Designer Times
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31. Invention Time - Autopia Automatic Clutch
By 1963 the overweight MK V Autopia cars had been replaced by a lightweight MK VI car designed and built by Arrow Development. The MK VI was the first Autopia car which used the center guide type track eliminating the need for wrap around side bumpers, thus saving a lot of weight. But the MK VI soon began to show problems in both it's design and it's purchased basic service parts. One of these was the automatic clutch, which had been a source high maintenance ever since the Autopia Ride opened in 1955.
The function of the automatic clutch is to allow the single cylinder gasoline engine to idle when the car was at rest, then begin to connect the engine to the drive wheels as the driver pushed on the accelerator pedal. This meant that there was a period when the clutch was slipping until the clutch was fully engaged to the engine when the car was moving a few miles per hour. The clutch would then remain fully engaged up to the maximum 7 mph cruise speed on the track. As the car would slow down the clutch would then smoothly disengage as the car came to a stop allowing the engine to return to idle speed.
The automatic clutch, sometimes called a centrifugal clutch, had been around for decades. It is a common item used on all kinds of industrial equipment. Many manufacturers have years of expertise in building successful automatic clutches. The first MK I Autopia car used a popular automatic clutch made by the Salisbury Clutch Company located in South Gate, California. By the mid-summer of 1955, we were having no end of clutch trouble, and Salisbury was very helpful trying to get their clutch to work properly. But in 1963, we were still tying to get a clutch that would have more than a short life.
I spent a lot of time over the years with the very patient Salisbury folks trying to solve the ongoing problems. I lost track of how many different experimental clutches they furnished to Disneyland, all of which were ruined by our little Disneyland Autopia test drivers. Going from a heavy car to a light car did not improve the situation. Disneyland began trying out clutches from several other manufacturers to no avail. In 1967 one manufacture gave us a fancy test clutch that they said would be better than any other clutch we had tried. This clutch didn't last one week. Now what were we gonna do?
My basic design philosophy was to always combine stock functional service equipment into our own custom framework configurations. This meant that all our service parts would have already been invented, perfected, and were available as stock shelf service parts at practical prices. No point being a boy inventor....I was too busy trying to design unique Disney equipment using stock parts. But this latest clutch failure prodded me into action. Maybe I should take time out and invent a clutch. I'd never invented anything basic before.
I told Arnold Lindberg, Disneyland Maintenance Chief, what I was going to do and was told to start right away. Since I was at Disneyland and faced the long drive back to WED, I had time to think about the problem as I drove up the Santa Ana Freeway. As it turned out, I had lots to start drawing up just an hour later. I had run everything thru my mind about every clutch I had seen in the past (12) years to understand the basic principles. And I now had a new idea as to what might work.
Here's what I figgered out: The crankshaft in a one cylinder engine does not actually rotate smoothly.....it jerks slightly in sync with each power pulse. All the clutches that had been tried had pivoting parts on pins whose axis was parallel to the crankshaft axis. Since these parts were to be affected by centrifugal force to engage the clutch as the engine speed increased, they would vibrate slightly in sync with each power pulse. But this meant that the clutch shoes would attempt to move outward to contact the clutch lining in a chattering manner rather than acting smoothly.
What would happen if I turned the pivoting parts pins 90 degrees to the crankshaft axis? I could interrupt the crankshaft sync chatter. All the moving clutch bits would not be influenced by the crankshaft vibrations. Also, all prior clutches had the engagement shoes rotating with the crankshaft while the clutch lining rotated with the drive wheels. This did not allow the clutch lining to be cooled at idle. If I made the shoes stay still at idle and the lining rotate with the engine, I'd get a cooled lining. I called this gag the "Reverse Polish Clutch", since it was backwards to the way everyone else built their clutches.
It didn't take long to design and build the first experimental MAPO clutch, but it would cost more than the price of the engine! Disneyland said that was OK if it solves the problem. One of our licensed German engineers specified the steel alloy for the clutch pressure plate. I selected a stock clutch lining from a Œ67 Chevy Corvair. This would give us a very generous and cheap service repair part in the future. But the new clutch failed quickly. Seems the engineered alloy was not right for the job. It was a high strength steel which sounded like the thing to do. So I looked into another material and chose a garden variety G3000 class cast gray iron like that used on big truck brake drums. Now the clutch worked like a charm.
Soon MAPO built these clutches by the hundreds, and all future Autopia cars have used this basic design ever since. The lesson learned was that we should not assume that cheap little one cylinder engines should always use cheap little industrial automatic clutches. Disneyland has it's own very special needs. Thirty five years later Arrow Development's Ed Morgan admitted that the cheapest Autopia car turned out to be the one that was so expensive to build originally that he thought Disney was nuts. The clutch story was the opening chapter in this economic reality. Coming up, the next Autopia car design follows the lessons learned in clutch solution.
oOo
Next month: Autopia MK VII
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-- Bob Gurr
Bob Gurr began working with Disney in 1954. He retired in 1981 but occassionally consults for the Company. Since Disney he's worked on the sinking ship at Las Vegas' Treasure Island, Universal Studios' King Kong, Godzilla for the film by the same name and much more. Among his proudest accomplishments he lists "making Walt tickled pink that some of the things he wanted to build actually worked. You could tell how proud he was when he would show off things to his friends and the press. Lincoln and the Monorail were two big ones for him."
Designer Times is normally posted the second Wednesday of each month.
The opinions expressed by Bob Gurr, and all of our columnists, do not necessarily represent the feelings of LaughingPlace.com or any of its employees or advertisers. All speculation and rumors about the future of Disneyland and the Walt Disney Company are just that - speculation and rumors - and should be treated as such.
-- Posted November 13, 2002
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