|
|
Thread Tools | Display Modes |
#41
|
|||
|
|||
Deriving a unicycle crank length formula?
By imperfect, I simply meant incomplete. It wasn't meant as an insult. Sometimes I use fairly sterile language like that and it can be misinterpreted. Sorry. I certainly agree that long cranks really come into their own on steep descents. That is their biggest single advantage. -- Mikefule So, do you ride with a club? No, but I carry a heavy spanner. ------------------------------------------------------------------------ Mikefule's Profile: http://www.unicyclist.com/profile/879 View this thread: http://www.unicyclist.com/thread/43478 |
Ads |
#42
|
|||
|
|||
Deriving a unicycle crank length formula?
Mikefule Wrote: Slightly behind. To ride a unicycle, you allow it to start to fall forwards, then you accelerate the wheel so that the uni never actually falls. When you slow down, you allow the wheel to overtake you, slightly. The better the rider, the more control, the smoother the ride, the more vertical the relationship between the hub and the contact patch. However, if the contact patch were exactly beneath the hub, you could never accelerate - including from a standstill. This is a mixture of truth and fiction. You are correct that the contact patch is slightly behind the center of mass *when you are accelerating*. On the other hand, when you are *decelerating* the contact patch is in front of you. It has to be or else you fall forwards. And, guess what? If you are maintaining a constant speed the contact patch is exactly beneath the center of mass. In reality you are never maintaining a perfectly constant speed. You constantly waver between accelerating and decelerating, and otherwise wobble, but it averages out to beneath you, with expert riders keeping the contact patch consistently closer to under the center of mass. -- Bruce Dawson ------------------------------------------------------------------------ Bruce Dawson's Profile: http://www.unicyclist.com/profile/1299 View this thread: http://www.unicyclist.com/thread/43478 |
#43
|
|||
|
|||
Deriving a unicycle crank length formula?
I think you'll find that at constant speed on a perfectly smooth level surface, the centre of mass is still very slightly forward of the contact patch. For a simple demonstration, balance a broom on your finger and walk with it. However, I agree that the better the rider, and the smoother the surface, etc., the more constant the position of the centre of mass relative to the contact point. A good rider is not constantly accelerating and decelerating, but exactly matches his speed to counteract the downwards deceleration of the centre of mass. It's a bit like an object in orbit, constantly falling but never landing. -- Mikefule So, do you ride with a club? No, but I carry a heavy spanner. ------------------------------------------------------------------------ Mikefule's Profile: http://www.unicyclist.com/profile/879 View this thread: http://www.unicyclist.com/thread/43478 |
#44
|
|||
|
|||
Deriving a unicycle crank length formula?
On Thu, 6 Oct 2005 01:17:43 -0500, Mikefule wrote:
I think you'll find that at constant speed on a perfectly smooth level surface, the centre of mass is still very slightly forward of the contact patch. I think you're right, but you don't state the reason. For a simple demonstration, balance a broom on your finger and walk with it. Balancing a broom on your finger and then walk with it is relatively easy indeed. Nevertheless, it's not a simple demonstration. How can you "simply" demonstrate an effect that is "very slight"? The reason for the contact patch being forward (both in unicycling and in the broom case) is air resistance. This effect is probably too small to discern casually by the naked eye. If you think you see it, then either your observation is distorted because you focus on the combination of tasks, or you are still accellerating overall. Klaas Bil - Newsgroup Addict -- "dit dit diddle diddle dit dit did-it, dit dit diddle diddle dit dit did-it, *dit* diddle dit dit *dit* diddle dit dit, diddle-diddle-diddle-diddle-dit dit diddle diddle dit dit did-it,... - Spudman" |
#45
|
|||
|
|||
Deriving a unicycle crank length formula?
Klaas Bil, I think I was wrong. I think you are right in that, in the absence of air resistance, it would be possible to ride at a steady speed without leaning forwards. If you could breathe. ;0) -- Mikefule So, do you ride with a club? No, but I carry a heavy spanner. ------------------------------------------------------------------------ Mikefule's Profile: http://www.unicyclist.com/profile/879 View this thread: http://www.unicyclist.com/thread/43478 |
#46
|
|||
|
|||
Deriving a unicycle crank length formula?
In message
essage.Poster.at.Unicyc list.com, Mikefule writes Klaas Bil, I think I was wrong. I think you are right in that, in the absence of air resistance, it would be possible to ride at a steady speed without leaning forwards. Only in the absence of rolling resistance and friction in the bearings. In that case, one could take ones feet off the pedals and continue in uniform, rectilinear motion until acted on by a force.... Martin/ -- Martin E Phillips nb Boden, Splatt Bridge http://www.g4cio.demon.co.uk martin/at/g4cio/dot/demon/dot/co/dot/uk Homebrewing, black pudding, boats, morris dancing, ham radio and more! The Gloucester-Sharpness canal page http://www.glos-sharpness.org.uk |
#47
|
|||
|
|||
Deriving a unicycle crank length formula?
I think that's probably right. Yes, Klaas was incomplete in his answer. If a force is tending to slow down the unicycle, and the unicyclist wants to maintain a steady speed, he will exert a force on the pedals to turn the wheel. Newton's law of equal and opposite reaction will then make the centre of mass move in the opposite direction. Therefore there needs to be a tilt forwards to allow the effect of gravity to counterbalance this tendency for the entire unicycle frame and rider to rotate in the opposite direction to the wheel. So, although I hadn't got all the details right in my head,I think my original intuition was right after all. -- Mikefule So, do you ride with a club? No, but I carry a heavy spanner. ------------------------------------------------------------------------ Mikefule's Profile: http://www.unicyclist.com/profile/879 View this thread: http://www.unicyclist.com/thread/43478 |
#48
|
|||
|
|||
Deriving a unicycle crank length formula?
On Fri, 7 Oct 2005 18:55:18 +0100, Martin Phillips wrote:
Only in the absence of rolling resistance and friction in the bearings. I do agree that my analysis was incomplete. Let's go through some other effects that push you off-vertical and that you have to compensate for in order not to fall.. Like Mikefule hints at, friction in the bearings would actually cause the centre of mass to be BEHIND the contact patch, to compensate for the fact that the turning wheel tends to push the frame forward. So with the "right" amount of friction in the bearings to compensate for air resistance at a certain speed, one would still be upright - apart from other effects mentioned below. Rolling resistance, however, acts in the tyre-wheel system and would have no effect on the uprightness of the unicycle. Celestial bodies, such as the moon, will attract you (gravitational force), like they do attract ocean water and cause tides. In fact, every body of mass will attract you: a mountain, a fellow unicyclist, a mosquito. And density variations in the Earth, although this depends on your definition of verticalness. If there is more light coming from one side, e.g. if you are riding towards a car's headlights, then the light falling upon you will tend to push you off-vertical. If you have a headlight yourself, it will exert a reaction force upon you. If you are not riding exactly towards the North or the South, the turning of the Earth will "push" you towards the equator. If you breathe out, the reaction force will push you backwards. This is different from air resistance, it also works in vacuum - though breathing out would be a different experience there. A similar story holds if you breathe in, except that this is not possible in vacuum. I'd rather stop now :-) Klaas Bil - Newsgroup Addict -- "dit dit diddle diddle dit dit did-it, dit dit diddle diddle dit dit did-it, *dit* diddle dit dit *dit* diddle dit dit, diddle-diddle-diddle-diddle-dit dit diddle diddle dit dit did-it,... - Spudman" |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Coker crank length learnings | tomblackwood | Unicycling | 4 | June 30th 05 04:10 PM |
ultegra octalink: tick Tick TICK TICK TICK! | H. Guy | Techniques | 44 | February 2nd 05 01:56 AM |
Rec.Bicycles Frequently Asked Questions Posting Part 1/5 | Mike Iglesias | General | 4 | October 29th 04 07:11 AM |
Crank arm length question | David Kerber | General | 13 | May 20th 04 06:19 PM |
Optimum crank length | Frank Day | Racing | 37 | December 3rd 03 03:35 PM |