Bicycles, tricycles, differentials, any thoughts?

  1. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    I can get away with that analogy - tracks only skid because of their length, OK - try disconnecting the brakes on one side of a car and see if it steers or not when you apply them!

    I agree that 2 freewheels will drive the slower wheel, that's what I said.
    The diff doesn't drive the outer wheels faster, it compensates for the fact that they go faster by allowing the carrier and planet wheels to rotate about the sun wheels.

    I agree that the effect would be slight on a trike, in an earlier post I expressed suprise that they use diffs on trikes, but research showed they do.
     
  2. Drains

    Drains Yeah, nah.

    Messages:
    7,715
    Location:
    Sefton, South Island, NZ
    Sorry to get picky.... I didn't say the diff drives the outer wheels faster. Wot it does is drive (or really, put a greater percentage of power to) the faster moving wheel. Hence when you lose traction in mud it's the spinning wheel getting 100% of the power. The non moving wheel gets none. So you stop.

    Unless of course you have a limited slip diff, which ensures both wheels get some power, so you should keep moving.

    And I still say skid steer has nothing to do with tricycles. As you say, tanks steer by braking. Brake a car on one side etc etc. You will have noticed that when your front brakes are uneven, the steering pulls to one side, right? But if you locked the steering on a car so the front wheels couldn't turn, what would happen? The car would stop in a straight line. (as long as the wheels didn't lock!)

    And we're not talking about braking, just semantics!!!

    Nice chatting with you rtb. I think we actually, largely agree with each other. No harm in havin a little argument though.

    Si
     
  3. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    Mind you, that said, if you lock one wheel the other will spin twice as fast!

    So does the outer wheel speeding up drive the carrier round, or does the inner wheel slowing down speed the outer wheel up?

    When going round a bend, does

    a) the outer wheel speed up a bit and the inner wheel slow down a bit?
    b) the outer wheel stay the same and the inner wheel slow down a lot?
    c) the inner wheel stay the same and the outer wheel speed up a lot?
    :)
     
  4. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK

    Gotcha - you said it drives the faster wheels, my mistake.
     
  5. Drains

    Drains Yeah, nah.

    Messages:
    7,715
    Location:
    Sefton, South Island, NZ
    lol
     
  6. Drains

    Drains Yeah, nah.

    Messages:
    7,715
    Location:
    Sefton, South Island, NZ
    Depends whether you're driver or passenger... ;)
     
  7. migmag

    migmag Member

    Messages:
    700
    North east


    You obiously cant understand basic mechanics if you are compairing a single driven wheel on a fixed axle on a flamin three wheel bike to a sixty ton tank using brakes to steer.

    I have a 250bhp rwd coupe with an LSD if I remove one rear drive shaft will it drive round in circles????

    No

    If I nip a rear flexy and brake hard it still wont pull to one side...
    Oh I have read the thread and to be honest wish I hadn't..........
    For god sake stop wafling on and build sumat.

    Sometimes prototypes can save (a lot of time).:rolleyes: :rolleyes:
     
    Last edited by a moderator: Apr 30, 2007
  8. rtbcomp

    rtbcomp Moderator Staff Member

    Messages:
    18,615
    Location:
    Sheffield UK
    The basic principles are the same whether you stop the wheels/tracks on one side of a Dinky toy or a tank, it will steer to the side that is braked.

    Read my posts - I am not comparing a single driven wheel with anything, I am talking about twin driven wheels.

    The effect of unbalanced brakes on modern cars is mitigated by split systems and computer control. Why do they have these features? because basic mechanics says that if you slow one side down or (speed it up) the vehicle will veer to one side. On a trike I guess these systems are not available, so interefering with your particular braking system is not quite the same and your comment irrelevant.

    Neither am I tallking about Limited Slip Diffs. so I don't know why you made that remark.

    If you wish to criticise what I say, be polite and copy & paste my comments.
     
    Last edited by a moderator: Apr 30, 2007
  9. davethecave Ouch! That hurts.

    Messages:
    11
    Gloucester
    Gentlemen,
    Please don't fall out over a silly thing like this. All of your points are interesting and valued.
    Maybe we could fix a diff to this thread and we could all move forward instead of going round in circles:artist:

    The arguments which have been going to and fro throughout this thread have been going on in my head already which is why I asked the question in the first place.
    I think I am going to take the bull by the horns and build something. The first prototype will drive both wheels. If its uncontrollable, I can always start again.

    hmm, should I have brakes on two wheels or three?
     
  10. bright-spark

    bright-spark Member

    Messages:
    164
    Wokingham UK
    Just noticed this tread about Recumbent Trike's a area that I am very keen on myself and thought I would include a Link from a very good mate that I know quite well.. http://www.ihpva.org/people/tstrike/trike.htm hope you enjoy..
     
  11. bright-spark

    bright-spark Member

    Messages:
    164
    Wokingham UK
  12. MrFluffy Member

    Messages:
    2,911
    Location:
    In the shed
    Actually thats exactly what a differential does. If you take a compass and draw two arcs out from a point, the point is the turning point, and imagine the inner and outer arc as being the inner and outer wheels. The outer arc is LONGER. Therefore if you have a fixed axle and turn it, one wheel must turn at a different speed to the other or the inner wheel must skid on the surface (scrub) to accomodate the extra length of the outer wheel path along.

    Childs toys generally scrub the inner tyre to achieve this. Youll hear a noise and therell be some effort causing the tyre to scrub, which is why the ebay item exists for people who really want to go the extra mile...

    Torque biasing and locking diffs are a whole different more complex issue.

    Id go for the single rear wheel, Ive built a trike like that in the past...
     
  13. Haze

    Haze is it can be hugs tiem ?

    Messages:
    638
    West London
    its not that hard of a theory :)

    now planetary gearsets... :(

    not really a trike then is it :p
     
  14. migmag

    migmag Member

    Messages:
    700
    North east

    You serious??????
     
  15. Haze

    Haze is it can be hugs tiem ?

    Messages:
    638
    West London
    umm yes? trikes need 3 wheels?
     
  16. bright-spark

    bright-spark Member

    Messages:
    164
    Wokingham UK
    [​IMG]

    A nice design I think

    Below Taken from a Design Overview

    Trikes

    * Be careful with the seat to crossmember distance on tadpole style trikes. The rider's calf muscles and heels sweep an arch that can easily interfere with the crossmember. On many machines it's almost too late to change this after it is welded up and can make for an unrideable cycle. I know of one builder that had to move the seat forward because of this that really became a problem as it only had a rear brake and braking performance was compromised further - also more (unsightly) structural material to mount the seat.

    * There's a lot of force on the crosmember on a trike. If you choose to have a main boom pass on the same line as the crossmember I'd suggest you cut the boom for the fit not the crossmember.

    Bikes

    * Seat to steering neck to bottom-bracket distance on SWB bikes can be tricky to get right. Heel to front tyre interference can be a problem in a turn, Knee to handlebar clearance on above seat steering machines are critical - it's nearly impossible to ride if your knees are hitting the bars and raising the bars too high really can look funny. (sit and beg)

    All

    * Chain route needs to be predicted in the design before cutting out the material. In fact one could argue the whole machine ought be designed around the chain route, especially if it a low machine.
    The lower number of guide rollers means less weight, less friction drag and less fabrication work. With under seat steering the handlebars and sometimes control rods pass near the chain - also the chain rises and falls with the different size cogs selected which can end with interference. Remember the chain moves sideways too as it goes from the larger to the smaller cogs and can easily interfere with the frame on it's full inside path. If you modify/totally fabricate the rear drive end be sure the chain clears the chainstays (forks) in all gears, especially the smaller cogs.

    * It's very rewarding experience carrying through your own design to completion and finding it works as intended but I would suggest for your first project using an already proven design. There's a lot to learn, especially if you're also learning a welding process for the project too and many things crop up that are very hard to predict/forsee till you've had some experience.

    MOre can be found at http://www.ihpva.org/people/tstrike/overview.htm

    Now I like this Power assist trailer that he has made
    [​IMG]

    http://www.ihpva.org/people/tstrike/electrailer.htm
     
  17. Drains

    Drains Yeah, nah.

    Messages:
    7,715
    Location:
    Sefton, South Island, NZ
    My point there was that the outer wheel is going faster than the inner wheel. What I said was that the diff puts more power to the outer wheel, not that it drives it faster. I spose it does drive it faster, but only cos it's going faster anyway! That's just a de facto situation which the diff is designed to cope with.
    Semantics, semantics, it's a wonderful thing.

    And as for the skidding bit/ necessity for a diff, or other compensating mechanism, I think we covered that a few pages ago Mr F!

    Haze - you got the thing about the three wheeled trike (with one at the back and two at the front) yet? Or were you thinking of a unicycle?

    Bright Spark. That trike looks the business. Me like.
     
  18. Haze

    Haze is it can be hugs tiem ?

    Messages:
    638
    West London
    hehe i've never seen that design before :O

    looks a bit camp
     
  19. bright-spark

    bright-spark Member

    Messages:
    164
    Wokingham UK
    I like the designs due to the Recycling (excuse the pun) of 2nd hand bike parts that you can find down your local tip (Oh sorry local Recycling center as they like to be know as now) Dump... I have 4 of the things now all old mountain bikes ready for the chop two of them had just been thrown away due to a flat tyres (thats life in this day and age sorry to say cant fix it throw it away get a new one) all I got to now is get the welder to play with it all someware on that site are the plans not that I'll stick to them much but will give me some hope of making it look as good as the one above...Oh then I'll spray it pink (NOT)
     
  20. bright-spark

    bright-spark Member

    Messages:
    164
    Wokingham UK
    Sounds like you know something about this Haze !!!!!!! :artist:
     
Advertisements