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

Excellent CONTROLLED test.

As I suspected, Tapered pistons are a farce for charging much too much for such a minimal amount of plastic. They are simply much too small for the tapering to affect anything much at these small scales.

Great bit of work. The bit I've always been interested in is the pack / impact testing and assumed non-linearity. RC racing is still in the dark ages with valving design and data around this aspect could be a game changer. Presume the challenge is test kit for this?

Very nice presentation. A couple of comments:

1. In the section of tapered piston and the % difference between compression and rebound showing up to 5.4% difference. The flat piston results are indicating the same difference, e.g. flat 2 1.7 4.54 also shows 5.4% difference for 400 cSt between comp/reb.
2. Can we also conclude that a greater total hole area is less influenced by temperature changes in the oil?
3. It would be nice to see some test with dual piston design (MIP, VRP, RC Shox).
3. The report does not tell us the accuracy/hysteresis of the shock dyno itself. Is this negligible in these results?

Awesome work Scott! Its great to see someone not only create such detailed information but also share it. Thanks very much.

One thing I would be interested to see is the difference in small stroke and large stroke behaviour. Most of these tests seem to be at a relatively small stroke which is good for handling simulation - I would really like to see the characteristics for large stroke (both low and high speed) for bump / jump simulation. Some higher piston speeds would also be useful.

Looking forward to the next instalment of data!

Ray

Many thanks ... especially clearing up the confusion on tapered pistons. As an engineer myself I have always told folks that I couldn't find the physics to explain the claim that tapered pistons (the face) changed the damping characteristics between rebound and compression a meaningful amount. The true way to do that is through tapered "holes" in the piston (Mugen makes these).

Great work !

-Johnny

This is a great resource, thank you very much.

After seeing this, I for one am very happy with how my own personal shock setup technique fits into this.

Thank you. This is one of the most valuable posts I have ever seen on an rc forum.

I don't even have words. I will be reading it slowly and thoroughly this night.

Big thank you Mr. Scott.

4 Posts and already one of the most useful threads started!!! Very cool!! and thanks for the info and amount of work that took.
thanks
josh

Thank you so much for doing the work and publishing this for all to read! This is a great resource to reference when discussing damper setups!

This is fantastic! I can't wait to see the rest of your testing. I never would have thought about the non-linearity caused by something like piston slop. And it's nice to see someone finally put an and to the bladder vs emulsion debate. Excellent setup AND presentation of data!

still i like emulsion most the time for 1/10... the reason is inconsistent fit the track. i can run a lighter oil and not bottom out from the shock or over rebound from the spring. kinda like having a dual rate spring (which i hate dual rate spring especially in rear trying to kick too much) but as a shock it works great.

like the test show bladder with foam is real consistent which is a good pick on a track where you have similar conditions from start to finish(for sure what i would pick for onroad) this is also what i like most the time for 1/8 buggy i guess because i run higher oil and having more weight the 1/8 conditions dont change as much as the smaller 1/10 on the same track.

I've been preaching non vented bladders for a while. I don't use foam. Since the fronts are different length than the rears, I back fill above the bladder with oil when the piston is pushed all the way in to give equal air space above the bladder in relation to shock piston and rod displacement due to travel differences. My favorite standard bore setup is AE shocks with Losi pistons due to tighter tolerances. I'm glad to see hard data that matches what took years of trial and error to learn.