MAAA Wingspan

21 Now, youmay ask: why do I need to know the power rating of themotor? This tells me howmuch power themotor is consuming to run flat out. The specifications given on the motor spec sheets are usually themax rates. If themotor is pushed to usemore power then I’mprobably going to burn out themotor. Now, this is going to be important when selecting prop and speed controller sizes with the battery combination you wish to use, and of course themodel I’m going to put it into. I’ll come back to this bit later. Now To Understand Motor Specifications Information Here is an example of a brushless motor spec information. D2830-11 1000 kv Brushless Motor Suggested Prop: 8x4 (4S) ~ 10x7 (2S) So, from the information on this motor I can gather the following important information. • The KV, (1000 rpm/v) • Max current in amps, (21 amps) • Max voltage, ( 15 volts) • Power in watts, (210 watts) I can also get information on the shaft size and physical size of themotor as well. This info is equally important whenmatching motor to aircraft, i.e: will it fit in the cowl? Themotor manufactures usually provide the prop sizes at the nominal voltage used. This is very important to take note of too. In this case on 4 cells they used a 8x4, while on 2 cells a 10x7 was used. Let’s look at the rpmdifference between the two prop sizes • 14.8 x 1000 = 14,800 rpmon the 8”x4” prop • 7.4 x 1000 = 7,400 rpmon the 10”x7” prop It’s most likely that each prop combo produced the same thrust, however the same plane with the smaller prop and higher rpmwould be quicker than the larger slower prop as there is considerably more drag from the prop diameter. Ok let’s look at the next example PRODUCT ID: D6354-210 50 Required: 6S~9S Li-Po Test Data: 22v - 21x13 Prop - 40A - 5100g Thrust 22v - 19x12 Prop - 29A - 3500g Thrust Suitable for sport and scale airplanes weighing 9 to 15 pounds (4–6.8 kg). So from the information on the table above we can gather the following important information. • The KV, (210 rpm/v) • Max current in amps, ( 60 amps) • Max voltage, ( 33 volts) • Power in watts, ( 2000 watts) So let’s have a look at the tested rpm: • 22.2 x 210 = 4,662 rpm • Now, look at the current difference using the same voltage 40 amps compared to 29 amps - this was achieved only by changing prop size. This is always good to remember when trying to work within the current rating specs. Next time I am going to share my latest learnings on Li-po Batteries. Till then safe landings! MAAALogo. FEBRUARY WING SPAN