I can field this one, my specialty is vibrations.

Undamped natural frequency = (square root of (stiffness/mass))/2pi

With appropriate and matching units of course. (Imperial fans, remember slugs for mass?)

In this case the stiffness is the essentially the effective vertical stiffness at the inner arm pivots (left and right combined). Need to consider the arm leverage on the shock, and the shock angle.

Similarly mass is the effective modal mass at that point. In rough terms the suspended-chassis mass at that end, plus a portion of the arm (would be one half if constant cross section) and the suspended portion of the shock with all of the position and angle considerations. Doesn’t include the wheel-spindle etc mass.

Whew, as alluded to that’s probably a little tricky to actually figure out. But the basic relationship is fairly simple and can be useful to estimate changes. Frequency = sqrt(stiffness/mass)

Is something like this simple enough, and about what you guys are looking for?

w w w .f-o-a.com/calculator. h t m l

It works great, the only issue with this calculator is that, since it is meant for full size cars they only go in pound increments for springs. But one with better hundredths of a pound results should be sufficient and hopefully easy enough for people to use.

I just started working on a spreadsheet that will do the same thing but with simpler required inputs. For example, having the total vehicle weight and F/R weight bias, instead of a specific corner weight, then calculate the corner weights from that. It will all be easily measured inputs, and I think will be a more than adequate simple calculator, especially for RC purposes (if this was F1, or other high level racing this would be a different story).

To be even more thorough would require a vehicle model either by someone writing it in a powerful computational program or by using a purchased vehicle dynamics software like OptimumK. If our little cars could be equipped with useful data acquisition (like linear pots on dampers, 6 axis accelerometers, etc), then we could definitely learn a lot more about them. However, even the EagleTree data acq stuff is too big and cumbersome for the little cars.

Okay, I seem to have found a balance with my car at this point. I've got balanced frequency springs, good damping for the track I am on, and what feels to me good balance between front and rear traction. Removing from the equation my horrid driving (working on that...SLOWLY), I have a hard time holding my lines with the car. I just can't keep pace with the faster guys and half the time can't really even manage to stay out of their way. With what I think is a balanced car, should I be looking at balanced roll center adjustments front and rear at this point to try to improve overall traction? If it makes any difference I'm driving an RC10B4.1 in open mod on a tight, technical med/high bite track.

bds, maybe you should get that old Hornet back together and race that for a few weeks and then go back to the B4. I'm thinking you'd think the B4 was the best thing in the world at that point...;)

Hey, now. I've only got so much time to devote to the hobby. I prefer to think of the lack of calculating of hairy equations on my part as being more along the lines of making effective use of my time using the bench testing method. Then again, sometimes I do feel a bit lazy, too...:nod::blush:

One thing for reference, the tight, technical track in which he is speaking of is 20x40 with 4 ft lanes..The racing line is the width on of SC, so even for a perfectly setup car, precision is a must..

Exactly. Traffic is killing me. My car (and driving) don't allow me to avoid crashes in front of me. If I could choose my lane through the traffic and around wrecks with a bit more precision I would probably gain myself at least another lap a race.

Looks like a useful calc for the spring rate, thanks, but doesn’t appear to support suspension frequency calculations?

Some questions about the OptimumK software:

Just kinematics, or does it support any dynamic behavior, mass modeling, etc, such as suspension frequency? Damping?

Does it support non linear stiffness elements, such as rubber bushings? (for production car applications) With the damping question again.

Is it a stand alone application, or compatible with ADAMS or similar? (easier to integrate)

Sorry for the thread jack, but I’m curious how it compares to other suspension modeling applications. SNAP, Mitchell, ADAMS, etc.

OptimumK is probably most similar to Mitchell, but less archaic and better GUI and animation . It is specifically a vehicle kinematics software, it does most everything other than taking into account non-linear stiffness elements.

Back to the weight ratio- I'm really wanting to try 60r/40front. Practiced Saturday. Kept moving the battery & weights, battery & no weights. Battery all the way forward no weights felt best. Want just a tad more in the nose.

Your mileage my vary.

My shortcourse truck was working best last season with 59% rear. I started out at a little over 61% and just kept dropping rear. The truck had alot more steering on power and out of the corner. Last season I had the stock AE SC10 front tires and some bowfighters on the back. This season I have a set of goosebumps for the front so it will be interesting to see how that affects it.

My buggy seemed happy around 65%. I tried it with the battery back and rear at 67.5 and it took too much steering away and wouldnt keep the nose down.

Nick

Has anyone balanced the springs for the new serpent 811be buggy? Just wondering what color springs you found that match up and what shock mounting holes your using. Im slowly narrowing down the spring selections but its taking a while. So far I have the pink springs up front and the green in the back, but I just took some slow motion video and found that the rear is still slower than the rear so I guess I have some work to do still.

I was working on my mid motor car last night and while I was driving it I was reminded of the fact that modern esc tuning and transmitter settings are very difficult to convey in words how to dial in for your vehicle. Sometimes you just need to back off the power a little bit to get the car hooked up. Let electronics technology do what mechanics can't.

As an example, I was having a problem with the car doing back flips from too much initial traction. Some people say add weight up front. That's fine and all but I'd have to go back and rebalance the spring rates again. I could run a different amount of slip on the slipper. I don't want to burn it up though. I could just use less throttle but the front comes up so suddenly that by the time you realize it, the car is doing cartwheels. The reason why I don't want to do these things is because I was just running the car in a parking lot messing around. My permanent settings weren't going to be determined here. Traction on dirt is very different so adding weight for parking lot play would ruin things for the track. The solution for the evening was to change the punch on the esc. I don't know if they are all the same or not but mine goes from 1-10 with 10 being full power immediately when the throttle is pegged. The lower the number the less the initial kick and transition to full power. Mine was originally set at 7. Wheels pulling up. Dialed it back to 5. Throttle was also a bit touchy in the corners so I gave it 25% exponential on the transmitter. The car was much easier to drive without going end over end all the time. I wasn't racing but was just playing and these easy changes made the car more fun to drive without changing anything on the actual setup of the car. These could be changed back very easily.

Going out to the off road track I'd change these settings a bit. The point is that with modern electronics, don't overlook their role in tuning too. They are quick and easy changes that can really affect how easy the car is to drive. The amount of drag brake, full brake, and punch in the settings may be able to take care of handling issues that you thought the suspension should take care of. Kind of like modern real cars where traction control and abs make the car easier to drive on the edge than an older one without. Learn your electronics too.

Here is a short video of my spring balance test. Do you think I have it balanced or do I have some more work to do? Took about three hours working on various spring rates and shock positions to get it this close.

http://www.youtube.com/watch?v=rJbqr...ature=youtu.be

The front still looks a little stiffer. Is the droop the same front to rear? I'm seeing the front hit full extension first so it's hard for me to tell if it's because the front is rising faster or because it hits full extension sooner.

Good point. I forgot to set the droop the same. I will redue the test. Thanks