Hello Gents,
I first have to apologize for the delay, being pretty busy with several thing, including doing my homework for this chart,to provide answers on a clear manner.
Quote:
Originally Posted by IceMike
my main question i guess would be could u make a shock filled with light oil and a big piston but with a really hard spring have near to or the same compression and spring bac rate as say a shock with hard oil and a soft spring. and how u would calculate this
|
Mike: As you know, the couple oil-piston works tougher to slow down the suspension movement, the spring on the other side want to return everything in the initial position. So, with light oil-small piston you get a certain effect and with heavy oil-large piston you get another effect. You may know this point, there is some tricky thing in fluid mechanics, the same fluid going thru the same surface can behave differently depending the shape of surface shape (round, square, oval) and the surface edges. For the spring, a soft (low rate) spring will need more travel (compression) to give the same amount of force as a hard (high rate) spring. To calculate everything tougher, you have to use some physics/mechanics, solving some equation. I won't go for the whole theory and dynamical equation but this theory ends with the following: damping coefficient (m for mechanical as it came form a mechanical equation) Cm = (2 x mass x spring rate)^0.5. This damping coefficient Cm is the one set by your mass and spring and it have to counter balance on some way the couple oil & piston which give a damping coefficient Ch (let name it so as it is fluid mechanics / hydraulic). Depending what you want to achieve, the type of car you are running basically, you want the damping ratio equal to a certain value. The damping ratio is Ch / Cm and, for passenger car, it is around 0.3 as for racing car such F1, it's around 1. That only for 1 side of the car, you now need to take in count the other and on the car as it is a whole mechanical system. If you use stiffer spring on one end, you get more mass on the other end. And now you entering in the process of testing and play with the car, in out case of RC car, rather than trying to do some math as math are not such straight forward to this point. I hope I'm clear.
Quote:
Originally Posted by Welshy40
What about traxxas pistons, from the TRX1 as an example. If your doing Kyosho the Traxxas will be just a fraction bigger than that.
|
Welshy: I can do the math for what ever piston someone provide data, Traxxas included.
As said, I did my homework as best as I can do. The following link (see below) provide much better data than the first document submitted (even if the link still the same
). Those data are from off road cars, I'm waiting for some additional information, italic number are an approximation to do the math on first instance, reason the document still in "draft mode". If you want to see some more data, you need to provide the following:
Piston diameter
Piston holes diameter
Number of holes
Rod diameter
Shock bore
A good vernier/caliper and tools handling can do the job, otherwise, you can use some more professional-industrial tools
Depending what data are provided, I might put tougher the document on the first post and this one or leave them separated.
http://www.petitrc.com/setup/ShockPistonComparison.pdf
Hope that clear and helpful, just let me know!