tether the bot to the central point. On the bot side attatch the tether to a spring loaded rotating drum with a pot attatched. Use the pot to determine how many times the drum has wound out and multiply that by the circumference.