silicone gripper robot

[punypenguin]

My daughter (5th grade) has made two silicone gripper robots. I believe we used the larger of the two possible molds to cast these. Im quite impressed she got this far, but now she is stuck! HELP... in both cases the robots inflated very unevenly and did not curl. We seem to have fixed the curl problem somewhat by adding an additional layer of silicone (we only used ecoflex 30, not 50). As per the troubleshooting section of this site we added more silicone to the fingers that inflated first. This did not work. Then we added silicone to the other side of the finger and that did not help. We made two grippers, so that we could have options. What we know is that there are no holes and no blockages...air stays in and all chambers/fingers do inflate (eventually- haha). She guessed that maybe the direction of the tubing influenced where the air would go 'first'- ie, that the two fingers in front of the tube were receiving air first so we added another tube opposite it and pumped together. This had no effect. We also tried sliding the tube into the fingers airway and even this didn't change anything. We have enough ecoflex to make 1-2 more grippers. I would like to get some responses from you pros before we do it again though. I don't mind buying more but we can only get it through the mail and time is a factor. Any advice you can give us would be greatly appreciated.
One bit of information we can share though...1) we had our mold made from 'detail plastic'.. we needed a good hearty application of 'krylon crysral clear acrylic coating' to remove the robot from the mold easily.This can be purchased at a craft shop for about $6. 2) we tried adding two different kinds of food coloring to color the molds and neither worked. The color simply did not incorporate. PLEASE HELP!! WE ARE STUCK. THANK YOU SO VERY MUCH FOR TAING THE TIME TO OFFER YOUR EXPERTISE.


[Project: https://www.sciencebuddies.org/science- ... #procedure]

[amyC]

Hi Punypenguin - Your daughter has chosen a really cool new project at Science Buddies!

Thank you for detailing the kinds of problems you have encountered and what you have tried. Other Experts may have some additional input, but I talked with some of our Experts at Science Buddies, and I was asked to share the following tips and suggestions:

1) It is very important to make sure the mold is level when the silicone cures. If the mold is tilted even slightly, that will cause the silicone to flow toward one side of the mold, and some legs will be weaker than others. This would result in the uneven inflation you are describing.

2) If you use too little glue between the two layers, this can cause the top and bottom layers of the robot to separate internally when inflated. If this only happens on one leg but not the others, then that leg will be weaker, and it will inflate first. This is a fine balancing act because if you use too much glue, you will clog the air channels.

3) Where the tube is inserted or where the air "goes first" will not have an effect. Air molecules move really fast and should expand throughout the whole robot pretty much immediately.

4) You have to vigorously mix the food coloring in to get it to work. The silicone is hydrophobic, so by default it will just cause the food coloring to bead up. You have to mix it much more vigorously than you normally would with food. If you are having trouble, you might try it without food coloring until you know the rest of the process works.

I hope these suggestions help. Please post back to this thread if you have other questions.

Amy
Science Buddies

[punypenguin]

Hi Amy, thank you for your tips. We did skip the idea of color as it was not of key importance. I have no blockages yet still when we inflate any of the (now) 3 robots we made, two fingers inflate beautifully and fast, two just don't. I feel like I'm missing the obvious. We did make the attached layering thicker than before so now we have a good curl but it doesn't matter because unless we manipulate the fingers by squeezing them, the other two fingers don't catch up. I did not check for level ness but it sure seems level. Any other thoughts on how to A) slow down the air to these two fingers, or B) increase air to the slower two fingers? If we added more silicone to weigh the fingers down about how much would we add? Is there another product we could add? I feel like we are missing something.... Three robots, same problem each time?? HELP!! Thank you!

[punypenguin]

The class has been given an extension on the project!! Just a few more days. So please- any suggestions would be appreciated! The issue now is we have a gripper that curls great but inflates unevenly. No clogs- all 4 fingers inflate but two are over inflated before the other two are inflated. How to we 1) slow down rate of inflation to two chambers or 2) increase rate of inflation to 2 slower chambers? My daughter has been working so hard and we are just stuck!! If you have suggestions we would be so grateful! Also, if we are supposed to add silicone to weigh the two fingers down to slow inflation rate can you please explain how to do that? I mean, do we add liquid EXOFLEX? Or better to take EXOFLEX that had already set (left over from making the bottom layer) and then use liquid EXOFLEX to stick it together? Thank you so much for your continued help!! My daughter and I really appreciate it!!

[kgudger]

Hello:

In looking over the experiment details, I'm wondering if your mold was made unevenly? If so, there's not much you can do about the mold at this point. If you think this is the case, and can offer tips to future students making this project, please let us know. The instructions imply that not "gluing" the 2 layers together exactly right can lead to this behavior, but I'm wondering if the mold was uneven to start with.

According to the troubleshooting tips:

If all four of your legs don't inflate to the same size and shape, first check each individual leg for clogged air channels, as described in the second troubleshooting tip. If none of the channels are clogged but the legs still don't inflate symmetrically, add a new, thin layer of silicone on top of the legs that are inflating the most. This should make it harder for them to inflate, allowing more air pressure to divert to the other legs. The material for your gripper robot has "nonlinear" behavior: instead of always inflating gradually with air pressure, it could not inflate at all and then suddenly "jump" and inflate. So, if one leg is slightly weaker than the others (due perhaps to some slight differences in wall thickness from the molding process), it might inflate first while the others don't inflate at all. Strengthening this leg with additional layers of silicone may prevent this.

I think I would start by adding layers of (liquid) ECOFLEX to the faster inflating fingers. If one layer isn't enough, try more. It sounds like you have several castings, so you can experiment with one.

Have you tried filling your casting with a colored liquid and watching the process? Maybe you can see where there are blockages or restrictions, if any?

As with all engineering experiments, we can learn a lot from the failures. I don't know who will be judging your daughter's experiment, but someone with engineering experience will understand that things don't always work as expected but look to see what she learned in the process and understands about what happened. In other words, if at judging time it still doesn't work properly, can she explain why and how she would go about fixing it in the future? Does she know applications for this type of robot gripper, and does she have some examples of how she can use this one to do meaningful work?

Please let us know what happens.
Keith

[amyC]

Keith gave you some excellent information and perspective. I have a bit of additional follow-up suggestions to pass along as well:

Unfortunately there is only so much you can do to fix a "broken" robot that isn't working very well. If the mold was even slightly tilted during the curing process, it can result in uneven-thickness legs that are hard to fix. If adding additional silicone isn't working, I would try two more things:

- Try to restrict the air flow to the two legs that are inflating early, by pinching the air channel shut at the base of the leg (the end closest to the middle of the robot), using a binder clip or a paper clip. Hopefully this will pinch the air channel shut or nearly shut, which will allow the air to more easily flow to the other two legs first. Try this first, before you try the next point.

- Try wrapping the legs that inflate early with either duct tape or electrical tape (be sure to go completely around the leg). Since the tape isn't very stretchy, it should help prevent the leg from expanding.

Basically both of these things are attempting to do what you've already figured out you can do by hand - squeeze the legs that are inflating early, to force some of the air into the other legs.

Please let us know how it goes!

Amy
Science Buddies

[punypenguin]

Thank you Keith and Amy! Your support has been so wonderful- just knowing you guys are there... in cyber space somewhere- haha. If your ideas work, we will love you even more. My daughter and I will try your ideas tonight. Ans since we are expecting a big snowstorm here we may get a few more days to experiment!
I forgot to mention one additional glitch...Once you inflate the robot even once, to find out two legs inflate to fast the silicone of those legs is stretched out and does not go back as taught as it was. So now when we add more liquid ecoflex, we are scare it wont have settled properly. I think we will inflate it just slightly so it is taught. We will keep you posted, and many thanks for your help and support!