5.6. Motor

There are many, many motors available, but only a few are suitable for each helicopter. This is because the rpm/V or the Kv of the motor is very important due to the fixed gearing ratio of the drive system.

There are seven main criteria to consider when choosing a motor:

5.6.1. Motor size

Some motors are too large to fit in the some helicopters. For example, the C50-13L is too large to fit in the ECO 8.

5.6.2. Motor weight

A quick guide to suitable inrunner motors is to allocate 10-15% of the helicopter's AUW to the motor So, the inrunner motors suitable for an ECO 8 (AUW ~1600 grams) will be between 160-240 grams in weight.

Outrunner motors can be lighter because they are more efficient at dissipating heat. For outrunner motors, it is only necessary to allocate about 7-10% of the helicopter's AUW for the motor.

5.6.3. Motor efficiency

Motor efficiency is important because the power not used to fly the helicopter is wasted as heat. For example, you might compare two motors, one with 80% and 90% efficiency. The difference appears to be only 10%.

In terms of heat generation, the 80% efficient motor will generate almost twice as much heat as the 90% efficient motor. If a helicopter requires 150 watts to hover, then the 90% efficient motor will use 166.7 watts of power and waste 16.7 watts as heat.

The 80% efficient motor will use 187.5 watts of power, and waste 27.5 watts as heat. This generates 65% more heat than the 90% efficient motor. So, motor efficiency is very important because efficient motors run much cooler.

5.6.4. Motor rated RPM

Some motors are rated for a very low maximum RPM, such as:

  • JETI motors have a maximum rating of 15k-20k RPM

  • Older Kontronik Tangos have a maximum rating of 25k RPM

If you use the motor past its rated RPM, then motor failure will probably occur (most likely the magnets will loosen from the rotor).

5.6.5. Motor Quality

The quality of motors is rather subjective, but here is a list of motors and their general quality:

Table 5.1. Motor quality

QualityManufacturer
BestPlettenberg, Lehner, Actro, Neumotor
BetterHacker, Kontronik, Mega
GoodMultiplex Permax, Astroflight
FairHimaxx, Feigao, JETI, Model Motors AXI

The motors in the best category are relatively efficient over a wide load range.

The Kontroniks are slightly better than Hacker for helicopters due to better part load efficiency.

5.6.6. Shaft diameter and available pinion sizes

Theoretically, an Orbit 15-16 (1067 rpm/V) will fly an ECO 8. However, you would need about a 28-30 tooth 5mm pinion, and the largest available 5mm pinion is 24 tooth. So, the available pinion sizes will limit your motor choices.

5.6.7. Cooling options

For inrunner motors, a heatsink or fan is recommended when flying in ambient temperatures over about 70F/21C or when flying for long duration with lithium-ion or lithium-polymer batteries.

The Hacker B20, B40, and B50 heatsinks are probably the most commonly used for helicopters.

GWS style heatsink

Table 5.2. Heatsinks

MotorHeatsink
20mm diameter motors (Hacker B20, HiMaxx 2015/2025 etc)

Hacker B20 heatsink

Sparrow Products 20mm heatsink

23mm diameter motors:GWS EHS-100 (green color)
24mm diameter motors (Speed 300 motors)GWS EHS-300 (red color)
28mm diameter motors (Mega 16/x/x, Hacker B40, etc)

Hacker B40 heatsink

Hacker B40 heatsink

Kontronik KK480 heatsink

GWS Speed 400c heatsink (GW/EHS-400) (blue color)

Sparrow Products 28mm heatsink

36mm diameter motors (Hacker B50, Kontronik 500/600, etc)

Hacker B50 heatsink

Kontronik KK600 heatsink

The Mega 22/20/3H has the shaft extending out the backside for mounting a small fan using a 5mm prop adapter instead of a heatsink. A fan can be made by modifying a Maxx Products MPIACC328. Cut off the top part of the prop adapter so the prop adapter looks like a cylinder with a disc attached. Next, disassemble a small computer fan to extract the fan portion, and epoxy the fan to the top of the prop adapter.

Be careful of motor amp ratings. These are usually specified for airplanes in a tractor prop configuration where the propeller blows air directly onto the motor. In a helicopter, there is no forced air cooling, so the same motor will only handle about half the max amp rating or less.

Most brushless motors use neodymium magnets. These magnets will lose their magnetization when operated at temperatures over 70C/158F to 120C/248F depending on magnet type. Therefore, it is important to keep the motor temperature below about 150F (by using a heatsink) to avoid demagnetizing the motor magnets.

Some brushless motors use samarium cobalt magnets (Astroflight, etc). These magnets will lose their magnetization above 250C/482F, so overheating is less of a concern with these magnets. The Hacker C40/C50 series is the same as the B40/B50 series except the C40/C50 series has a built-in heatsink so no additional heatsink is necesary. The Hacker B40/B50 series require an additional heatsink available for $15.

The easiest way to install a Hacker B40/B50 heatsink onto a motor is to use a drill bit that is slightly larger than the gap in the heatsink, and press the base (not the spiral side) of the drill bit into the gap to force it open, then slip the motor inside. This technique works extremely well. To install a B40 heatsink onto a Mega 16/15/3, you should use a 4mm drill bit.

The Hacker B20-xxS/L, Feigao 138084xxS/L, Himaxx HA20xx, and Model Motors MiniAC 1215/xx motors have a "bearing bump" which makes installation in helicopters rather difficult. Maxx Products sells the a motor adapter (ACC3900) which eliminates this problem.

Motors are listed from mild to powerful. Please note that I have no experience with most of these motors therefore the ordering should only be considered a rough guide, and not absolute oracle. In general the lower Kv motors with a larger pinion are milder and better for duration flying, and the higher Kv motors with smaller pinions are better for sport/aerobatic flying.

For more info on motors and pinion sizes, I recommend searching the RC Groups electric helicopter and micro helicopter forums for people's opinions on various motor and pinion combinations.

5.6.8. For the Corona

Ideal Kv: 2700-3000 rpm/V - Main gear: 102T, 32 pitch

  • Graupner Speed 500 Race #6307 (brushed) mild

  • Kyosho Atomic Force (brushed) mild

  • Astroflight 020 helicopter motor (4 turn) (brushless) ???

  • Mega Motor ACn16/15/4 (brushless) mild

  • Mega Motor ACn16/15/3 (brushless) mild

  • Hacker C40-12S (brushless) powerful

  • Mega Motor ACn22/20/3HTDS (brushless, 8 cells/15T)

    Note: The Mega Motor and Astroflight motors are very good for duration flights in the Corona. 10+ minute flights are possible with some moderate wind.

5.6.9. For the FP Piccolo

Ideal Kv: 1800-2000 rpm/V - Main gear: 100T, 0.5 module

  • Astro Flight Astro 010 (brushless) mild

  • Team Orion Modified Elite (brushed) powerful

  • Hacker B20-36S (brushless) (8T pinion) powerful

  • Model Motors ACn1215/20 (brushless) powerful

Note: The Astro 010 is very good for long flights.

5.6.10. For the CP Piccolo main motor

Ideal Kv: 2700-3000 rpm/V - Main gear: 100T, 0.5 module

  • Hacker B20-36S (brushless) (10T pinion) mild

  • Astro Flight Astro 010/14T (brushless) mild

  • Team Orion Modified Elite (brushed) powerful

  • Astro Flight Astro 010/10T (brushless) powerful?

  • Hacker B20-31S (brushless) (8T pinion) powerful

  • Model Motors ACn1215/20 (brushless) powerful

  • Hacker B20-20L (brushless)

  • Hacker B20-18L (brushless) (8T pinion) powerful

Note: The B20-36S is good for duration flights.

The B20-18L is good for aerobatics.

5.6.11. For the Hummingbird FP/CP, GWS Dragonfly main motor

Century Hummingbird: 140T, 0.5 module

GWS Dragonfly: 120T, 0.5 module

Others: 0.5 module

  • HiMaxx 2015-4100

  • Model Motors ACn1215/16 (brushless)

5.6.12. For Piccolo, Dragonfly, Hummingbird tail motor

Main gear: 0.5 module

  • GWS EDF50-2 motor (brushed, can draw >2 amps)

  • Feigao 1208436L (brushless)(direct drive or geared use)

    Feigao 1208430S (brushless)(geared use only!)

5.6.13. For the Hornet CP

Main gear: 135T, 0.4 module

  • HiMaxx HA3026-3600 (brushless)

  • Hacker B20-26S (brushless)

  • Model Motors ACn1215/16 (brushless)

  • Razor Micro Heli V2 (brushless)

5.6.14. For the Maxir SE

Main gear: ?T, 0.4 module

5.6.15. For the Zoom 400

Main gear: 132T, 0.5 module

  • Himaxx HA2025-4200 (brushless)

  • Hacker B20-15L (brushless, 9-10T, 3S LiPo)

  • MiniAC 1215/20 (10T, 3S LiPo)

  • Eflight Park 400 4200 (8T, 3S LiPo)

  • Motor Max Motors 400DH (9T, 3S LiPo)

  • NeuMotors 1105/3Y (10T, 3S LiPo)

  • Do not use the Chili Pepper 3600 - it burns out

5.6.16. For the Align T-Rex 450X/450XL

Main gear: 150T, 0.5 module

  • Himax 2025-4200 (8T, 3S LiPo

  • Astro 020 4T (11-12T, 3S Lipo)

  • Mega 16/15/3 (13T, 3S Lipo)

  • Neumotor 1105/3Y (9T, ?S LiPo)

  • Lehner 1020/17 (11T, 3S LiPo)

  • Medusa Products MR-028-040-3400 (11T, 3S LiPo)

(Best low-cost choice is currently the Mega 16/15/3)

5.6.17. For the ARK X-400

Main gear: 138T, 0.5 module

  • Mega 16/15/3 (?)

5.6.18. For the Voyager E

Pinion: ?

  • Hacker C40-10T (brushless)

  • Hacker C40-8L (brushless)

5.6.19. For the Robbe Eolo

Ideal Kv:

3.17mm shaft motors: 3000-3300 rpm/V

5.00mm shaft motors: 2700-3000 rpm/V

Pinion: 0.7 module

The available pinions are 14-18T for 3.17mm, shafts, and 19-22T for 5mm shafts.

  • Hacker C40-9L (brushless) (8 cells/18T)

  • Hacker C40-8L (brushless)

  • Mega 22/20/2 (brushless)

  • Kontronik Twist 3700 (brushless)

  • Aveox 27/39/1.5 (brushless)

  • Lehner 1930/6 (brushless)

5.6.20. For the ECO 8

Aerobatic flight - ideal Kv:

3.17 mm shaft motors: 2300-2600 rpm/V

5.00 mm shaft motors: 1800-2000 rpm/V

Duration flight - ideal Kv:

3.17 mm shaft motors: 2100-2300 rpm/V

5.00 mm shaft motors: 1500-1800 rpm/V

Main gear: 180T 0.5 module

The ECO 8 has a 180T main gear, and the available pinions are 10T-17T for 3.17mm shafts, and 13-24T for 5mm shafts

  • Magnetic Mayhem (brushed) mild

  • Mega 16/25/3 (brushless, 10 cells/13T) mild

  • Hacker C40-13L (brushless) mild, good for duration

  • Aveox 27/30/1.5 (brushless) ???

  • Mega 22/20/4 (brushless, 10 cells/19T) mild

  • Aveox 36/15/1.5 (brushless) ???

  • Ikarus X-250-4H (brushless) mild, discontinued

  • Hacker C40-14S (brushless, 8 cells/9-10T) mild

  • Hacker C40-12L (brushless, 8 cells/12-13T, 10 cells/10-11T)

  • Aveox 27/39/1.5 (brushless, 10 cells)

  • Aveox 36/15/1.5 (brushless, 10 cells)

  • Ikarus H8 (brushless, 8 cells 22-24T, 10 cells 21-24T, 12 cells 20-24T) ???

  • Hacker B50-22S (brushless, 10 cells/16T, 12 cells/13T)

  • Hacker C50-22S (brushless, 10 cells/16T, 12 cells/13T)

  • Hacker B50-18S (brushless, 8 cells/14-19T, 10 cells/13-15T) powerful

  • Hacker B50-15L (brushless) powerful

  • Hacker C40-10L (brushless) powerful

  • Mega Motor ACn22/20/3H (brushless) powerful

  • Kontronik 500-19 (brushless) (8-10 cells, 13-15T) powerful

  • Hacker B50-13L (brushless) very powerful

  • Plettenberg Orbit 15-14 (brushless, 10 cells/24T) powerful

  • Lehner Basic 2400 XL (brushless) ???

  • Lehner Basic 2800 XL (brushless) ???

  • Hacker B50-11L (brushless) insanely powerful(requires very good matched batteries)

5.6.20.1. Best inexpensive motor for ECO 8

Mega Motor ACn22/20/3H

5.6.20.2. Best overall motors for ECO 8

Hacker B50-15L

Plettenberg Orbit 15-14 (10 cells/23-24T)

Note: The C50 motors will NOT fit in an ECO frame.

The smaller motors (C40, etc) may overheat in warm weather (70+F) so be careful.

5.6.21. For the ECO 16

The ECO 16 has the same main gear and pinions as the ECO 8.

  • Mega 22/30/4 (brushless, 16 cells, 17-20T)

  • Ikarus H16 (brushless, 16 cells, 20-24T)

  • Plettenberg Orbit 20-16 (brushless, 16 cells, 22T)

  • Mega 22/30/3 (brushless, 16 cells, 13-15T)

5.6.22. For the Viper 70

The ECO 16 has the same main gear and pinions as the ECO 8.

  • Mega RCn 400/15/5 (brushless, 3s lipo, 17T)

  • Mega ACn 16/15/4 (brushless, 3s lipo, 10-12T

5.6.23. For the Logo 10

5.00 mm shaft motors: 1800-2000 rpm/V

Pinion: old models: 0.5 module, newer models: 0.7 module

The main gear is 200T, and the available pinions are 14-23T for 5mm shafts.

Pinion:0.5 module

  • Aveox 36/24/2 (brushless) ???

  • Kontronik Fun 600-15 (brushless) powerful

  • Hacker C50-15L (5s3p, 13T)(brushless) powerful

  • Mega ACn 22/30/3 (brushless) (5s3p, 13T)

  • Astro 040 (brushless) ???

  • Kontronik Fun 600-15 (brushless) (12 cells, 14-16T)

  • Aveox 36/24/2 (brushless)

  • Hacker C50-14L (brushless) (5s3p, 13T)

  • Hacker C50-13L (brushless) (12 cells, 14T, 14 cells, 13T)

  • Kontronik Fun 600-17 (brushless) (12 cells, 15-19T)

  • Kontronik Fun 600-18 (brushless) (12 cells, 14-18T)

  • Plettenberg Orbit 15-16 (brushless, 1070 rpm/V) ???

  • Plettenberg Orbit 15-14 (brushless, 12 cells, 17T) ???

  • Mega ACn 22/30/2 TDS (brushless) (6s3p, 10T)

  • Hacker B/C50-11L (brushless) super powerful (requires very good matched batteries)

Recommended:

  • Plettenberg Orbit 15-14 (12 cells/17-21T)

  • Plettenberg Orbit 15-16 (14 cells/17-21T)

  • Hacker C50-13L (12 cells/13-17T)

5.6.24. For the Logo 14

5.00 mm shaft motors: ?

There are two main gears included with the Logo 14: 200T/0.5 module and 140T/0.7 module.

  • Hacker C50-13XL (5s4p, 11-13T)

  • Hacker C50-14XL (6s3p, 10-12T)

  • Hacker C50-15XL (7s3p, 10-11T)

  • Hacker C50-16XL (8s3p, 10T)

  • Hacker C50-17XL (8s3p, 10-11T)

  • Hacker C50-18XL (8s3p, 10-11T)

  • Hacker C50-19XL (8s2p, 10-11T)

  • Hacker C50-12XL (6s3P, 13T)

  • Hacker C50-11XL (5s4p, 13-14T)

  • Hacker C50-10XL (5s4p, 13T)

  • Plettenberg HP 300/30/A2 Heli (5s4p/15T)

5.6.25. For the Logo 20

5.00 mm shaft motors: ?

138T main gear for the older model, 98T main gear for the newer model

5.6.26. For the Quick EP 10

The main gear is 120T, and the available pinions are 10-14T for 5mm shafts.

  • Aveox 36/20/2 (brushless, 12 cells, 11-12T)

5.6.27. For the Quick Sweet 16 EP

The main gear is 120T, and the available pinions are 10-14T for 5mm shafts.

  • Aveox 36/38/3 (brushless, 20 cells, 12-13T)

5.6.28. Summary

If you choose a brushless motor, then an autorotation gear is highly recommended. Most brushless motors have extremely high torque so when the motor spools down, the "braking" effect will be very strong. This will very likely break the main gear teeth if you do not have an autorotation gear. The only exception to this is the Corona; the main gear on it is very tough and can handle a brushless motor without an autorotation gear.

The older sensored Aveox motors (12xx and 14xx series) are only rated to 20,000 rpm, and the JETI motors are only rated to 15,000 rpm. You must be careful not to exceed these rotational speeds otherwise the rotor may eject a magnet (i.e. "throw a magnet"). Therefore, I do not recommend these motors for helicopter use. The better motors such as the newer Aveox, MEGAs, Hackers are typically rated for 50k-70k rpm, which makes them a better choice for helicopter applications.

The Model Motors 2814/10 is not recommended for an ECO 8. The motor seems to have problems with the rotor wobbling and touching the stator windings which burns out both the motor and the ESC. There are also some reports that the magnets are not epoxied very well to the rotor and may shift position. Also, these motors are not very efficient, and run very, very hot when used in a helicopter.

Most of the HiMaxx motors are not very efficient and therefore are not very good for larger helicopters because they generate large amounts of heat. There was one report of an HB 3615-2100 used in an ECO 8, and it became "too hot to touch". The HiMaxx seems to work okay in microhelis such as the Hornet CP and Zoom. The choice of a motor with a proper Kv for a collective pitch helicopter is very important, because most motor ESCs are not efficient when running at much less than 90% throttle. If you run an ESC continuously at low throttle, the ESC will probably overheat. Therefore, you should select a motor + pinion combination that will allow the motor ESC to run at 90-95% throttle for best efficiency.

The Kv choice for a fixed pitch helicopter is less strict because the motor will be operating at partial throttle most of the time. However, the Kv should be high enough to allow hovering at between 50% - 60% throttle which will give enough reserve to allow hovering at about half throttle and should have enough reserve to allow recovering from mistakes.

Pole counts for motors are unfortunately difficult to find, and are necessary to program some ESCs correctly. Here are the pole counts that I have managed to find:

  • 2 pole: Hacker, Kontronik, Lehner, some Plettenberg

  • 4 pole: Aveox, Neumotor, some Plettenberg

  • 6 pole: Mega 16 and 22 series, some Plettenberg

Also see Tohru Shimizu's helicopter brushless motor page at: www.dokidoki.ne.jp/home2/tohrus/motorindexE.html

[Note]Note

Check the length of your motor mounting screws before mounting!

If they go too deep into the motor they will short out a winding which will damage the motor. Even worse, if you try to run a motor with a shorted winding, it will burn out the ESC. So test the screw length by screwing it into the motor with your fingers before mounting in the frame.