Let’s do some rough
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.
hum, looks like it has a 4
hum, looks like it has a 4 meters range…
But maybe i’m wrong, again! -_-v
Thanks all for the
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!
With a single transmitter
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.
about the second idea… i
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).
sorry, you are right, i
sorry, you are right, i never got my ping to work at those ranges though…
Now we’re getting somewhere
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.
Hmm, the problem with your
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.
You might find it’s easier
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.
they also don’t seem to be
they also don’t seem to be too costly http://www.rainbowkits.com/kits/sdf-1p.html
The above one is quite big though, but you get the idea…
But maybe you could use a
But maybe you could use a simpler solution : you carry several IR leds as a beacon and your bot has two IR receivers to seek it, and you use the ultrasonic rangefinder just to be sure your bot stay at a safe distance…
Thanks, but would that work
Thanks, but would that work reliably in both light and dark conditions i.e. in sunlight ?
You’re right, i have to stop
You’re right, i have to stop thinking only indoor…
Maybe with a strong beacon? But i don’t think so…
(jeez, i just keep being wrong on this thread!)
No thanks for your efforts !
No thanks for your efforts ! I can’t believe how quickly people have contributed and replied, I’ve got so much food for thought now. Much appreciated.
The project is an
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…
I would think so, with a
I would think so, with a pack of 5 ir emmiters I think it would be possible to get some good range. heck with a pack of 3 emmiters you should be able to get some decent range…even in sunlight.
As mentioned before, you
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…
If you plan on going this
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)
Mummy where are thou
You could have the following setup.
1) The robot sends an ultrasonic pulse at a certain frequency (it’s basically yelling ‘MUMMY WHERE ARE YOU?’. This pulse will take a certain time to travel to the receiver of mummy
2) Mummy receives this message and …
3) responds by sending an ‘I am here you little twit’ back (same distance, same time lapse).
4) twit receives the signal and calculates the distance to mummy. If distance to big, than move, if too small then just stop/slow down.
If 2 doesn’t happen then mummy is out of range and the robot has to stay put. (mummy is in the shop just wait until she’s back).
I am not sure about the directional stuff though …
YCD
P.S. Sigh… replied to the wrong message in the string… sorry
I am doing the same type of project
My TOBI will do something similar that you are wanting to do. I am going to be using 3 Ping)))'s and two IR on sweeping servos for distance detection, object avoidance and keeping the proper distance behind me or the next TOBI [in the chain] that it is following. For homing in on me, I am planning on using a Thermopile, IR Beacons and RF for getting a heading of my location [2 out of 3 provides a heading]. For the RF part I am going to use an array of 4 antennas that measure signal strength with reflectors to affect the signal.
My page is here: https://www.robotshop.com/letsmakerobots/node/7025
A similar project is here:
https://www.robotshop.com/letsmakerobots/node/8527
