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Sat, Dec. 24th, 2005, 11:19 pm
Adult Ride-On Toys

How about if there was a ride-on toy which you stood on and jumped, and the drive always happened on the down-stroke, freewheeling until your rate of fall made the rate of motion imparted to the wheels exceed the rate at which they're currently rotating? The advantage to this approach is that it can operate quite efficiently at a wide range of inclines and speeds, plus it's a fun bounce-bounce-bounce motion, and it has the benefit of being just plain different.

(I was going to draw an analogy with diabolo whipping, but all the web pages on diabolo whipping get the physics all wrong. Ah well.)

The mechanism for one of these turns out to be quite simple. There's a single wheel on a regular fork in the front, and two wheels on a single axle at the back. The platform you stand on is hinged at the front and you stand towards the back, right in front of the rear wheels. There's a spring under the platform to keep it pressed against your feet as you jump (alternately you could strap your feet in, but that sounds neither safe nor fun, and would increase the amount of impact on your legs). There's a segment of a very large gear sticking up from the back of the platform you stand on, and it meshes with a gear which can freewheel which is attached via a chain to the rear axle. The gear segment can't directly hit the rear axle beacuse it would need to extend downwards to mesh at the top of the stroke, which would then make it dig into the ground at the bottom of the stroke.

For maximum stability and control the front fork should angle backwards chopper-style and have a large wheel on it. There should also be a hand brake which goes directly to the rear axle. (I have an otherwise very nice jogging stroller which for some unfathomable reason has the hand brake go to the front wheel, rendering it utterly worthless when going downhill.) Yes I'm aware that this would look completely ridiculous, but this is my fantasy vehicle, and I like my fantasy vehicles to look like the world's dorkiest harley.

A nice feature of this vehicle is that it's in principle quite practical. It can go uphill, (it's a simple exercise to show that the gearing ratio directly controls the maximum incline you can go up at), can achieve quite decent speeds, is simple to ride, and is fairly low impact. The downsides are that due to the lack of variable gears it's a little bit of work to drive fast (but quite good at getting your leg press to a really good weight) and it has a very long dead zone in the stroke, so it can't sprint like a bicycle. For overall efficiency it's unclear how it would compare to a bicycle, but on general principle I'm going to guess it's less efficient, but my guess is not horrendously so.

Sun, Dec. 25th, 2005 09:52 am (UTC)

I gotta admit, Bram, you have some strange ideas! Interesting and perhaps genius, but strange!

Sun, Dec. 25th, 2005 02:39 pm (UTC)

Front wheel brakes are far more effective at stopping you than rear wheel brakes. The decelleration caused by the braking puts more weight on the front wheel(s) and less on the rear wheel(s). You can try this out easily on a bike. However, if your rear wheel goes into a skid it is easy to recover, but if your front wheel goes into a skid you have lost control of the bike, so to safely brake a bike you use both front and rear wheels.

Sun, Dec. 25th, 2005 03:55 pm (UTC)

there's also the small problem of the bike/stroller/whatever's rear wheel lifting off the ground or pitching the rider forward if you slam on the front brake

Thu, Dec. 29th, 2005 06:20 pm (UTC)

On all the vehicles I mentioned almost all the weight is on the rear wheels, so the effect of braking pushing the front wheels into the ground is fairly small. Bicycles have a much more even distribution of weight between the two wheels.

Sun, Dec. 25th, 2005 05:07 pm (UTC)

I'm having a hard time following your description, but there was a "bouncy bike" at Burning Man in 2004 and 2005. The front wheel provided steering, while the rear wheels (actually, it was a tricycle not a bicycle) had the hub offset from the center. The rider stood on a platform attached to the rear hubs, and by pushing down with her legs at the right time was able to provide rotary force on the rear wheels.

Tue, Dec. 27th, 2005 07:28 am (UTC)
chronicfreetime: a simpler construction


Thu, Dec. 29th, 2005 06:21 pm (UTC)
bramcohen: Re: a simpler construction

That's a very cool web site! I linked to some of their vehicles in the next post.

Tue, Jan. 3rd, 2006 12:47 pm (UTC)
saltation_lj: == "Kangabike"

We used to ride these as kids in Australia at school fetes and things. They were a little more primitive than your description (fixed rear wheel) but worked pretty much the same way you describe. Loads of fun zipping round basketball courts and ovals on them, then juddering to a halt if you get the rhythm wrong.

Looking back with fuzzy memory warped by now being twice as tall, I'd reckon they were scooters with the rear wheel's axle re-welded off-centre.

Thu, Jan. 5th, 2006 12:49 am (UTC)
bramcohen: Re: == "Kangabike"

Can you give more details? Is this a one or two-wheeled vehicle? (It sounds like two.) Did you stand on it or sit on it? Were your feet on the pedals or on a pogo assembly?