Lotus Elan

Knock-off Spinner Tightening Rationale (Yet Again)

PostPost by: Craven » Mon Jan 12, 2015 2:51 pm

Hi,
Probably more than just these two issues but firstly why would a spinner come loose and secondly what can be done to stop it coming completely off.
It is after a spinner comes loose that advantage can be taken of the force that exists between the wheel and the spinner. I think Chapman?s argument is sound and I tried to give my visualisation of how there can be apparent contradiction in its action.
Ron.
Craven
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1069
Joined: 14 Sep 2013
Location: south coast uk

PostPost by: abstamaria » Mon Jan 12, 2015 11:03 pm

Thanks, Steve. Yes, both methods work, but I am just trying to understand why. Colin Chapman took the time to explain his theory to his colleagues at Lotus, so I am curious if I could make sense of it. Obviously, over a hundred years ago, Rudge and company understood, too. They were applying the same theory as Chapman, but taking into account the difference between female and male tapers.

I'm 66 years old, and this mental exercise is supposed to keep one young! :)

Warm regards from the tropics,

Andy
abstamaria
Third Gear
Third Gear
 
Posts: 320
Joined: 12 Nov 2010
Location: Manila, Philippines

PostPost by: abstamaria » Mon Jan 12, 2015 11:46 pm

If it were braking that loosens the spinner, I suppose the theory is that (on the right side of the car) when brakes are applied, the hub stops but the wheel wants to keep turning clockwise. The friction between the wheel and the stationary spinner turns the spinner clockwise, thereby tightening the spinner.

But that works only on the Lotus Elan spinner. On an MG spinner, which is left handed on the right side of the car, the friction would loosen the spinner.
abstamaria
Third Gear
Third Gear
 
Posts: 320
Joined: 12 Nov 2010
Location: Manila, Philippines

PostPost by: stevebroad » Tue Jan 13, 2015 12:03 am

I rest my case -)
stevebroad
Fourth Gear
Fourth Gear
 
Posts: 918
Joined: 08 Mar 2004
Location: Essex, England

PostPost by: abstamaria » Tue Jan 13, 2015 1:06 am

Here's food for thought.

A bicycle pedal is threaded so that it tightens as the bicycle moves forward.

On the left side of the bicycle, the pedal thread is left-handed, that is, one turns it counterclockwise to tighten it into the crank.

On the left side of a bicycle, the crank spins counterclockwise, but the pedal itself spins clockwise on its axis. This is probably similar to the quasi-epicyclic motion that we discussed and which Chapman demonstrated.

However, since the the pedal has left-handed thread, its clockwise spin should loosen it, but it doesn't.

From the article on mechanical precession linked above, it seems mechanical precession acts OPPOSITE to the spin (i.e., counterclockwise in a clockwise rotating pedal). The effect of that would be to tighten the pedal.

The forces of mechanical precession are said to be very powerful, so it would seem long term forward motion would be more relevant than braking.

if the analysis is right, then on the right side of an Elan, as the wheel turns clockwise, the spinner will mimic an epicyclic motion and spin counterclockwise on its axis. (Actually it is the load on the spinner that notates around the spinner in a anti-clockwise direction.) Mechanical precession will then exert an opposite, clockwise force, thereby tightening the spinner.

I am not an engineer and probably have this all wrong. Corrections appreciated.

Andy
Last edited by abstamaria on Tue Jan 13, 2015 6:55 am, edited 1 time in total.
abstamaria
Third Gear
Third Gear
 
Posts: 320
Joined: 12 Nov 2010
Location: Manila, Philippines

PostPost by: abstamaria » Tue Jan 13, 2015 1:17 am

On the power of mechanical precession, the Wikipedia article says this-

"Bicycle pedals are left-threaded on the left-hand crank so that precession tightens the pedal rather than loosening it. This may seem counter-intuitive, but the torque exerted due to the precession is several orders of magnitude greater than that caused by a jammed pedal bearing."
abstamaria
Third Gear
Third Gear
 
Posts: 320
Joined: 12 Nov 2010
Location: Manila, Philippines

PostPost by: Craven » Tue Jan 13, 2015 11:33 am

So all we need to do is have finger tight spinners and let physics do the rest. Why then do we flog up the spinners to 200 ft/lbs or so.
Craven
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1069
Joined: 14 Sep 2013
Location: south coast uk

PostPost by: jimj » Tue Jan 13, 2015 12:41 pm

What we need is for someone to loosen a spinner until it`s only just touching the wheel and mark the position. Then accelerate aggressively and see if it loosens further, then brake hard to see if it tightens. I`d do it but it`s cold and snowing here. Maybe someone somewhere warmer, maybe the tropics?
Jim
P.S. I`m convinced this epycyclic (and other long words) effect is hocus pocus. It`s just inertia and momentum surely.
jimj
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1134
Joined: 25 Feb 2008

PostPost by: john.p.clegg » Tue Jan 13, 2015 12:46 pm

Craven wrote:So all we need to do is have finger tight spinners and let physics do the rest. Why then do we flog up the spinners to 200 ft/lbs or so.

Maybe the inertia/momentum can produce around 100ft/lbs?

John :wink:
User avatar
john.p.clegg
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 5682
Joined: 21 Sep 2003
Location: Manchester

PostPost by: abstamaria » Tue Jan 13, 2015 1:23 pm

They say that if are able to have someone make you a bicycle crank with right-hand thread for the left side of a bicycle, screw in a pedal as tightly as you can into the crank, and ride off. You will be surprised at how quickly the pedal unscrews itself.

Or perhaps swap the left and right front hubs, and see what happens,

Formula One uses handed centerlock wheel nuts. It is interesting to note in this video that they use left-handed nuts on the right side.

https://m.youtube.com/watch?v=PeIqXgaoSNM

Andy
abstamaria
Third Gear
Third Gear
 
Posts: 320
Joined: 12 Nov 2010
Location: Manila, Philippines

PostPost by: abstamaria » Tue Jan 13, 2015 2:40 pm

It's 19C in the mornings here, Jim, so we are all freezing. I may have to stop wearing shorts.

The reason I didn't think braking provided the loosening force is that in a bicycle there is no braking force applied to the pedal (except in the few back-pedal brake bikes). The culprit is the force or load applied to a point on the diameter of the pedal shaft. In the book Lotus Engineering, there is are drawings that show where that point is on the RW and Elan spinners.

On all this being hocus-pocus, there were several instances when I was studying the issue when I began to take that attitude. But apparently, automobile engineers take the issue seriously (the centerlock nuts on the current Ferrari 458 Challenge cars are handed, with the reverse thread on the right side of the car). I then concluded I am just not thinking hard enough or aren't bright enough to understand, more likely the latter.

By the way, some years ago I was following a friend in his Jaguar E-type, traveling quickly on a straight highway, when a wheel came off his car. No major damage, but it was apparent from the markings on his spinners that they had swopped the hubs.

Far earlier than that, when I was in college, a friend had an Austin a Healey Le Mans that kept losing its wheels. The mechanic had swopped the hubs around, too.

Andy
abstamaria
Third Gear
Third Gear
 
Posts: 320
Joined: 12 Nov 2010
Location: Manila, Philippines

PostPost by: jimj » Tue Jan 13, 2015 4:00 pm

It feels like 19F here. A pal just left here, a minute ago, in his 100/4 but he had his roof up....and all 4 wheels on.
A separate interesting, well I think so, little experiment: Imagine a bike with, say, the right hand pedal at the lowest point. Tie some string to that pedal and imagine what would happen if you pulled it rearwards. You`d think the crank would rotate, at least a bit, and drive the bike forwards but the opposite happens.
Jim
jimj
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1134
Joined: 25 Feb 2008

PostPost by: 69S4 » Tue Jan 13, 2015 4:44 pm

jimj wrote:What we need is for someone to loosen a spinner until it`s only just touching the wheel and mark the position. Then accelerate aggressively and see if it loosens further, then brake hard to see if it tightens. I`d do it but it`s cold and snowing here. Maybe someone somewhere warmer, maybe the tropics?
Jim


I did that some years ago (not deliberately) and got about six miles through winding Chiltern roads before the wheel came loose. My wife was not impressed. :(
Stuart Holding
Thame UK / Alpe D'Huez France
69 S4 FHC
Honda GoldWing 1800
Honda CBX1000
Kawasaki H1 500
Yamaha XS2
69S4
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1199
Joined: 23 Sep 2004
Location: nr Oxford UK

PostPost by: abstamaria » Wed Jan 14, 2015 6:08 am

Just in case one got the theory wrong ...

Bugatti wheel.jpg and
abstamaria
Third Gear
Third Gear
 
Posts: 320
Joined: 12 Nov 2010
Location: Manila, Philippines

PostPost by: JohnDanbyRacing » Sun Jan 18, 2015 1:46 pm

Small hole in the wheel spinner and through the thread of the drive peg, lockwire between them will prevent the spinner coming very loose
JohnDanbyRacing
First Gear
First Gear
 
Posts: 42
Joined: 30 Sep 2014
Location: Colchester,Essex
PreviousNext

Total Online:

Users browsing this forum: Dale Harvey and 9 guests