6S CRT.5 Neu motor question

[VintageMA]

I've been reading that a 1506 should be fine to push a CRT.5 and a 1509 may be overkill. Looking to move from a 3S to a 6S setup to reduce amp draw and increase efficiency gearing for a modest 40mph - nothing crazy. Would like to keep the motor RPMs around 30-35K.

A few choices: (assuming quality LiPos holding 3.5v/cell under load - 6*3.5 = 21V)

1506/3Y 1850 = 38850 rpm

1509/2.5Y 1450 = 30450 rpm

So which do you think would run cooler with less amp spikes and overall draw?

The 1506 is a smaller motor and will draw less overall, but with a higher kv it may pull larger spikes trying to spin-up.

The 1509 will have more torque and a more mellow spin-up amp draw, but it's a larger motor and the added torque will come at the expense or more current.

I'm only getting 10 minutes run-time with 3S and a LMT 1930/6. Motor and esc cool, but lipos are touching 130*.

[sleebus.jones]

If you're going to run 6S on a MM, you are going to be just over the 25v limit with a fully charged pack. I would think that 5S would be more than plenty for your application?

I'm surprised you're having trouble with heat, but a 130 degree LiPo is HOT, as in ready to burst into flame. I run a MM 5700 in my T4 stadium truck with 3S A123. I get 13+ mins runtime, motor temp = 130ish, ESC = 115ish, Batts = warm. Have you checked driveline for binding, too tight gear mesh, etc? I think something else is at work here.

[VintageMA]

Originally Posted by sleebus.jones

If you're going to run 6S on a MM, you are going to be just over the 25v limit with a fully charged pack. I would think that 5S would be more than plenty for your application?

I'm surprised you're having trouble with heat, but a 130 degree LiPo is HOT, as in ready to burst into flame. I run a MM 5700 in my T4 stadium truck with 3S A123. I get 13+ mins runtime, motor temp = 130ish, ESC = 115ish, Batts = warm. Have you checked driveline for binding, too tight gear mesh, etc? I think something else is at work here.

I think a lot of it has to do with my bashing style (I don't live anywhere near a track right now) which is a lot of WOT acceleration and running with some hard braking in large parking lots and grass fields. The drive train is very smooth, the gear mesh is nice with just a littlespace in the gears for chassis flex, and I blow all the in's and out's till they're spotless with an air compressor after every run. (Translation - I am a anal obsessive compulsive clean freak)

I know that the MM won't support 6S so that means either moving to a Quark or a MMM hen available. There is also a substantial capital investment involved in moving to 6S as my balancers only work to 5S and I will have to get 6S packs (which are to $$$ in the 2200mAh-2600mAh range) and may break down and get a TP 1010C charger with 210V balancer (been checking them out and like how they can work together). I've been using a TP 205V balancer up till now and all my packs have TP balancing connectors.

This is why I'd like to hear from some more people that the investment will pay off to some extent (other than that it becomes an expensive experiment, but I'm dying to try something new with spring here not having spent much $$$ on RC over the winter). Plus I expect the 6S investment to pay off when the e-revo is available as I hope to get one towards the end of the year.

[jhautz]

Just a thought... Here is a cheap(er) way for you to try and reduce battery heat and increase run time.

The Lehner motors can be reconfigured to run in eithe delta or wye wind by changing the sloder path on the back of the motor. If you change your 1930/6 it will become a 1930/10 at 2090kv. On a 4s pack that will give you around 30K motor rpm. You could run that on your MM and reduce amp draw a bit from your current set up and you could do it all with the ESC and Motor you alreay have.

BTW: I'm curious what batteries you are running. I run a 3s 3700mah Polyquest, MM and Hacker 8L (3019kv) and don't have any heat issues and get run times of easily 15-20 minutes beating it very hard. I actually have a 1903/6 here and was thinking about putting it in the CRT.5 to see how it ran.

[VintageMA]

Jeff - I'm using the MA 3S-5000mAh packs (about a year old now, but were strong when i first bought them).

I started out with the same motor as you B50 8L and was getting just about the same runtime as you. Then I got the 1930/6 and with the same gearing got a great speed boost and things were just in check (if maybe close to the edge).

With the RCM extended chassis and 30 series wheels it seems the current draw has gone straight through the roof.

I actually REALLY like your idea on re-configuring the LMT to a 1930/10 to lowe the KV - I hadn't even thought of that. I didn't want to have to ditch the LMT - I love their motors. Are you sure changing from a delta to a wye config will produce that end result?

[BrianG]

Originally Posted by VintageMA

...With the RCM extended chassis and 30 series wheels it seems the current draw has gone straight through the roof.

Well, the extended chassis added some weight, and the larger tires effectively increased your gearing, so that makes sense. I would've gone down at least 2 teeth on the pinion to keep close to the same roll-out ratio and to help compensate for the added weight. Of course, this assumes you don't mind losing a bit of top speed.

[sleebus.jones]

Hm, your bashing style sounds very similar to mine, because it's pretty freakin' flat around the house. I probably run mostly on concrete tho. I still dont' see high temps. *shrug* Sounds like the drivetrain is set up just like it's supposed to be. Have your entered your stuff in the top speed calc to see if it's set up to run the speed you want? it's possible it may be set up to run much faster, but they system can only pull it so far (which may lead to the hot batteries you describe).

I would warn against a Quark. I have heard of many many instances where 6S = smoke. As far as i'm concerned, where big ESCs are concered, the MMM is the only way to go. We all know it's going to be designed beyond tough, and their CS is excellent.

[VintageMA]

Doing some digging I found this link:

http://www.lehner-motoren.com/downlo...use_s10-22.doc

from an old thread of Jeff's. I'm going to give that a try as I have a 4S 4000mAh pack lying around.

It'll end up saving me spending $$$ I don't have right now. But I really wanna buy a new charger MUST..... RESIST..... URGE..... ;)

[jhautz]

That is exactly the documant I was going to link you to.

And yes it works. I did it on my 1930/6 and made it a 1930/10 for a while and ran it in a 1/8 buggy on 5s and a Quark 80B. Ran like a champ, but just a little to small of a motor in the long run for the 1/8 buggy. Should haul a .5 around with some authority though.

[jhautz]

Dont forget the external BEC on the MM for 4s though.

[VintageMA]

Originally Posted by jhautz

Dont forget the external BEC on the MM for 4s though.

No worries there - ever since I did a test and found the MM heats up a lot just from using it's BEC on 3S I've been running a CCBEC for anything over 2S. Thanks for the reminder though.

I'll try this tonight and let you know how it goes.

[Finnster]

The only limitation going HV on a CRT.5 is that the small mah batteries tend to really suffer considering power to weight (mah/g) ratios. The p/w ratio in lipos is not linear, so you end up having to use a much heaver (and bigger/taller dimensions) batt to get the runtime and current capabilities you need. My 4S 2500 batt from Neu seems about as big as I'd want to run. 5S may be doable w/ 2100 cells.

[VintageMA]

I agree completely as I have moved towards trying to get batteries that balance out the motor side of my vehicles lately (at least to within 50grams) if possible.

Right now the receiver and MM are mounted dead center, so i don't count them. The motor (LMT1930 is 230grams) and servo is ~60 grams. So my weight for batteries is ~300grams to keep things mostly in balance.

That puts the exact cell you are talking about - Neu 30C 2500's at 278g right up there with the other ones I am looking at TP eXtreme V2 4S 25C 2600 a 277g. http://www.rctoys.com/rc-toys-and-pa...BATTERIES.html

Both look good, but is this new setup works I'll probably try out the TP packs as they are a little longer and it'll be easier to bias the front/rear weight distribution - and not quit as tall.

[VintageMA]

Weekend update - Finally got a chance to run the new setup today. Ran it for 11:45 min with a MaxAmps 4S 4000mAh pack (god I can't wait to get rid of all my MA's and replace them) and drained 2.17Ah from the pack with a max Amp pull of 62.56Amps (830 Watts). And I ran the car HARD!! Lot's of fast high speed runnig with gearing back up to 17/46.

That is excellent news - with the max amp draw where it was I should have no problem running the TP 2600mAh 4S packs (to lighten weight) and still get at ~15 minute runtimes.

[lincpimp]

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We need pics!