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RC Shock Dyno Test Results

Old 02-24-2018, 08:05 PM
  #106  
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Originally Posted by gticlay
Great stuff to both you and Ray - thank you for doing the work. I'd mostly be interested in the "pack" stuff. In my mind, we are trying to achieve what the HSC adjustment does on bicycles and other more adjustable suspension when you have a high shock piston velocity - it makes an incredible difference when you are going down a fast trail at a bike park.
I think pack is what a lot of people are interested in. I did find it more difficult than I thought to consistently measure it, and especially quantify and define it, but I think I have a way that is showing to be repeatable. What I found to be interesting was what I am calling the "pack ratio" which is the the amount of damping above the linear low speed damping that I measure with the dyno. I believe with this knowledge, racers will be able to tune each of these separately depending on their piston and oil assortment. I hope to take the guesswork out of what to choose if you like your ride handling, but need more pack. These results are coming soon, as I'm working on them right now.
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Old 02-24-2018, 08:27 PM
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Originally Posted by shannow
Thank you a lot for all these precious informations !
Do you know where I could find something to hook my computer and measure strain like you did ? Could only find expensive specialized computers to do so, which isn't surprising.
I would have the project of making a motorized table that would oscillate front/rear left/right (roll and pitch) and I would then be able to see what happens dynamically on each tyre, giving me the graphic curve of the roll resistance. And then I could even see the actual relationship between the 3 roll actors (viscous, kinematic and elastic) .
What you probably need for all that is displacement, velocity, and force measurements. Displacement and velocity are fairly easy, simple instrumentation with no specialized conditioning. However, the Force (strain) is very different and is what instantly jumps up the cost of building one of these.

For each strain gauge transducer, you will need a higher end strain conditioner. I've seen some on eBay or other places for as little as $400 (Omega was the brand I saw, Daytronic 3270 is what I have), but really not much cheaper. I first tried to use a $20 strain conditioner used in your typical digital scale. It worked, as in, I could measure a static weight, and it was very accurate. However, as soon as I used it dynamically, I found it no longer worked. My first set of results gave me a VERY high amount of hysteresis. I thought it was the way the shock actually worked. But after further investigation, and borrowing a high end conditioner, I found it was in fact the $20 conditioner. Electronically, it has a high amount of lag in it. So, it works fine if you have time to let it settle, but if you are looking for a quick response, you need a high end conditioner.

For the data acquisition, I use a Windaq DI-155, but they have a replacement (better) one now. I tested/compared this one to a $12,000 acquisition system, and for what I was measuring (force, displacement, velocity at 400Hz), this one was perfectly accurate. The computer only needs to be a basic PC. I also use an add-in to send data directly to Excel, which makes using the windaq a lot easier. This is only a 4 channel system though, so if you want to build a multi-axis table, you will certainly need more channels, and that will greatly increase the cost as well.
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Old 03-18-2018, 01:25 AM
  #108  
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icecyc1, would it be possible to generalize a rule about correlating shock oil to spring rate? I touched this on my dyno thread, but I thought I'd bring the question to you.

The question is, assuming the piston stays the same, does the ratio between the viscosity of the shock oil and the spring rate have a meaningful relationship that stays constant over the typical range of conditions, like temperature and shock piston type?

If I have a known viscosity oil in my front shocks, and I know my front and rear spring rates, will solving a simple ratio tell me what shock oil I should be using in the rear?

I stumbled on this, and it seems plausible. I found a combination of shock oils that appeared to have matching damping properties, and the math roughly corresponds. (I didn't prefer this combination, but technically it is best.) My slow motion footage shows the mathematical solution appears control front and rear tires the same.

It is interesting to me because normally when increasing shock oil, I will increase both the same amount. But that may not always be right. In my case, I calculated combinations of oils (converted into Losi) based on this ratio:

30/22.5
35/25
40/30
45/35
50/42.5
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Old 03-18-2018, 07:05 AM
  #109  
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Originally Posted by fredygump
icecyc1, would it be possible to generalize a rule about correlating shock oil to spring rate? I touched this on my dyno thread, but I thought I'd bring the question to you.

The question is, assuming the piston stays the same, does the ratio between the viscosity of the shock oil and the spring rate have a meaningful relationship that stays constant over the typical range of conditions, like temperature and shock piston type?
Yes, there is a general rule that correlates shock oil to spring rate. Actually it's the damping ratio, which depends on the Damping Coefficient, spring rate, and mass of the components supported. You may find that your best matches will converge on a consistent damping ratio number.

Here is the wikipedia explanation for Damping Ratio: https://en.wikipedia.org/wiki/Damping_ratio
The main thing to take away is that there is something called Critical Damping, which is the amount of damping needed to most quickly get back to not moving without overshooting (bouncing). Think of it as a "plop" without the car rising back up. The fastest time you can have that happen without bounce back is critical damping. If it comes back up, you have "underdamping", if it slowly settles down even farther (but doesn't rise back up), it's called over damped.

If you notice, Damping Ratio, is simply that... the ratio of your actual damping coefficient to the Critical Damping. Critical Damping is a purely physics based value that you can calculate yourself if you know your mass and spring rate. c_{c}=2*sqrt(k*m). You can change the critical damping by either changing your spring, or changing the mass. Your Damping Coefficient is purely based on what you do to your shocks, which includes your oil and your piston choice. So, if your mass stays the same, and you can change your spring rate, you will change the critical damping. If you don't also change your damping coefficient (oil and piston), your damping RATIO will therefore change.

It turns out, theoretically and supported by race car drivers, the "ideal" damping ratio is about 0.67. This value, theoretically, is underdamped and allows your suspension to get back to steady state as quickly as possible (even faster than critically damped, even though it has overshoot). This allows your suspension to be active but not overactive.

Now, while I said 0.67, this is not a hard and fast rule. Some forms of driving/racing will find a lower or higher value is more ideal. For instance, your average passenger car is made to be around 0.25 or so. This provides a comfortable ride. I've read where F1 race cars are over damped to around 2.0, but they have very advanced and special reasons for doing so. Autocross finds 0.65-0.70 tends to be the best overall. I have calculated damping ratios on our off road cars, and they tend to be around 1.0-1.1 for a box stock setup. I've hypothesized that the reason for this is the jumps, and is the compromise you must make because it's such an important part of the race.

So, to make it more complex, there are different damping ratios you can calculate. The DR you are seeing on your bench is the typical one where you are controlling the motion of your tire/wheel/suspension. This is the main one in which the numbers above support. Then, you have another damping ratio, where your Mass is your sprung mass, or the chassis of the car. In this case, you assume your wheels are locked to the ground, and you are controlling your body motion on a landing of a jump. If you notice, your chassis (divided by 4 for distribution on each shock on your car) is much heavier than your tire/suspension. So, your damping ratio will be different in that motion.

Thus, I propose a different way to approach shock setup and use what I call a "pack ratio". Pack ratio is simply the ratio of your damping coefficient under impact, vs your damping coefficient under normal slow speed operation. Then, if you can control that ratio (think VRP game changer pistons), you can independently control the damping ratio for driving (normal damping range controlling wheel motion while driving), and impact damping when you land jumps.

RC Crew Chief does have the suspension modeling, and now one of the setup numbers it provides is now the Damping Ratio. In this program, you enter all of your dimensions, mass, springs, oils, etc, and in the end, it will calculate Damping Ratio for you. If you enter your car into that, and try out different springs/damping, you should start to see a good correlation between the number shown, and what you see on your dyno.
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Old 04-27-2018, 03:32 AM
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Hello icecyc1,

Your tool is indeed very very useful. Thank You very much for sharing to us.

Just last week, I was racing at FEMCA 2018 in Batam, Indonesia, and pitted close together with Mugen Japan Team. Atsushi Hara was one of the Leading Driver on the Qualifying day, although Kyle McBride TQ'ed the race, at the end was Hara San comes out as the winner. An interesting information from the Mugen Team that they are using 8 holes Piston with 4x1.0mm and 4x1.4mm holes. I tried the Piston set at the remaining 5th and 6th Qualification and felt very nice. Low speed felt plush that generate good traction as the surface is relatively slippery but also have a very solid impact damping keeping the chassis not to bottom out.

Now, could adjust the tool so that we could calculate this kind of mix/stager hole Piston Type?

Cheers..

Originally Posted by icecyc1;15164056[url
https://drive.google.com/file/d/1Q6xFRzMUFWw6QGVKcraYzGybSxl1JhWA/view[/url]
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Old 04-27-2018, 05:26 PM
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Originally Posted by stanleyw808
Hello icecyc1,

Your tool is indeed very very useful. Thank You very much for sharing to us.

Just last week, I was racing at FEMCA 2018 in Batam, Indonesia, and pitted close together with Mugen Japan Team. Atsushi Hara was one of the Leading Driver on the Qualifying day, although Kyle McBride TQ'ed the race, at the end was Hara San comes out as the winner. An interesting information from the Mugen Team that they are using 8 holes Piston with 4x1.0mm and 4x1.4mm holes. I tried the Piston set at the remaining 5th and 6th Qualification and felt very nice. Low speed felt plush that generate good traction as the surface is relatively slippery but also have a very solid impact damping keeping the chassis not to bottom out.

Now, could adjust the tool so that we could calculate this kind of mix/stager hole Piston Type?

Cheers..
Stanley, did you notice what springs they were using? I'm curious if their spring set-up was similar to what I've chose and what you were trying out.
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Old 04-27-2018, 06:41 PM
  #112  
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Originally Posted by stanleyw808
Hello icecyc1,

Your tool is indeed very very useful. Thank You very much for sharing to us.

Just last week, I was racing at FEMCA 2018 in Batam, Indonesia, and pitted close together with Mugen Japan Team. Atsushi Hara was one of the Leading Driver on the Qualifying day, although Kyle McBride TQ'ed the race, at the end was Hara San comes out as the winner. An interesting information from the Mugen Team that they are using 8 holes Piston with 4x1.0mm and 4x1.4mm holes. I tried the Piston set at the remaining 5th and 6th Qualification and felt very nice. Low speed felt plush that generate good traction as the surface is relatively slippery but also have a very solid impact damping keeping the chassis not to bottom out.

Now, could adjust the tool so that we could calculate this kind of mix/stager hole Piston Type?

Cheers..
Glad you find the tool useful. Interesting to hear about their pistons. A little tidbit... based on what I had learned using the dyno, I had developed a multi size hole piston a couple years ago. What I had found is that you need the smaller holes to be 1.0mm or less. We used 0.7 and 0.8 mm small holes along with 1.7 or 2.0 mm holes. I did a 3 hole (large) with either 3 or 6 additional smaller holes. What this effectively did was increased the pack ratio, or the high speed damping compared to the low speed damping. Small holes any larger than 1.0mm did next to nothing more than just a basic piston could do.

I have made my own spreadsheet that does in fact predict the damping of these multi hole pistons. Unfortunately, it gets pretty complex and causes me to have to think deeply every time I use it. The basic rules for multiple size holes is to find the damping coefficient for each "set" of similar sized holes, then add them up as though they are in parallel with each other. For example, If one set of holes give a damping coefficient of 0.9, and the other set of holes gives a damping coefficient of 1.3, then combining them you will get 1/(1/0.9+1/1.3) = 0.53. It will always be lower than either one of them.

If you want to try to simulate the tiny hole multi-hole pistons, you can try this: First, take your large holes and ignore the smaller holes to find the damping coefficient for just them. Keep the low speed DC value, say it's 0.9. Also, keep the Impact value, say it's 1.6. In your hybrid pistons, the 1.6 will be your final hybrid Impact DC value. Now, run the same calculation on ONLY the tiny holes, say they give you a DC of 2.2 (because they are so small, they will be very stiff). Now, you can use the equation above to find your low speed damping value: 1/(1/0.9+1/2.2) = 0.64. So, as you can see, the low speed damping was reduced quite a bit by the holes, but the assumption is that the tiny holes "close up" during impact compared to the large holes and effectively don't exist. This isn't exactly true, but it's reasonably close (your impact DC will actually be slightly lower than the large hole Impact DC in reality) So, in summary, if you ran a piston with just the large holes, you had DC values of 0.9 and 1.6 giving you a pack ratio of 1.78. Your hybrid pistons have DC values of 0.64 and 1.6, giving you a pack ratio of 2.5. So, you kept your impact value the same, but you greatly reduced your low speed damping. This should help you keep your pistons stiff for landings, but soft for handling.

I really believe the compromise for off-road damping ratios of about 0.9-1.1 are because you need it for landing, so you compromise the "ideally perfect" 0.67. Increasing the pack ratio allows you to get closer to the ideal range while not having to compromise your landing damping you need.
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Old 04-27-2018, 09:56 PM
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Hello fredygump,

Hará San use F 1x4/1.4x4, Mugen 9.5-1.6, 600cst and R 1x4/1.4x4, Mugen 10.75-1.6, 500cst.

For me as I'm running HB D817, I readjust the setting a bit, F 1x4/1.4x4, 8-1.5, 550cst and R 1.1x4/1.5x4, HB Yellow, 550cst. When I use the same 1x4/1.4x4 Piston at the rear with 100cst lower oil than the front, the Rear end felt had too much pack. So, I made 1.1x4/1.5x4 piston and put same oil as the front to get similar pack between front and rear.

Interestingly, in Hara San's Car, even though He is using same Piston Configuration, the "Pack" of His car felt the same between Front and Rear. I'm still think that the Wide Rear Pivot Point/Short Arm Configuration makes the same piston configuration setting give "not too far" Pack feeling between Front and Rear.

Please kindly share Your opinion..

Cheers..



Originally Posted by fredygump
Stanley, did you notice what springs they were using? I'm curious if their spring set-up was similar to what I've chose and what you were trying out.
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Old 04-27-2018, 10:38 PM
  #114  
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Hello icecyc1,

When You developed a multi size Piston, was it with 16mm diameter Piston (1/8 scale size) or 1/10 scale's piston?

And Thank You again for Your guidance for calculating Multi Size Piston DC.

Cheers..

Originally Posted by icecyc1
Glad you find the tool useful. Interesting to hear about their pistons. A little tidbit... based on what I had learned using the dyno, I had developed a multi size hole piston a couple years ago. What I had found is that you need the smaller holes to be 1.0mm or less. We used 0.7 and 0.8 mm small holes along with 1.7 or 2.0 mm holes. I did a 3 hole (large) with either 3 or 6 additional smaller holes. What this effectively did was increased the pack ratio, or the high speed damping compared to the low speed damping. Small holes any larger than 1.0mm did next to nothing more than just a basic piston could do.

I have made my own spreadsheet that does in fact predict the damping of these multi hole pistons. Unfortunately, it gets pretty complex and causes me to have to think deeply every time I use it. The basic rules for multiple size holes is to find the damping coefficient for each "set" of similar sized holes, then add them up as though they are in parallel with each other. For example, If one set of holes give a damping coefficient of 0.9, and the other set of holes gives a damping coefficient of 1.3, then combining them you will get 1/(1/0.9+1/1.3) = 0.53. It will always be lower than either one of them.

If you want to try to simulate the tiny hole multi-hole pistons, you can try this: First, take your large holes and ignore the smaller holes to find the damping coefficient for just them. Keep the low speed DC value, say it's 0.9. Also, keep the Impact value, say it's 1.6. In your hybrid pistons, the 1.6 will be your final hybrid Impact DC value. Now, run the same calculation on ONLY the tiny holes, say they give you a DC of 2.2 (because they are so small, they will be very stiff). Now, you can use the equation above to find your low speed damping value: 1/(1/0.9+1/2.2) = 0.64. So, as you can see, the low speed damping was reduced quite a bit by the holes, but the assumption is that the tiny holes "close up" during impact compared to the large holes and effectively don't exist. This isn't exactly true, but it's reasonably close (your impact DC will actually be slightly lower than the large hole Impact DC in reality) So, in summary, if you ran a piston with just the large holes, you had DC values of 0.9 and 1.6 giving you a pack ratio of 1.78. Your hybrid pistons have DC values of 0.64 and 1.6, giving you a pack ratio of 2.5. So, you kept your impact value the same, but you greatly reduced your low speed damping. This should help you keep your pistons stiff for landings, but soft for handling.

I really believe the compromise for off-road damping ratios of about 0.9-1.1 are because you need it for landing, so you compromise the "ideally perfect" 0.67. Increasing the pack ratio allows you to get closer to the ideal range while not having to compromise your landing damping you need.
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Old 04-28-2018, 05:08 AM
  #115  
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Originally Posted by stanleyw808
Hello icecyc1,

When You developed a multi size Piston, was it with 16mm diameter Piston (1/8 scale size) or 1/10 scale's piston?

And Thank You again for Your guidance for calculating Multi Size Piston DC.

Cheers..
1/8 scale pistons.
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Old 04-29-2018, 10:20 AM
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Originally Posted by stanleyw808
Hello fredygump,

Hará San use F 1x4/1.4x4, Mugen 9.5-1.6, 600cst and R 1x4/1.4x4, Mugen 10.75-1.6, 500cst.

For me as I'm running HB D817, I readjust the setting a bit, F 1x4/1.4x4, 8-1.5, 550cst and R 1.1x4/1.5x4, HB Yellow, 550cst. When I use the same 1x4/1.4x4 Piston at the rear with 100cst lower oil than the front, the Rear end felt had too much pack. So, I made 1.1x4/1.5x4 piston and put same oil as the front to get similar pack between front and rear.

Interestingly, in Hara San's Car, even though He is using same Piston Configuration, the "Pack" of His car felt the same between Front and Rear. I'm still think that the Wide Rear Pivot Point/Short Arm Configuration makes the same piston configuration setting give "not too far" Pack feeling between Front and Rear.

Please kindly share Your opinion..

Cheers..

Stanley, you need to be careful not to look at what one person does and create a formula to copy exactly. Using the same pistons front and rear should work just fine, as long as you match the shock oil correctly. It seems likely that you should try even thinner shock oil than what you tried. I would do that before creating new piston sizes.

The math I suggested a little while ago: ( front shock oil viscosity / front spring rate ) = ( rear shock oil viscosity / rear spring rate ) ***This assumes the same pistons front and rear***

Hara's spring rates:

9.5T 1.6mm = 840 N/m (front)
10.75T 1.6mm = 719 N/m (rear)

Hara's setup using this handy little ratio:

600 / 840 = .714
500 / 719 = .697


Stanley's first set-up with same pistons front and rear. I'm assuming about springs...the description of front springs looks like a Mugen spring, but correct me if I'm wrong.

Mugen 8.0T 1.5mm = 820 N/m
HB Yellow (rear) = 624 N/m (same as Mugen 8.5T 1.4mm (rear))

550 / 820 = .671
450 / 624 = .721

Based on this, you are correct that you had more damping in the rear. But if you went down to a 400 CST in the rear, or up to 600 CST in the front, you would have found a much closer balance. The "perfect" oil fir the rear would be 418 CST.....
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Old 04-30-2018, 08:10 PM
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Originally Posted by icecyc1
If you want to try to simulate the tiny hole multi-hole pistons, you can try this: First, take your large holes and ignore the smaller holes to find the damping coefficient for just them. Keep the low speed DC value, say it's 0.9. Also, keep the Impact value, say it's 1.6. In your hybrid pistons, the 1.6 will be your final hybrid Impact DC value. Now, run the same calculation on ONLY the tiny holes, say they give you a DC of 2.2 (because they are so small, they will be very stiff). Now, you can use the equation above to find your low speed damping value: 1/(1/0.9+1/2.2) = 0.64. So, as you can see, the low speed damping was reduced quite a bit by the holes, but the assumption is that the tiny holes "close up" during impact compared to the large holes and effectively don't exist. This isn't exactly true, but it's reasonably close (your impact DC will actually be slightly lower than the large hole Impact DC in reality) So, in summary, if you ran a piston with just the large holes, you had DC values of 0.9 and 1.6 giving you a pack ratio of 1.78. Your hybrid pistons have DC values of 0.64 and 1.6, giving you a pack ratio of 2.5. So, you kept your impact value the same, but you greatly reduced your low speed damping. This should help you keep your pistons stiff for landings, but soft for handling.
Also thanks icecyc1

With the available pistons and oils in my arsenal, your spreadsheet helped me locate an equivalent piston and oil setup with a (slightly) lower speed DC while maintaining a similar Impact DC. I punched in some numbers and boom! I now have multiple 5 hole piston combo's that is within range for me to try out. I managed to test one 5 piston combo over the weekend and it worked great! I was previously using a 6 hole piston setup.

To preface, I also run a HB Racing buggy and staggered pistons front and rear are currently the norm/base in most recent online setups. For example Front 6x1.3, Rear 6x1.4 or Front 5x1.5, Rear 5x1.6 depending on the track conditions. I'm now noticing hybrid pistons being experimented, expanding upon on the existing base shock setups:

Some examples:-
F 6x1.3, R6x1.3/1.4 (3x1.3, 3x1.4)
F 5x1.5, R5x1.5/1.6 (3x1.5, 2x1.6) or (2x1.5, 3x1.6)

An extreme example I noticed using a 4 hole piston combination used on a bumpy track
F4x1.5/1.6 (3x1.5, 1x1.6), R4x1.6/1.7 (3x1.6, 1x1.7)

Using your spreadsheet together with your hybrid/multi-hole piston simulation theory, and focusing on hybrid pistons combinations mentioned above. You may have noticed, there's either an equal amount of 'smaller' and 'larger' holes or a slight variation of it. I would assume the formula (1/(1/a+1/b)) for the hybrid Low Speed DC value remains unchanged, but how about the final hybrid Impact DC value? Is the thought process still the same by ignoring the smaller holes?
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Old 05-01-2018, 07:57 PM
  #118  
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Originally Posted by TRiN
Also thanks icecyc1

With the available pistons and oils in my arsenal, your spreadsheet helped me locate an equivalent piston and oil setup with a (slightly) lower speed DC while maintaining a similar Impact DC. I punched in some numbers and boom! I now have multiple 5 hole piston combo's that is within range for me to try out. I managed to test one 5 piston combo over the weekend and it worked great! I was previously using a 6 hole piston setup.

To preface, I also run a HB Racing buggy and staggered pistons front and rear are currently the norm/base in most recent online setups. For example Front 6x1.3, Rear 6x1.4 or Front 5x1.5, Rear 5x1.6 depending on the track conditions. I'm now noticing hybrid pistons being experimented, expanding upon on the existing base shock setups:

Some examples:-
F 6x1.3, R6x1.3/1.4 (3x1.3, 3x1.4)
F 5x1.5, R5x1.5/1.6 (3x1.5, 2x1.6) or (2x1.5, 3x1.6)

An extreme example I noticed using a 4 hole piston combination used on a bumpy track
F4x1.5/1.6 (3x1.5, 1x1.6), R4x1.6/1.7 (3x1.6, 1x1.7)

Using your spreadsheet together with your hybrid/multi-hole piston simulation theory, and focusing on hybrid pistons combinations mentioned above. You may have noticed, there's either an equal amount of 'smaller' and 'larger' holes or a slight variation of it. I would assume the formula (1/(1/a+1/b)) for the hybrid Low Speed DC value remains unchanged, but how about the final hybrid Impact DC value? Is the thought process still the same by ignoring the smaller holes?
Hybrid pistons are definitely more complicated to calculate. The equation I provided assumes you have an equal amount of two different sizes holes, not a 3x and 1y hole pattern. I haven't tested that, but my initial guess would be that it should still work, although perhaps not exactly in that ratio in reality, I really don't know. The reason this equation works in this situation is because the holes act as a resistance to motion, and they are in parallel with each other. In electrical terms, if you have current running through two resistors in parallel, you simply add them up as noted above, to get the overall Effective resistance. That's what we are doing hydraulically, and the dyno results verified that.

When I described the hybrid functionality where you can ignore the small holes for impact, I am also assuming significant difference between hole sizes. You won't get a significant difference between a 1.3 and 1.4mm hole, not enough to create more pack. I think your DC and Impact values would be exactly as the hybrid formula would predict for both, with holes that close in size, you cannot ignore the smaller hole. I believe the only time you can ignore the smaller holes for the impact DC is if the smaller holes are less than 1.0mm (even that big might be pushing that assumption). Larger than that, it's essentially just another hole. I think the holes function sort of like a slender rod, where the length/diameter ratio is critical to it's strength. So, above 1.0mm in a 2.3mm thick piston, the L/D ratio isn't enough to provide a "lock-up" behavior, but less than that, it begins to show those effects. If for instance you have a tapered piston, that L/D ratio would be even less, so it would require an even smaller hole diameter to matter. (A tapered piston behaves the same as a flat piston, but due to the smaller profile, or thickness, it provides less damping, or a lower DC for the same oil, holes, & diameter)
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Old 05-01-2018, 09:20 PM
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Thank you for your insights!
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