PMW Shocker

[liveforphysics]

I'm confused a bit with the dampener method used in these rubber designs. Getting the wheel to move up and down and behave like a spring is the very simple and definately not the goal of a suspension system. Giving the wheel the ability to move the wheel when needed to keep the bike platform stable, and then NOT behave like a spring afterwards is the big trick to good suspenion (aside from rigidity of course).

The goal is not to mount tires onto the bottom of a pogo-stick, you would handle much better a rigid bike.

I must be missing some critical element that prevents them from behaving like a rubber band.

Can anyone help me to better understand?

[Miles]

Well, there there is some internal damping when using rubber as a spring. Also, the lighter the unsuspended weight, the less the level of dampening required....

The Moulton New Series bicycles use a fluid damped conical rubber suspension unit, for the rear suspension.

[northernmike]

Wow, Greeves bikes are shockingly nice...

[Sheriff Jon]

I'm confused a bit with the dampener method used in these rubber designs.

It is quite simple really, not all that hard to figure out. It is very much like the link that Miles put up except on my Hoverboard the large tube is square and the center arm is diamond shaped and it uses 4 rubber compression rods instead of three. I don't know 'why' it works as well as it does, but it does. Perhaps your confusion is because you are over complicating matters by trying to compare it to more complicated suspension systems with their inherent strengths and weaknesses?

[northernmike]

Hoverboard 1.0

No CIDLI.

[liveforphysics]

I don't have any trouble seeing how it can behave like an elastic material, and cause the suspension to follow hooke's law and behave like a pogo stick. No trouble seeing the function of the spring portion of the suspension at all. I'm puzzled about dampening.

Now Miles said the Moulton uses a fluid in a cone shaped rubber piece to behave as a dampened spring. I could definately see this working, and working very well for low travel quanities with a low frequency of actuations.

However, something with 12" of suspension travel, moving at 60mph across rough terrain dumps and increadible amount of heat energy into the shock oil. So much energy that large aluminum tubes in the path of strong air flow get too hot to touch, and overheat. Everytime a fluid damper functions, it functions by time shifting the kenetic energy release of the energy stored in the spring that absorbed the bump. This process works by internal friction on a viscous fluid being made to transfer from one chamber to another through a small orifice. The internal fluid friction energy is huge to be able to dampen 12" of wheel travel. At speed over rough ground, it easily becomes thousands of watts of thermal energy, which is why the entire fork tubes get burning hot/overheat etc. This is because time shifting the kenetic energy on the forks return travel inherently involves a lot of energy conversion with high fluid friction losses between each step.

How does this bike's dampener system function, and transfer the waste energy by product of functioning away from the thermally sensative elastomers? I think he said, no fluid, no seals, no stiction. Does this also mean no dampening? Or if the dampening is internal to the elastomer, does this mean dampening for 30seconds at a time at speed on rough ground before the temperature exceeds the plastic zone on the elastomer? How does he reject the dampener energy and internal friction from an elastomer without fluid?

If the suspension is 12" travel without dampening... That's seems criminally negligant to put on something capable of high speed offroad use. 60mph trampoline. All it would take is hitting a set of dips spaced at the resonate frequency, or multiples of it, and the machine will loose control and wreck. Doesn't matter how good you think you are, taking a bike offroad that is out of shock oil results in a prompt loss of control. Dampening, rigidity, and geometry are the keys to suspension function. Take away any of them, and you took away the ability to control the bike effectively.

[Miles]

This is quite a good summary of the Moulton car suspensions:
http://www.miniweb.org.uk/mainPages/alexMoulton.html

[michaelplogue]

I'm just theorizing here - But the compression/heat phenomenon is not just a one way street. Decompression has the opposite effect. So - in theory at least - one should end up with a zero net change in temperature.

[liveforphysics]

Compression and Decompression of a gas, yep. For most things, it's internal friction of deformation both ways, but with some energy absorbed in the relaxing state, but certianly a net gain of energy from internal friction.


However, again, I'm not concerned with the spring function, or the energy absorbed by the spring function. It's the dampening that I don't understand. For example, in a standard fork, it's over a liter of fluid in each leg, with a piston and internal seals. The piston is on a rod with an orifice, and a needle/seat valve to regulate the useful diameter of the orifice. When the fork compresses, it has to accelerate fluid to a high speed and move it through the orifice into the other chamber, then on it's return path, it has to go back. Each way the fluid gets accelerated to high velocity, and this internal friction of the fluid is what provides the energy absorbtion medium to time delay the return of the stored kenetic energy in the springs of the fork. Otherwise it would be a pogo-stick with a wheel on the bottom, and you would be better off and much safer with a rigid fork.

The spring function of suspension is very simple, and I understand it well. The dampening function is where ALL the design work occurs in making a shock, and it's what has the biggest impact on the way the suspension behaves. Just a few ticks on the clickers to adjust the dampening (spring rate stays constant), and the whole attitude of the machine changes. I'm not saying he needs adjustable dampening or raceing adjustments and things. I just want to understand the mechanism that causes the dampening to function in this design, and how the thermal energy by-product of dampening is dealt with.

[huskydave]

It seems to me that because you have a pivit point you would require a much smaller, shorter shock for dampening because the arm acts like a lever. I think a small shock on the end of the lever mounted above the torsion box world work great for dampening.

[PatmontS]

Luke,
Thanks for the excellent and pertinent questions.
The compression and damping on this CIDLI suspension system is both bench and field tunable for desired performance characteristics over the 13.5" of travel front and rear.
As there are sensitive patent and trade secret issues in that area, suffice it to say...if we tells ya more we gots ta kiiillls ya.
Yes, shockingly we have eliminated the heat generation always found with traditional high performance, high travel suspension systems.
If you're able to make it to Minden in beautiful Northern Nevada we'd love to get an unbiased opinion of the prototype's capabilities from an expert with no "skin in the game". We assume you'd have no problem with the usual NDA formalities concerning these and other not yet disclosed but equally shocking details contained in this forward looking project.

[PaulM]

It seems to me that because you have a pivit point you would require a much smaller, shorter shock for dampening because the arm acts like a lever. I think a small shock on the end of the lever mounted above the torsion box world work great for dampening.

The overall energy to absorb does not change. A small damper like this would have an even harder time to get rid of the heat.

Yes, shockingly we have eliminated the heat generation always found with traditional high performance, high travel suspension systems.

Shocking indeed. With all the hype this "Shocker" is getting, I will be shocked if it ever sees the light of day. Surely the Japanese will buy the project and mothball it to keep it from embarrassing their own machines.

[huskydave]

I will wait to pass judgement until I talk to someone who is unbiased that rode this bike and tested it properly. The forces on the frontend are the same but at the end of that lever it requires less energy to dampen it much like a rear suspension on a swingarm. The arm acts like a lever you don't see 2 15" shocks on the rear of a bike because the swingarm transfers only a percentage of the actual force on the bike to one small shock that can handle the forces. This design will imo transfer less force past the pivitpoint. Will it work in realworld conditions? who knows but I think it has potential.

[PaulM]

The arm acts like a lever you don't see 2 15" shocks on the rear of a bike because the swingarm transfers only a percentage of the actual force on the bike to one small shock that can handle the forces.

The swingarm is amplifying the force seen by the shock. That is why the spring on a rear shock is many times heavier(stiffer) than fork springs.

[liveforphysics]

The arm acts like a lever you don't see 2 15" shocks on the rear of a bike because the swingarm transfers only a percentage of the actual force on the bike to one small shock that can handle the forces.

The swingarm is amplifying the force seen by the shock. That is why the spring on a rear shock is many times heavier(stiffer) than fork springs.

That's right. You can make the stroke displacement that the shock body itself moves be 1mm or 1m, but the force changes by the same multiplier, so the energy is the same either way.

Lift a 10lbs weight 10ft, or life a 100lbs weight 1ft, and the energy is the same.

The energy in this situation it determined by the weight on the wheel, and the amount and rate that it moves. No matter how you configure the linkages, this is still he amount of energy the suspension deals with.