4.4. Motors and related items

4.4.1. Motor

For more details see Section 28.4, “Motor selection guide” and Section 28.5, “Motor selection table” in the Chapter 28, Technical Appendix

Each motor list in this section is sorted from mildest to most powerful. The mildest motors are usually better for duration, and the powerful motors are better for aerobatics.

If you are a beginner, it is generally recommended to select a motor near the middle of the list. If you pick a mild duration motor which is near the front of the list, you may not have enough power to recover from a severe hovering mistake. If you pick a powerful motor which is near the end of the list, then the helicopter will cause more damage to itself when you lose orientation and crash. 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.

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


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.

4.4.2. Pinion

For more details see Section 28.6, “Pinion selection guide” in Chapter 29, Glossary

Most helicopter manufacturers supply a range of pinions for their helicopters. You may require pinions with more teeth for some reason. The most common reason is for running outrunner motors which usually have a fairly low Kv and therefore require a pinion with a higher tooth count.

Some helicopters use metric pinions, and some use English pinions.

The smaller brass press-on pinions (1 and 1.5mm) can be very difficult to remove from motors. I do not recommend the GWS pinion puller for these - I have personally destroyed two GWS pinion pullers trying to remove this type of pinion. The Maxx products pinion puller (ACC650) is much sturdier than the GWS pinion puller. Also, many brass pinions can be pulled off motor shafts by using heat since brass has a high coefficient of thermal expansion.

The best way to remove these brass pinions is to clamp the motor in a vise, then press a hot blunt tip soldering iron on the end of the pinion (for maximum heat transfer), wait about four seconds to allow the pinion to become hot and expand, then pry off the pinion using needle nose pliers. Do not skip the soldering iron step, because otherwise you will pull the shaft out of the motor.

The best way to install a brass pinion on a motor is to use a vise. Put the motor and pinion between the jaws, and screw the vise shut to push the pinion onto the shaft. Be sure the back end of the shaft is pressed against the jaw otherwise you may damage the motor bearings.

When selecting pinions, be sure to check your helicopter manufacturer's pinions first. The pinions from the helicopter manufacturer usually work best for most models.

If you apply a threadlocker to a pinion setscrew, then it will be nearly impossible to remove later. The best way to prevent a pinion from turning on the motor shaft is to create a flat on the motor shaft.

4.4.3. Motor connectors

The standard connector for nonmicro helis is the 3.5mm bullet-style connector. These work well for up to 70 amps and are supplied with Schulze controllers.

For the main motor of FP micro helicopters and for tail rotors of micro helicopters, the most commonly used connector is the crimp pin from a D-sub connector. These are good up to about 4 amps and are available from Jameco Electronics; the female pins are part #43369 and the males are part #43377

For the main motor of CP micro helicopters there really is no standard. I personally use the MP Jet 1.8mm gold connectors, which are available from Aircraft World.

4.4.4. Main motor ESC

(See Chapter 29, Glossary for a definition of ESC)

If you plan to use a brushed motor, you will need a brushed motor ESC. If you plan to use a sensored brushless motor (like the X-250-4H) then you can use either a sensorless or sensored brushless motor controller. For the sensorless brushless motor controller, the sensor wires (connector) from the motor will not be connected to anything because the sensors are not required by the controller.

The sensored brushless motors may need to be sent back to the motor factory to reverse the motor direction if your rotor head is spinning in the wrong direction. Therefore, I recommend avoiding sensored brushless motors unless you already know the timing is for the desired direction of rotation.

If you plan to use a sensorless brushless motor, you will need a sensorless brushless motor controller. This motor type is not usable with a sensored brushless motor controller (such as the older Schulze Booster-40b).

An ESC used for main motor control must have the following characteristics are required (or must be programmable):

  • No brake. If the ESC has a brake, then the motor may strip the main gear when the throttle is reduced.

  • No reverse. A helicopter rotor should never spin in reverse.

  • Slow start-up. If the ESC does not have a slow startup, the heli may spin when throttle is applied, tip over, or strip the main gear.

  • No low voltage cutoff or programmable very low voltage cutoff. (As low as possible, must be less than 0.7 volts/cell for Nicad/NiMH or less than 2.5 volts cell for LiPo.

Most airplane ESCs are not suitable for helicopters because they have low throttle resolution, include a brake and have a fairly high low-voltage cutoff.

For the micro helis, the following are poular as main motor ESCs:

  • Pixie-7P (brushed ESC, 7 amp)

  • Schulze Future 11.20e (brushless, rather heavy)

  • Castle Creations Phoenix 10 (brushless, very light)

  • Piccoboard/Piccoboard Plus/Piccoboard Pro

  • GWS ICS-100E (brushed main motor ESC, 5 amp)

  • Cool Running H-12 (brushless, 12 amp)

  • Cool Running H-25 (brushless, 25 amp)

For the Corona, the following work:

  • Castle Creations Pegasus 35 (brushed)

  • Castle Creations Phoenix 35 (brushless)

  • Hacker Master 40-3P (brushless, do not use the BEC on this ESC because the ESC will overheat on 3 servos?)

For the ECO 8/16, the following work:

  • Schulze Future 12.46k

  • Schulze Future 18.46k

  • Hacker Master 40-3P Heli

  • Kontronik Jazz 55-6-18

For the Logo 10, the following work:

  • Schulze Future 18.46K

  • Kontronik Jazz 55-6-18

Do not use the SMILE 40-6-18 in the Logo 10 - it tends to burn out!!!

The Hacker Masters seem to burn out in the Logo 10 as well due to ESD problems.

The JETI Micoprocessor (red label series) is not suitable for helis because the throttle control is not smooth and is rather "steppy". The Advance (blue label series) is supposedly better, but nobody I know has tried this.

Some ESCs have an optocoupler (usually called OPTO) instead of a BEC. The optocoupler electrically isolates the ESC from the control signal which reduces the possibility of interference from the external BEC.

The Kontronik ESCs have a good soft start and governor mode for use on helicopters. However, they do not have thermal overload protection.

The Schulze ESCs also have a good soft start and governor mode, and they do have thermal overload protection.

The Castle Creations Phoenix works fine in the Piccolos and the Corona but does not work well in the ECO 8/Logo 10 and larger helis. The current version of the firmware has a problem in three areas:

  • The soft start doesn't work properly. It may kick your heli around 180 degrees and/or tip your heli over.

  • The governor mode doesn't work properly with a heading hold gyro. The RPMs will go up and down even when hovering, which makes the tail wag back and forth.

  • The controller seems to have less glitch filtering than other ESCs. When the Phoenix is used in a heli, it requires a receiver which has a fail-safe mode or glitch filtering, such as a PCM receiver or a Berg DSP receiver.

Therefore, the Phoenix is not suitable for larger helicopters until these firmware bugs are fixed.

If you are mounting the Phoenix ESC with double-stick tape, be sure to put the tape on the BEC side and not the FET side. The FET side generates the most heat, so it needs to be exposed to free air.

Phoenix 35 ESC showing the BEC side

The FET side is the side with the regular pattern of identical chips. The BEC side has a random collection of chips. Do NOT use a switch between the battery and ESC. Most switches will not handle the current and will become very hot. Also, if the battery is plugged into the helicopter, you should consider it live for basic safety reasons anyway.

4.4.5. Tail motor ESC

(See Chapter 29, Glossary for a definition of ESC)

You will only need a tail motor ESC if the heli has a tail motor, obviously.

For the tail motor ESC, two characteristics are important:

  • High throttle resolution (256 steps or more)

    Many airplane ESCs have very low throttle resolution (typically 32 steps) because airplane radios typically have a ratchet on the throttle stick which limits the throttle resolution anyway.

    If a heading hold gyro is used with an ESC with low throttle resolution, the tail will "wag" as the gyro tries to find the correct throttle position to hold the tail still.

    If a yaw rate gyro is used with an ESC with low throttle resolution then the tail will creep left or right because you will be unable to set the tail throttle to the perfect value with the revo mix.

    The GWS ICS-50E and probably other GWS ESCs are known to have only 16 steps of throttle resolution

  • High switching rate (>50 khz) (for brushed motors)

    Many micro helis use metal brushed tail motors. Theses are easily recognizable because there are two types:

    • The popular "N20" style motors all use metal brushes.

    • The IPS-style motors with grey endbells use metal brushes.

    These metal brushes are very fragile and are easily destroyed by the high current surges generated by low switching rate ESCs. Therefore it is desirable to use a high switching frequency ESC to extend the operating life of the expensive tail motors.

    The IPS-style motors with black endbells use carbon brushes which are less fragile, but they will still last longer with a high switching frequency ESC. IPS motors (both grey and black endbell) are rated for about 2 amps max current.

    The GWS ESCs are described as "high frequency" but they're only 2.8 khz. It's high frequency compared to the 50 hz control signal but it is not high frequency compared to the the TREC and other high frequency ESCs.

    Some people are using the Feigao 1208436L brushless motor + Phoenix 10 ESC for tail control, but this combination has wagging problems and does not work as well as a standard brushed motor + high frequency ESC. See also Section 28.1.7, “How gyros work” for more info on tail motor ESCs and mixing options.

    The following ESCs are usable as tail motor ESCs

    • JMP HF100 (brushed 100khz switching, 256 steps, 1.5 amp)

    • Schulze Slim-105He (brushed, 100 khz switching, 256 steps, 5 amp)

    • Dionysus Design TREC ESC (brushed, 78 khz switching, 256 steps, 5 amps, low voltage LED)

    • Castle Creations Phoenix 10 (brushless, 10 amp, ? steps)