head speed and pinion/motor advise :)

[dieselcarb]

hi there guys still learning here as always but i ive got a clone trex v2 witch i set up was i bit larey but i built a v3 pro it its beautiful to fly now i believe both helis have a 13 t pinion the old v2 had a 4000kv motor which i believe to of had a dangerouse head speed and the new v3 has a 3500 or 3550 kv

the kit for the v3 says on website it has a 14t pinion but i think its 13 (just counted 3 times but didnt remove motor) now i just wonderd what pinion and moter combos people use and recomend and is my head speed still too fast i work it out at3367 rpm and old heli at 3848 i werked these out with an android app at 11.1v thanks

terry

[dannyhough]

Hi Terry, don't know what app you \are using but do you know if it takes into account motor efficiency and mechanical drag???? With a 3500Kv motor on a trex 450 clone with 150 T gear and 13T pinion i worked it out to 2700rpm (ish) and the HS calc i use came up with 2718 rpm, 14t goes up to 2927rpm.

With 4000Kv motor and 13T on 3S you're looking at 2900rpm this though is worked out on nominal voltage so you will get more, the claims by motor manufacturers especially the budget brands are to say the least ball park some are far lower KV than stated others far higher.

Best bet is a tacho, but if it feels good and you're using quality CF blades then go with it

[bolders]

On a 3500kv motor and a 150T main and 13T pinion I get the following values

3440rpm Start of flight (12.6V)
3030rpm End of flight (11.1V)

If you are a beginner I would recommend either dropping down 1 tooth on the pinion or pulling your throttle curve down to around 85-90%

This will give you approx. 3000rpm to 3100rpm at start of flight and 2700 - 2800rpm at the end of flight.

On a 4000Kv motor I would recommend running an 11T pinion max and preferably 10T if you are still learning.

[dannyhough]

On a 3500kv motor and a 150T main and 13T pinion I get the following values

3440rpm Start of flight (12.6V)
3030rpm End of flight (11.1V)

If you are a beginner I would recommend either dropping down 1 tooth on the pinion or pulling your throttle curve down to around 85-90%

This will give you approx. 3000rpm to 3100rpm at start of flight and 2700 - 2800rpm at the end of flight.

On a 4000Kv motor I would recommend running an 11T pinion max and preferably 10T if you are still learning.

Not sure i agree fully with that, with noobs i tend to suggest a reasonably high HS and 20% expo and reduced collective pitch (max 8 or 9 deg). The increased HS helps with the overall stability of the heli whilst the dumbing down on the sticks and reduced collective helps calm the bird down, for instance too lower HS and the heli nods and stability is reduced, yes? Ergo higher HS increases the stability.

So long as the blades are upto the job and the HS isn't excessive.

Having said that a good HS for a 450 in the hands of a noob would be (IMO) around 2800 rpm, now unless you can govern the HS it's gonna change throughout the flight as you said. If you start at say 2600rpm at 12.6v (12t pinion + 3500kv) by the time you hit 11.4 (3.8v per cell) youy will be down to around 2100 rpm (ish) at which point there will be a noticable difference in the stability .

Starting at a higher HS means you maintain a higher HS and more stable bird throughout the flight.

There are of course other things to consider but as a general rule for beginners on trex 450 or clone i would suggest a 3500Kv motor with a 13t pinion. Remember that even some HS calcs only take into account motor efficiency and not mech drag as well which is another 10% or thereabouts even on the smoothest running heli.

[bolders]

Not sure i agree fully with that, with noobs i tend to suggest a reasonably high HS and 20% expo and reduced collective pitch (max 8 or 9 deg). The increased HS helps with the overall stability of the heli whilst the dumbing down on the sticks and reduced collective helps calm the bird down, for instance too lower HS and the heli nods and stability is reduced, yes? Ergo higher HS increases the stability.

So long as the blades are upto the job and the HS isn't excessive.

Having said that a good HS for a 450 in the hands of a noob would be (IMO) around 2800 rpm, now unless you can govern the HS it's gonna change throughout the flight as you said. If you start at say 2600rpm at 12.6v (12t pinion + 3500kv) by the time you hit 11.4 (3.8v per cell) youy will be down to around 2100 rpm (ish) at which point there will be a noticable difference in the stability .

Starting at a higher HS means you maintain a higher HS and more stable bird throughout the flight.

There are of course other things to consider but as a general rule for beginners on trex 450 or clone i would suggest a 3500Kv motor with a 13t pinion. Remember that even some HS calcs only take into account motor efficiency and not mech drag as well which is another 10% or thereabouts even on the smoothest running heli.

I can see your point about a high HS but you may notice that with the numbers I stated should give a HS in a band of approx 2800 - 3000rpm so im not sure what you are disagreeing with here. I was simply stating that there is no need to be running in excess of 3000rpm as its going to give you less flight time and sound more intimidating and a 13T pinion is going to give you around 3400rpm at the start of flight at 100% throttle.

(KV x Voltage x Efficiency x pinion) / MainGear
(3500 x 12.6 x 0.9 x 13) / 150 = 3439

Also head speed calcs do not need to take into account mechanical drag (assuming the motor can can produce enough power to react against the torque on the rotor head at the desired speed) the current should just increase as a function of the load to maintain rpm. I also suspect that motor efficiency has nothing to do with HS calcs and its really just a fudge factor to compensate for sagging of the lipo voltage under load

[dannyhough]

Hi Bolders

Yep my bad, only just woke up when i read your reply. To me it seemed you were suggesting a far lower HS my means of reducing pinion size and reducing the Throttle curve.

On the subject of motor efficiency, i have come to think that it's there to take into account both inefficiency in the motor due to energy loss through heat etc and to some extent the lipo efficiency, of course the higher end lipos will produce a far more constant output.

The mech inefficiency is a thing that is mostly overlooked, i have come accross quite a few people mainly with scale projects who have missed this factor when aiming for a desired HS and ended up with lower HS as a result. They then either have to mess about changing pinions or in the worst cases get themselves a new lower KV motor.

As per Bolders equation with the Mech drag at 0.9% at the end eg: (3500 x 12.6 x0.9 x13) / 150 = 3439 x 0.9 = 3095 @12.6v, 2800 @11.4v.

Reduce to 90 throttle curve for 2785rpm @12.6 & 2520rpm @ 11.4v.

In this case i just want to make the new guys aware that it is a factor to be considered.

For the OP, i think we concur that you should be using a 13T pinion with your 3500Kv motor and perhaps reduce the throttle curve to around 90%. If your ESC is has reasonable govener mode then try putting it to use it may help

As a wise man once said to me many moons ago "Don't be afraid of the noise, after all it's only noise"

[dieselcarb]

guys thanks for the replys very detailed i have a shite esc but saving up for an align 35 amp i believe that has a govenor and as for noise i want more lol was looking at a very good priced 600 on ebay but herd they get expensive to run as they eat lipos happy days i thinks i stay 13t and may get a 12 just to try for added flight time but i like how she flies i use 5 expo may reduce to none cant do 20 i find it imposible to fly (as they tighter the better) i do have 5 batteries mabe its time to charge them all up only done 6 4 min flights last 2 were well fun used the whole field yeah baby (must confess i did do about 10 hours on sim and about an hour on mcpx) and again cant fly that on low rate only high got a dx4 for that

[bolders]

guys thanks for the replys very detailed i have a shite esc but saving up for an align 35 amp i believe that has a govenor and as for noise i want more lol was looking at a very good priced 600 on ebay but herd they get expensive to run as they eat lipos happy days i thinks i stay 13t and may get a 12 just to try for added flight time but i like how she flies i use 5 expo may reduce to none cant do 20 i find it imposible to fly (as they tighter the better) i do have 5 batteries mabe its time to charge them all up only done 6 4 min flights last 2 were well fun used the whole field yeah baby (must confess i did do about 10 hours on sim and about an hour on mcpx) and again cant fly that on low rate only high got a dx4 for that

Just to note that the gov on the align ESCs is generally considered to be a poor performer and the recommendation is to generally not use it. If your current ESC is working fine then switching to an align unit may be a waste of time.

I'm currently running a Castle Creations Phoenix 35 (no longer manufactured - has been replaced by ICE series) on my 450 and the gov works very well and it has so far performed faultlessly. I have also got a CC ICE 100 on my Atom 500 and that has also produced good results although the gov took a little more tweaking to get it running well.

[dieselcarb]

i just want an esc to fit under battery tray on 450 pro but thanks for the heads up on the gov beiing naff