4 blade Trex 500 target head speed??? - HeliFreak
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Old 07-16-2012, 10:25 AM   #1 (permalink)
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Default 4 blade Trex 500 target head speed???

Hi helifreak friends, im hands on in a trex 500 with the align 4 bladed head and heliartist scale blades, to be mounted ina heliartist hughes 500D with 3gx module. Im a bit confused with head speed for this machine. Ive read in some threads that i need to lower head speed with multibladed. Low head speed with the original motor-pinion combo will raise temp, so i need to pick a new motor pinion combo. Can you with your experience tell me where to start? Thank you all!!!
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Old 07-17-2012, 03:47 AM   #2 (permalink)
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I would guess somewhere around 1800rpm for a 4 blade 500, but I only have a 1300rpm 4 blade 600, so I don't know for sure.

Assuming you have something like (for 3D heli);

1600kV x (6 x 3.7V) x 0.9 (Efficiency) x 15T / 162T = 2960rpm at 100%

You might want something like;

1210kV x 22.2V x 0.9 x 14T /162T = 2090rpm at 100%, so 1800rpm would be governed at about 86%. Could even go with a 15T and govern closer to 95%.

Something like a CC Ice 75 may be useful as it has a nice big heatsink and would not get as hot inside a fuselage.

Colin
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Old 07-17-2012, 02:09 PM   #3 (permalink)
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Head speed is a matter of preference and a factor of total weight, type of blades, motor type, voltage and gear ratio.

You need to do your math:
(Motor kV) x (# cells x 3.7V) x (Efficiency) x gear ratio = RPM

My recommendation is to first find the ideal head speed with your current stock configuration by testing it at different flat throttle speeds (65% - 75% - 85% etc) to see if the heli lifts well and flies well (doesn't feel too heavy).
If you have your throttle well matched to your ESC you can determine your preferred RPM by matching the % efficiency without using and external tachometer and plugging in the numbers into the equation.

Warning: don't run the motor below 85% for too long or you'll overheat...

Once you found what head speed you like (i.e.; anywhere from 1500 to 2000 rpm), do your math to find the best combination of motor, batteries, and gears.

Best bet is to start with a motor around 1200kv 6 cells 162t gear 12t pinion and that should get you 1800 rpm with a Castle ESC.
With that you can experiment at the cost of a pinion by going little lower to 11t on the pinion or higher up to 17t.

Good luck,
Fabrizio
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Old 07-17-2012, 08:23 PM   #4 (permalink)
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I recently finished my first scale build: an Align A-109 fuselage with TRex 500E mehanics, Align 4 blade head, 3GX, Align 3g blades, and stock 2 blade tail and 500MX motor.

Using 162T main gear and 12T pinion. I ended up setting a head speed of 2000 RPM in governor mode on my Castle Ice 75. This seemed to be the best balance of efficiency, performance, tail authority, and available parts.


Hope this helps.

~Pete
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Old 07-20-2012, 07:02 PM   #5 (permalink)
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Thats exactly the same I using, the only difference is that im using hobbywing platinum 60A esc. I will try 85% flat and tach with two blades installed.... will see....
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Old 07-24-2012, 02:42 PM   #6 (permalink)
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I have the Align UH-60 with the four bladed head, and I'm running Edge 473 blades at 1850, and it flies really well. I plan to start dropping the headspeed until it no longer feels good, as 1850 seems high for 4 blades. I really want to find a 4-bladed tail and tail blades that are closer to scale. I'm worried about the micro gears in the tail holding up though. I've been thinking of changing over to belt instead of TT. Has anyone done this?
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