XRAY - Model racing cars

Yeup.....I did it...
Tekin RX-8 w/ 1900kv
Hyperion 4S 4200
It weighs 3.24kg!!!

That looks like a lot of fun right there.

I predict these brushless buggies and other rigs are going to change the way RC tires are made. I predict that soon they wil be cutting treads on carpet tires. If they aren't already they should be. Most of the brushless rigs I have seen are hell on tires.

He is getting that run time because the motor is only 1900KV. That is all you need in a buggy running 4S. Anyhting more will be too fast and your runtimes will drop.

I am running 6S 3300mah and I am getting 15-16 min.

My car weights 3409 grams on 6S.

cool! looks good Rocco! wanna do one soon myself.

I'm p*ssed about the 4S limit appearing (many look at ROAR rules and take them over). Higher voltage is often better and so it seems to be better on the 1:8E also. Unfortunately it seems to be wise to stick with 4S to be able to run some sanctioned races. It would be a costly thing to run both 4S and 6S...

I already dismissed the idea of getting Tekin but now I have to reconsider again

BTW Rocco's setup gets only max 30k RPM (4S with 1900kV). If you gear it right does it have enough power with good efficiency? I've heard that you should go to around 40k rpm to get good power/efficiency from those motors, of course depends on the specific motor. Guys run 2650kV with 4S (much higher motor rpms) - XB808 with 4900 4S and locally done mount+batterytray weighs 2300g (no lighter option parts on the car). We run 10min qualis and 3x10min finals here. So running 22min really isn't an option - too little power or too big battery

Good info, thank you guys.

There are a couple of important things in getting efficiency:

1. Multiply the motor's kV by the nominal voltage you use to get maximum RPM. If this is between 28000RPM and 35000RPM you are good to go. Outside this range and you lose efficiency - this is why 2650kV is too much for 4S - max RPM is 39220 RPM.

2. Gear correctly. Use calculator to help gear correctly. You want to gear for just under 40 mph with 0.5" of tyre balooning for buggies (1" for truggy LPR tyres).

3. The MMM is as powerful as the Tekin RX8, but it isn't sensored, which is why the Tekin is popular with racers. The main issues the RX8 combos have are that the V1 rotors didn't like staying bonded, but they appear to have figured that one out. Anyone who gets a rotor failure is sent a new rotor by Tekin for free.

I used to run 4S 4350mAh Flightpowers and I got 11-12 minutes, and that was whilst I had the fastest car on the track, I wasn't driving as smoothly (which is also important for efficiency), and I hadn't used punch control or timing.

One thing I have never understood though I follow the rule is why use nominal voltage when calculating motor rpm? I dont have a logger & havent actually checked or asked some one with a logger but does lipo not put out actual voltage under a heavy load?Does it drop all the way to nominal? All my packs peak at 4.2V per cell so why not use say 16V or something for a 4s calculation? I know all the enerland based cells I use have super punch for the first couple laps then level off to feel the same till I pull the cars off the track but I have no idea what the voltage is once the pack levels.