D.a.v.e

iTrader: (8)

Thanks for the feedback I think I'm going to try the lower KV motor higher voltage approach to keep the current draw down which in turn should keep things cooler? Also thinking I would not need to fork out for such high rated c packs and maybe I would get longer run times?

What all of this translates to in reality though I have no idea? Guess I'm going to get very familiar with how to program a RX8?

Has anyone played with the higher volt lower kv motors vs lower volt higher kv motors? I'm not interested in theory but am interested in actual experience with on road?

rcwck

iTrader: (2)

Yes, more voltage and less kv will make heat control more manageable and no I don't think it's been done here except maybe Russ might have tried it. Some people use their sedan(2S) packs in series to make 4S. Not sure how easy it'll be to keep the chassis in balance with a 6S pack. It depends on what pack(s)and how they can be arranged in the car. Using two 3S packs in a car set up for two separate packs would be the ticket. Using the 1/10th sedan 2S packs makes it nice if you run sedans. Some speeders are marginal when running the 6S voltage including the onboard bec.

There's not a bunch of tuning to the RX8. It only runs in dual mode. Nothing like the RS esc. Careful with a bunch of timing. These big heavy vehicles don't like it.

Here's a fun calculator to play around with and seems pretty accurate if you use the nominal voltage of 3.7/cell. Shoot for a top speed around 55-60mph.
http://www.scriptasylum.com/rc_speed/top_speed.html

D.a.v.e

iTrader: (8)

My plan was 2 3 cell lipos but I don't have those right now so buying 4 of those may be a bit steep for testing thus was hoping someone went before me here

Looking forward to getting my kit next week!

FLoJo

iTrader: (2)

I think ive seen those two chumps on the left hand corner before

Voltron989

iTrader: (5)

Lolol

Voltron989

iTrader: (5)

Might be some guys running 6s low KV motors on the other threads like the GTP2e. It's not a common setup. Never ran 6s except for a speed run.
Buying 4 3s batteries to try it out is a expensive risk especially if it doesn't work out then the batteries and the 1700kv motor is useless.
I'd be interested to see how it would work out though lol

D.a.v.e

iTrader: (8)

Guess we'll find out in April Everyone I have asked so far says it should work, that they have seen significant differences when running off road, and it should be significantly cooler (at least the speedo). I just wonder what it will do to the powerband of the motor? I would guess I might loose some top end but may gain a lot in the low to middle end?

I think the real story will come when I stick my Eagle Tree in and can perhaps compare the data with another car

Next question. Does one use a 1/8 scale setup station for this car and do I need a on road or off road one?

rcwck

iTrader: (2)

A 6S set up would be interesting to test. Just not sure about how much added weight will be involved. Some road racers are very anal about any added weight. I wouldn't be anxious about a few extra ounces as long as the chassis remains balanced. These cars are heavy weights and our track is pretty much wide open. Have you figured out any weight for 6S as compaired to 4S? Weight versus capacity is usually a straight line graph. Run time has to be greatly increased with 6S so much lighter lipos(lower capacity) can be raced if you want the weight to remain about the same. We once raced 8 minutes and that was marginal for most cars as to lipo capacity. We have now switched to running all 7 minute races. I need around 6000mah for the 7 minute runs. Most other drivers get by with 5000mah. I just be more throttle happy than most. Just thinking, using the same capacity for 6S as for 4S you'll be adding ~50% more lipo weight. That will mean you'll need to increase run time by ~ 50% so that you can run 50% less capacity(weight) for 6S to keep total car weight about the same. Doubt if efficiency switching to 6S increases by 50% to alllow 50% less capacity. As to more punch, you have to baby the throttle on 4S on most days and the heat is manageable even on 150F degree track temp days. It'll be fun and interesting to experiment. Hope all this makes sense and that I'm thinking close to correct.

As to set up. A big flat set up board, large set up wheels close to 3.8" diameter, camber and ride height gauges is all that is needed. You would need an expensive 1/8th buggy set up station if so desired and no one here uses one of those.

D.a.v.e

iTrader: (8)

I think the weight will be a wash or maybe even an advantage for the 3 cell as I should be able to use a smaller pack? Seems weights are all over the place when it comes to various packs? I saw the calculation somewhere on how to figure the equiv 4 cell vs 6 cell in mah but just taking a swag and looking at hobbyking's softpacks a 6000mah 2cell weighs 423grams vs a 5000 3 cell pack at 404 grams vs a 5000 2 cell pack at 325 grams.

So the difference between your 6000's and if I go with a 5000 would make you .08 of a pound heavier based on a 2 pack setup? If we compare the 5000 2cell vs 3 cell I would be .34 of a pound heavier? Which appears to be about the difference of using a soft vs hard pack setup but may allow a car to make a 8-10 min main?

Of course the next question is will they even fit in the car? Best I can find is someone saying the measurements are 140x50x25.. Can anyone confirm those?

C@T

140x50x25 mm is the standard dimension of a hardcase lipo, that is correct.

That is also the size the battery holders of most of the cars are made for.

The height (25mm) is not critical, most boxes will also accept a few mm more.

Hardcase is a must for cars for safety reasons as you will see in those classes already having a ROAR or EFRA sanctioned rulebook.

Looking for batteries for a 1/8 scale onroed should follow that guideline.

There are 2 cell packs (1/10 GT) and also 3 cell packs (1/8 OR) available on the market.

If you plan something to do racing with others on a circuit there are two major limitations.

One is the amount of power that can be used/ubused by the motor before it does give up by overheating. The second one is the time you need to run to complete a heat.

With a total weight of a car of around 4 kg (8.8 lbs) and a peak power of the motor in the range of 2 - 3 kw you get a idea what the current may be.

The current as an exaple for a 4s setup a 2 kw peak will be 135 Amps. (2000/14,8=135)

This is more than the banana plugs will be able to carry. Well there are packs available with dual plugs, but those are also top level in price.

Going with 6s same powerrating the current will go down to 90 Amps.

Weight of the batterypack for same amout of energy stored ( 100 Watt/hours) will be nearly the same.

My point of view that are clear arguments for 6 s.

rcwck

iTrader: (2)

145L x 50W lipos will fit in my OFNA cars. I just did some quick searches and a 6S set of lipos that I would be confident to run comes in at 12 oz heavier than what I have run using a 4S set up. 3/4 of a pound heavier but I call lipos and motors "Good" weight. I would run at least a 40C rate lipo. I will probably try a 6S set up sometime just for grins if I get a new car set up for twin packs. I have a Tekin 2050 laying around somewhere.

rcwck

iTrader: (2)

Don't worry about the added expense of hardcase packs if you're planning to run with us. We do not require them. These cars have a plastic tray that offers some protection and we have had no issues at our outdoor track concerning onboard lipos.

D.a.v.e

iTrader: (8)

Thanks.. I figured the built in trays in this car would be the equiv or better then a lipo case & for this project I'm going to try some cheap lipos like genace or maybe sky as it does not appear the nano techs will fit?

Not to mention I'm not a good enough driver for it to come down to a battery war

Voltron989

iTrader: (5)

Which ever 3s u choose will most likely fit the tray but you won't be able to shut the top d on them so u will have to remove them and install Velcro straps.

D.a.v.e

iTrader: (8)

Finally ordered the car today. A Main had them on sale for $25 off and then added the coupon code for an extra $25.

Looking forward to building it. Its been about 10yrs since I last built one of these from a kit.