RADIO CONTROL GIANTS
Sal Calvagna, 1335 Broadway Ave., Holbrook NY 11741; E-mail: [email protected]
WHEN WE PURCHASE a new radio system, it normally comes with a 600 or 700 mAh, four-cell, AA Nickel-Cadmium receiver battery. This battery is just fine for flying 40- or 60-size models, but a poor choice for larger models.
Many times I have been asked, "What size receiver battery pack should I use for my Giant Scale model?" This is a tough question because there are so many variables involved, such as the number and type of servos, size and weight of the aircraft, and type of aircraft.
Don't fret; there is a fairly accurate way to determine what size receiver battery you really need without relying on a wild guess. All you need is a charger and cycler. That's it!
Choosing a Receiver Battery
I suggest that if you are going to fly a Radio Control (RC) Giant that weighs more than 15 pounds, you consider using a sub-C cell. Sub-C cells come in different heights and mAh ratings, and the easiest way to tell you have a sub-C pack is if an individual cell measures roughly 7/8 inch in width. A sub-C cell has a lower impedance than the smaller A-class or AA-class cells, which means that it can deliver more current.
Testing Battery Capacity
Fully charge your test pack. For this test, let's say that we are going to use a 1200 mAh battery pack. You should slow-charge a Nickel-Cadmium battery by using the 10% rule. If you are going to charge a four-cell, 4.8-volt, 1200 mAh battery pack, you should charge it at 120 mAh for 14–16 hours. Once the pack begins to feel warm, it is fully charged.
- Put the pack on a cycler and discharge it at 250–300 mAh.
- When the pack is fully discharged, record the reading. It is important to charge and cycle a battery pack because you need to know its actual capacity. The label on the outside of the pack stating that it is a 1200 mAh pack is not good enough. The only way to truly know the capacity and performance of a battery pack is to cycle it.
- Now that you have an accurate reading on the capacity of your pack, fully charge it again. For the sake of simplicity, let's say that our test pack has cycled exactly to 1200 mAh.
- Install your freshly charged receiver battery pack in your model and take a 10-minute flight. During this flight put the aircraft through all its paces; don't hold back. At the end of 10 minutes, land the model, remove the battery pack, and place it back onto the cycler to discharge it.
If your pack cycles to 1000 mAh after the flight, you have used 200 mAh on your 10-minute flight. With this information you can safely compute what you would use in a typical day:
- Four 10-minute flights: 200 x 4 = 800 mAh.
- Six 10-minute flights: 200 x 6 = 1200 mAh.
Since you now know how much capacity is being used by this particular model, you can determine what size receiver battery to install. Don't leave yourself short; make sure you select a battery pack with a capacity that will more than handle a typical day of flying.
Remember, always use a good voltmeter (with a 200–300 mAh load) to check your voltage after each flight.
Securing Connectors
Parsons Products of Baton Rouge, Louisiana, produces a Radio Plug Safety Retainer Clip that is used to keep your battery, servo extensions, and other connectors tightly coupled. Anytime you have a high-vibration, high-stress situation, such as those common in Giant Scale applications, you should use a device such as the retainer clip to keep the connectors from accidentally pulling apart.
I have seen modelers use all sorts of tape and homemade fixes. The Parsons retainer clip really does the job and comes specially made for different radio-system connectors such as:
- Futaba
- Airtronics
- JR
- Hitec
- Others
I know of one incident where a receiver battery separated from the switch harness while in a loop because the battery pack became dislodged. Had a retainer clip been used, that airplane could still be flying today. You can purchase this product from your local hobby dealer or directly from Tower Hobbies.
Other Products
The Flying Scotsman Co. of Bennington, Vermont, manufactures the Quick Fueler.
Transcribed from original scans by AI. Minor OCR errors may remain.
