Our shocks are just plain to small to even consider some of the damper technology that’s been posted within this thread.

You also have to consider an R/c cars scale speed if you transferred this up to full size then I am afraid your full size cars suspension would react the same as your R/c car.

Racing today was fun. perfect weather for it up here in oil country.
One of the new guys had a Schumacher Cat SX2. Schumacher sure do make cars that look good. like an engineers wet dream. I want one.
The shocks are mega silky smooth and the springs dead run true. nicely made.

Most likley there were ques of people lined up to tell Patek Phillippe, in the late 18th century, that his idea was utterly impossible.

I don't understand what you mean. Can you explain please?

I think Ollie means that for all our cars are "10th"scale they only weigh approx 1/100th that of full size?

I think what he means is that if we were truly 10th or 12th scale then the full-size version would be doing something like 250 to 350mph. Imagine what the suspension of a Baja buggy doing 250mph would be doing - apart from tearing itself to pieces!!

If a 1:1 WRC car on something like the Acropolis Rally was doing 100mph across rough terrain, then our cars should be doing something like 10mph. If you drive your car at that speed, the suspension is very well behaved!! I'm guessing Off-Road cars do something like 25mph, and at least 5mph in the tightest turns. That would mean the WRC car doing 250mph on the straights, and about 50mph in a tight turn. Just imagine what that would do to the suspension!!

A 10th scale car doing 10mph does not equate to a full size car doing 100mph. Simply multiplying the speed by the scale does not work.

An example from the real world:-
A whippet can reach speeds of 35 mph and is very close to a half scale grey hound. Yet you do not see a grey hound running at 70mph. More like 40mph.
Similarly, the top speed of a humming bird is equal to that of a goose.

The scale speed calculation which provides the most realistic performance where the scale model performs in a realistic manner:-
The speed is found by multiplying the 'real' speed by one over the square root of the scale.

A 10th scale model doing 25mph equates to a full scale speed of about 75mph.


maybe 1000th even?

(thats weird.. i think my spell check messed with the 'th')

Sorry, dude, you're going to have to provide evidence on all that above.
I've not spoken to a whippet recently, but I also don't remember a whippet ever claiming it was a 1/2 scale greyhound

Ok. I will give it my best shot. or to be more specific, I will give it Bob's best shot.
First check out Bob's creds.http://www.astroflight.com/index.php...roducts_id=166
here is a link to a PDF file that Bob wrote on scale.http://docs.google.com/viewer?url=ht...ScaleSpeed.pdf
Not all of this stuff applies but none the less an interesting read.

Some of you may remember the Micro-Racing Cougar, an 80's 1/8th nitro buggy with adjustable oil loop shocks.
http://www.twf8.ws/new/other/museum/cougar.jpg



Wouldnt it be (kind of) easier to scale down Bose-type suspension? Electromagnetic computer-driven suspension, that is.



That's so cool BTW :woot:

The way i see it is, If your 2.2 inch 1/10th wheel and tyre hit a 10mm bump at 30mph on your model car that would equate to your average 15 inch wheeled 1/1 scale car hitting a bump of about 70 mm. With a model car you would struggle to notice the bump, if you drove your family saloon up a kerb at 30mph you would at least smash your alloy wheel and worst case push the strut through the bonnet. You would need a monster truck like the Gravedigger to get a reaction similar to that of a model car and those monster trucks DO have great big disproportionately large dampers and 2 for each wheel at least. Our little toys have simple yet highly effective dampers really all things considered.

Any active suspension is illegal per ROAR, EFRA, and IFMAR rules. As per the scaling factor, prove to me that it exists in fluid dynamics and win a nobel prize :thumbsup:

Honestly though, we run a power to weight ratio in excess of F1, with chassis stiffness that they could only dream of in relation to their damper rates. From an engineering perspective, it is a very interesting design problem.

I have decided to build a shock dyno. I plan to use a real time force measurement device (load cell on datalogger) and get real data. I have a full CNC machine shop at my disposal, and CAD software. This is the best comprise, aside from a 7 post shaker ( which I hope to someday build, someday:drool:).

Fluid mechanics are really, really complicated. Aside from doctorate level math, I really think the only way is trial and error on a repeatable test device.

FYI; the spring damper equation is:

Force= Spring Rate (K, in lb per inch) times spring compression (X, in inches) + Damping Coeffecient (C, in lbs per inch speed) times velocity ( in inches per second)

So

F= KX+CV

The objective of the shock dyno is to find a graph of C versus velocity . I plan to post these for most popular piston/oil combos, but if anyone else has this info, please share :)

thought i could share some pictures of our rigg.
we can measure 1.5hz(stroke per second)to 55hz
thats about 2meter/second
To simulate a car dropping from 0.5 to 1 meter we have the weight with
the wheel on.
I will post testresult on our homepage when i have some time over.

Brilliant!

From http://en.wikipedia.org/wiki/Microfluidics:

"The behavior of fluids at the microscale can differ from 'macrofluidic' behavior in that factors such as surface tension, energy dissipation, and fluidic resistance start to dominate the system."

Elvo, exactly my point. Folks were trying to relate what is going on in their shocks to some linear scaling factor, ie 1/10th, 1/2, etc. Microfluidics is really cool subject matter, and there is still a ton to be learned ie fluid behaviour.

My point exactly - you can scale the size and weight but you can't scale the Laws of Physics. All these phenomena are present in full-size cars, gas turbines, etc.

Scale is an easily defined word, it means to use numbers to measure or compare the level of something. In that sense, we can scale everything that we do in modeling and make comparisons. However, it doesn't work that well when things start to move. However, you can't say there is no comparison since, if there weren't, none of the experiments above would be worth doing!!

The last time I looked a whippet was about 20" tall and a greyhound about 28", so hardly half-scale. And, according to Science Daily, their high athletic ability is probably due to a genetic mutation. Apart from that, great analogy!! :p

Hi Ronny,
Thank you for posting those pictures. That's a nice setup you have there.
Looks easy enough to make but would be a whole new project deciphering results!


I would like to apologise to any disgruntled whippets.

What are people's understanding of the term 'pack' in regards to damping levels?

something to this
 

Hello Guys,
this thread is very intersting, so my 5 cents:
the " problem " of our shocks seems to be, that high-speed ist to strong, which unsettles the car. But we need strong damping in low speed ( 0.5-1.5 Hz ) to give a driveable feeling and controlling wheigt transfer.
Some companies like Asso or Tamiya and Losi have these shocks witout blades, there is an oil/air mixture in it, which helps to soften the highspeed because the air bubbles expand under the piston.
Shocks like that have been used in those stadium trucks ( the real ones) in the 80is. The where position sensitive too...some iteresting books about that are availible

As somebody said, chaning stacks and stuff would make our cars very hard to setup, so the way is to think about floating pistons, maybe to slow down the last few mm's in rebound and to use an air/oilmixture in the shock.

One thing, chassis roll does not induce weight transfer, otherwise a pan car would not have weight transfer...its the moments which make the weight transfer.

Sorry for my english.

Maurice

I figured it may be something like this.
http://www.oople.com/forums/[IMG]htt...gg538/pack.jpghttp://www.oople.com/forums/[IMG]htt...gg538/pack.jpghttp://www.oople.com/forums/[IMG]htt...gg538/pack.jpghttp://www.oople.com/forums/%3Ca%20h...38/th_pack.jpghttp://www.oople.com/forums/[IMG]htt...gg538/pack.jpghttp://i471.photobucket.com/albums/r...538/pack-1.jpg

Firstly can i see i have read through this thread a few times now and find it completely fascinating, both the mechanical and the fluid dynamics guys seem to be getting there point across.
So can i please just ask a (relatively) simple question, where are you now. are we looking at a 2 stage piston with a external reserve, or link from one to another. a different internal piston design or mix of the both. you have all been talking about dampers and of course it is a major component but i think that the "bump stop" issue was a bit lightly glossed over and is still a very important part of the whole situation as is spring rate. which does of course effect shock shaft speed, and hence low and high speed shaft speed.
Please forgive for intruding on a highly fascinating thread but racing 1/8th rallycross i find striking the right damper rate imperative. and would love to gleam all the information i can.