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Old 05-28-2014, 09:01 AM   #1 (permalink)
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Question First Scale Build - Motor/Pinion and Headspeed?

Hello

I'm building a 500-sized HeliArtist MD500D (Police) from a T-Rex 500 and it's my first scale build. I've been reading this forum and have learned that lowering the headspeed isn't as simple as merely adjusting the throttle curve or pinion size as it can strain the ESC and generate lots of heat.

I have the Align 4-blade rigid head with the recommended carbon fiber 425 Align blades and a Spectrum AR7200BX.

If I plan on keeping my current CC Phoenix ICE 75A ESC, what size motor/pinion combo and headspeed would you suggest? (I currently have a Turnigy SK3 1600kv motor)

Thanks for all the great advice!
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Old 05-28-2014, 02:52 PM   #2 (permalink)
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I run 1400 on my 600 sized Quad blade heads...So for a 500 size it may actually be higher...at any rate here is the formula you need to calculate head speed once you determine what that is. If the calculated head speed is not what you need then changing pinions or motors is probably on the only to get close to what you want. You can then use throttle curves to get exactly what you want.

Battery Voltage * Motor KV * Pinion Teeth * .9 / Main Gear teeth = Max head speed at 90% efficiency.

25.5 * 1600 * 9 * .9 / 121 = 2731 RPM @ 100% throttle at the beginning of the flight..

Here's an easier way:

http://heli.dacsa.net/calcv3/Default.aspx
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Old 05-28-2014, 11:21 PM   #3 (permalink)
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12T is the smallest available pinion for 500 class motors.

For the 500 size scale model:
1210kv Motor w/12T pinion
Head speed around 1600-1700 rpm for a 4 blade rotor head.

Using a 6S-3300mah 25C LiPo, I get about 7-8 minutes of flight time, on the 4 blade rotor head,
and 5 minutes of flight time on the 5 blade rotor head.



FYI - Multi Blade configuration for Hughes/MD 500's:
500C = 4 blade main rotor/2 blade tail rotor/ "V" tail/ round nose
500D = 5 blade main rotor/ 2 blade tail rotor/"T" tail/ round nose
500E = 5 blade main rotor / 2 blade tail rotor/"T" tail/ pointed nose
A/MH-6J = 5 blade main rotor/ 2 blade tail rotor/"T" tail/ round nose
A/MH-6M = 6 blade main rotor/ 4 blade tail rotor/"T" tail/ round nose
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Old 05-29-2014, 05:07 AM   #4 (permalink)
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I fly me UH-1N 500 using a Savox 1300kV, 12T and Ice 75 at 1700rpm (2x 465mm main blades), and it flies well but the ESC runs hot. I think I am governed to about 87% which is a bit lower than ideal.

I would suggest that the Ice 75 would be fine with a 1200kV motor (Savox or Hyperion), 12T pinion, and between 1600 & 1700rpm of 4 blade or 5 blade.

I get 2x 5 minute flights off a single 5000mAh 6s.

Colin
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Old 05-29-2014, 03:43 PM   #5 (permalink)
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Thanks a million to all of you.

I really appreciate your input. I'll start looking for the 1200kv motor as I have the 12T pinions.

Really beautiful birds you have there as well!

Thanks again, Helifreak and you guys really make this hobby/sport infinitely more enjoyable and a lot less expensive than if I had to go it alone!

Cheers from Boston!
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