Hi everyone! I have a question about sensors for making my robot realize it's fallen over. I see it now in a couple of robots and semi robots, where a bot can determine if it's fallen over. I did a bit of research and found a couple of options, but i'm not sure which one would be best. I saw an acellerometer, buthose are expencive, tilt sensors look more like what I'm after cuase they seem cheap and are not as dangerous as mercury switches. I'm not exactly sure what would be best or if I'm missing something. I figure if they made rumble robots and soldthme for 30 dollars, there has to be a really cheap and effective way ot make my robot tell it's fallen over. it's also suppsoedot tell which way it's fallen over, and I figured out how ot do it with three wit the mercury or turn sensors. it's humanoid in shape with two arms, a head that turns, torso and wheeled legs. The bot is also an estimated 5-6 inches tall, so it's not too large.
Thanks for any help, I've been trying to figure this out for a bit. I'm also using the pickaxe and the 28x1 supplied in the start here robot.
Tilt switches are indeed
Tilt switches are indeed what you probably want to use here, since they’re cheap and require virtually no coding to integrate. It looks like you’ve already figured out that you can tell whether you’ve fallen left/right/forward/back/upside-down with only 3 switches aligned at different angles.
They’re harder to find, but you can also get multi-axis tilt switches which use a little metal ball inside a nice housing. One or two of these would be easier to add than 3+ single-axis tilt switches if you can find them.
If you connect one terminal of each tilt axis unit to a digital input (with internal pull-up resistors) on the PICAXE, and the other terminal to ground, you will have a very simple and effective way of setting up the circuit.
light sensor under the
light sensor under the robot, enclose, it to be dark… read it into a variable and compare… if more light, its fallen
Also had an idea to use
Also had an idea to use various resisters to send different signals so I only have to use one port. Not sure if that would work, unless I used the code that’s used in the rf sensor and modified it to detect specific ranges. But if you know where to get those multi-axis tilt switches, that would be awesome! The less room I use on my robot, the better! 
Thanks for your help!
If you use an analog input
If you use an analog input instead of a digital input you can definitely use a resistor arrangement to detect which tilt switches are on/off.
I’ll have a look around my usual suppliers and see if they stock multi-axis tilt switches - what county do you live in?
In the U.S… Still looking
In the U.S… Still looking around for tilt sensors at all, but all i keep finding is accelerometer @_@
Thanks again for your help! I really appriciate it!
Meant to say that I’ve been
Meant to say that I’ve been trying to locate tilt sensors, but am having trouble. Sorry about that.
I’ve used optical tilt
I’ve used optical tilt sensors like these ones before too - they’re slightly more complex but you get a nice reliable signal and they’re pretty small too.
Here’s a link to a classic ball-bearing tilt switch, complete with a nice set of instructions on how to use them effectively.
quick and dirty
This is the absolute simplest way to tell if your bot has fallen over. One digital (or analog) input
Full Make-article here
