2wd Motorized Bicycle

Discussion in 'General Questions' started by BigBlue, Dec 9, 2013.

  1. BigBlue

    BigBlue Active Member

    I decided to start my own thread as I was posting to another members thread and wanted the information in one place. This is a proof of concept idea. I'd like the ability of using my motorized bicycle off-road.

    I have been thinking of building a 2 wheeled drive (2wd) motorized bicycle for some time. I am currently finishing building a custom longtail motorized touring bicycle. It will be powered by a 51cc (3.2hp) Zenoah Goped GZ51N that I purchased several years ago. The engine will be connected to a Staton 18:1 dual output gearbox. I plan to a 72cc (4.6hp) Zenoah leaf blower engine that will have to have a custom mount and flywheel made, but that's another post.

    My idea is to connect a flexible shaft to the outside shaft and connect it to spiral gears that power the front wheel. Several companies have sold bikes in the past with this concept - BWA, Jeep and Ovation. Christini currently makes a similar bike, as well as a 2wd motorcycle. Some of the other companies used plastic straight bevel gears. Here's some sample pictures of other companies products, showing the front drive. This is how Jeep, BWA, Christini and Ovation, attach(ed) the bevel gears on the front wheel:
    131_0601_03_z jeep_rubicon_classic_awd_bike front_wheel.jpg frontWheelDrive.jpg front-wheel-drive-bevel-gears.jpg legacyfdrive.JPG

    The first picture is the Jeep version; the 2nd is the BWA version; the 3rd is the Christini version; and the 4th is the Ovation version. it looks like the Jeep and Christini are the same or similar products.

    I recently purchased a set of spiral bevel gears from Ebay. The were $15.39 with free shipping. If this idea pans out, then I'll purchase some better quality gears.

    Here are the specs and pictures of the spiral bevel gears. The depth of the crown (large gear) is 0.325 in the flat area. The flat area on the face of the large gear between the bevels is 50mm.
    Gears1.jpg Gears2.jpg Gears3.jpg GearSpecs.jpg

    The last picture shows a comparison of the drive side freewheel (15t) to the large spiral bevel gear.

    My idea with the spiral bevel gears is to mount the small gear like the Jeep and Christini. I plan on using a BMX flip flop hub on the front wheel and make a custom mount that screws onto the small side of the flip flop hub. I have some 2" (50.8mm) aluminum rod and need to purchase a 30m X 1 tap for $36.88 on Ebay to make the adapter. Some of the BMX flip flop hubs are 110mm wide and have a small 30mm freewheel and a large freewheel. It is also possible to remove a nut or spacer on some hubs to reduce the width to 100mm.

    I would have liked to use a 135mm front fork and a freewheel hub, purchase a ready made 55mm disc brake adapter, but it would have left 1mm between a 5mm bolt head and the bevels. The spacing for the bolts on a 55mm disc adapter is 44mm, the bolt heads add another 9mm and the area between the bevels is 50mm.

    My plan cut the shaft off the rear of the large gear with a fiber wheel attached to a die grinder which will be mounted onto a tool post holder on my mini lathe. I then will have to purchase some M42 Cobalt drills and end mills to work on the large spiral bevel gear, so I can mount it to the adapter with some 5mm bolts.

    For the small gear I'll make a shaft that steps from 11mm to 5/8".

    I have to purchase some additional tools for my lathe before I can work on this idea and also have to finish my current build and work on getting the 72cc engine mounted.

    Other uses for the bevel gear drive that could be connected to a PM motor to generate electricity. The motor could be bolted to the front fork. Or after all the expense and time, use the flex shaft to power a blender:)


    AKA: BigBlue
    Last edited: Dec 9, 2013

  2. bluegoatwoods

    bluegoatwoods Well-Known Member

    Sorry. I'm not quite enough of a gear-head to digest everything you posted there.

    But it looks like you're on a project that'll be really, really cool if you can make it all work well.

    Best of luck. I'll be rootin' for you.
  3. jaguar

    jaguar Well-Known Member

    2wd would give better traction but would reduce engine power just from the added friction. These small engines dont have additional power to lose.
    But it looks like a fun project. It would make it safer to ride on snow or ice.
  4. butre

    butre Well-Known Member

    I think 2wd would sap too much power from one of the typical 50cc 2 strokes but with something incredibly torquey like a Predator 212 geared to about 10:1 then I think it may work.
  5. HeadSmess

    HeadSmess Well-Known Member

    use a heavy cable ;)

    http://www.fdrive.com.au/docs/Sect 12 Flexible Shafts.pdf

    note the 1/2" cable is only rated for 1.5hp at 1500rpm. power declines with lower speed. flexibility declines with diameter :( (im a parrot! squawk! aarrrk! aRRRRRKKKK!!!)

    roughly 3:1 with the bevels...(spiral bevel and helical gear ratios are not always calculated from number of teeth!) and at 500 at the wheel, on a 26" thats over 60km/h! (dual contra rotating cables one on either side of wheel?)

    i been obsessed with a central dif but...if you could get your drive from the rear cluster... make sure the front is geared say, 5% higher than the rear, and any slip in a straight line will be taken care of with the rear freewheel! it will be a front wheel drive, but as soon as you lift the front...the rear is engaged :)

    what you do not want is the tendency for the front to slow down and skid as you take a turn.

    i just deleted a whole page cus im not giving away my ideas now!

    anyways. tungsten carbide tools usually do the job on hard stuff. need a diamond file and to get them really sharp, not normally good practise with carbide. it breaks. light cuts, run it full speed.

    you know to hold a gear by making a ring that just takes the gear, slitting it, and chucking with the ring? ensures no runout. mark the ring! you end up with a collection of them!

    you may be lucky and find that its only the teeth and the central hub thats particularly hard. cant see it in the pic, but therell be a distinct line where the temper starts if so! or try the file test. i can see some scars in one pic!

    get it right, friction will be minimal. a cables not good for that ;)

    but...i doubt you would gear 2wd for road use and expect 60km/h... more like, gear it down so it will crawl up any hill while lugging a dead moose... let the engine do some work.

    id be ferpectly content with a HT48 on a 44t for most of my riding... maybe a 52 or something for bush bashing...
    Last edited: Dec 9, 2013
  6. BigBlue

    BigBlue Active Member

    I plan on eventually using a 4.6hp Zenoah engine. That would give me over 2.0hp per wheel. I can make some minor adjustments to the intake and carburetor and boost the hp output.

    A new thought - I could probably grind out the center of the crown gear to 29mm and have a machine shop thread it for 30M X 1.0 or possibly try to tap it myself. That way I wouldn't have to make an adapter. I could just screw the crown bevel gear onto the flip flop hub. In my OP, I figured the depth of the crown gear face to be approximately 0.325 inches. Measuring the threads on my 15t freewheel, the depth of the threads are approximately 0.354 inches.

    AKA: BigBlue
  7. BigBlue

    BigBlue Active Member

    I've been looking at these transmission type flex shafts which give all the technical data: http://www.suhner-transmission-expert.com/site/index.cfm?id_art=14308&vsprache=EN There are different types of flex shafts.

    Thanks for the tip on gear ring - didn't know that.

    Yes there is a distinct line approximately 3mm from the teeth. I'll have to try the file test. it would be nice to be able to grind and tap the bevel gear. As I posted above, I think it would be easier to thread the crown gear and screw it directly onto the flip flop hub without using an adapter.


    AKA: BigBlue
    Last edited: Dec 10, 2013
  8. LR Jerry

    LR Jerry Well-Known Member

    Blue is your build going to be able to switch between single and all wheel drive? I was thinking about the all while bikes and thought about the things trick riders could do on them. Think how cool it would look somebody riding a sustain front wheelie.
  9. BigBlue

    BigBlue Active Member

    All wheel drive. But I wouldn't rule out the possibility of developing an engagement mechanism so I could go single drive.

    AKA: BigBlue
  10. BigBlue

    BigBlue Active Member

    Did a file test on the back of the gear. Was able to file a nick into the central hub that will be removed.

    AKA: BigBlue
  11. windtrader

    windtrader New Member

    how is this going?

    I'm curious how this sort of drive system is working out. What is the latest? Thanks
  12. Luka

    Luka Member

    That gear setup is just like an old fashioned "egg-beater" drill. (Or egg beater, for that matter. LOL) This is just personal opinion, but I don't think I'd trust that setup to last very long if you are over 150 pounds, and/or do much steep hill riding.

    I would suggest that you instead put two motors on the bike.
  13. windtrader

    windtrader New Member


    After checking this option out a bit more, it may be unique not all that practical.
  14. LR Jerry

    LR Jerry Well-Known Member

  15. windtrader

    windtrader New Member

    amazing engineering

    That thing is amazing. I had to watch the video twice to even see how the front wheel power was being delivered. That took one hell of a lot of time and energy and precise fitting to all work. It must add a decent amount of weight with all the extra gears and shafts and such. Still a very unique build.
  16. LR Jerry

    LR Jerry Well-Known Member

    Christini now makes a bicycle. The cool thing is you can switch from single to two wheel drive with a switch.
  17. HeadSmess

    HeadSmess Well-Known Member

    considering its electric, i wonder why go to all that effort to drive the front wheel...when a hub wheel front and back does much the same thing? with less mechanical losses.

  18. LR Jerry

    LR Jerry Well-Known Member

    Well it is a shifter bike as well. All this is being done with a single motor instead of two
    Also he's got two batteries. This bike should really have some good range and climbing abilities.

    What I think is the most important thing is this build could be done with a gas engine. Would be cool to see that done.