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[ Original M.A.D. | Second M.A.D. ]
[ Second M.A.D. ]
Nevin Davis made the first MAD, or Motorized Ascending Device. This was the first and perhaps only motorized ascender whose details were widely published. Others made earlier claims but never published many details (e.g., one never even mentions what the power source was) so I tend to discount them. The M.A.D., however, was well-documented, and certainly exists. I bought the original MAD from Nevin at the 1989 Old Timers Reunion. Without a doubt, this is the most complex, and most interesting item in my collection.
Nevin has written that the MAD was developed for people who
"do not view vertical caving as an end in itself but instead
want only to visit the cave at the pit bottom and then exit in
the most comfortable manner." I've spoken to Nevin and feel
that there was a second motive: to show that it could be done,
and to illustrate that some of the people who had speculated about
motorized ascenders had underestimated some of the problems. When
he built the MAD, Nevin proved that the engineering difficulties
could be overcome.
The MAD is powered by a one horsepower Olsen and Rice gasoline engine. The engine has an integral centrifugal clutch and gear box. Further gear reduction is provided by a set of lathe change gears contained in a fabricated gearbox. The original MAD had a motor-cycle grip throttle, but this was later replaced by a smaller and lighter handgrip. A "kill" switch completes the controls.
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Top View, showing upper rope guide and idler pulley. |
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The is threaded much
like an old-fashioned movie projector - i.e., you have to take
a cover plate off and feed the rope by hand. The rope enters the
top of the MAD through a machined rope guide. From there it passes
a Jumar cam that keeps the MAD
from sliding down the rope when the engine is stopped or idling
with the clutch disengaged. Next it loops around the drive pulley.
Finally it passes around an idler pulley that directs the rope
downward and out of the MAD.
The drive pulley has a V-shaped groove with a 30° included angle. This angle is critical, if it is too large it won't grip the rope, while if it is too small there will be too much friction and the rope will bind in the pulley. Nevin designed the pulley for Goldline and Samson 2-in-1, which were the primary caving ropes when the MAD was built. I think that a smaller angle is needed for the modern, stiffer caving ropes, because I find the MAD slips on them unless one hangs about 15 kg (30 pounds) on the rope. Nevin's articles suggested one third that amount for the older ropes.
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Climbing with the MAD is, well, unique. Fill the gas can first - omitting this step might leave you 800 feet off the pit floor with a 22-pound ascender to haul out. Attach the ascender to the rope, and clip your seat harness to the attachment point. Most people will also want a chest harness to hold them upright. Pull the cord to fire the engine. At idle, the centrifugal clutch will disengage, and you'll be hanging from the Jumar cam. Its best to have a backup (float a Gibbs) in case the cam fails, otherwise terminal velocity is determined by the gearbox friction and lubricant viscosity. Add power, and you're off. Motor to the top, walk the edge, and hit the kill switch. With the MAD, you'll be out of El Sótano de las Golondrinas in 25 minutes, just a couple minutes behind the faster cavers, but hours ahead of the tourists.
| Specifications | |||
|---|---|---|---|
| Weight | 10 kg | 21.5 lbs | |
| Engine | 750 Watt | 1 Hp | |
| Fuel Consumption | 860 meters per liter | 2 miles per gallon | |
| Engine Accessories | 6921:1 Integral Compound Gear Reduction and Steel Centrifugal clutch | ||
| Maximum Engine Output Shaft Speed | 900 rpm counter-clockwise | ||
| Gearbox Reduction | High Gear | 12:1 | |
| Low Gear |
24:1 |
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| Maximum Load | High Gear | 90 kg | 200 lbs |
| Low Gear | 180 kg | 400 lbs | |
| Speed | High Gear | 23 meters per minute | 74 feet per minute |
| Low Gear | 11 meters per minute | 37 feet per minute | |
I've included some construction details extracted from Nevin Davis' article Motorized Ascending Device MAD in The Nylon Highway #19. Believe it or not, the 1971 parts cost for the M.A.D. was only $120 U.S!
[ Original M.A.D. | Second M.A.D. ]
In December 2006, Ken Kramer delivered a second Motorized Ascending Device. James Wells made this M.A.D. using blueprints obtained from Nevin Davis in the early 1970s. James donated the MAD to my collection via other cavers, and it took a while for it to arrive at my house, passing from one caver to another over many months. Until it arrived, I did not know that a second M.A.D. existed.
When
Ken and I opened the box containing Wells' M.A.D., we noticed
that it was not complete. Most of the work had been finished,
but the throttle assembly had not been attached. Nevin's original
MAD had a motor-cycle grip throttle, but he later replaced it
with a smaller and lighter handgrip. James had parts for a grip
throttle, so I decided to use them to complete his M.A.D. I used
my lathe to make a mounting post to attach a motorcycle grip throttle
and a kill switch to the right side of the M.A.D. I also milled
a bracket for attaching the other end of the throttle cable to
the engine. You can see this bracket just above the yellow fuel
cap in the photo.
Ken and I found a broken gear in the parts that came with this
M.A.D., and also found a box and receipt for a replacement part.
We assume that James had started the engine on his M.A.D., and
that it had failed. For this reason, I have not tried to restart
the engine.
Since this MAD followed Nevin's blueprints, there are many similarities, but some differences as well. I decided to describe Wells' M.A.D. using photographs of the two versions sitting side by side.
The rear view shows what the user sees. The most apparent difference is the motorcycle handgrip sticking out from the right side of Wells' M.A.D. James included a copy of Nevin's blueprint for the M.A.D., as well as a number of photographs. Some of these showed the original motorcycle grip design, which differed from my design completion in several ways. Nevin's original design had a second handlebar sticking out on the left, but I did not include this when I finished Wells' ascender.
Here we see the right side of the two ascenders. As you can see, Nevin removed some excess material from the cover plate to lighten the ascender. James' version is about 400 g heavier than Nevin's, part of which is due to using a different engine and a larger fuel tank. Such a small weight difference is not important. Another difference is that Nevin put bushings on his cover plate to help support the two gear shaft bearings. I did not bother adding these when I completed the Wells M.A.D.
The large hole on the right side of Nevin's ascender is where he located his handlebars.
Here are the two ascenders with the cover plates removed. Wells' still has Dykem from the layout process; I haven't taken time to remove it. As expected, the internal working of the two are similar.
This shows the front view of the two ascenders. (The views are not quite equivalent because James' M.A.D. has a larger, rectangular gas tank that holds his M.A.D. in a more upright position than Nevin's). From this angle, you can see why I chose not to add a left-hand handlebar to Wells' M.A.D. - sitting in front of the engine, it would have had to stick out very far to the side.
James and Nevin used different brand engines, but they are both small, integral clutch models. James' uses a much larger fuel tank than Nevin's. When comparing the photos, remember that the rectangular gas tank holds James' M.A.D. in a more upright position than Nevin's.
[ Original M.A.D. | Second M.A.D. ]
