Testing
We used our final batches of ecoflex and with all our care and passion, created the perfect 4-arm PneuNet gripper using paper towels which worked repeatedly. Although all the arms still did not inflate at the same time, the gripper was successful in lifting objects less than 3/2 pounds. The addition of sticky tape and magnets further amplified our successes.
We tested the different objects the gripper could grab, and the effect of loads on the arm.
Testing the Grabber
In order to test our grabber, we gathered together a collection of common workshop items that can be found in any toolshed. We measured each item's weight in ounces using an electric scale. Next, we stated if the item was magnetic (and thereby influenced by the magnets attached to our grabber). We then proceeded to test if the grabber can successfully grasp the object and if the item could be held. We also used sticky tape to pin down the magnets but we soon noticed that the sticky tape could pick up light objects that were neither too big or too small for the grabber to grasp.
Item to be picked up | weight | Magnetic? | Can it be grasped? | Grasped by sticky tape? | Can item be held at all? |
| |||||
Jar of wood stain | 18 oz | yes | yes | no | yes |
Jar of wood filler | 6.625 oz | yes | yes | no | yes |
3 pound weight | 48 oz | yes | no | no | no |
screwdriver | 4.125 oz | yes | no | no | yes |
Cup full of leftover ecoflex | 4.25 oz | no | yes | no | yes |
Can of spray paint | 14.875 oz | yes | yes | no | yes |
Glue bottle | 1 oz | no | yes | yes | yes |
marker | 0.75 oz | no | yes | yes | yes |
Gorilla wood glue bottle | 19 oz | no | no | no | no |
Bottle of glass cleaner | 30 oz | no | no | no | no |
Sheet of paper | 0.125 oz | no | Yes (from side of table) | yes | yes |
Can of coke | 13.875 oz | no | yes | no | yes |
Bundle of leaves | 0.125 oz | no | yes | yes | yes |
Wallet | 3 oz | no | yes | no | yes |
Additional Facts and Data
-The bulb must be squeezed at least 8-9 times in order for the grabber to grasp a normal sized object (size comparable to the grabber itself)
-Takes anywhere from 10-20 lbs of force to push down on the air bulb (pressing down 3/2 inches or 0.0381 meters) which is equivalent to approx 66.7 newtons of force.
-Takes 23 joules of work to grab something
-According to the Topend sports website, the poorest grip strength (26.7 lbs) in both males and females ages 10+ should still be more than enough to successfully squeeze the air bulb.
-However, some items were shaped in such a way that they couldn't be grasped despite being very light.
http://www.topendsports.com/testing/tests/handgrip.htm
http://www.topendsports.com/testing/norms/handgrip.htm
Grabber and Comparisons
In addition to testing the grabber's abilities, we also tested its durability and rigidity compared to conventional, store-bought grabbers. In order to make our grabber lighter and easier to handle, we used a tube of pvc piping. The conventional grabber used a tube of aluminum for its structure. We decided to test how much both tubes bend while holding on to a weight. As expected and as shown on the graph, our pvc pipe underwent much more displacement than the aluminum pipe. However, just this statistic does not necessarily make the aluminum pipe the better choice. The pvc pipe is able to undergo much more bending before the point of breaking; the aluminum one would most likely break if it underwent a similar amount of displacement that was experienced by the pvc.
