PartTime

iTrader: (10)

I wonder what the performance level of a 2cell and 21.5 would be like? Kinda like a 13.5 on 4 cells ??

DK

RC8

iTrader: (3)

I was running my little 3S micro motor 1/12 with "them" 3 years ago. It takes time for it to sink in, "they" are kind of slow. Remember when Trinity was running thier ad bashing brushless? Ah, the good ol' days. Funny stuff.

Perhaps an offshoot of this thread could be, "How the heck do you get it through to people a better way to do things without making them dig in?" As I age I see it always comes down to politics and marketing. You can have the best idea or product in the world, but it won't go unless you "do the dance". It's all in the politics and marketing, sad really.

Fred_B

iTrader: (1)

For the oval guys it's about the same as 4 cell 13.5 or a little faster. Probably not the best thing to get new people to start racing.

Higher voltage will need to have one of two things. Nonstandard motors or limited capacity. Nonstandard motors is a bad idea as far as I'm concerned and anything over 21.5 is going to be a real pain to gear. Limiting capacity will limit the speeds by causing the cars to dump.

Nothing starts a battery war like having less capacity than what you need to finish. Plus, we all know that lipo's just love to be dumped completely.

andrewdoherty

iTrader: (49)

I've read a couple posts asking for scientific data, or personal experiences.
I consider myself a scientist. Controlled testing of a single variable while holding everything else as controlled as possible is critical in these situations. I agree. So here is my experience with a 2 cell lipo in a CRC pan car and a 21.5

Problem/Question:
Will a 21.5/2 cell lipo powered car perform comparably to a 4 cell 17.5 powered variant.

Hypothesis:
If the motor's power is reduced to a 21.5 and the battery's voltage is doubled, then the cars speed and handling will be a little faster than 4 cell/17.5; perhaps more like 13.5 4 cell.

Equipment:
CRC WGT car
Jaco Spec tires
Novak 17.5
Novak 21.5
Ener-G cells
CORE R/C 7.4 v 5k lipo
Indoor carpet facility

Test & Data:
I ran the car with a 4 cell pack and a 17.5 for 4 or 5 packs making small changes to the center spring and sauce time/amount to get a baseline figure. The car doesn't belong to me so I wanted to be sure I had a good amount of laps to get a decent fast and average laps total. I hovered around a 12.6, with a 12.4 FL. The motor was geared for lap times and was coming off around 150*
That same night I then swapped out the 4 cells and 17.5 for the 21.5 and the Lipo. I ran about 4 lipo packs through it with same set up that gave me the FL with the 17.5. The data here is misleading so please red to the end for the explanation; the numbers don't tell the whole story. I was only able to muster a 12.5 FL and my average was a good second above that. At the time I tested this our track layout was new and the limiting factor to the lap times was the traction. With a 17.5 I could hang on to the car and get it around consistently. The 21.5 with the 2 cell felt like a 4 cell car with a 10.5 in it to me. It had so much rip, I couldn't control it consistently on the low grip. I geared it for the fastest lap times as best I could, and it was coming off at 150* as well. It was clearly obvious to me that counting on a 21.5 on 7.4 volts to act as a entry level speed was out of the question. Maybe a 31.5 would work . . .LOL

Conclusion:
The 21.5 lipo option is much to fast for the masses, let alone comparable to 17.5 4 cell. It appears the voltage gained is much more dramatic than the loss in motor power.

trailranger

I'll stick with the 3.7V solution. Battery Packs already exist as I pointed out with the TeamCheckpoint and SMC is already has pack designed for 4-cell cutout trays comming very very soon.

PRS (Precision Racing Systems) has already annonuced that they will supply pinions and spurs needed in Single Cell setups. If new sizes are needed they will make new sizes.

With 3.7V testing in oval, the gearing is only about 10 teeth higher on a 13.5 Oval car and PRS already makes pinions to 65teeth and Spurs as small as 72T. So just to put that in perspective. Using the largest Pinion and Smallest Spur PRS makes with a tires trued to 42mm rollouts up 119mm are possible and more than enough to proper gear a 1:12 for the back straight-a-way!!!

With the lower weight limits and proper gearing a 13.5 3.7V LiPO Oval car can be just as quick as a 21.5 7.4V LiPO car. So with a 17.5 motor, stock speeds can exsist without the worry of out-classing racers as a 7.4V solution would present.

PartTime

iTrader: (10)

andrewdoherty....thanks. looks like you put a lot of work into the test. Nice job. Did you bring the 2cell car up to the same weight as the 4cell car? How far off were they to each other??

DK

RC8

iTrader: (3)

Oh my, don't tell the TransAM folks that! They swear they are equal systems. It's right in the Vintage TA rules. 27T 4 Cell = 17.5BL 4 Cell = 21.5BL 2S LiPo.

trailranger

Hmm.... ROLLOUT LIMITS...

I guess things could appear eqaul since not the battery or motor is being pushed to the limits.

But open the gates up and reduce the min weight some and there will be some differences in performance.

andrewdoherty

iTrader: (49)

No , I didn't. I didn't weight either version. I didn't feel the need as the 5K CORE Lipo I was using was only 25 grams lighter than the 4 cell pack. That being the only change (unless the 21.5 and 17.5 are significantly different) I am confident the cars were within 30 grams of each other.

AndrewNicholas

Here are some pics of my new FF07 A123 Chassis. Jari was nice enough to allow me to make a couple for my own personal use. These are not for sale.
They actually need to be re-done. The cell spacing needs to be moved out a bit.
I ran my 2s car at the last club race and with the proper gearing it was about even with the faster 4 cell car.

RC8

iTrader: (3)

That's pretty cool. Good job.

Der Dicke

@AndrewNicholas: Does this chassis fit a brushless esc? I had many problems fitting a SP LPF with 2s A123.

bs6ef

Very Nice

AndrewNicholas

Yes it does. I am using the Tekin RS Pro.

nrtv20

iTrader: (9)

I completely agree here, I dont want to run any type of receiver pack in my car at all and why should we, the battery capacities are so high that its pointless. As far as the high turn brushless motors... I think We'll have to go higher then 21.5 to equal current stock speeds that the cars are running.