adamhay
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| posted on 17/8/04 at 07:24 AM |
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Propshaft Options
I have searched for info on this matter and can't really find an answer . . . . Anyway, I have a Caterham and a Hayabusa fi engine. I'm
still sussing out the bits I'll need and I'm not sure what to do about the prop/reverse setup. Is it possible to use a single prop on a De
Dion car if I am not fitting a reverse in the middle of 2 props (as most people seem to do)? I can see why a 2 piece prop is needed for a live axle
but not for De Dion. Also, if 1 prop is an option, where would an electric reverser go? I've heard about problems with alignment of 2 piece
props and it's just one problem I would rather avoid if at all possible.
http://www.youtube.com/watch?v=lnp0WDDW7xs
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JoelP
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| posted on 17/8/04 at 07:32 AM |
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i think one piece props stuffer from more vibration. obviously bike engines need longer props due to the absence of a gearbox that extends into the
transmission tunnel. hence, it would be very long. since vibration is linked to the square of the length, it gets exponentially worse. vibrating props
can only lead to bad things!
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Jasper
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| posted on 17/8/04 at 07:39 AM |
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It MUST be a 2 piece prop due to the length
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stressy
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| posted on 17/8/04 at 08:21 AM |
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The bike engine was designed to have a sprocket mounted on the output shaft. By mounting even a short propshaft you put a lot of load on the shaft
which it was not designed for. As the prop gets longer so does the load on the shaft......., The centre bearing restrains the niddle of the prop to
and therefore reduces the load considerably. The best bet is a VERY short forward prop and a LONGER aft prop.
Cheers
Chris
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adamhay
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| posted on 17/8/04 at 08:21 AM |
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Thanks - I suspected that may be the issue.
2 piece prop it is then....however, regarding reversers, do they sup power and do they have limitations as to the amount of torque they can handle? If
they don't go in the middle of the props, where do they go?
http://www.youtube.com/watch?v=lnp0WDDW7xs
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Peteff
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| posted on 17/8/04 at 08:41 AM |
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In the bin after you've done cleaning up the oil spill according to most I've read about. There's always someone trying to figure
out an alternative to them from what I've read on various lists. I've only read about them being mounted between two short props but I
suppose they could be mounted between the rear prop and the diff flange but you would need a linkage to operate the lever or a rubber elbow in your
left arm.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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locoboy
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| posted on 17/8/04 at 12:57 PM |
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Agree with Peteff, only ever heard bad things about them, noisy when going forwards, sapping power in normal use but most concerning of all is the
regular reports of them breaking and wither locking up the prop shaft or leaving you with no drive at all just because an intermediary box of gears
has bust itself.
And at upto £500 i would rather keep my wits about me when driving/parking etc... and spend it on beer 
ATB
Locoboy
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adamhay
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| posted on 17/8/04 at 01:33 PM |
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So they're rubbish then? . . . . I 'll scratch a mechanical reverser gearbox from the list of stuff to find then.
Is there any other way to make a car reverse? How do electric reversers work? Where are they fitted? Are they any more reliable?
TIA.
http://www.youtube.com/watch?v=lnp0WDDW7xs
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locoboy
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| posted on 17/8/04 at 01:53 PM |
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by their very nature of having to be small and powerfull they are all expensive. Some attach to the chassis/diff and are made to turn the diff flange
via some form of sprocket or ring gear.
I beleive John Ison is looking at making an electric one that pops a wheel down to the ground and reverses just using power from that one wheel.
There are many ways just need to get your thinking cap on
ATB
Locoboy
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JoelP
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| posted on 17/8/04 at 06:12 PM |
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quote:
Originally posted by adamhay
Is there any other way to make a car reverse?
one common way to achieve this is the old mechanical push technique, sometimes also called the pasanger push technique. you can guess what it
involves!
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The Shootist
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| posted on 17/8/04 at 07:31 PM |
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Drive shaft stress, electric reverse etc......
The length of driveshaft, and the change from chain to shaft should have very little to do with any problems.
Now balance and alignment on the other hand.... that's a another story. In a typical rear wheel drive set-up, care should be taken to be certain
that the trans output, and the diff input are parallel. The reason for this is that a universal joint is not a constant velocity coupling. If you
watch very carefully the angular change between the trans flang and the shaft, causes the shaft to acelerate, and then decelerate, as they rotate.
This happens twice per rotation, and becomes more intense as the angle increases.
The trans and diff shafts must be parallel because then the pulses from the front and rear cancel each other out, but the center shaft is still
accellerating and decellerating every rotation. his causes a pulsation in the required input power. (It takes power to speed up and slow down the
shaft's mass).
Ideally in a car with a dedion or indi rearend (any solid mounted diff) the trans and diff shafts could be in a straight line, and the pulses
wouldn't happen because the lesser angles produce less accelleration in the center shaft.
Now if you go to the trouble to align the trans and diff, then there is little need for anything other than perhaps a torque plate between the
trans/shaft/diff flanges.
As for reverse
A small starter motor with a ring gear on the drive shaft will certainly move a car as light as a Locost. In place od a starter motor, a gearmotor as
is used for wheelchairs and mobility scooters use in place of the starter motor would give slower, more controlable speed, and may have more
torque.
I wouldn't bet on a swing down wheel/motor moving a car on a wet surface.
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adamhay
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| posted on 17/8/04 at 07:50 PM |
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Shootist: So why could I not use a single piece prop in a de dion with a rigidly mounted engine? Sorry if that's a dumb question - I've
got a lot to learn.
Wheelchair motors - that's interesting!
http://www.youtube.com/watch?v=lnp0WDDW7xs
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The Shootist
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 posted on 17/8/04 at 09:29 PM |
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Also accumulating bits...
I looked up the McSorley plans, and saw that a driveshaft for a BEC would be about 55". I then looked at two pick-up trucks in the parking lot
outside my office and both have 2 piece driveshafts, BUT one piece of each is at least that long.
I looked up some tech data and found that in addition to u-joint angles, "critical speed" is the other dominating factor. ( in addition to
balance)
The Tech info came from these sources...
Hotrod Magazine
and
Mark Williams
These should give the engineering data needed to make a choice.
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bikerush
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| posted on 17/8/04 at 11:54 PM |
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Wheelchair motors - that's interesting!
why not just put the busa engine in the wheelchair?
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adamhay
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| posted on 18/8/04 at 06:21 AM |
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bikerush: I think tyre choice for wheel chairs is a little narrow. It would have a good power:weight though.
Shootist: Thanks for the info. If I'm reading Mark Williams' figures correctly, even a 60" long 3" steel prop has a critical
speed below what I'd need, i.e. 4020 prop rpm. That would cater for 11000 rpm and 3.54 diff wouldn't it? Mark Williams' data is
aimed at more powerful engines with live axles that don't rev that high - I'm going to have to do the proper calculations I guess.
http://www.youtube.com/watch?v=lnp0WDDW7xs
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The Shootist
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 posted on 18/8/04 at 05:40 PM |
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Busa revs
I get a calculated 6608 RPM @ the sprocket @ Redline in 6th gear.
Given that, you could go with a 4" mild steel shaft @ 54", or a 3.5" aluminum shaft @ 54".
My length is based on a book chassis, give or take a bit. Make sure you count for the distance that the diff snout goes into the tunnel, and be sure
you figure the shaft length from center of yolk to center of yolk.
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