EB48 2.1 Club Racer

[CosmoM3]

Purchased a brand new EB48 2.1 kit from a forum to replace my racing Typhon TLR that I have been using at my club races and had great success with.

I intend to be very thorough with my RC Build Blog on this journey with my second E-Buggy racer and I hope you all enjoy and maybe learn something along the way.

Prologue

The first I did on the EB48 2.1 after completing the build was to weigh the entire chassis to figure out its unsprung weight and weight distribution between both front and rear (and all four corners) to determine the correct spring rates for the car. While the stock spring rates of Orange (4.92 lb-in) fronts and Yellow (3.59 lb-in) rears work fine for most "out of box" setups, it's not the most ideal for your specific car and more of a "one-size fits all" type of setup.

I have a background in track driving my 1:1 cars for the past 20+ years and tuning, chassis dynamics, etc were always something I enjoyed tinkering with and bringing out the best out of the car by tuning it to be balanced.

Current Setup:
Electronics: Hobbywing XR8 G3 ESC + 4268SD 2200kv G3 Motor
Battery: CNHL Racing LiHV 4S 6000mAh (475g)
Servo: REEFS RAW 500
Shock Oil: Stock 650/550cst
Pistons: Stock
Sway Bars: Stock
Springs: _________

That being said we're going to get into spring rates as that is the most important starting point when tuning a car before you get into anything else. To get started, I weighed the finished chassis on the SkyRC corner weight scales and came up with these numbers:

From here, you start to get into the nerdy stuff regarding physics using weight distribution, natural frequency and most importantly: motion ratio. You need to calculated all this to get the the best spring rates that best matches your car's current weight and weight bias.

Using mAtHs and physics I was able to calculate the motion ratio for the stock EB48 2.1

Front
d1: 65mm
d2: 105mm
Motion Ratio: 0.62

Rear
d1: 73
d2: 115
Motion Ratio: 0.63

I chose the natural frequency for the car based on some of the spring rates I've seen from other manufacturers from AE, Mugen, Tekno, etc and I figured out that most of them use a natural frequency of around 2.5 - 3.0 Hz, most only on the higher end. Using both the motion ratio calculation, the weight and weight bias of the car and choosing a natural frequency as a baseline, I was able to determine the following:

Ignore the other stuff below "High Grip (Indoor Clay)" as that's just stuff I had to label them with as natural frequencies can go VERY low, and irrelevant for off-road racing.

I had determined that the best spring rate combination for the EB48 2.1 in its current state to be in green front and red in the rear vs. the box stock spring setup.

I went ahead and ordered the correct springs based on the calculation and conducted two drop tests to simulate the suspension frequency between the front and rear of the car.

To make a point, this first test shows what an unbalanced car looks like with the wrong spring rates:

Unbalanced (on purpose)

Unsprung Weight: 3.08kg Race Ready (it's light)
Weight Distribution: 49 Front / 51 Rear
Front Spring: Green (4.15 lbs-in)
Rear Spring: Yellow (3.59 ln-in) (Stock)

You can see the rear end kick up more and bounce unevenly.

Front Spring: Green (4.15 lbs-in)
Rear Spring: Red (3.83 ln-in)

They both compress and rebound on the same plane. It's amazing what a 0.25 lb-in difference in spring rate can do to the car.

The car is now balanced and I don't have to touch the springs again. Tuning going forward for the shocks/springs are just going to be shock oil weights and pistons. This process literally takes the guesswork out of finding the correct springs for your car.

Remember, the purpose of the springs are to bear the vehicle's weight, absorbing the shocks and jolts from the road.

Lateral grip, cornering, etc all come from tuning the leverage of the car, such as camber links, alignments, sway bars, etc - not springs. 99% of the time, after you you pick the correct spring rates, you keep them forever and you're done.

Balancing spring rates is nothing new and it goes as far back as the legendary thread from RC Tech from the user "fredswain". It's at 148 pages as of today and every page was worth the read. It was actually the most active/top thread on the "Electric Off-Road" sub-forum ever.

I've done this exact same setup process on my Typhon TLR build blog on another forum and it was very successful.

 

[CosmoM3]

My body arrived and mounted.

 

[CosmoM3]

Took the car out for its first shakedown test and it was an interesting experience as I was comparing it to my highly tuned Typhon TLR.

A couple of things of note after my first 20 minute session with the stock geometry/roll center setup (except for the spring rates) vs. my race proven Typhon and not about the car itself:

• There’s a ton more initial steering to mid-corner but lacks steering at corner exit and on-power
• The Tekno felt more “plush” overall
• Cornering from a high speed straight into a 90 degree turn into another high speed straight, I had to let off the gas and brake to make the corner vs. letting off and just turning in in the Typhon
• The car felt more “on-track” vs. “in the track” on the Typhon

Basically the Typhon was faster than Tekno in box stock form in raw times. The Tekno felt slower but the times were still pretty good, so I see potential here to tune the car, therefore I’m excited to get the car dialed in by next month’s club race.

I also decided to lower the wing mount from the middle to its lowest setting because I felt that the car’s balance during the doubles were just inconsistent outdoors using the larger JConcepts RAZOR wing with the holes cut out. The car just flies flatter with the smaller wing on its lower mounting holes.

My tuning parts arrived as well from Tekno:

I've made some minor setup changes (removed some of the box stock front kickup of 0.5 down to 0.0) and raised the rear camber link up one hole on the shock tower.