DIY Friction Drive Experiment

Here's a pic of the mockup. It's the same as the finished version except
the rope i used as a belt is looped thru the frame in the pic.(DUH!)
In the final setup the belt goes behind the brake caliper with 3/16"
clearance on both sides. That ain't much, but it's enuff.
 

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What pulley sizes & final drive ratio are you running here in the pic (using a vbelt, not the rope)?
I had a whizzer sheave on 700c wheel with 1.5" vbelt pulley but the gearing was way too tall w/subaru robin eh035. When I made my own same size rim to rim pulley the gearing worked out much better. To test for the final drive ratio, mark your engine pulley & roll the drive wheel one complete revolution (from vertical valve stem around to vertical valve stem) with weight on the bike. Count how many times the engine pulley spins around.
-Lowracer-
 
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Looks like my reply just got sent to the administrator, so I'll have to repeat it.
My primary pulley is 7/8" made from 2 inverted belleville washers with a 1/4"
spacer 3/4" in dia. the 3L600 belt wedges in a 1/16" from the spacer, hence 7/8"
Since the tireless rim is 15.5 inside the ratio is about 19 t0 1.(hill/town pulley)
I haven't yet used my 1.25 hwy/flats pulley which can be switched in 2 min.
It should cruise at 22mph@4200rpm with about 45@8000rpm. It's really meant
for my 52cc, but should work for the gx35 on the flat.
If you plan to mount an old fric. channel, you'll have to cut some very precise
spacers,( I used alu tubing from an old pr. of crutches), and find a suitable
shaft.
I may have led you to believe the is easier than it is. Some very close tolerances
are involved. My initial break down resulted from a part 1/32" off. That fixed, it
works just fine now.
the trick on the pulley is 8 radiating grooves from the hole 1/64" deep. These
grip the belt without wear making small dia. pulleys possible without the need for
cogged belts or pulleys. I can even use 5/8" for the really steep stuff.
 
:giggle:P.S.
It's a lot simpler to do the math than counting the wheel going 'round. The actual ratio is 17.7 to 1, my bad.
 
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rawly old,
Sounds good...I like the way you solved the small vbelt pulley challenge.
I too do the math 1st using the online ratio calculators. Vbelts ride into the pulleys so there is always a degree of inaccuracy trying to do just the math.
The rollout method is more accurate & never equals my math (but close).
Cheers
-Lowracer-
 
:confused:Golly, they have calculators? Now what am I supposed to do with all these pencils?
 
Lowracer,
Funny u should mention that, I too have just converted an old fric-drive
to a v-belt with a 20" bike rim for a sheave. Geez, it works GREAT! My
gx35 would only do 23 mph with a 7/8" fric roller on the flat. Same
engine with the belt, 33 mph. Woohoo!

At 8000 RPM, a 7/8 inch friction roller has a top end of about 21 MPH.

Using a 7/8 inch primary pulley, and an (approximate) 18 inch secondary pulley results in about 20.5:1 reduction, with a top end about 30 MPH.

A 1.25 inch roller would be equivalent to your pulley setup.
 
Ah yes, but my secondary pulley is 15.5" giving a ratio of 17.7 to one
yieldind a theoretical top spd. of 34.8 mph. Actually, as the belt never
quite makes contact with the inside diameter of the primary it may be
closer to 1". Remarkably, the belt does not need to be terribly taut to
function well. AS a result it pedals with considerable more ease than a
friction drive.
 

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Loquin,
Perhaps this diagram will clarify how my primary pulley works.
The belt effectively wedges to the sides of the pulley without ever
contacting the center
 

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What, no comment?
you know a bunch of people told me I couldn't build a better belt drive than
G.E.B.E, but I have. It's sturdier, faster (with equivalent engine), and cost a
a heck of a lot less, despite some unforeseen prolems in the making.
 
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