Bicycles, tricycles, differentials, any thoughts?

  1. davethecave Ouch! That hurts.

    Messages:
    11
    Gloucester
    I'm thinking about building a recumbent trike.
    I am really struggling with the rear axle and have a few questions.

    Is there any advantage in driving both rear wheels? Presumably, if I drive just one wheel, I don't have to worry about differential.

    Do I really need to worry about differential anyway?

    How does a trike cope with corners?
    Does the rider lean in the same way as a bike? Does the outside wheel leave the ground?

    Any thoughts or experiences would be very much appreciated.
     
  2. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    From over 50 years ago when I used to have a trike only one of the rear wheels was driven. I don't remember leaning into corners, but I did used to fall off a lot!

    [​IMG]
     
    Last edited: Apr 15, 2007
  3. Drains

    Drains Yeah, nah.

    Messages:
    7,715
    Location:
    Sefton, South Island, NZ
    If you want to be really smart, build a three wheeled recumbent with the two wheels on the front. Much more stable, and a bit more difficult, cos you need something fancy to deal with the steering, though not necessarily a rack. At least you won't have to worry about a diff though.

    For a comparison of stability, look at a Reliant Robin, famous for rolling, especially when handled by bikers without a car license, at speed (eg various mates of mine in the 80's lol), versus the old Morgan 3 wheelers, which were raced, and stayed glued to the road.

    Check out also
    http://www.windcheetah.co.uk/
    http://www.kinetics.org.uk/html/recumbents.shtml
    and for designs
    http://www.recumbents.com/wisil/whatsup.htm
    it's all there!

    I just googled "recumbent"
    Forget that. Google "recumbent trike project". More plans and pics than you can shake a stick at.

    Si
     
    Last edited: Apr 15, 2007
  4. Nial Member

    Messages:
    45
    Edinburgh

    You might get some ideas here...

    http://www.atomiczombie.com/



    Nial.
     
  5. cobminor

    cobminor Member

    Messages:
    458
    West Sussex
    A trike copes with corners with a diff, that's what they are for, to enable the wheels to turn at different speeds.

    With only one wheel driven the thing will try to go in a circle and you will have a pull on the steering.
     
  6. Justme

    Justme Member

    Messages:
    2,798
    Location:
    Pwllheli Wales
    Drive the single back wheel then.

    Justme
     
  7. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    Be that as maybe, certainly kids trikes only drive one wheel, maybe more specialists ones have a diff.
     
  8. cobminor

    cobminor Member

    Messages:
    458
    West Sussex
    Kids trikes are built down to a price, the kids dont care or notice.
     
  9. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
  10. davethecave Ouch! That hurts.

    Messages:
    11
    Gloucester
    Thanks for all the responses and the links.
    Atomic Zombie looks good and they have plans.
     
  11. migmag

    migmag Member

    Messages:
    700
    North east
    Why would need a diff if you use two convensional drive wheels the existing hub rachet would remove any scrubing as they would run independantly...........
     
  12. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    The hub ratchet only transmits drive from the chain to the axle and allows freewheel on overrun, on kids trikes it drives one rear wheel, the other wheel is not driven and runs free. On posh trikes the chain drives the diff (like the pinion drives the crownwheel in a car) which transmits drive to both wheels, there is no differential action in the ratchet.
     
  13. migmag

    migmag Member

    Messages:
    700
    North east
    I did not say there was a dif in the rachet cos it would be a diff and not a rachet.

    What I am saying is why go to the expence of buying a diff when you could engineer it to be twin wheel driv..

    Having said that you could us a diff from a quad????
     
  14. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    What exactly do you mean by twin wheel drive? Both wheels locked together? two chains? two sets of pedals? two riders, each driving one wheel?
     
  15. Haze

    Haze is it can be hugs tiem ?

    Messages:
    638
    West London
    it wouldnt turn very well without a diff and twin wheel drive.
     
  16. shenion

    shenion Tool Pack Rat

    Messages:
    7,588
    Location:
    Stone Mountain, GA USA
    You drive both wheels. Each wheel has the ratchet from the gear mechanism. AFAIK, you would just remove the gear and axle and run a shaft through both. Then drive shaft with gear in the center.

    That will drive both wheels but allow the outer one to turn faster when turning.
     
  17. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    Still not 100% clear. If you mean have one rear sprocket driving two pawls, each driving its own ratchet wheel, with each ratchet wheel in turn connected to one rear wheel then what would happen is this:

    Driving in a straight line power would go to each wheel equally.

    Say turn right, the left wheel would be on the outside of the curve, will try to go faster and overrun the ratchet, which sounds fine, but drive will only go to the right wheel, which is on the inside of the curve, and this will try to push the trike to the left.

    So you reall do need a diff if you want to corner smoothly.

    As mentioned earlier, kids' trikes only drive one wheel, the other is free, this will cause oversteer in one direction, understeer in the other.
     
  18. migmag

    migmag Member

    Messages:
    700
    North east
    How will it push to the left??

    Have you done any prototypes??

    All the recumbants I've seen even off road BMX stlye thing are one wheel drive with two wheels at the front....

    I honestly think you need to start chopping some scrap bikes up to get your head around the problem.
     
  19. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    One wheel drive no problem.

    This thread is getting confused, people talk about driving two wheels and then it swaps back to driving one!

    I think you really need to read all the posts properly and in context to get your head round the subject.

    It will pull to one side if one wheel on a two wheel axle is driven. This is how tanks are steered, they slow the tracks down on the left to turn left.

    And no I haven't built any prototypes, I don't need to to understand basic mechanics.
     
  20. Drains

    Drains Yeah, nah.

    Messages:
    7,715
    Location:
    Sefton, South Island, NZ
    Er... I'm not sure tanks have wheels that steer rtb.. I don't think you can use that analogy and get away with it! Tanks use skid steer:- totally, utterly, nothing to do with three wheeled bicycles! Sorry, tricycles.:D

    The basic difference between a twin rear wheeled bike with a diff and one with two freewheels is that when going round a corner, the diff bike will drive the faster (outer) wheel, and the freewheel bike will drive the slower (inner) wheel.

    The latter bike would probably show only a small tendency to pull, because the front steering wheel is pointing the bike in the right direction (not like a tank). Which you could easily get used to/ allow for.

    But if you're really tanking it (no pun intended) round a corner and go onto two wheels, you will lose traction and your little legs will go round at the speed of light. When your inner wheel comes down, the bike will really pull, and you will probably crash into a double decker bus coming the other way. Fini.

    Two wheels at the front is generally, better.
     
    Last edited: Apr 29, 2007
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