Sunday
Feb212010
FAN CALC 1.1
This is a great resource to help you figure out everything you nee to know about Radio Controlled EDF fan calculations.
NOTE: This program only works for PC's.
Friday
Feb192010
TORQUE ROLL RULE
Prop Rule of Thumb to Minimize Torque Roll Tendencies
Whenever you are building a pusher prop, jet type plane, to minimize the effects of torque roll, always keep the prop diameter 1/3 (33%) of the wingspan or less. With a 28" wingspan, a 9" prop is 32% of the wingspan and would be a good choice. A 12" prop is 43% of the wingspan and will generate a large amount of torque roll.
On the larger models, if you can keep the prop down to 25% of the wingspan, there will be almost no discernable torque roll tendancies. My 166% F-18 has a 48" wingspan, and I am running an APC 11x8.5 prop on it. In this case, the prop diameter is 23% of the wingspan, and it has almost no torque roll coupling.
Lucien
Friday
Feb192010
MOTOR EFFICIENCY
Calculating Efficiency of Electric Motors
(Example Motor)
Volts = 14.2
Amps = 28.0
Io = 1.1A (no-load amps at the operating speed)
Rm = 0.055 Ohm (internal resistance of motor)
Input Watt = V x A = 14.2 x 28 = 397.6 Watt
Copper Loss = Amps ² x Rm = 28 x 28 x 0.055 = 43.12 Watt
No-load Losses = Volts x Io = 14 x 1.1 = 15.62 Watt
Total Losses = 43.12 + 15.62 = 58.74 Watt
Output Watt = Input Watt – Total Losses = 397.6 – 58.74 = 338.86 Watt
Efficiency = Output Watt / Input Watt = 338.86 / 397.6 x 100 = 85.23%
Please note that we calculated the efficiency of the motor with a given prop.
Friday
Feb192010
MOTOR GUIDE
MOTOR BASICS
R/C Electric Motors For EDF and Pusher-Prop Parkjets
If you have any Motor Information or if you would like to see a specific manufacturer's motor information listed here, please CONTACT PARKJETS.
Axi: The first two digits of the number are the stator diameter in mm: the second two, its length. The full designation of the motor includes the number of turns of the winding, found after a slash. For example, the 2212/34 has a 22mm diameter stator that is 12mm long, and it has 34 turns of wire.
Mega motors: Similar designations - Mega 22/30/3 has a 22 mm-diameter case x 30-mm-long rotor, and a three-turn stator.
Aveox: An Aveox 27/13/3 seems to use the following: 27-mm diameter of the outside of the motor (not the rotor!) and 13 mm is the length of the rotor while three is the number of turns of the stator.
Hacker: A Hacker B20-26S is 20 mm in diameter, with the “S” indicating short length (L is for long) and is a 26-turn stator.
KV ratings: Kv gives the rpms produced by a motor per volt applied, i.e . if the motor has a Kv of 2000 and you run it on 6V it will turn at 12000 rpm.
Number of Turns: Turns are much like gearing! The higher the number of turns, the larger the propeller you can swing, however, the lower the maximum current it can withstand. Brushless motors that come in 1-, 2-, 3-, 4-, and 5-turn varieties are usually the internal-rotor type (but not always like the Hacker!). Brushless motors with high numbers of turns (say 10-30) are usually the external rotor (outrunner as we call it) type like AXI, Nippy, PJS, and the new little Hacker Baby.