MBX7R Eco Standard Spring Vs. Dual Rate Springs
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- Опубликовано: 8 окт 2024
- (Disclaimer: this video made in Final Cut Pro, b/c I hated the demo of Premier elements. Don't assume that because previous videos have the Adobe Premier banner through the middle, that I must have liked it and decided to continue using it.)
In this video I am comparing the standard suspension to a modification where I installed small springs inside the shocks that create a dual rate effect.
What is very clear on the bench, and which can also be seen on my dyno, is that the dual rate springs allow the vehicle to return to it's static ride height much quicker. In the split screen comparison, it is clear that the dual rate springs allow the chassis to settle after 1/2 a rotation of the dyno wheels, compared to the standard springs, where the chassis has not yet settled after a full rotation of the dyno wheels.
The way these dual rate springs work is that when the vehicle is at ride height or when the shocks are compressed, the standard spring is supporting the vehicle as usual. The inner springs are just floating inside the shock. But on rebound, when the suspension rebounds past the static ride height, the inner spring is compressed. The effect is that the spring rate of the main spring drops off rapidly. At full droop, there is almost no force pushing the tires down.
There is a lot of adjustability with springs like this, depending on what you want to achieve. The springs I chose were intended to cancel out the spring's force at full droop of the suspension. If I chose a softer spring, I would have a little more spring force at full droop, and likewise, if I chose a stronger spring, I would actually limit suspension droop.
To spec out the springs, I first had to know the spring rate of the main springs. And then I measured to find out how compressed the spring is at static ride height, and also at full droop. I need to know how much space there is inside the shock, between the bottom of the piston and the bottom of the shock body. Ideally my spring should match this length.
To determine what spring rate I needed, I made a spreadsheet that showed the force the spring exerts between full droop and static ride height. Then I experimented with what spring rate I would need for the inner spring to cancel out the force of the main spring at full suspension droop.
Intuitively it would seem like a very strong spring would be needed, but as the suspension rebounds, the main spring is progressively applying less force. I only need to cancel the spring's force when it is extended, when it exerts the least amount of force.
This project is quite a bit more complex than just buying a spring from the company that makes my kit. If you try it, it might take a couple tries; it took me two tries to get it right. To get the right result requires taking measurements to determine the correct spring strength, spring length, and compressed spring length. It isn't terribly difficult, but it requires a lot more work than normal "upgrades" to an RC.
impressive work man ! so the little spring inside pushes the big spring outside right ? in my mind it acts as if the oil would be thinner, what do you think ?
It is actually a bit more like a thicker shock oil, because the inner spring slows the rebound as the suspension gets closer to full droop.
Notice how the chassis settles quickly after hitting the bump, and is completely settled before the next bump comes around. But without the inner springs, the car settles much slower, and does not completely settle before the bump comes around again. I think this is why the car seems to be more affected by the bumps with the inner springs--without the inner springs, the car has not returned to it's static ride height before it hits the bump again.
Another thing is that without the inner springs, the wheels would snap down, and the droop screws hit the stops pretty hard. The stops were getting worn out! Of course this is because I am using the Fioroni bypass pistons (i.e. ball bearing valves for rebound), so they rebound much faster than normal shock pistons.
The faster rebound is good and bad. It is good for keeping the wheels on the ground after hitting a bump, but it also causes the car to lift, which makes it unstable. But with these inner springs, I have rebound that starts out fast, and gradually slows/ gets weaker the further the suspension rebounds.
With the inner spring, there is very little spring force being applied to the suspension when it is at full droop--the two springs are pushing against each other, cancelling each other out. As the suspension compresses, the inner spring rebounds, causing the effective spring rate to increase progressively. When the inner spring is no longer compressed, the spring rate is linear.
The intent is that the transition from progressive to linear spring rate will occur at the static ride height. This will reduce the tendency of the ride height to change as the car accelerates or hits bumps.
The reason I want to do this instead of other options is because I want the benefit of more droop when landing big jumps, but I need to fix the problem of dynamic ride height always changing, always being much higher than what I set it to on the bench. That was causing the car to be unstable/ unpredictable. I could go back to standard pistons and greatly reduce droop, but I still think the dual rate pistons should be an advantage, if I can get all the adjustments right.
longest youtube reply EVA !! lol, thanks for the detailed answer, i copied it to your thread on rc tech because it is so detailed. as a jumper, the most interesting setting for me is small holes is the pistons, shocks as close as possible to the wheel ( tekno suspension ) : this "pack" allows me to jump higher
If I were you, I would investigate getting stiffer springs rather than relying on shock damping/ pack to launch properly. I'm thinking double the strength of the standard springs? Stiffer will launch and land better, but won't handle rough stuff as well. If they're significantly stiffer, they will need to be shorter... You'd have to do what I'm doing and order from McMaster-Carr, or some specialty company that specializes in springs. You can buy anything you want if you know the specifications.
thanks for the tip, i indeed use the stiffest spring i found in RC. good thing is that the GPM shocks i use have stiffer spring. ordering at mc master is a real problem for me : they don't send to my remote island ! i wished i could buy some quality aluminium sheets from them !