6.3. Batteries and related items

6.3.1. Batteries

Helicopters need batteries that can deliver high current. If you use cheap batteries, your helicopter will probably not fly well. The Sanyo CP2400 and RC2400s are the best choices for beginners on nonmicro helis because they are reasonably priced and can discharge at high rates. NiMH batteries are usually higher capacity but deliver less current than Nicad batteries, so they are better suited for duration flying.

One exception is the Sanyo HR-SC which is a NiMH battery specially built for high current drain which performs slightly better than the CP2400/RC2400 (HR-SCs must be used immediately after charging for best results).

NiMH batteries require about 5 charge/discharge cycles to reach full capacity. They work best immediately after charging - if you allow them to sit and cool off they will not work as well. Both Nicad and NiMH battery packs should be slow-charged on the first charge to ensure all cells in the pack will reach a full charge.

If this is not done, the cells in the pack may be at different states of a charge and the pack may never fully charge properly. If you notice a big drop in capacity in your battery packs after a few months of use, this is probably due to the cells in the pack having different states of charge. If this happens, you should try to "rebalance" the cells in the pack by slow charging them at a constant current of C/20 for 24 hours. This will usually restore the pack to full capacity. This should only be done for Nicad and NiMH packs, and not for other battery types such as Li-ion or LiPoly. Your batteries will last much longer if you do not allow them to become too hot, because the primary cause of battery failure is the deterioration of the separator which is accelerated by higher temperatures. Therefore, you should allow your battery packs to cool a little after use before charging them again.

The batteries known to work well are:

Corona / Logo 10/16/20 / ECO 8/16:

  • Sanyo CP1700SCR (NiCad 1700 maH, 5.5 milliohms)

  • Sanyo CP2400 (NiCad 2400 maH, 4.5 milliohms)

  • Sanyo RC2400 (NiCad 2400 maH, 3.2 milliohms)

  • Panasonic HHR300SCU (NiMH 3000 maH)

  • Panasonic RC-3300HV (NiMH 3300 maH, 5.0 milliohms)

  • Sanyo HR-SC (NiMH 2600 maH, 4.0 milliohms)

  • Gold Peak 3300 (NiMH 3300 maH)

  • Gold Peak 3700 (NiMH 3700 maH)

  • Thunder Power lithium-polymer batteries

  • FlightPower lithium-polymer batteries

  • Common Sense RC lithium-polymer batteries

Micro helis (Piccolo and clones, Hornet, etc but not T-rex or Zoom):

  • Sanyo HR-AAAU (NiMH 720 maH, 35 milliohms)

  • PowerEx AAA NiMH


  • Thunder Power lithium-polymer batteries

  • FlightPower lithium-polymer batteries

  • Common Sense RC lithium-polymer batteries

(milliohms is a measure of internal resistance; LOWER IS BETTER)

If you are buying batteries not on this list, then you should ask the manufacturer for the internal resistance of the cells. If the batteries do not have an internal resistance as low as the cells on this list, then it is probably not suitable for helicopter use.

If you intend to fly aerobatics, do NOT use commercial battery packs. Most of these packs use a flat springy metal to connect the battery terminals and the springy metal will melt at high (50-60+) currents. Be sure to use your own inline-soldered battery packs if you intend to do hard aerobatics with your helicopter.

Lithium-polymer batteries are NOT recommended for helicopter beginners. They are fragile and incur damage easily, and when they are damaged they can IGNITE up to ten minutes later.

There was a story posted on RC Groups about a guy who crashed his plane powered by Li-Pos, and he put it in his SUV. Several minutes later someone told him his SUV was on fire. He posted pictures of the totaled SUV, and the interior was completely burned.

NOTE: The 17mm-long N20 motor used on some micro helicopter tails (some Piccolo models, all Hummingbirds, etc) will burn out quickly (5-20 mins) if the motor is run on 8 cells. Be sure to use only 7 cell battery packs to extend the tail motor life.

6.3.2. Battery connectors

Heavy-duty battery connectors are recommended to minimize power loss.

The following connectors work well for the Corona/ECO/Logo:

  • 4mm gold-plated Corally "bullet" connectors

  • Astroflight "Zero-Loss" 50 amp connectors

  • W.S. Deans Ultra connectors

  • W.S. Deans micro connectors (micro helis)

  • JST BEC connectors (micro helis)

If you use the 4mm bullet connectors, you may want to use one male and one female plug on the battery otherwise you may plug in the ESC backwards, which will definitely damage it.

The Astroflight connectors are expensive but they are polarized and of extremely high quality and highly recommended.

These connectors may have some problems:

  • Anderson's PowerPoles

  • Sermos Connectors

  • Tamiya connectors

The Tamiya connectors do not handle high current well. They will become very, very hot when conducting large amounts of current. Unfortunately,these connectors are supplied with Corona kits. It is highly recommended to replace these connectors.

JST connectors are only good up to about 6 amps burst, and should only be used for micro helis under 400 grams. If used for larger helis such as a Zoom or T-rex, they will become very hot.

Some people do use Powerpoles or Sermos with helis, but evidently some ESC manufacturers are claiming these connectors have problems.

There has been a report of Schulze refusing to honor a controller warranty due to the usage of Powerpole connectors.

Also, Rumrunner Hobbies' webpage states:

"Lehner/BK warrantee does NOT Warranty (and is not limited to):... If Sermos, Powerpole, or Tamyia style connectors are used in the application."

Also mentioned:

"When connecting your new LMT controller to your batteries be sure to use Deans style connectors or 4mm Gold connectors (gold connectors are for racers only). Other connectors such as Sermos, Powerpole, and Tamiya connectors can NOT be used and WILL VOID your warrantee.

These style connectors have a tendency to arch (sic) and or spark as your vehicle is in motion. They also have a much higher resistance factor. If the connector does arch (sic) during operation of your vehicle it will short out the motherboard and render your controller useless!"

6.3.3. BEC (battery eliminator circuit)

(See Chapter 31, Glossary for a definition of BEC)

If your heli uses up to 8 cells and uses only analog servos, then you can use the BEC which is included on many ESCs such as the Schulze Future 12.46k and the Castle Creations Phoenix 35.

Some controllers can handle up to 10 cells with four servos, but 10 cells is very marginal for most linear BECs, and the BEC will run very hot. I recommend using an external switching BEC when running battery packs over 10 volts (more than 8 cells NiCD/NIMH, or more than 2s LiPo).

If you are using any digital servos, then you will need to check the ESC's onboard BEC amperage rating. Most ESC BECs are rated for only 1 or 1.5 amps which is insufficient to run a digital servo + 3 analog servos. One digital servo with three regular servos can easily draw well over one amp, so if your ESC's built-in BEC is rated for only one amp, you will definitely need to use an external BEC. If you overload the ESC's BEC in flight, it will overheat and shut down. You will then lose control of the helicopter and it will crash.

To use an external BEC, you will need either a free servo/battery position on your receiver or a Y-lead for the BEC's output power plug.

Currently there are several popular BECs. The first is the Kool Flight Systems Ultimate BEC, also called the UBEC. This is a large 20 gram BEC which can deliver 3 amps continuous. There are two models for 5 volt use, one for up to 29 cells and other for up to 36 cells.

The second is the Firmtronics SBEC. This is a very small and light (8 grams w/o switch) BEC which can deliver up to 2.5 amps continuous and can work with up to 40 cells. Some people have reported interference problems with the SBEC on 35 Mhz radio systems, however.

There are now two more choices, which are the Medusa Research "Potencia" 2 amp/6-25 cell and 3.5 amp/10-33 cell BECs (12 grams). I have not seen any reports from people using these on helicopters, however.

Dimension Engineering manufactures two BECs which are usable for helicopters: the ParkBEC and the DE-SW050. The ParkBEC is rated for 1.25 amps and 33 volts of input and includes a built-in Y-lead. The DE-SW050 is rated for 1 amp and 30 volts of input and requires some extra soldering to use. Both the ParkBECs and the DE-SW050s can be wired in parallel to increase the current capacity of the units.

The highest output BEC currently available is the R/C Model Works UberBEC. This BEC is rated for 3.5 amps of otuput on 3S to 13S lipo. There have been no reports of this used in helicopters, however.

General recommendation

  • Helis using micro servos (HS-55/56 size): ParkBEC

  • Helis using mini servos (HS-81/85 size): SBEC

  • Helis using full-sized servos: UBEC

To use the ParkBEC with an ESC with a built-in BEC, the throttle wire should be plugged into the ParkBEC header and not the receiver. This will automatically disable the ESC's built-in BEC.

To use the ParkBEC with an ESC without a built-in BEC, then both the ParkBEC and ESC must be plugged into the receiver (using a Y-lead if necessary). If the ESC is plugged into the ParkBEC, then the ESC will not receiver 5 volt power and will not initialize.

To use an (non-ParkBEC) external BEC with an ESC which already has a BEC, then you will need to disable the built-in BEC of the ESC. To do this, check if the ESC has one or two plugs which plug into the receiver. If the ESC has two plugs (like the Schulze Future 12.46e), then one of the plugs will have three wires and the other will have only two wires. The plug with only two wires is the BEC plug. If you do not connect this plug to the receiver, then the ESC's onboard BEC will be disabled. If the ESC has only one plug (like the Castle Creations Phoenix series) then the plug will have three wires and the middle wire should be red or orange.

Either pull this red wire out of the connector and tape it with electrical tape to prevent it from touching other wires or use a servo extension with the red wire pulled out and taped. This will disable the onboard BEC of this type of ESC.

Some people have reported the SBEC causes interference with 35 Mhz R/C systems. If you have a 35 Mhz system, you should be careful of the SBEC.

As a beginner, you should use a 5 volt BEC and not a 6 volt BEC. The 6 volt BEC will provide better holding power for the servos, but this will not be very noticeable unless you are performing extreme 3D aerobatics. Also, the 6 volt BEC will increase the wear on your servos and decrease the servo life.

6.3.4. Wire

(The Corona kit does not need extra wire if using the Fusion 35, Pegasus 35, or Phoenix 35 controller)

The motor and battery wires are especially important on an electric helicopter. If the ESC to battery wire is too thin, then you may experience ESC shutdown problems when the motor is spooling up or the wire may become very hot.

If the ESC to motor wire is too thin, then the motor may stutter while the helicopter is in flight.

The following table lists the recommended wire sizes for various currents:

Table 6.1. Wire size recommended by current capacity

12 gauge41 amps
13 gauge35 amps
14 gauge32 amps
16 gauge22 amps
18 gauge16 amps
20 gauge11 amps
22 gauge7 amps

For an Corona, ECOs, and Logos, you will need good quality 12-14 gauge wire for the motor and battery leads. This wire will work well:

  • Castle Creations W13RB (13 gauge)

  • Astroflight wire (13 gauge)

  • W.S. Dean's Ultra Wire (12 gauge)

  • Team Orion (12 gauge)

The 12 gauge is very heavy and only recommended for extreme flying and/or larger helicopters with high current draw (>30 amps). The 13 gauge wire should suffice for most types of flying.

For the Piccolos and Hornets, you will need good quality 20-22 gauge wire for the motor and battery leads. This wire will work well:

  • Castle Creations W20RB (20 gauge)

Sometimes wire is sold as "square mm cross-section" instead of AWG. Here is a quick table for conversion:

  • 1.5 sq. mm 15 AWG

  • 2.5 sq. mm 13 AWG

  • 4.0 sq. mm 11 AWG

6.3.5. LiPo battery monitor

If you are using a LiPo battery pack, you may want to use a LiPo battery monitor to avoid overdischarging and damaging your expensive battery.

There are several LiPo battery monitors:

  • The BattSignal by Jim Bourke Model Products weighs 4 grams and protects 2s to 6s LiPo battery packs. It autodetects the number of cells in series and will provide an audible indication of the capacity left as the battery is discharged.

  • The HRPoly-X by Custom Idea weighs 3.9 grams and protects 2s to 4s LiPo battery packs. It works similarly to the BattSignal and can also log the battery voltage for 42 minutes, and the data can later be downloaded to a PC.

  • The Li-saver by New Creations R/C is not suitable for electric helicopters because it pulses the main motor to indicate a low voltage condition.

  • The MicroScream is a $5 DIY low voltage monitor for 2s or 3s which was posted to the RCgroups DIY electronics forum. Search the forum for more info.

6.3.6. Battery mounting strap

Some helicopters may need a velcro strap to hold the battery to the frame.

For micro helis, the 1/2 inch Velcro Get-A-Grip strap can be used, which is available in 8, 12, and 18 inch sizes. The 8 inch size is most often used for micro helis, and is Office Depot item #369220.

For larger helis such as the Logo 10, the 3/4 inch Velcro Get-A-Grip strap (also called One-wrap strap) works well. The 3/4" x 9' strap is Office Depot item #193464.