Friction Drive Ideas

[powdersummit]

I've been doing some pondering on how to make a friction drive system that would work good for steeper off road conditions and wet conditions using a heavy tread mountain bike tires. I know neither one of these situations are a prime application for a friction drive but the installation is just so darn simple.

Idea 1: Using a larger drive wheel with a "Gear" reduction. The standard spindle size is anywhere from 1" to 1 3/4" from what I can find. My idea is to use a larger spindle somewhere from 3" to 4" but gear things down 2:1 or 3:1 for a slower spindle speed. This would give a larger contact area and lower rotational resistance.

Idea 2: Use a grooved rubber covering on the spindle. Take a look at the coefficient of friction of steel on rubber and rubber on rubber. I can't remember the exact numbers but rubber on rubber is almost twice what steel on rubber is. It is even better than tires on asphalt.

Idea 3: Use 2 driven spindles. By using 2 spindles there would be greater surface contact for better grip on the tire and less chance of slippage. You would link the spindles on a 1:1 belt or chain.

These are just some of the ideas that have been floating around in my head. My ultimate idea is to use all three idea on a single setup to put on a full suspension downhill mountain bike for some really good off road action.

Carl

[ibdennyak]

Few more ideas I haven't gotten to yet.....mount a pneumatic scooter tire to a multispeed hub. I have a 3-1 reduction box and a scooter wheel and tire, and a Sturmey Archer just waiting to be combined. Should work pretty well.

[Richard H.]

I know neither one of these situations are a prime application for a friction drive but the installation is just so darn simple.

~~

My ultimate idea is to use all three ideas on a single setup to put on a full suspension downhill mountain bike for some really good off road action.

Not to be a naysayer but I'm seeing cross purposes here; it doesn't sound like using friction drive to get what you want will be that simple at all, especially implementing and configuring all three ideas outlined. It seems like gearing a chain drive system for wet, off-road use would be far simpler with a whole lot less frustration.

ps
friction drives are great in the right context but they all slip to some degree in the wet, it's just the nature of the beast.

[powdersummit]

ibdennyak - I had thought of using a pneumatic scooter tire as a drive spindle, you would have some great contact area. Using a 3 speed hub with the tire would be a good idea also. I really like the idea of the internal gear hubs (price isn't bad either) but for a friction drive you would be running higher RPMs and I'm not sure how they would hold up. If you do manage to make one I'd love to see it.

Richard H. - I know that doing a chain drive would be a lot easier for setup on a single bike. I really like the thought of being able to swap drive units out and being able to use them as loaners on friends bikes without having to reconfigure their rear axle/wheel. I know that there is going to be slip at times no matter what I do. The idea is just to maximize the "hookup" between the tire and the drive spindle.

This may seem like quite the project but I do have a full machine shop at my disposal. One of the benefits of being shop supervisor on graveyard and not all the machines are being used at night.

I would like any constructive criticism/ideas before I start a main design process and start cutting metal.

Carl

[Alaskavan]

I can't find the thread, but somewhere on the forum is a bike with a scooter motor mounted on a rack using the scooter tire to drive the bike tire.

[ibdennyak]

ibdennyak - I had thought of using a pneumatic scooter tire as a drive spindle, you would have some great contact area. Using a 3 speed hub with the tire would be a good idea also. I really like the idea of the internal gear hubs (price isn't bad either) but for a friction drive you would be running higher RPMs and I'm not sure how they would hold up. If you do manage to make one I'd love to see it.

Carl

Yep, there is the speed issue. My tire is slightly over 6 inches diameter. I am thinking 4-5 to 1 ratio for the speed I am looking for. The hub would be turning at 12-1500 rpm. That is substantially higher than the design speed, but Professor and several others have been using them at this speed successfully as an intermediate transmission. This is also the max speed, so normal speed would be less. I am hoping that with attention to lubrication, it would have a reasonable life span at 8-900 cruising rpm.

I like the simplicity and portability of FD, but the problems for me are slippage in wet, and single speed nature. The pneumatic tire spindle should minimize slippage to a manageable degree, and if I can unitize the thing, it should be easy to transfer from one bike to another, not to mention eliminating the wear points of chains with high mileage applications. Also, from a legal aspect, the laws that actually spell out the nonshifting are written assuming that the average bicyclist doesn't have the skill to clutch and shift a transmission such as found in a motorcycle. With a handlebar mount shifter (same as a front derailleur) there should be less objection to that aspect. I intend to run a Subaru Robin 35, so keeping it in its torque curve is helpful.

I at one time did own and drive a Mack dump truck with a quadraplex twin stick that I successfully shifted.....while smoking a cigarette, so I feel confident that I personally can handle the shifting aspect. To those who aren't familiar with the quadraplex, it is a 20 speed, non synchronized transmission that is shifted with two levers, one of which is usually shifted with one arm through the steering wheel. I feel that if I promise not to smoke while twisting my shifter, I should be reasonably safe, and add to my general well being by not being exposed to all the noxious chemicals found in tobacco.

Anyway, that is my plan to combine the advantages of FD, and eliminate or reduce the disadvantages.

[powdersummit]

ibdennyak - It sounds like you have most of the details worked out. I'll be looking forward to your build thread. What size drive tire were you planning on using? About the smallest I could find in a pneumatic tire was about 8 inches. That should work good for your 4-5:1 gear reduction.

It would be nice to find a material that could conform to the tread of the bike tire for drive spindle. Maybe something that you could heat up with a heat gun and it would conform to the tread of the bike tire. Some kind of heat activated memory foam. It would more or less be like knurling on a lathe only it would conform to the tread of your bicycle tire.

Just kind of an odd thought before I head off to bed

[ibdennyak]

The tire I'm looking at is from an electric Goped. Diameter is a bit over 6 inches. That is about the smallest suitable tire I could find too. Tires can become bulky very quickly.

I've thought about the cogged tire too. The really aggressive mt. bike tread would seem to be ideal, but in reality seem to slip the worst. I guess your cogged idea is some what happening by the pattern on the spindle deforming the tire temporarily. Maybe steel tires and pneumatic spindles.

Actually, my parents had a Jari sickle mower when I was very young. It used a cogged spindle engaging a cogged set of drive wheels. It did work very well, even in mud, but the non pneumatic nature of the tire would make for a rough ride I think.

[darwin]

In wet weather even your brakes will not work if rim brakes, guess my point is your crazy to ride these in traffic when its wet out.

[ibdennyak]

Actually I am more comfortable with the term psychotically challenged. I agree that rim brakes with steel rims are less than suitable. I have had pretty good luck with alloy rims with the right pads. Obviously they aren't 100%, but not too bad in the wet. I seem to need about 1 revolution before they grip with any real authority, but after 2 revs, they are almost normal. It isn't any worse than driving on ice....slow down, and preplan farther ahead. The biggest objection I have is the squealing I get when they do grip...sounds like I am torturing a half dozen cats in a barrel.

My rim brakes do very well, almost the same as dry as long as I don't have a buildup of dirt or road oil on them. I drag them occasionally to clean them off.

My objection to discs is pad wear. I go through a set of pads in a month or two.Not the worst, but I think I have found something better. The scooter I got the wheel from had a very nice floating caliper on it with the pads having about 6 times the area of bike calipers. I put it on the front of the stretch, and haven't noticed any appreciable wear so far. Plus it takes less effort to apply, and modulates very nicely. Also, the cats finally escaped. I did have to fabricate an adapter to mount it, which was a time consuming affair, but am happy with the results so far. BMI sells the pads and calipers, so I shouldn't have an orphan either.