I wanted to make you all aware of a pretty cool material called nitinol. The product is sold in wires. When you apply a current to the wire, it heats up and the wire contracts by about 5%. This all actually only takes a fraction of a second with an appropriate current. Nitinol is very cheap and virtually weightless. The wire is also very strong; a 0.015" diameter wire works with a 2 kg (~5 lb) load.
Now this obviously has limited applications, but I can think of many mechanisms for FIRST where it would be a great alternative to a solenoid or pneumatics.
Small Parts sells Flexinol, a type of nitinol actuator. We are considering using it for one of our mechanisms on our 2004 RoboCup team. The item we ordered mysteriously disappeared from Small Part’s website, so here is another link I found:
By following figure 4-1 (the flowchart) in last years rules, Nitinol may not be used. It is not a kit part --> It is designed to conduct electricity --> It would be classified as an actuator --> It can not be used…
Actually, by that reasoning, you could use it if you managed to find a way to heat it with legal materials (not as a conductor of electricity, but of heat)…let’s say, stall a drill motor, and have it dump about 450 W into that little wire. That ought to do it.
(No, don’t do this.)
Unfortunately, it’s a Ni-Ti alloy, and Ti is prohibited as an exotic material. Though they don’t specifically state that alloys of exotic materials are prohibited, that’s probably implicit in the rule.
This material barely is covered by the rules as it is so far outside anything that has been covered in the rulebook. If I was asked to rule, my first response (and simplest) is that the wire is not a specified wire size (minimum) for use on the robot. Even if insulated by teflon tubing, it still poses a hazard albeit a slight one. It would be interesting to experiment with a speed controller to vary the heating/contraction distances though.
Another issue may be the voltages that are usually applied to them, I rember when I built an stakito (sp) robot that used theise it reccomended around 3v, (9 was waaay too much applied directly to it, it would nearly jump but dident last very long) and when it is used in robotics I seem to rember that you apply an higher voltage for a very short time to get it to contract then lower the voltage to keep it hot and contracted… such as 3v to start then lower to 1v in about .5 sec or so. While resistors are allowed in the materials list, they are only allowd in the custom boards that can only attach to the sensor inputs or serial port of the rc, not inline with the power. Altho like AL said, you may be able to use an speed controller to do this with PWM.
We were going to use some nichrome (spelling) wire last year to burn through cord to release a spring mechanism. We got it working really well too. We even showed videos to FIRST of exactly what it did and how much smoke it produced and how we would contain the smoke and make sure there was no chance of fire, but they would not let us use it. It still is really cool stuff to play with though.
Nichrome wire is used in heating coils for toasters and irons. Although it is great for those applications, it does present a fire hazard and it is considered exposed wiring since it is conductive. A draw back is that it is fragile when heated if not well supported. Just look into the top of a toaster and you will see what I mean.