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Old 29-10-2009
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Default Novak Ballistic 6.5 running hot...

Hi all,

I have a 6.5t Novak Ballistic in my B44, running vampire lipos via a spread spektrum GTB.

Another guy at my club runs roughly the same setup, same vampire lipo's, standard GTB and Novak Velociti 6.5....so very similar.

On our tranny's, he runs with his exp down by 30%, mine is down by 25%, his end point is 100%...mine is set at 85%

On our tracks, in the same heats with similar lap and race race times his motor temps come off in about the 120's (F) mark, whereas mine have been coming off in about the 150's-160's (F) mark.

We run in a small(ish) hall and are both geared on 21's on kit spur, which for me runs in the 160's. I've played around going to smaller pinions down to an 18 or 19 from memory, which reduced temps a little...down the the 150's.

Esc temps are fine as well by the way.

Transmission all spins freely and feels good as far as we can tell.

So, my question is this...could my driving style...throttle control inparticular cause such a dramatically different running temp? Could the EPA setting be having an effect? Or is there something else that could be causing it? Really want to get my temps down if I can.

Any suggestions gratefully received!!!
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Old 29-10-2009
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My guess is that it is UNDERgeared. If the motor is hot, but the ESC and Lipo are both cool, then it is an indication of undergearing. I've had to use this before in brushless 1/8, and in fact, gearing up reduced motor temperatures.
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Old 29-10-2009
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I've wondered this myself...but got put off a little by the temps going up 10 degrees+ when I changed from an 18/19 up to the 21...maybe I should try higher and that 10 degree change was actually just a different race thing then?!?!

Still unsure why it should vary so much in temps from another car that is very similar though???
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Old 29-10-2009
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Why aren't you running 100% EPA Andy?

It seems to be the only difference in setup.

I know people say the brushless speedos aren't bothered by limited EPA in the way that brushed speedos were... even if that is the case, the limited EPA is probably tempting you to hammer the throttle more.

Full power and a softer finger on the trigger may be the answer.
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Old 29-10-2009
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I only checked the epa after we'd finished last week, first thing on my list is to turn it back up this week.

The 4wd responds sooo much more directly than the 2wd that it was a bit of a shock when I first got it! I found it easier to run indoors with it turned down to begin with...just felt a bit safer

When we gonna see you over at Caldicot again by the way? It's been a while!
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1/10th drives: Yokomo BMax2MR & BMax4
1/16th drive: Carisma GTB
Racing in South West: http://www.mendiprcraceway.co.uk/
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Old 29-10-2009
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Quote:
Originally Posted by blue_pinky View Post
I only checked the epa after we'd finished last week, first thing on my list is to turn it back up this week.

The 4wd responds sooo much more directly than the 2wd that it was a bit of a shock when I first got it! I found it easier to run indoors with it turned down to begin with...just felt a bit safer

When we gonna see you over at Caldicot again by the way? It's been a while!
Having a few electrics related issues. Need to upgrade to LiPo and brushless but haven't decided how to spend my money just yet... not that I have any money.

Also been doing a little *ahem* touring car *ahem* racing at Chippenham. But my touring electrics are dead also!
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Old 29-10-2009
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I used to run 18/78 (11.3) on a 6.5 Novak using 3600 LiPo's.

21/81 is about 10.2ish, overgeared me thinks?

If you are running big fat 5000mAh LiPos you might find you need to sell that 6.5 for something a little softer?

Oh, and try and get some ventilation on the shell too

I agree with David about full EPA and a gentle finger. Throttle jamming cos of the expo wont help matters.
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Old 29-10-2009
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My Novak Velocity 6.5L was more than happy geared 23/78 (RB5 and B4 use the same internal ratio) .... never even slightly warm
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Old 30-10-2009
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Cris, shell is ventilated and lipo's are the vampire 4400's. Throttle jamming...maybe ...but 40 degrees difference to Dave and Bill's running temps on similar setups? That's confusing me

Novak say it's optimum running temp is under 160...so maybe I'm worrying too much? Was getting 150's with the 18/19t pinion on so maybe that's fine and the way to go!

Next question then...

Brushless motors get hot when they rev too high for too long, do they also get hot when they rev too slowly for too long? My gut instinct is saying they don't.

I know that ESC's get hot at that point as they need to push more current to make the motor spin undr load...wondering if the motor does the same or just stays coooool?!?!
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Old 30-10-2009
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Have you checked that you don't have a duff bearing in your motor? They can heat things up as well. As far as I know the bearings are fairly tight in Novak motors.

If all else is cool and you say that it is so direct to the point of having to turn down the EPA it could well be undergeared and revving it's nuts off. How long does it take you to get up to speed? Is it kind of instantaneous or does it feel progressive? If it feels like an on/off switch that would be another indication of undergearing.
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Old 30-10-2009
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Quote:
Originally Posted by blue_pinky View Post
Next question then...

Brushless motors get hot when they rev too high for too long, do they also get hot when they rev too slowly for too long? My gut instinct is saying they don't.

I know that ESC's get hot at that point as they need to push more current to make the motor spin undr load...wondering if the motor does the same or just stays coooool?!?!
If you are referring to gearing, then the first situation you mention is undergearing, whilst the second is overgearing. Motors will not get really hot if you are simply driving slowly with correct gearing as they pull only as much current as they need. Current pretty much equals heat, so as it draws less current, it will be cool. ESCs on the other hand do not like 'partial load' applications, as they are least efficient then.
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Old 30-10-2009
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@ Roger - Roger running outdoors with my B44 last year on a 5.5R I was pretty similar to you using between a 21-23 tooth pinion, Caldicot is a relatively small indoor track which is usually quite technical and there is definatley a need to gear down.

@ Pinky - I ran at Caldicot a few times this year with my CAT SX and last with my B44 and always with the 5.5R in on a GTB and Trakpower Lipos, I would suggest you gear down as the track dose not justify a big pinion and top end heavy power...

In my CAT I ran a 22 outdoors pretty much all season but when I came over there I needed to drop to a 17, would have gone to a 16 if I could have got the motor close enogh to the stock spur, It still got a bit warm and I did try with my undertray off to help with the ventilation too..

Your 6.5 on a stock spur (84 If I remember correctly) and a 17 Pinion will give you a final drive ratio of 12.352 which in theory should be fine..

Try and be smooth on the throttle too as this will help
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Old 30-10-2009
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Sparrow, the motor is pretty new, so hadn't considered bearings. Definately be worth a look.

The 19t pinion felt to me as though it was a little short, getting to full throttle too quickly on the tracks we run on, which is the reason I went back to the 21t. But then it ran at a temp that Novak consider to be ideal with the 19t, and with epa down, it would have had more to give if I let it, so maybe it wouldn't have felt so short in reality?!?!

Marvin, I wasn't really referring to the gearing, I'm ok with that part of it I think, I was purely asking about the motor and how it should theoretically behave ?

I figure if I can understand each component on it's own as much as possible, then that's more chance of understanding the whole system.

Thanks for the comments so far guys, think I'm gonna put the epa back to 100% where it belongs first, then try the various pinion sizes out again and see what the temp gun says. I should check the bearings out to be sure as well.

It's just confused me a little seeing very similar setups running sooo much cooler, but then if I'm running at Novaks advised ideal temp, then maybe I'm worrying too much anyway
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1/10th drives: Yokomo BMax2MR & BMax4
1/16th drive: Carisma GTB
Racing in South West: http://www.mendiprcraceway.co.uk/
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Old 30-10-2009
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Panch, thanks for that, might have raced with you at Caldicot at some point then, although in the past I've mostly raced my X6, only recently really with the B44 really.

The more I think about it, the more I think that smaller is maybe better in this case...our indoor tracks are relatively small, and maybe the motor does gain some heat by running too slow on too big a pinion...not what people seem to suggest should happen, but seems to be the case in practice for me and my throttle finger.

Gonna keep playing and seeing what works for the best anyway, one day I'll understand it properly!

Cheers guys
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1/10th drives: Yokomo BMax2MR & BMax4
1/16th drive: Carisma GTB
Racing in South West: http://www.mendiprcraceway.co.uk/
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Old 30-10-2009
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Have you checked to see if your rotor is bonded or sintered? Bonded rotors tend to get hotter than sintered... could be worth checking
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Old 30-10-2009
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It's a ballistic motor...so I've assumed it's sintered!
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1/10th drives: Yokomo BMax2MR & BMax4
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Racing in South West: http://www.mendiprcraceway.co.uk/
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Kept running by: Yokomo via MB Models & www.tracksidespares.co.uk
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Old 30-10-2009
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My bad ... as indoor racing wasn't mentioned directly I figured the guy would be racing at a proper track .. one without a roof

Don't really do indoor racing these days, would make an exception for PDA though

I normally try to gear so that the car reaches full speed about 2/3rds the way along the straight.
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