Weaknesses in Beidelman/Flatmo IPU???

[DrDiabolical]

So I have finally reached the point where I can ride my new machine. I tried it out and immediately discovered several weaknesses in the drivetrain. The machine is a "tadpole trike" with two 5 ft. dia. front wheels, and one 21" rear steering wheel salvaged from a 1973 Yamaha. Each front wheel is powered independently by two pilots sitting in tandem. There are 4 pilots total, but no combining shaft or diff. Each pilot powers an "Independent Pedal Unit" based on the ones used by Beidelman/Flatmo/Funguy at the Kinetic Sculpture Lab. Basically, its the bottom bracket, chainstays, and part of the seatstays from a mountain bike. The IPUs are welded to the frame rails of the machine which are made from rectangular steel tube similar to a boat trailer. The chainstays are welded to the frame just behind the bottom brackets. The Seatstays are welded together with a 5" wide bridging tube about 4" up from the dropouts, then that bridging tube is welded to the frame of the kraft. This positions a modified bike hub just under the frame rail of the kraft. I'm using a standard freewheel on the right, and a welded-on sprocket on the left. The left sprocket drives a chain connecting the IPU to a jackshaft. Two IPUs drive each jackshaft, then the jackshaft drives a chain to a halfshaft bolted to a wheel. The gear reduction puts me at less than 5 gear-inches in low.

Here's the problem. When I drop the machine into low gear and apply power, the chainstays and seatstays of the IPU flex like crazy and absorb at least 1/2 to 3/4 of a pedal revolution at about 10 ft/lbs of input force. I expected that they would, given the colossal forces involved. But I have noticed that none of the CA machines using a similar setup have any additional bracing in this area. Am I doing something wrong? Or do theirs flex that much too? I doubt the CA teams are dealing with flex. It was a major issue for me when trying to ride up a 10% grade on asphalt and felt like I was about to tear the drivetrain apart.

I should mention that the rear IPUs power chains that run forward to the jackshafts, while the front IPUs power chains that run rearward to the jackshafts. Therefore, the rear IPUs are in compression, while the fronts are in tension. Yet both flex wildly. Any insight or experience with this type of setup would be helpful. I'm about to just brace the hell out of everything.

Thanks,
Dr scott Diabolical

[Elliot]

Hey Scott. I'll be no help at all. This just happens to be the day I drop in for my irregular visit to see if anybody has posted anything. And I cannot speak for anyone else.

The layout of your vehicle sounds excellent to me -- except for the lack of high speed gears, which you may not have any use for.

I understand your mounting of what I call the "rear triangles". A common arrangement. I did this once, and it seemed to work fine. But in that vehicle I failed to have my gearing anywhere near so low as 5 G.I. Generally, if it flexes it needs to be stiffer!

In most of my builds I fasten the mechanical parts directly to the frame. I use one-piece cranks, and install them in a piece of automobile muffler tubing that's almost the right size. Front derailers can be finicky, but rear derailers are remarkably tolerant of home-made mounting.

Any chance you can post pictures? And/or describe which direction things flex? Sometimes the Devil is in the details.

[DrDiabolical]

Elliot,

Thanks for the reply. I'm using single 2x3" steel frame rails (one per side) instead of a pair of 2x2" laddered per side. Otherwise its almost exactly the same setup as Funguy for the frame rails and "rear triangles". I'm not having a problem with the bottom brackets or crankarms. Those are working well. As are the jackshafts. I was having a problem with flexing in the 1" go-kart axle half-shafts I'm using, but I solved that by adding and relocating the pillow block bearings as close to the sprocket as possible. Good and solid now.

The weak spot dejour appears to be the ends of those "rear triangles". I can see the chainstays visibly bow and move sideways when power is applied. I thought maybe I missed something, but I watched the video of "Revenge/Wrath of Funguys" in the mud pit at Corvalis. And I can see by the way Mr. Slayton is pedaling that he probably has the same problem. Maybe to a lesser extent due to differences in gearing, but its still there. When I get a chance, I'm going to brace the hell out of everything and tie it as much as possible to the frame rails. Then I'll look for the next weak spot. I'm expecting a chain failure at some point. I'm at sub-four GI right now and I think I can get it even lower. The goal is to Ace-ride out of the lake and up a 40% grade with minimal effort. Nobody else in CO can even come close to doing it. And I want to administer a definitive kinetic ass-kicking the next time I race.

High gears aren't an advantage here in CO. Most of the rides I have scheduled are parades. And the LKSR land course is less than 1/2 mile. Its essentially a boat race that occasionally climbs hills. So a top speed of 10 mph is fine for a konveyance with a gross loaded weight of 1600 lbs. If I need to go faster, I can change my jackshaft sprockets in about 5 minutes.

If I can find your personal email, I'll send you a few photos. I'm putting in the steering this weekend.

Thanks,
Dr. scott Diabolical
evil genius
metal sculptor

[Elliot]

I skipped the mud in Corvallis this weekend. Been stuck in that before; don't need to do it again. Instead, I conquered their sand dune while sipping a glass of lemonade.

You can try sending pictures to elliot.naess@att.net.

[DrDiabolical]

LOL! I just watched the video of last year's sand dune climb. Hoosier tires work on dirt & sand, don't they?

I also saw that FunGuy blew up his drivetrain twice trying to get up the dune. I couldn't see details, but the fact that he threw chain #1 (the chain connected to the pedals) tells me that his "rear triangles" flex as much as mine do. Bummer. I hate it when I benchmark something that looks fantastic but doesn't work very well. Time for significant bracing and/or re-engineering.

I'm also starting to think about how to address the sand. My main wheels are only 2" wide. They work great on hard surfaces, but I know they'll sink in sand. Ethafoam looks like a great solution until you consider the $$$. Currently out of my budget. I'll have to experiment with other materials and designs. I've seen a few WW-1 era solutions that look promising.

I'll send photos to your email adress next week. I'll be in the Lab all weekend rigging the steering and inventing a way to get up on the silly thing.

Dr. scott Diabolical
evil genius
metal sculptor