12T vs. 13T pinion on Sonix/HDX 3550 motor

[MarcinCP]

Hey guys,

I'd like to post a review of an experiment I did today. I know some of you have been wondering about which pinion to use with the Sonix/HDX 3550 motor. Till now I've been using a 13T pinion on my all aluminum EXI.

This afternoon after running a few packs of good stunt flying (flips, rolls, inverted punchouts and inverted hovers ) I decided to put a 12T Rhino pinion and see what the difference would be. In theory the flight time should increase a bit, and the response should drop a bit due to about a 200-300 RPM drop in head speed. (3179 with 13T and 2935 with 12T) To offset the lower headspeed, I increased my throttle curve from 80% mid stick to 85%.

1) At first I flew figure 8's and a few stall turns. The bird seemed a bit more tame.
2) I did a few punchouts, and observed a noticable slowdown in the climb rate
3) Lastly I did some flips, inverted hovers, and upside down punchout, and the helis was more sluggish, and really seemed to struggle to gain altitude while inverted. Motor boggung was noticable
4) I finished up with some tame sport flying in normal mode to see how long the 2200 lipo lasts. It lasted 6:30, which is exactly the same flight time I can expect with a 13T pinion. Double

Conclusions? On the EXI (or a Trex) there are no advantage of using a 12T pinion with the 3550 motor.
I can see the 12T being appropriate on the Belt CP, since it has less teeth in the main gear, and it seems to require less head speed.

[helihathnofury]

Wouldn't argue with that. One comment I would add is that the plastic frame of the BeltCP is not good at handling the extra stresses of higher head speed. In fact mine ripped itself into two!!
Most on here would concur that 3000rpm is a pretty good compromise head speed for this size of copter, however you achieve it.

Skip

[Heli Yea!]

Ive been running the HDX3550/13t on my Belt for a while now and have a HS of 3300 I want to get a 12t to see for myself how it does in hopes of better flight times.(5.5 minutes currently) On the other hand I still need to get lipos for the belt since I turned all 4 into 2 packs for the 500. So the ol' belt will be sitting around in the hanger for a while.

[helihathnofury]

That's low Chad. I am at 3100 average and get about 7 to 8 mins from a 2250 to 2450mAh LiPo, with the T-Rex gearing setup.

Skip

[Heli Yea!]

I think most of the problem is big pinion and small MG I'm betting if I dropped my throttle curves I'd get much better flight times. On the 500 I'm running a 20t pinion on a 94t MG but my throttle curves max out at 75% giving me a HS of 2710 and getting 6 minutes of flight. I'm wondering if I dropped my max throttle to 90% on the belt it would give me a HS of 2970 and I'm betting it would give me a whole extra minute of flight. I'll have to test my theory when I get more lipos and I'll also pick up a 12t pinion and see which is better. It'll be a while since I'm dead broke now but work is starting to roll in but rent is coming up too.

[MarcinCP]

Hey Chad, 5 min is really low. I think switching to a 12T pinion on the Belt would make sense. You won't even notice any difference flying in your living room, and you may gain some flight time