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Motorized Ascenders

Nevin Davis' Original 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 own it!). 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 underestimates some of the problems. When he built the MAD, Nevin proved that the engineering difficulties could be overcome.

Engine side

The engine side. Note the handgrip.

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.

Top view

Top View, showing upper rope guide and idler pulley.

 Front view

Front view, showing drive & idler pulleys and hand throttle.


Cover in placeCover removed for riggingThe 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.


Opened ascender, showing safety cam and clip-in point.


Ascender with rope threaded.

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.

 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 


 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!

James Wells' 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.

Cable bracket in placeWhen 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.

Davis MAD Rear views

Rear View: Well's Second M.A.D., Davis' Original M.A.D.

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.

Right sides

Right Side: Well's Second M.A.D., Davis' Original M.A.D.

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.

Davis MAD Right Sides, cover removed

Right Side, cover removed:
Well's Second M.A.D., Davis' Original M.A.D.

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.

Davis MAD Front views

Front View: Well's Second M.A.D., Davis' Original M.A.D.

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.

Davis MAD Left sides

Left Side: Well's Second M.A.D., Davis' Original M.A.D.

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.