Interesting article on experimental gripper

I just came across this article and video of a new type of robot gripper using a soft bag filled with coffee grounds. When pressed against an object, the bag conforms to it. A vacuum pump then removes some of the air from the bag causing it to shrink slightly and turn rigid with the object firmly held.

From the video, it looks very simple and effective - seems like something that would be fun to experiment with…


  • Dean

this is a very cool device, now i want to make one.
i want to see if it can pick up a tube.

If only they allowed a vaccum, coffee, and a rubber balloon in VRC! :rolleyes:
That’s a really cool gripper!

Pneumatics, groundup plastic Vex parts, and latex rubber tubing are legal, so you are good to go. Some adaptation required…

Has anyone tried Vex pneumatics with Vex latex tubing?

As far as I am concerned there is no VRC without coffee!:smiley:

You really think out of the box :smiley: - good thinking!

The reservoir should be able to hold a vacuum, though probably only enough for a few actuations. Also, the tubing is probably stiff enough to not collapse under vacuum.

But I doubt the 3-way (double acting) solenoid valve will work properly if the inlet port has a lower pressure than the outlet. You’d probably have to use a pair of 2-way (single acting) valves to handle the grasp (deflate) and release (vent) cycles.

I like the idea of plastic shavings instead of coffee grounds, though I do think coffee would make for one aromatic robot!

If only balloons were allowed, I think you’d have all the makings of a competition legal vacuum-bag gripper.


  • Dean

wow, i just love the new engineers that “think outside the box”
this just inspires me (and many other people i hope) to become an engineer :slight_smile:

More Exo-boxicisms:

  • balloons are made of latex, so is Vex latex tubing; We already know it is stretchy, ‘just’ stretch it in the other direction.
  • Or if you really must have a ballon, use a light sensor as feedback for the gripper, now the balloon is allowed as a ‘color filter’
  • You don’t need a reservoir to store the vacuum, or a switch to move it from place to place;
    – treat a gripper plus piston as a closed system; use some other prime mover to expand/contract a piston plunger to move air out-of/in-to the gripper.

Not quite
<R7> Robots are allowed the following additional “non-VEX” components:
a. Any material strictly used as a color filter for a VEX Light Sensor.


Doesn’t seem practical. If the latex is under too much tension, you won’t be able to impress around the object to be grabbed. I suspect the exact properties of the filling and bag material are very important to the performance of the gripper.

That is a very good idea - I’m not sure how much air volume needs to be moved, so you may have to gang more than one cylinder.

I’ve got balloons, coffee, and an air cylinder.
Hey Ferb, I know what we’re doing today!

Seems like the balloon is the missing ingredient for a competition friendly verson of this. But we need a catchy name for it. Bag Gripper? Balloon Hand? Vacuum Clencher?

  • Dean

Overall, this would be a good idea, but even if you made a custom balloon out of tubing, I’d be inclined to think it would pop very easily. Not only that, but you are making a round object out of long strands, and if you reformed the latex completely, I don’t know how well that would go over with judges as you would have fundamentally altered the part, making it difficult to prove that you used vex parts and not just a black balloon.

My kids and I just experimented with this a bit. It was amazingly easy to get it to work!

We used a regular latex balloon filled with coffee. (We used the cheapest vacuum-packed stiff we could find.) We then rigged a pneumatic cylinder to a hose. At the end of the hose, we attached an air filter (to keep coffee out of the hose and cylinder). The filter was inserted into the coffee-filled balloon and secured with a zip tie.

As soon as we moved this piston rod, the balloon began the clench and harden. The transformation is quite stunning; it really does go from being fairly squishy to being nearly solid.

To make it pick something up, you have to press it down pretty firmly so that it can squish around the contours of the object. When you draw the air out it solidifies and shrinks slightly. The more more “undercut” the object has, the firmer the grip.

I did have two minor problems: First, the coffee kept compacting, so I would have to take the balloon off to top it off again. Presumably it would eventually stop doing that. Second, getting rid of all the air leaks (particularly around the balloon) was very difficult. I don’t think it is practical to purely treat this as a closed system. You will need at least a valve to equalize the pressure to atmospheric when unclenched.

To make this a practical gripper, some thought would have to be given to mechanically securing the balloon to its boom/wrist. Having it attached only by its neck made it very floppy and therefore difficult to press onto the object to be picked up without a lot of human intervention. I think a small funnel-shaped holder would work pretty well.

The cylinder we used had a ¾" bore, and we had to use about a 3" stroke to get the balloon to completely clench and unclench. This corresponds to about 1⅓ cubic inches of air displacement. The Vex pneumatic cylinders have a volume of about ¼ cubic inch. That means you’d need to use 5 or 6 Vex cylinders in a parallel circuit to displace as much air as we seemed to need. You might be able to get away with fewer if you very carefully tuned everything, but you’d almost certainly need more than one.

We’ll probably keep experimenting with this, but I thought I’d post since we did replicate the results shown in the video with very little effort.


  • Dean

Wow… Great work! :slight_smile:

Cool! replication is a key element of the scientific method. any pictures?
Airleaks and non-closed system and need a larger volume are all similar problems. A potential solution is two vex pistons, or a single double acting piston, and some valves, configured as a motor powered air/vacuum pump.
Using an electric motor to power a piston removes some of the utility of a pneumatic powered gripper.
An alternate solution in contests where polycarbonate is allowed is a custom polycarb piston with larger volume. The lack of available legal glue makes cylinder creation problematic.

No pictures yet - I’ll post some once I’ve gotten a bit more done.

Last night we decided to fill a latex glove with coffee and try that. I adhered a non-compressible band down the back of a couple fingers in the hope that the fingers would curl when the vacuum was applied, but I only got a small deflection. I think this is because it just doesn’t compress very much, so the length differential wasn’t sufficient for a useful curl.

It was supremely creepy, though, and something that will probably find its way into a haunted house at some point. The hand was limp and squishy, and then it would stiffen and hold whatever pose you put it in. It had a throbbing effect as the pressure varied, and under vacuum it takes on a grainy & wrinkled texture.

Yep - there are a variety of configurations that could be made to work. As long as the system’s flow rate significantly exceeds the leak rate, it should be able to clench and hold its grip.

True, though I think the novelty here is the way it clenches. I’m always fascinated by simple mechanisms that yield complex behaviors (this conformal gripper, or a bristle-bot’s motion). I hope to build a working system suitable for use in classroom demonstration.

I’m not sure how practical it would be in any current competitions, since most designs seem to require managing multiple game elements at the same time. Once I get a working system, I will try it on a few Vex game elements just to see if it is any use at all.

Something like a sealed bellows might work very well. Simple to construct, less leaky than a piston, and easy to move with a motor.

As for competition-legal, I think the ballon is more of a deal-breaker than the vacuum source. Even if you could make it, I think the game-specific manipulators already in use will always outperform this design in competition (unless, perhaps, if the competition requires you to manipulate a wide variety of shapes).

More to come…

  • Dean

SparkFun Electronics is now selling a small 12V vacuum pump. It is about the right size for a small universal gripper, and should be pretty easy to interface to Vex using something like this.


  • Dean