Background: Introductory robotics competition for college freshmen; Bot has to open 8 jars (with two balls in each of them) in ten minutes and load the balls into a shooting mechanism.

So, we were doing this project and we hit upon a challenge that the jar is not opening like we originally intended to. So we decided to get a rack-pinion mechanism and use it for unscrewing the lid. However, it is too large and we are unable to fit the bot in the required dimensions

The actual question: Are there any wires or rigid columns/things which can contract ~1 cm when electricity is passed through it? And what would their price range be? Our budget is also in the list of constraints for the bot

Edit: We can include a wire of length <1m or a column of length <30 cm. Also, the wire needs to contract only more than 7mm

  • $\begingroup$ Can you post a diagram of the setup? Why wouldn't a winch work? $\endgroup$
    – Ian
    Oct 9, 2015 at 21:06
  • $\begingroup$ Winches are too big to fit in a 5*5 setup. $\endgroup$ Oct 10, 2015 at 10:12

2 Answers 2


It sounds like you are looking for an artificial muscle. I see you've already looked at one type of

Have you looked at

It seems more natural to me to use normal rotary motors to rotate the screw-on lid of a typical jar, so I am curious to see how your system works. Good luck!

  • $\begingroup$ Thanks for the links. The rotary motor does not fit into the constraints of using it in a 5*5 cm^2 pipe. $\endgroup$ Oct 8, 2015 at 5:26
  • $\begingroup$ I don't understand the constraint you mentioned, but I don't see it in your question (so far). You really need more detail. Is this a homework question, if so is there more information? $\endgroup$
    – Andy
    Oct 8, 2015 at 9:50
  • $\begingroup$ @Andy It isn't a homework question. It is for a competition between hostels( fraternities for the Americans). I forgot to add the constraint in the question but, we have to fit the opening mechanism in a pipe of radius 2.5cm or a 5cm by 5cm box channel. $\endgroup$ Oct 8, 2015 at 13:06
  • $\begingroup$ Understood. That's a tight space! I would have gone for two or three geared motors with rubber drive wheels, to "spin" the lid off, but there isn't room for anything like that... unless the motors are somewhere else and the pulleys driven by long axles. Alternatively, can you put rubber grips inside the pipe/channel and make the pipe itself rotate to unscrew the lid? Just a thought... $\endgroup$
    – Andy
    Oct 8, 2015 at 13:47
  • $\begingroup$ We tried that but didn't work out. Anyway, we finally finished two models - one with leadscrew and the other with Flexinol. I'll post the pics and our method soon for future reference. $\endgroup$ Oct 9, 2015 at 13:00

Have you looked at linear actuators? However you might be better with a motor and a pulley.

Have you considered alternatives such as:

  • Wrap a rubber loop around the edge of the lid, put it tight with a high torque motor, and then twist it off with another motor.
  • Do the rules say you have to open the jars by removing the lids? If not a arming your robot with a hammer may be an option.
  • $\begingroup$ Yes, we're working on the linear actuators - this is just a backup idea I got after running through this pdf as for the rubber loop suggestion, we have to remove the lids of 8 jars in 10 min and this is definitely not going to cut it. And smashing it? are you even serious $\endgroup$ Oct 7, 2015 at 14:11
  • $\begingroup$ I like the smashing jars idea Matt half-suggested by the way. After all, safety wasn't mentioned at all in the rules. ALWAYS consider novel solutions before abandoning them... $\endgroup$
    – Andy
    Oct 8, 2015 at 13:49
  • $\begingroup$ +1 for smash with a hammer. Imagine the judges' faces when the hammer comes out from behind a panel and you start destroying their course. "Nothing in the rules said I can't!" - You become legend, because every year after that the competition organizer says, "And you can't break anything. I have to say this because so-and-so won the competition by smashing a dozen jars with a hammer." $\endgroup$
    – Chuck
    Oct 9, 2015 at 13:57
  • $\begingroup$ @Chuck, The problem statement explicitly mentions that the jar must not be damaged. Also, the threading of the screw must not be damaged. Otherwise, I wouldn't be here asking questions $\endgroup$ Oct 10, 2015 at 10:14
  • $\begingroup$ @RecursiveCursive, damn someone got there before you :( $\endgroup$ Oct 10, 2015 at 22:23

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