Saturday, October 19, 2013

Crazy Robot Hand

The box has very cool graphics with few parts

You'll need a helping hand to assemble this crazy robot hand, which is not entirely possible to assemble the way the instructions intended.

The kit is called Robotic Hand and is made by Kid Labs 4M and recommended for ages over 8. The price was about US$16 and was purchased overseas.

The parts for assembly had no shortages. The kit included one extra finger tip, as if they knew the finger tip would not work.

In fact, there are several flaws with this kit. One, at least two of the finger tips are too large to fit the finger tubes, which likely had mold shrinkage during the manufacturing process. The others didn't full fit the tubes either.

Showing knots in two nylon chords
Above, the wire was substituted for the nylon cord
We tried sanding down the finger tip, sanding the finger tube, knotching the tube on the back side, knotching the tube on the font side, and super gluing the finger tip to the finger tube. Nothing worked.
At top, a finger tip does not fit the finger tube

Next, the nylon fishing string had problems. It was too thin, stretched, knots were very tedious to tie, and would slip, and it was very difficult to handle. It was obviously a poor choice of string material for the kit. What was needed was a wire that would have minimal expansion and stretching.
The next problem that resulted, because the design calls for two sets of two fingers to be moved two at a time, the location recommended for tying the knot was next to
Finger tubes must be rear seated
impossible to space evenly and sym- metrically and this caused one of the two fingers in the set to curl and bend first before the other. This simply was not acceptable. All is not lost however. We decided to take matters into our, er, own hands... First, we took a defective retractable USB cable, cut off the two ends and removed the retracting spring mechanism. Then the end was spit with a scissors and pulled apart to make two very long black wires. The remaining parts went into the junk box and the wires were saved for the project. These would replace the worthless nylon string. The ends of this wire connects to servo horns so that the fingers can be individually programmed for more precise positioning and repeat control.

As far as the finger tips are concerned, this problem will be solved with another kind of superglue, gluing the tips in place. Also, due to the thicker wire used, five finger tip holes need to be drilled to accept the larger diameter cord. We're still working on this project as it involves a lot of work, a power drill, a bench vise, wire cutters, and is not suitable for children.

4M Industrial Development Limited

Instructions English