Hi, Just a thought - would it be possible to build a quad bot that climbs smooth walls using just bathtub-style suction cups (see pic) - the kind you bend-to-pull the inside soft suction cup (so no vacuum pump needed, just something to tighten and release the cup)
If this works, then I guess the robot can support itself on 3 cups, while releasing and sticking again the 4th leg
Is this at all feasible in your opinion?
What is this robot going to do in your bathroom? 
I think 6 legs would be faster.
if you have simple cups that are connected to an eccentric shaft, the motor could pull the cup to make a vacuum. two motors with some elaborate linages and you could make it work.
if you are only going in a straight line, then you only need one motor to move forward or back.
To me this sound like one of those fine in theory but imposable in practice sort of projects. It depends on if the suction you get is strong enough to support the robot and the motors and mechanisms necessary to operate the suction cups.
dave-in-nj:
if you have simple cups that are connected to an eccentric shaft, the motor could pull the cup to make a vacuum. two motors with some elaborate linages and you could make it work.if you are only going in a straight line, then you only need one motor to move forward or back.
Interesting, Can you elaborate more on the one-more/two-motor scheme?
I'm actually planning for it to climb a glass wall and stop here in there to write stuff on it
Those cup are quite strong, supporting two towels each (here is a new weight unit for you)
supporting two towels each
What sort of towels?
Name Dimensions
washcloth 12” x 12” or 13” x 13”
fingertip towel 11” x 18”
guest towel 16” x 24”
hand towel 15” x 24” or 16” x 30” or 18” x 28” or 19” x 30” or 24” x 41”
bath mat 22” x 34” or 22” x 36” or 24” x 35”
bath towel 27” x 50” or 27” x 52” or 27” x 55” or 30” x 45” or 30” x 54” or 30” x 56”
oversized bath towel 30” x 56”
bath sheet 30” x 64” or 30” x 66” or 33” x 66” or 35” x 60” or 35” x 70” or 36” x 70” or 40” x 70” or 47” x 59”
A person can apply a lot of force to the suction cup when applying it. The trick is to get as much of the air out from under the cup as possible before triggering the lever. If your robot is held on by 3 suckers, then it can't push very hard on the 4th.
Vacuum pumps can be very small. I have several that are only a little bigger than a USB thumb drive. With pumps, you don't need to press the sucker against the glass very hard as the pump does all the work. They are easy to switch on and off. Flipping up the lever on the towel suckers is going to be a complex mechanism.
6 legs are great because you can use them as 2 tripods. Suck down 3 (one vacuum pump) and move the other 3. Suck down the 2nd tripod, then release the first. With only a little mechanical complexity, you can drive the motion of all 6 legs from one motor. If you are only going straight up and straight down, you don't need any steering.
a suction cup of correct size, you can 'pull' the cup with a motor.
consider an eccentric shaft such as car driveshaft.
it could pull the cup of many that are connected.
rotate the shaft and it could lift the cup....
or could lift a piston, creating a vaccuum.
or you could have a small vac pump
you could have one motor on each cup and some stabilizers and only need two cups.
everything depends on the amount of vacuum you need and weight of what is being lifted
mmatty:
I’m actually planning for it to climb a glass wall and stop here in there to write stuff on it
A Graffiti-duino, eh?
Thanks everyone! I'll come back when I have something to show..