8s help? just let the smoke out!!!

[cd5]

Hi
I just cooked my stock gaui 850kv motor running 8s, While this was inevitable as it was only rated for 25 volt , i was just after some advice so i dont do it on my next motor.
Will the z20a 950 kv motor work in the the hurricane.
and secondly , i use the revco 68 ist gear, so what revco pinion should i gear this motor with.
And what throttle curve should irun.
Thanks for any help
simon

[bstock]

Hi Simon,

The Z20 will work in your Hurricane. Check out: http://www.helifreak.com/showthread.php?t=46418

I think you meant to say 980kv.

I haven't tried this motor yet, but I am seriously thinking of getting one. Hurriken has one, and is updating us on his findings in running it - in the thread above. Right now, the only place I have found it available, and at a reasonable price, is flying-hobby.com

I am assuming you are also using the revco 61 tooth gear, with your 68t

The pinion for the revco gears, depends on what head speed you are looking for.

At 850kv, a 22t revco gear was giving you 1711 HS, factoring in a 10% drag

At 850kv, a 23t revco gear was giving you 1789 HS, factoring in a 10% drag

At 980kv, a 22t revco gear will give you 1973 HS, factoring in a 10% drag

At 980kv, a 23t revco gear will give you 2063 HS, factoring in a 10% drag

I would run the same throttle curve that you are currently using, to start with (it should be close) - and then adjust it in the field, to match your new motor and head speed. The Z20 will most likely have more torque, than the stock motor you were using.

Please get back to us here, and let us know what you see and are experiancing with your new setup.

[concept1]

what esc were you running with 8s?

[ukgroucho]

If you're running 8S and want higher performance for 3D (as opposed to longer flights) then the z30 may be a better choice. The 1100Kv seems to be the choice for 8S although I guess the 800Kv would also work with a suitable pinion.

[Hurriken]

Simon,

The Z20 should be alright on 8S according to specs. It runs a bunch cooler than the stock Gaui 850, I could see how you smoked the 850! Mine is too hot to touch on 6S after 7 min of hovering, slow FF 165° F

Motor choice is totally dependant on what type of flying you want to do. I don't plan on being out of the sport flying realm for quite some time. But if you want to do 3D the Z-30 is your best choice. Price is the same either way.

Watch your gearing though. I think bstocks headspeed calcs were at 6S not 8S, see attached, 18, or 19 tooth would work pretty good on 8S

Just curious what runtimes were you getting with 8S on the 850, and what Mah packs were you running?

Ken

[bstock]

Damn it... good catch Ken... I was using 6s.

So used to using 6s all of the time... got off on the wrong track.

I was half asleep Sun morning. I need to wake up before I post anymore ;-)

[cd5]

thanx for the help so far
as for the questions asked, i am running the following set up.
E watts pentium 80 HV 80 amp esc
revco 68 spur against revco 22 tooth pinion
idle 1 at 75 % flat curve
2 * flightpower 4s 2500mah
After a 4.5 minute flight i am putting back around 1600 to 1700mah. the flight consists of 1 minute orientation hovering .2 min figure 8s and stallturns and for the remainder of time i am doing broken 3d. ie flip hver roll hover loop hover tictoc hover. So ithink i could stretch out to 5 min and use 2000mah as my collective management improves. I am also going to try the kong power 2200mah as they are cheap and hopefully between the weight saving and the fact they are more forgiving on over discharge , hopefully i can still maintain th 4.5 to 5 min flights

So also is that 18 tooth pinion the revco as they have a different pitch to the standard gaui ones??

thanx again
simon

[ukgroucho]

Hang on.. is this with the z20 950Kv?

With a 68t Primary (RevCo) and 61t Main - and 22t pinion your gear ratio is 9.92:1

3.7v (nominal ) x 8S x 950 Kv x 0.9 (efficiency) = 25308 RPM / 9.92 = 2551 headspeed.

.. and that's not full throttle on a fresh pack. Either 75% throttle is too little (motor running outside efficient rev range) or the HS is simply too high - so it's eating your pack.

Do you know what the HS is?

[cd5]

ukgroucho
the motor i fried was the stock gaui motor . i ran the throttle curve low because i wanted the motor to have less voltage, closer to 6s as that is what it is rated for.
With the z20 980kv motor iwas think of runninthe revco 18 tooth pinion against the revco 68 tooth primary, then ramping up the throttle curve to the 95% mark. going buy the readyheli hs calc this willgive me a headspeed of around 2300 while improving the efficiency by running a higher voltage.
Do you think i am in the ballpark with this set up. ? Does the gearing and throttle curve sound ok. ? I really dont want to burn the new motor.I hope this is ok cos the only pinions i have are the revco 18,21 and 22. should i run a larger gear and less throttle to hit the hs of 2300 or am i on the right track with the 18 and higher throttle.
Thanks
simon

[ukgroucho]

Ahhh I got mixed up by the tense of your message you said "I AM puttung back..." so my read was that you'd managed to get hold of a replacement motor and these were 'new world' numbers.
As I understand it running the throttle curve lower does not reduce the voltage used in a brushless setup - it changes the 'size' of the pulses sent to the motor in each phase. I've made that mistake myself and been set straight.

Incidentally you might have done better to have run the motor faster and reduce gearing - it is possible it was not running efficiently and cooked itself. That's water under the bridge now of course.

OK for your z20 980 the calculations look very good. I run the same gearing on 10S with an 800Kv z30 and I'm easily getting 2300HS.
10S x 800 = 8000
8S x 980 = 7840
Everything else is identical (gear ratios) so the resulting HS should be very close assuming that the z20 can pull it happily.

With the z30 and 500mm RCP blades I see peaks in the mid 50 amp range, I have seen 60 a couple of times. If the z20 can cope with it then I'd expect you to see over 60 amps on occasion.....

I'd expect flight times to be in line with your expectation but you need to verify.

[cd5]

Ukgroucho
Thanks for checking over the gearing plans, it has layed my mind at ease, And thanks for clearing up how the voltage changes the pulse to the motor, I have heard people touch on this subject but their explanations were not so clear and didnt make much sense, but i understand the way you worded it . This peice of knowledge is pretty important to know or otherwise you coild easily get things wrong as i did.
I am waiting for the new gears and motor to turn up, i wont be airborne in the hurricane til next weekend as a result. But when the set up is sorted and i get a number as far as flight time and motor temp are concerned , i will post a report on "power systems that work" . coz i think yhe 6s boys have it nailed, and you seem to be on top off the 10s setup . but i havent seen too many 8s users.
thanx again
simon