Heavy weight lifting

I built the two robots described below for Lego Mindstorms Forum Community Contest 9: Crane. Here are the contest rules.

Pimousse^®

Named after a small but strong flavored candy (motto: "strong but beefy"), Pimousse is a tiny and simple travelling crane, but able to raise very heavy weights.

Construction details

	The concept is borrowed from this kind of equipment.
	Side and top views.
	Pimousse rolls on rails placed on the edges of a slit in a table.
	The hook assembly is equipped with 2 metallic and 4 pulleys...
	...and form a 8 threads hoist with this construction. The pulling force of the winch is multiplied by eight (neglecting some friction losses). The hoist has one drawback: properly placing the cable in all 7 pulleys races is a nightmare!
	The kite line I used is rated 40 kg / 80 lbs. With the multiplication of the hoist, a whopping theoretical 320 kg/640lbs could be lifted! The cable is not the weak link here for sure...
	The hoist is powered by two 47154 "Monkey" motors, each driven by a separate RCX output. They deliver about 1.1W of mechanical power. A rotation sensor counts the winch turns, rough estimate (because of the uneven placement of cable on the drum) of the lift height.
	The moving chassis has eight wheels driven by two motors. A second rotation sensor monitors distance travelled. The hard rubber tires are able to bear a heavy weight.
	A 72x down-gearing enables slow but powerful drive. During preliminary testing, I was able to climb on the chassis for a short travel. Quite unexciting race ;o)

RCX program

 Here is the NQC program.

First lift: 19.2 kg

Actually this was not really the first, since I did some preliminary tests before...
 

	The load (19.2 kg / 42.3 lbs)...
	...is hooked.
	Ready...??? Go ! Ouch, that's heavy...
	Video of the attempt (4Mb, DivX 5 compressed). The full run lasted 105 seconds. Note the LEGO rulers, both measuring 30cm.

Second lift: 44 kg

This time Jean-Louis organized a "weight lifting party" with several FreeLUG contestants taking part in CC9. He provided us with a dumb-bell as load...

	The load (44 kg / 97 lbs).
	During the attempt. The weight is slowly rising and moving at the same time. Compared to the first attempt, the hoist was geared down 3 times. Total time was thus much longer, 5 minutes for complete cycle. Most probably an heavier weight could have been used, but the tiled floor under the load was not mine, and failure of a part would have been dramatic...
	Video of the attempt (2.5Mb, DivX 5 compressed). To save space and nerves, this movie was 5x accelerated. The full run lasted 5 minutes in real time.

Twinhead

My friend Richard told me about a lifting technique used on ships to move heavy loads along the gangway. Dual hoists are used to lift and shift heavy weights. This method sound interesting so I decided to try it on CC9... As I missed time (and some parts already used in Pimousse), I simplified the design: only one motor was used for each winch, and hoists have only 4 thread. This setup was nonetheless able to lift and move my 19.2 kg load... before failure!
 
Construction details 

	Twinhead is equipped with two winches and two hoists. It is to be placed on the edge of a table while two battery packs on rear act as counterweights.
	Winch details.
	As my rotations sensors were engaged in Pimousse, I used a light sensor facing a black and white tile instead. A bit more difficult to program, but quite effective.
	The hook. It proved to be the weak point, as it failed under load...
	Twinhead, during a 9 kg attempt.

RCX program

Here is the main NQC program. The calibration program measures light levels and leaves values in variables used in the main program.

19.2 kg raising

Video of the attempt (1.5Mb, DivX 5 compressed). Here again, the movie is 5x accelerated. The full run lasted 3 minutes in real time.

When things go wrong...

	During the first try at 19.2 kg, a gear slid on a winch axle. The load went down slowly, but with an awful grinding noise! Listen it in this video... (400 kb, DivX 5 compressed)
	I made a third run at 19.2 kg because I feared that the movie was not so good. It was too much for one axle in the right hook... It went out of its hole, the load fell with a loud noise. Unbalanced, Twinhead itself fell and broke into pieces...
	The failure was filmed...(260 kb, DivX 5 compressed)

(® Pimousse is a registered trademark of "La Pie qui Chante")