Build Thread Tekno EB48 2.1 - 1/8 E-Buggy 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 thing I did on the EB48 2.1 after completing the build was to weigh the entire chassis to figure out its total sprung 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.

New JConcepts S15 painted body came in and mounted:

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 the 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 2x club races that I have coming up.

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 on the pills from 1* down to 0*) and raised the rear camber link up one hole on the shock tower.

 

[kaladeth]

Subbed! Hoping I can follow this and apply the same setup / process to my Limitless racer.

 

[Luke66]

Will you still be racing the TTLR?

 

[CosmoM3]

Will you still be racing the TTLR?

Not actively, but it's still race ready if I decide to take it out (love that thing).

 

[LibertyMKiii]

Beautiful rig!
Thanks for sharing!!!

 

[CosmoM3]

Time attack results with the EB48 2.1:

The car felt very, very balanced thanks to the spring rate setup and the equal weight distribution, but the Typhon had a greater sense of speed considering it weighs almost 300g more than the Tekno.

The Tekno, however, might have felt slower, but I was clocking my best times with it more consistently than my Typhon. This mind fuckery is something I'll have to overcome as the Tekno just feels so much lighter on its feet.

 

[CosmoM3]

My new Tekno LF springs arrived today in the same spring rates as before. You can definitely notice a difference on how they feel.

My previous front spring on the left and new LF spring on the right (both similar spring rate). With the car both running LF springs front and rear, the lack of spring tension was noticeable.

 

[CosmoM3]

This is a perfect example of using the correct/balanced suspension frequency for the chassis but how the shock tower locations can make a difference:

Stock Shock Tower Location (3rd Hole):

You will notice that the rear end rebounded faster (didn’t have this issue with the non-LF springs, but interesting nonetheless) compared to the front.

2nd Hole from the outside (less lean):

The less “lean” the shocks have, the more linear the rear springs will act. This pretty much leveled out the chassis as the suspension frequency is now balanced between the front and rear.

The matched spring rates between the LF Rear (Pink) vs. Regular Rear (Green) isn’t perfect, but it’s very, very close.

Next is to nail the shock dampening via piston and oil viscosity.

Picked up a set of MIP Bypass1 shock pistons with 10x blank holes for me to drill out to my liking to fine tune the amount of dampening and pack. So far I’ve come down either 1.3x6 or 1.2x8 (which I consider “standard” for myself) based on the calculations below by RC Car Engineering:

 

[CosmoM3]

Updated my shock calculator for shock pistons:

 

[LibertyMKiii]

Updated my shock calculator for shock pistons:

View attachment 382998

I love the detail. This is the sort of thing I do with speed runs. Tons of data and analysis to make sense of what is happening and how to go faster.

 

[CosmoM3]

First race with the Tekno this weekend:

I’ve had two days of practice with the Tekno these past couple of weekends and based on my experience on this track with this new platform, I’ve actually tried to do something different and experiment with ChatGPT 4o (latest) on figuring out the handling predictions of the car given the track conditions, ambient temps and my current setup (shock oils, diff oils, suspension geometry, ride height, etc).

This may be the first of its kind and I’ve test the math calculations it was giving me was sound and it told me that my current chosen spring rates give the specs of the weight, weight distribution and motion ratio of the suspension system was “balanced” and “correct”.

Here is what I should be expecting based on the track conditions (it’ll be raining the day before the race) and ambient temps will be around 85*F.

I had it summarize my current setup after days of painstakingly measuring the geometry (arms, links, height, wheelbase, track, tire size, etc):

What I hope to get out of this is hopefully train the AI on becoming my technical director of sorts on the track where it literally memorized my entire setup on the car, getting a general idea of the track conditions based on the photos I’ve uploaded (it can scan photos) and give me recommendations on what I should do to make the car handle like I want. To do this, it will take a ton of data entry points from me, as the driver, to let the AI know how the car feels to me and it will make adjustments. Since it already took account the ambient weather temps and how the temps will change throughout the day, I need to let the AI know how the track conditions will also change.

Anyways wish me luck as I pioneer this build blog with the help of AI.

 

[CosmoM3]

USRC's VP-Pro 2024 Challenge was completed and I'm happy to announce that I won first in Sportsman class (my first).

Q1 Update

The weather was around 80 degrees at the time and the track had just finished drying from being watered down earlier in the day and there were a couple of heats before mine (I was Heat 5 of 9) so the the track conditions were optimal.

Prior to my Q1 start, I put in about half hour of practice and notice that the rear shocks didn't have enough pack from some of the steeper jumps, therefore I switched out the 725cst I had in there before and replaced it with a heavier 750cst. Since I'm running relatively larger piston holes in the rear (1.4x4 + 1.5x2) which gives me a hybrid suspension feel of both smoother handling (larger holes) and pack (this is dependent on shock oil), I can afford to run heavier viscosity, especially if you also account for the hotter weather. Since the shock oil thickens back up again at room temperature between heats, the trick was to let the car sit outside in the sun before my heats to let the shocks warm up to optimal viscosity.

I also changed out the MIP Bypass1 valve for the rear pistons from thinner "Blue" (0.005" thickness) to the "Clear" (0.007" thickness) to slow the rear's rebound after landing the jumps because the quicker rebound after landing from the jumps made the car unsettled and reacted a tad too quickly.

Tires: JConcepts Reflex (A2)
Length: 6:00 Minutes
Temps: 80°F
ESC Changes: Boost +5 (from 0) - the boost was needed because the Reflex didn’t have the same forward bite as the Relapse to clear some of those long jumps

I was ranked 15th overall in all of the 1/8 Buggy classes (including Open + Sportsman):

I was pretty happy with the results from Q1 but I was looking forward to Q2 since I knew the weather was going to warm up and the car was going to perform better after shaking off the initial Qualifying nerves.

Q2 Update
I made some minor adjustments to the ride height (more like making sure it was consistent) and I was torn about switching over to the JConcepts Relapse tires since the temperatures warmed up to 85*F and the track started to develop a groove, but I wanted to stick with the Reflex for now and decide at the time of the Mains if I was going to change the tires.

I did however change replace my rear wing from the factory Tekno wing as it was banged up from previous bouts of practice weekends, to the JConcepts F2I low profile wing. I noticed due to the overall balance of the car and how well the car took the jumps. It turned out to be a good call because the car remained balanced and overall grip level turned out to be good. This seemed to be the going trend for me as I noticed that a balanced setup tend to make the car to jump evenly and adding a larger wing would be detrimental for me.

I had a very good run this time:

I was bumped to 18th overall, even though I did very well during my qualifying, which means everyone just got faster.

1/8 Sportsman E Buggy (A-Main)

It was time for the mains and I've decided to stick with the JConcepts Reflex tires because I was just used to the grip level from qualifying, but in retrospect, I wished I had used the Relapse instead since the track had developed a blue groove. Something I took note of and will start to apply to my tire strategy.

When the grid was determined for the Main, I was able to nab Pole Position due to my successful runs from my past qualifying results from earlier in the day. It helped because I was able to manage to hold this position (Lap 2-3 had a bad crash from the other drivers) so I had to slow down to avoid the wreck. I also managed to hit my fastest lap during this time.

What I kept telling myself was not to drive fast, but drive consistently.

What killed me though, was the 8:00 minute race because it felt like an eternity.

My consistency, however, had dropped because the last 5-6 laps were painful for me as my nerves were getting the best of me and I started to make mistakes from the fatigue. I had to remind myself to breathe and keep cool while trying my best to not over-drive the car because my brain is telling me that I wasn't going fast enough. I knew that I just had to hold on and be smooth and clean with my laps to keep my position as first place.

What made me think introspectively, was that if the car was setup a little bit too sharp (like ackerman, camber gain, roll centers, etc) or more responsive, I feel like some of my mistakes from the fatigue would have been catastrophic from spin outs instead of gradual understeer.

This was painful and I was mentally exhausted.

Anyway, I'm very happy with the results and I have another race next weekend as it's the last race of my Summer Point Series (Race 4 of 4), but I'm going to soak up this win and build up my confidence and trust in my driving and the car.

Post-Race cleaning, maintenance and inspection:

...and good thing I did because one of my shock shafts were bent:

Setup Changes

This time around while I was replacing the shock shaft, I've decided to change up the shock oil for both the front and rear:

Front: 725cst -> 750cst (no changes to the shock pistons)
Rear: 750cst -> 800cst (no changes to the shock pistons)

Front Roll Bar: 2.3mm -> 2.2mm

 

[CosmoM3]

It was not my best day and not a great way to end the season.

I didn't manage to squeeze into B-Main and I don't know what was going on, but the car and I just didn't mesh well today and I only managed to get into C-Main and placed 3rd.

First of all, I did not like how the car landed on the jumps and it felt like it was getting bent out of shape. I've decided to not use the MIP Bypass1 pistons after this race and reverted back to the factory spec pistons. Although the car would still bottom out from a hard landing with the stock pistons, I feel like I need to manage it with better landings and fine-tuning the shock weight oil.

Going back to:
Front: Tekno Piston (1.3x4 + 1.6x2 + 0.8x4) + 650cst
Rear: Tekno Piston (1.2x4 + 1.6x2 + 0.8x4) + 550cst

As the weather starts to cool down, I feel that the oil viscosity will work fine.

Well the season is over and we've got a long break before the famous Invitation series (3 day weekend event in October) and before the Fall series starts up.

 

[CosmoM3]

While I was giving the buggy a teardown to make sure she was squared away while there was a nice break between now and the Invitationals, I noticed that my REEFS RAW 500 was acting up. I think the mystery as to why my car felt so "off" this past weekend can be explained now.

Earlier in the morning during practice and qualifying, I noticed that my car wouldn't turn after the main straight and sometimes felt inconsistent on the other corners as if it wasn't reacting fast enough or it would feel stuck.

I've reached out to REEFS and they said that they're cover it as long as it's not gear related.

I've ordered a replacement servo from NitroPro Racing and I hope this will hold up a little better than the REEFS.