How many teeth on the main gear for the Trex 450? - RC Groups
Jan 14, 2005, 12:52 PM
Registered User

# How many teeth on the main gear for the Trex 450?

How many teeth on the main gear for the Trex 450?

What head speed are most of you guys running?

I'm just trying to figure out what kv motor would be best and with what pinion just doing some basic math.
 Jan 14, 2005, 01:07 PM Registered User 150T. With a Neumotor 1105/3Y (3500 kv) and a TP1320, we get a headspeed aroud 2700 with a 9T pinion. -- Gary
 Jan 14, 2005, 01:23 PM Registered User What is the desired head speed for sport flying? I ran 2400 on my Shogun.
 Jan 14, 2005, 01:29 PM Registered User Razor 2500 at 3850kv 150 tooth main and a 10 tooth pinion 15 to 1 3850kv x 11.1v = 42735rpms / 15 = 2849 head speed 150 tooth main and a 9 tooth pinion 16.6 to 1 3850kv x 11.1v = 42735rpms / 16.6 = 2574 head speed 150 tooth main and a 8 tooth pinion 18.75 to 1 3850kv x 11.1v = 42735rpms / 18.75 = 2279 head speed
 Jan 14, 2005, 01:36 PM Registered User Now I see why people are using a 12-14 tooth pinion with those low kv motors.
 Jan 14, 2005, 01:43 PM Registered User Trying to equate the Kv of a motor with the actual head speed of the heli is wishful thinking. It's a measure of the no load speed. And saying that a 3s lipo will put out 11.1 volts under a heavy load is also wishful thinking. You'll most likely see a voltage of 10 volts under load and the Kv is probably at least 10-30% less under load. The numbers you list are interesting to look at but are certainly not realistic. I'm using a Himax 2025-4200 with 8 tooth pinion and 3s Lipos in my T-Rex and the calculated head speed is 2466 RPM. The max I've measured is only 2000 RPM. And the motor runs pretty hot even with the 8 tooth pinion. It's 160 degrees after just a few minutes of indoor hovering. Here's a head speed estimator: http://www.e-helis.com/helicalc.php
Jan 14, 2005, 02:12 PM
Registered User
Quote:
 Originally Posted by GGoodrum 150T. With a Neumotor 1105/3Y (3500 kv) and a TP1320, we get a headspeed aroud 2700 with a 9T pinion. -- Gary
Is this on 3s or 4s Lipo?

Toshi
Jan 14, 2005, 02:27 PM
Registered User

# Batteries

When BATTERIES think TANIC or APOGEE they're like running 30% TP'S are like 10% the rest are like FIA fuel if you can relate to glow power i can't say that about polyqest i haven't tried then
Last edited by Dunedinflyer; Jan 14, 2005 at 02:30 PM.
 Jan 14, 2005, 03:01 PM Registered User Dunedinflyer, I agree. The main difference seems to be the capacity rating. I've never gotten close to the rated capacity at even low current drains on the TP and Kokam packs I've used. But the Tanics and Apogees, they deliver like the US postal service, rain, sleet or snow;-) TMorita, If a 3s TP1320 can deliver enough juice to a T-Rex to get the head spinning 2700 RPM I'd be really surprised.
 Jan 14, 2005, 03:09 PM Registered User even at o pitch mayme at 10degrees negative full power from 500 ft
Jan 14, 2005, 03:29 PM
Registered User
Quote:
 Originally Posted by Dunedinflyer even at o pitch mayme at 10degrees negative full power from 500 ft
Ha! Maybe through a wormhole!
Jan 14, 2005, 05:13 PM
Registered User
Quote:
 Originally Posted by thunder1 Trying to equate the Kv of a motor with the actual head speed of the heli is wishful thinking. It's a measure of the no load speed. And saying that a 3s lipo will put out 11.1 volts under a heavy load is also wishful thinking. You'll most likely see a voltage of 10 volts under load and the Kv is probably at least 10-30% less under load. The numbers you list are interesting to look at but are certainly not realistic. I'm using a Himax 2025-4200 with 8 tooth pinion and 3s Lipos in my T-Rex and the calculated head speed is 2466 RPM. The max I've measured is only 2000 RPM. And the motor runs pretty hot even with the 8 tooth pinion. It's 160 degrees after just a few minutes of indoor hovering. Here's a head speed estimator: http://www.e-helis.com/helicalc.php

Say what ya want but that equation was dead on perfect with my Shogun... granted I use Apogee packs that can keep up and deliver whatever the motor asks too. Sure the crappy Kokam packs may not keep up but the Apogee's have no problems.

Also note that thos number are true for running with zero pitch or no load on the blades. I ran my Shogun with a Himaxx 2025-3200 and a 10t pinion. At 100% throttle it would turn 2800 on the head speed. I ran it in high governor mode with the throttle backed down so that it maintained a constant 2400 on the head speed. It was the sweetest running spot I found for the Shogun and I tested many, many setups. This is why I'm having a hard time deciding on another Shogun or the Trex 450.
Jan 14, 2005, 05:19 PM
Registered User
Quote:
 Originally Posted by Dunedinflyer When BATTERIES think TANIC or APOGEE they're like running 30% TP'S are like 10% the rest are like FIA fuel if you can relate to glow power i can't say that about polyqest i haven't tried then

Amen to that... if you ask me Apogee is by far the best pack on the market.

As for the TP 1320's... do this. Discharge the pack at a 1amp discharge and tell me how many mah's it takes out. Thunder Power packs are still 8C packs... but they are able to claim 10C because the 1320's are actually 1550-1600 packs. 1600 at 8C is about 13amps.... or 1320 at 10C. It's just a numbers game.
Jan 14, 2005, 06:18 PM
Registered User
Quote:
 Originally Posted by GGoodrum 150T. With a Neumotor 1105/3Y (3500 kv) and a TP1320, we get a headspeed aroud 2700 with a 9T pinion. -- Gary