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RC Shock Dyno Test Results

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RC Shock Dyno Test Results

Old 03-01-2015, 11:33 PM
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Originally Posted by icecyc1
Do you want to see Force-Velocity curves for an RC car damper that were measured on a shock dyno? If so, here it is!

A very common and reoccurring question is concerning the performance of R/C dampers or shocks. There is constant argument about the oil viscosity, piston holes, number, size, bladder, emulsion, low speed, high speed, pack, and any other characteristic that can be changed. Everyone has opinions about it, some are better than others, many are based on experience, some are based on speculation. It becomes confusing for the person who just wants to know what actually happens with each of the changes they have available to them. The bottom line is everyone wants to know how to best tune their shocks so they get the best performance out of their car.

In the full scale industry, it is widely known by top race teams that in order to get the best performance, you have to know what is happening. A shock dyno is the industry standard to get those performance values. Unfortunately, this option does not exist (but for a few select companies) for the average R/C racer. This is what frustrated me, and motivated me to generate the results myself. I also figured, why not share it with everyone else too? I know I'll never be a top racer (if I ever even race!), but if I can help out others, I'll get satisfaction out of that.

I have a 15+ year career as a test engineer. I've used a lot of instrumentation, and have tested many different things. I feel comfortable around test equipment and setups, enough to have confidence that the data I'm collecting is correct. It's the interpretation that can sometimes steer you in the wrong direction, but I feel my experience has helped me interpret correctly more often than not now.

This test data is for you, the racer, to help educate yourself with some actual data, and not someone's opinion. See the data, and make up your own mind. Much of the data shows results you probably already know, or can intuitively predict. That's OK, as at least now, you have gained the power of confidence in your assumptions. Some of the data might be different than you were assuming, and you might be fully enlightened to a whole new world of tuning. That's awesome, you will now do a better job of tuning.

This presentation is the first part of hopefully several. It is intended to show the basics, the general trends, and to answer some basic questions. It's NOT intended to give you the answer to "What oil and piston should I use in my car at The Super Fast High Flying Track I'll be racing at this weekend?". It is intended to give you a more educated guidance to help your decisions for your setup. The context of the results as applicable to your individual car is a whole separate topic. I'm hoping at some point to provide information towards that. In the meantime, check out the references.

I would love hearing feedback based on this report for what people would like to see from shock dyno results. I have ideas as to what I'd like to focus on next, but I think it would be worthwhile to get the direction straight from the racers.

cheers,
scott
Just FYI for those of us viewing this on the mobile version there is no link or anything
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Old 03-01-2015, 11:39 PM
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Originally Posted by icecyc1
The effects of heat and air expansion causing fade is interesting. I'll see if I can come up with a way to make a test that is repeatable to measure those effects. What do people believe are the most critical components to causing fade? Piston type? Oil? Bladder/type? (yes, I know heat is the issue, and that's caused by the shocks working hard and heating the oil over time) What do you racers typically do to prevent or minimize the fade? I can then test a worst case and a best case scenario and see how much different it is.
run bigger shock lol... but before the new big shocks i would put higher weight oil in. different types/brand of oil should for sure change. i think that angle of the shock might have effect on heat/fade. as far as inside hole size, piston area...like cone piston/hole like you already did. rebound of the shock itself would be a good test. also shock shaft size i would think would play a role. material of the shock/piston/shaft but that going a little too far.
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Old 03-02-2015, 01:00 AM
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Originally Posted by mydudrevo
Just FYI for those of us viewing this on the mobile version there is no link or anything
Here you go:
https://sites.google.com/site/rccarengineering/home
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Old 03-02-2015, 03:40 AM
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Originally Posted by icecyc1
Springs are out of scope at this point, but it is interesting, and I'll keep it in mind for the future. Most of the time springs can be characterized simply with a scale and a ruler because they are displacement dependent and not velocity dependent. I'm not too familiar with the claims of the springs you mentioned.
Something that would be interesting is to see the friction effect caused by springs on / off. Springs, no matter how well they are wound, cause some side loading on the rod and can increase friction. Larger diameter springs are less susceptible to this than smaller springs, and as far as I understand it this was one of the main advantages in shifting to the larger diameter springs a few years ago.

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Old 03-02-2015, 03:56 AM
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speaking of large vs small, I'd be interested in some sort of analysis between big bore and small bore shocks. Are these new big bore shocks really worth the extra money and weight? Jorn Neuman TQ'd the '13 4wd worlds with slim bores...
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Old 03-02-2015, 04:07 AM
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The best post I've seen yet on RCTECH!! I'm interested to see whatever you decide to test next.
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Old 03-02-2015, 04:35 AM
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Originally Posted by RC10Nick
speaking of large vs small, I'd be interested in some sort of analysis between big bore and small bore shocks. Are these new big bore shocks really worth the extra money and weight? Jorn Neuman TQ'd the '13 4wd worlds with slim bores...
+1 i'd be very interested in that, too!


PS.: thx scott, for that excelent explanation and tests!

Last edited by micholix; 03-02-2015 at 05:03 AM.
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Old 03-02-2015, 06:55 AM
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Awesome post with good information.

Without any high speed piston testing I think its impossible to come to any conclusion on what is better.

How did you determine what the best speeds were to test the pistons?
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Old 03-02-2015, 06:59 AM
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I'm glad someone else bought that $100+ book and is putting it to use as well. LOL Overall great write up. Considering we are dealing on 1/1oth of a scale of full size, you have to consider the smaller changes to be bigger changes than they show. Though .02 doesn't seem like much to the full size, .02 might be a huge change at 1/10th that size.
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Old 03-02-2015, 07:35 AM
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Great test!

One thing what I have on my mind is that how your shock dyno simulates hits what comes in real life to shocks? Basically they are constant force pressing shock. If force is too great then piston will go as far as is physically possible. Now in dyno piston moves up/down with variable speed and has lowest speed in both ends.

But anyway great job!
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Old 03-02-2015, 11:24 AM
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Originally Posted by icecyc1
Springs are out of scope at this point, but it is interesting, and I'll keep it in mind for the future. Most of the time springs can be characterized simply with a scale and a ruler because they are displacement dependent and not velocity dependent. I'm not too familiar with the claims of the springs you mentioned.

Per Losi: "The LF springs have a higher coil count than the traditional TLR Spring, which provides a lower frequency and a much less progressive feel. On the track, this translates to more overall grip around the track, and a less aggressive spring rebound which really helps the car settle after landing jumps."
I'm wondering if these springs make a difference or if its just marketing hype.
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Old 03-02-2015, 11:35 AM
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There's probably a bit of both. The LF part is all about marketing. Springs come in many different rates. What Losi did was to have springs on the lower end of this range be wound with more coils rather than having them wound with fewer coils. There would certainly be an advantage to that compared to fewer coils but to be fair we need to compare only springs of equal rates and not low frequency vs higher frequency. That would be invalid.
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Old 03-02-2015, 07:24 PM
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Originally Posted by RC10Nick
speaking of large vs small, I'd be interested in some sort of analysis between big bore and small bore shocks. Are these new big bore shocks really worth the extra money and weight? Jorn Neuman TQ'd the '13 4wd worlds with slim bores...
I do have 10mm and 12mm big bore shocks (1/10 scale), so I can test the differences between the two. I'll see what kind of story I can illustrate with data, but it will follow the basic physics of force, area, and velocity. Since the larger bore pistons are larger area, and would be subjected to the same forces, the internal pressure should be lower, and a fluid subjected to lower pressures would heat up less, making them more consistent over time. So, yes, they should be better. (in theory anyway). It would be good to show it with data though.

One thing about the pro's though... you could probably give them a Tamiya Grasshopper, and they'd still smoke the pants off most of the rest of us.
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Old 03-02-2015, 07:30 PM
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Originally Posted by WillS
I'm glad someone else bought that $100+ book and is putting it to use as well. LOL Overall great write up. Considering we are dealing on 1/1oth of a scale of full size, you have to consider the smaller changes to be bigger changes than they show. Though .02 doesn't seem like much to the full size, .02 might be a huge change at 1/10th that size.
I won't argue with you there. Right now, all we have are full scale rule of thumb guidelines, experience, plus our brains are wired toward full scale tolerances. So, sometimes assumptions could be incorrect when it comes to considering something to be negligible. I'll try to consider that closer.

When things get smaller, like our cars, it gets harder to measure because our measuring equipment precision is the same, the noise floor is the same, the tolerances are the same... as the full scale counterparts. Problem is, the application is scaled down. So yes, .02 could be significant. I'll see what I can do to identify some tolerances (both with measurement and with what a driver can actually feel or notice). But, I'll need a gifted driver for that. I'm just happy that if I only hit the rails 6 times per lap, I consider it improved my car's handling!
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Old 03-02-2015, 08:22 PM
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Originally Posted by cokemaster
Thankyou.

Very interesting read. Looking forward to seeing more of your work Ice.
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