Motorized Penny Farthing?

[duivendyk]

The size of the driven wheel is immaterial in a friction drive.All will have the same circumferential velocity and the same road speed determined by the size of the roller&engine rpm.Come to think of it,considering that this bike was a product of the steam age,when fabricating a roller chain was difficult&expensive, it would be appropriate to equip it with a steam engine instead of a noisy newfangled IC engine,a piercing whistle would also come in handy
A Stanley type 2 cyl. horizontal direct drive engine with the cranks on the rear wheel and the tube boiler on top would be just the ticket.It would put much needed weight on the rear wheel.
The controls would be a bit tricky,but I am sure that someone in Good Old Excentric England could be inveigled into make this his life's work.
Someone over there perfected a steamdriven standard bicycle last year to much acclaim.I must confess to having criticised this effort citing safety concerns.But with the PF approach the basic concept is already so hazardous that just adding a steam engine won't make all that much difference anymore in my opinion
It has come to my attention (Google) that there is a thriving PF movement in Austria, of all places.They craft their machines themselves,hold meets etc and seem to have a ball.I seem to remember that Mr Stevens of PF fame was extremely popular in Austro-Hungary,coincidence or genetic factors ?,food for thought !.

 

[bluegoatwoods]

Let's see, am I picturing this friction drive thing wrong?

(Not that it's terribly important. But let's see if I can figure it out just for fun)

If you pictured one particular friction drive mounted on two successively larger wheels, that would be a good place to start. Wheel B has twice the diameter of wheel A. When the drive is mounted on B, it would seem that it is delivering twice the torque it did when mounted on A. It would seem that a road speed divided by two would be a necessary result.

On the other hand I can see how a wheel with diameter doubled would be reduced by half in speed. but the doubled circumference would seem to counter-act that.

hmmm....it seems we have a conundrum.......

Any help would be appreciated. But then we run the risk of hijacking this thread.


But if I've been throwing out bad info, then my apologies.

 

[Tinker1980]

Let's see, am I picturing this friction drive thing wrong?

(Not that it's terribly important. But let's see if I can figure it out just for fun)

If you pictured one particular friction drive mounted on two successively larger wheels, that would be a good place to start. Wheel B has twice the diameter of wheel A. When the drive is mounted on B, it would seem that it is delivering twice the torque it did when mounted on A. It would seem that a road speed divided by two would be a necessary result.

On the other hand I can see how a wheel with diameter doubled would be reduced by half in speed. but the doubled circumference would seem to counter-act that.

hmmm....it seems we have a conundrum.......

Any help would be appreciated. But then we run the risk of hijacking this thread.


But if I've been throwing out bad info, then my apologies.

A friction drive turns the wheel by the outer circumference. Since that outer circumference is moving at the same speed as the road it's rolling on, the friction drive roller is, for all intents and purposes, rolling directly against the ground.

-Mark

 

[duivendyk]

I'm afraid you're all wet (this is a common misconception).Forget about torque that does not enter into the picture.If you have a rolling wheel,you can imagine that as a movement forward of the hub at road speed, picture the wheel as just hovering over the road surface.Now rotate the wheel,if the circumferential velocity of the wheel cancels out the forward translation speed at the road surface it effectively means that it is rolling along.So the forward speed of the hub (and the bicycle) is equal to the circumferential speed of the wheel measured with respect to the hub center.The roller circumferential velocity equals that of the wheel (if it is not slipping) and is equal to the forward speed of the bike,the diameter of the driven wheel is irrelevant but the roller diameter is not, of course.It determines the road speed.It's as if the roller is rolling along the road surface so to speak.BTW the speed at the top of the driven wheel is twice the forward speed of the bicycle (circumferential speed + translation speed).

 

[Flapdoodle]

The powered penny farthing is not new...
http://brassgoggles.co.uk/brassgoggles/200609/more-steam-bikes

 

[Revorunner]

Interesting site!!!!!!!!!!!!!!!

 

[duivendyk]

So they actually did put a steam engine on the thing,simply amazing.Mr Stevens matter of factly mentions taking "headers".I never found out from the book how he got on nor how he stopped.Apparently there were scads of them all over England&Europe.They aptly called themselves "Wheelmen" and escorted him from Liverpool to London and beyond

 

[Alaskavan]

Thanks for the link, Flap. Some interesting stuff there.

 

[duivendyk]

Come to think of it,a steam powered vehicle would have certain advantages,relative silence,low emissions,oodles of starting torque and no need of for a transmission, plus the difficulty by officialdom in determining horsepower.Of course fuel economy is not going to be one of them.Would be ideal for a directly driven pusher trailer in stealth mode,could be disguised as kiddie carrier.
A 12" rear drive wheel at 600 rpm is good for 22 mph.That's a good speed for a small steam motor.The best arrangement would be 2 side by side single acting cylinders from 2 stroke engines,steam is admitted through the spark plug hole,with some kind of rotary variable cut-off steam distribution valve above the heads.That's the hard part to come up with.Lot's of fun for hardcore machinists.
A burner from a waterheater,and a tube boiler.The controls would be a challenge though, considering the location.RF servo setup?