Author Topic: Bamby P50  (Read 50489 times)

Big Al

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Re: Bamby P50
« Reply #45 on: April 19, 2015, 09:06:57 PM »
Meanwhile in another field, on a disused runway, Root and I found genuine Peel wheels with tyres. Topped off with some Villiers airfilters and other misc stuff. Nice local jumble. £2 entry. Brill.
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richard

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Re: Bamby P50
« Reply #46 on: April 20, 2015, 01:28:06 PM »
Ex go-kart probably . Trobikes / karts are the same I think too . Nice one  ;)
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Big Al

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Re: Bamby P50
« Reply #47 on: April 20, 2015, 05:02:46 PM »
Week 2:

Having a coffee after a bad afternoon on a BX that has just managed to fail elsewhere each rime I repair something.

The king pin pictured is a long way from the centre of the wheel on this. No idea what the original looked like mind you. However, as in the Tri Tech, (also Freeway by the sound of it) this wheel hub is going to exhibit making a semi circle around the king pin centre, rather then rotate open the centre line of the king pin. As such it will take a great deal more input to turn the wheel, moving an entire structure with friction, then it rotating on a spot under the tyre. The geometry will promote inaccurate steering, as their is leverage of length between turn centre and effect. So any high speeds might be alarming, with slow speed steering heavy.
Now this is an observation, not a criticism, as I do not know what the intention for the car is. Unlike a Tri Tech, its probably not going to have greater performance than the car it follows. For hobby use, therefore, its probably not a issue, should it prove to exhibit what I suggest. If it does 'get in the way' of enjoying it, then I would point to this design, as being the source of handling issues. Be interesting to see how it turns out.
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Bob Purton

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Re: Bamby P50
« Reply #48 on: April 20, 2015, 05:46:47 PM »
This pic shows the running gear of a real one. You are right, the Bamby P50 kingpin will send the wheel hub orbiting around it rather than axising on it. Quite what that does to the handling I dont know either. I guess its just what happens when you buy a Chinese quad and alter it enough to turn it into a P50 rep rather than design a purpose built one from scratch.. Like you say, not a criticism but more a consequence.
I wouldnt think it would make the steering heavy enough to be an issue though.
The Evans's have obviously made a few by now and tested them well so cant really see a big problem.
« Last Edit: April 20, 2015, 05:51:02 PM by Bob Purton »

Peel replica, Steve Fisk

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Re: Bamby P50
« Reply #49 on: April 20, 2015, 06:45:54 PM »
I'm trying to understand what you to are talking about because it sounds interesting , I don't know any thing about steering Geometry bit worrying as I've built the steering already , ive only had experience driving my peel at about 15mph , slow steering feels fine , get abit of speed and it's really twitchy , I thought it needed a steering damper , or is it set up wrong ?

1bubble10 (paul smith)

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Re: Bamby P50
« Reply #50 on: April 20, 2015, 07:16:38 PM »
Steve - I would imagine that once the camber and tracking have been set up correctly then the handling would improve considerably. It may be worth speaking with Alan Even to see if he tracks the wheels in at the front or out at the front and by how much. It will be a bit twtichy on the basis that the suspension is on rubber (not springs) and the steering rack is such that the steering wheel needs little turn to get a large response at the wheels. When I have seen videos of original peels being driven at speed the driver is constantly making adjustments to the steering even on a straight road.

Alan claims that he has improved the handling of his replicas - weight distribution across the front wheels is more or less equal unlike the originals so less likely to lift a wheel. The P50 and the trident are not fast machines even at the top end - I should imagine the nerve goes before getting anywhere near 38mph (flat out). Wear in steer on any car is not a good thing!
Bamby P50, Piaggio Ape 50

1bubble10 (paul smith)

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Re: Bamby P50
« Reply #51 on: April 20, 2015, 07:40:59 PM »
It is interesting what you are saying about the semi-circular movement - once I have got the car I shall report my findings on the handling.
Bamby P50, Piaggio Ape 50

Bob Purton

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Re: Bamby P50
« Reply #52 on: April 20, 2015, 09:57:54 PM »
"When I have seen videos of original peels being driven at speed the driver is constantly making adjustments to the steering even on a straight road."

Welcome to the world of microcar driving!

1bubble10 (paul smith)

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Re: Bamby P50
« Reply #53 on: April 20, 2015, 10:42:01 PM »
"When I have seen videos of original peels being driven at speed the driver is constantly making adjustments to the steering even on a straight road."

Welcome to the world of microcar driving!

I have never experienced it on my isetta, bond, or piaggio ape 50
Bamby P50, Piaggio Ape 50

Rob Dobie

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Re: Bamby P50
« Reply #54 on: April 20, 2015, 11:11:21 PM »
I never had steering and wobbling problems with my P50 in '76 as far as I can remember. Even driving it mostly at top speed of 40 mph, (caught by a following motorist) even faster down hill. Oh, the joy of the yesteryears.  :D ;D
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Big Al

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Re: Bamby P50
« Reply #55 on: April 21, 2015, 12:20:18 AM »
This has been discussed on a previous thread, I forget which.

In a nutshell if you have something to turn, that is able to roll, you can demonstrate to yourself with leggo, meccano or what ever.

First take a wheel and make a hub with a kingpin such that the wheel is as near to the centre of the point of rotation of the king pin. On most two wheel axles this will fall within the tyre area on the ground. Turn the kingpin and the wheel pivots with a slight roll to one way. Return in the opposite direction and it will slightly roll in the opposite direction, this is progression, to allow the wheel to turn some 60 degrees.
In fact most cars have toe in to aid directional stability and caster angle. In other words they will tend to want to go in a straight line, rather than turn. Thus it is that to manoeuvre and protect your tyres you should creep as you manoeuvre, allowing the rolling wheel freedom to take up the angle input progressively, rather than by force, stood still.
None the less the energy required to turn the wheel is not to great and lightens as soon as the wheel is in motion. The movement of the trackrod is short, equal to the degree of turn and does not extend far beyond the kingpin if well designed.

Take the model of the Tri Tech and have some factor of three wheel widths from the kingpin centre of rotation out to where the wheel is. Now the wheel is not pivoting about itself on a spot. It has to physically roll the wheel in the direction of the steering input. It describes a semi circle rather than tiny loop round a point under the tyre. It needs more energy put into the control to do this, and the resistance to movement is greater, not least through leverage that does not exist in the first model.
To acheave full lock the track rod has to travel will past the king pin in a long movement. It, itself, has to describe a slight semi circlular motion to achieve lock to lock. Thus the steering input is proportional, not constant. And suspension movement, and more than likely the different length of track rod to suspension member, create another problem. To achieve up and down movement means a change in the length of steering travel by a proportion, too. So the steering force required to turn is heavier, not constant, and the suspension movement is likely to alter the value of the steering input, in differing amounts, in differing places, as bumps are absorbed. Attempting to smooth out these deflections of direction by steering wheel risks the car loading the suspension the other side of the car and finding the car over corrects. At about 45 mph in a standard Tri Tech the amount of feed back is beyond the ability of the steering control to correct fast and smoothly enough. The car effectively has a steering axle tank slapper and goes out of control. As you approach that point the loadings to correct the steering increase markedly, making accurate input impossible. The imbalanced changing loadings, plus the leverage of the wheels well away from the king pin, continually fight any kind of control. Its a very frightening experience and not unlike a rear blowout on a two/one trike.

The theory that covers much of this is Akerman angle theory. Though on three wheelers it is more difficult to follow. A read through that, and model tests, should provide you with an idea of the possible problems. On the Tri Tech my mod was to increase the track of the car with a spacer mounted on the inner stub axle either side. This made the distance of the wheel to king pin less of the full axle length. I altered the drum and wheels to 10 inch on scooter tyres to bring the wheel centre in board, again shortening the king pin to wheel distance. The car then became drivable at 50 mph and was lighter to drive. The owner seemed happy, but has done few miles.
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1bubble10 (paul smith)

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Re: Bamby P50
« Reply #56 on: April 21, 2015, 06:39:00 AM »
The P50 replicas are not going to reach anywhere near the sort of speeds you are talking about - P50 are also inherently unstable so cornering at speed (30mph) would be very gentle - anything less than gentle would be taken at lower speeds. The front suspension on the Bambys and Steves P50 is not a spring with shocks system (a thick engine mount rubber which at best compresses a millimetre or two on negotiating bumps). The answer is in the test drive which I shall do some sort of report on at a later date - but I am thinking that based on the above i would expect any symptoms to be not noticeable.
Bamby P50, Piaggio Ape 50

Big Al

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Re: Bamby P50
« Reply #57 on: April 21, 2015, 09:16:49 AM »
I hope so. The original car must have had a similar problem, as how do you put a king pin inside such a small wheel? I think most of the Peel replicas are being made for fun. So this should not deture folk from what they are doing. I think making a Peel handle like a racing car would be rather difficult. In effect it would end up as a Kart with a Peel shell on it. I have heard of no one heading off in that direction, so the shared knowledge is probably handy enough for all.

As for Akerman, there are great cars, and racing cars, out there, that threw away these theories! If it works as an answer to the problem, then its good enough to go. That said it is interesting to be aware of 'what you should do'. If microcar makers followed that, half the cars would not exist. But there is enjoyment in tuning out the errors they made, and increasing the efficiency of the design.
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Bob Purton

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Re: Bamby P50
« Reply #58 on: April 21, 2015, 09:46:56 AM »
"When I have seen videos of original peels being driven at speed the driver is constantly making adjustments to the steering even on a straight road."

Welcome to the world of microcar driving!

I have never experienced it on my isetta, bond, or piaggio ape 50

Well steering wander is common on a lot of microcars and indeed a lot of big cars of the 1950's. Its called Hollywood steering appropriatly named after all those film scenes of folk driving along with the driver constantly throwing the steering wheel from side to side. ;D
In my experience I have found single front wheeled cars like the ones you mention dont suffer from it but Isetta's and Schmitts often do, both my schmitt and my current Isetta 'Thumper' did quite badly when I first got it, sorted now though by swapping to radials and getting most of the play out of the steering system also correct toe in.  I have never experience the steering shake of death that some Isetta drivers have had though. Steering geometry is a complex thing but as Al said it either works or it doesnt. The one I can never understand is the Nobel/fulda set up, talking more the suspension here rather than the steering as the king pin set up is pretty normal. The suspension is however a bit balmy, wheel hubs bolted to each end of a single leaf spring with no wishbone or any other set up there to resist forward or backward thrust. However in practice it still works, Al and others may disagree but I've had a few and they all steered straightish and went around corner ok. As I said, if it works it works and I'm sure your Bamby will work also within its intended use.

1bubble10 (paul smith)

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Re: Bamby P50
« Reply #59 on: April 21, 2015, 10:53:21 AM »
This makes an interesting read assuming I can upload it!!
Bamby P50, Piaggio Ape 50