Simple "V" belt motor drive does work

[professor]

The idea was to get away from the chains, idlers and jackshaft set up I had been using because they have a lot of drag, just rotating all that.
The bike is a 26" Mongoose mountain.

I mounted a 20 inch bike rim onto the back wheel spokes, motor on a rack with 2 inch pulley, switched power ( no controller) and the thing was too fast, slow pick up too. Had to pedal full speed in high gear to get the motor up to speed.
Gear ratio too high, went to a 1 1/5" pulley and the ratio is still high but useable if I had a controller.
Do get some belt slip because of the very small drive pulley ( am using a 3/8 belt with a pulley for 1/2 inch belt to get a smaller effective size- belts and pulleys are sized in 1/8 inch increments, therefore, I am using a 3L belt and 4L pulley). Ideally, I think a 20 inch rim attached to a 20" wheel and a 2" pulley would be best, along with a controller. I am using a HT clutch lever to work the belt tensioner.
As for drag, I haven't gotten to do a battery range test to compare because I goofed up one of them, but I think drag must be less, I can pedal with the motor off and engaged and it seems like only slightly more work than spinning the chains (with the freewheel not spinning the motor) as before.

 

[Wheres my dog]

How in the world is that rim connected onto the larger rim?

Pressure fit between the spokes?

 

[MikeJ]

Hi Professor -

It's good to see you again. I am thinking along the same line as you for the long bike I have running around in my head. I am thinking that a 1.5 inch pulley and a rim from a 24 inch wheel will be the right ratio for me. If I want more speed, moving to a 2 inch pulley should be easy to do

Did you find any concerns with the clearance between the driven rim and the bike frame? Obviously, you got the wheel rim to work; did you have to narrow the space between rim edges?

MikeJ

 

[professor]

It's an evolutionary fit- you just leave them together for a couple million years then-presto! Success! Just kidding- a little jab at today's fairy tale.

The rim is held on with equa-distant tabs braised onto the "Pulley"- between pairs of spokes, plus tie wire on every spoke. I have been hearing a little click noise as I go, so glueing the attachment points is next. Apparently there is yet some slight movement.

As I said, ideally, a same size rim (Pulley) could be riveted to the drive wheel's rim and this would get away from spoke mounting. However, frame widening would probably be needed to accomidate the xtra width of the drive "Pulley".

Mike- I did widen the rear traiangle on the pulley side with frame re-working and on one section - heating the inside of a tube and collapsing it there, with a vise-grip.

You are going the right direction with the 24 inch wheel too, I think.
I thought about using a 24 inch rim for my pulley but the V brake post was in the way, besides needing spacers to get the pulley out away from the tire.

The thing about the 1.5" pulley is the smaller belt wrap allows more slip verses the 2" pulley. But with a controller, if you take off easier- slip is lessened.

 

[professor]

Mike I just noticed your question about the rim width.
No- I sure didn't want to narrow it.
The belt rides very close to the rim lip but seems fine. It is close to the knob edges of the tire too but again, doesn't hit. A street tread would give more room.

 

[happycheapskate]

I like it. I have been thinking of making a similar bike, but using an AC motor, a 12v deep cycle battery, and an inverter.

You can connect the rim to the spokes using machine screws and washers, surely. How do the Wizzer wheels work? Maybe you could buy one of those.

I have thought also about using 2 20" wheels. That should be easy if you have 2 steel rims or 2 aluminum rims and access to a welder. Clamp them together, and make a bead for every spoke hole. Then you can just lace and true it like a conventional wheel (use one rim or the other, not both.)
You would probably do best with a coaster brake, unless you use two narrow kids BMX jr wheels, or a Jr wheel welded to a wide BMX rim.

Rivets suck.

 

[professor]

Happy, the thing with the inverter is they are not efficient.

 

[happycheapskate]

Well, I don't know much about motors.

How about a 12v windshield wiper motor?
A lot of people are using those for the giant battle robots.

How about using the motor and belt to turn a hub as a pulley, or small BMX wheel, which uses its freewheel to turn a Happytime ragjoint cog. When the bike is pedaled, the freewheel will, well, freewheel. That ought to give you plenty of reduction options, and a full coasting abillity.

 

[JzzzCustom]

Professor you should look at pulley driven CVT you could change the gear ratio
as needed Im looking into this type of drive to run an electric motor to the
rear axle on a trike im working on