swinging engine suspension
Moderators: Dan J, Diesel Dave, Crazymanneil, Stuart
swinging engine suspension
hi guys, does anybody know of any serious design problems around using a swinging engine rear suspension ( as used commonly in scooters)? obviously these are small light- engined units as opposed to a dirty great cast-iron lump - but what i'm really asking about is are there innate problems such as handling/braking characteristics of this design? any thoughts or internet leads greatly appreciated, cheers jon.
-
Byrdman
- I luv the smell of Diesel...
- Posts: 156
- Joined: Tue Jan 09, 2007 5:43 am
- Location: Chicagoland, Illinois, USA
- Contact:
The only issue I would see, besides packaging of course, would be unsprung weight. Unsprung weight has a pretty dramatic effect on motorcycle handling, especially turn-in.
http://en.wikipedia.org/wiki/Unsprung_weight
http://en.wikipedia.org/wiki/Unsprung_weight
-
Diesel Dave
- Site Admin
- Posts: 1016
- Joined: Sat Dec 02, 2006 1:21 am
- Location: Essex, UK
- Contact:
Unsprung Weight
Unsprung weight is always a problem.........
Think of it like this; get hold of a full tin of beans and swing it back and forth- see how much effort it takes to change it's direction once moving?
Now eat the beans and try again -much easier yes!
So this is the same as trying to deflect a heavy unsprung weight; it resists moving and when it does it wants to keep going in the direction it started out.
So a heavy wheel weight does the same thing, when you hit a bump in the road it strikes it hard and then wants to keep traveling upwards away from the bump. To control this movement you need a lot of damping = harsh ride!
This is why alloy wheels on a car improve handling.
No as someone who has raced 50cc auto scooters with swinging engines I can say that it only works because the engine assembly is sooooo light - I can pick one up with the wheel attached in one hand. CVT transmissions don't weigh anything either.
If you are intent on going with this idea I'd try to put the motor on the point of balance (fulcrum centre) - this way it moves as little as possible. Same goes for the vertical position too although this will give you some chain alignment problems. The easiest way would be to have the motors output shaft in alignment with the swing arm pivot.
It's something I thought about when designing a Cushman Look-a-like however the need for a final epicyclic gear reduction killed this one off early.
All ideas are good ones in the diesel bike world!
Dave
Think of it like this; get hold of a full tin of beans and swing it back and forth- see how much effort it takes to change it's direction once moving?
Now eat the beans and try again -much easier yes!
So this is the same as trying to deflect a heavy unsprung weight; it resists moving and when it does it wants to keep going in the direction it started out.
So a heavy wheel weight does the same thing, when you hit a bump in the road it strikes it hard and then wants to keep traveling upwards away from the bump. To control this movement you need a lot of damping = harsh ride!
This is why alloy wheels on a car improve handling.
No as someone who has raced 50cc auto scooters with swinging engines I can say that it only works because the engine assembly is sooooo light - I can pick one up with the wheel attached in one hand. CVT transmissions don't weigh anything either.
If you are intent on going with this idea I'd try to put the motor on the point of balance (fulcrum centre) - this way it moves as little as possible. Same goes for the vertical position too although this will give you some chain alignment problems. The easiest way would be to have the motors output shaft in alignment with the swing arm pivot.
It's something I thought about when designing a Cushman Look-a-like however the need for a final epicyclic gear reduction killed this one off early.
All ideas are good ones in the diesel bike world!
Dave