Electric power question
 

Greetings

I am planning on building a foam "have a few beers, stand back and squint" Cesna Skymaster. I want to use two speed 400 motors.

Questions:

Whats better, series or parallell for motor runs?

What size ESC/BEC will I need?

What battery packs would be compadible?


Any help would be greatly appreciated

RE: Electric power question
 

Hawk,

Although each technique, series or parallel motors, has advantages, I would put the two Speed 400 motors in parallel and use a single ESC to control both at once.

Each motor can draw about 10amps so select a 25amp (or greater) controller.

There are many packs available that can deliver the 20amps you'll need for both motors. Depending upon the wingspan and wingarea of the plane (I am not familier with it) you can choose heavier packs that will prolong your flight duration. The compromise here is between flight duration and flying weight.

Typically, we start with a minimal 1AH (or 1000mAh) capacity per motor. Therefor, you can optionally use these cells:
[ul][*] CP1700SCR NiCd[*] 1800mAh HECELLs NiMH[*] 1950mAh 5/4FAUP NiMH[*] 1900SCR NiCd[*] CP2400SCR NiCd
[/ul]

Good luck!

RE: Electric power question
 

Let us, for the purposes of discussion, assume each motor uses 10A at 10V. In a parallel connection each motor will see 10A at 10V and the battery will see 20A at 10V. Each motor will use 100 Watts. In a series connection each motor will see 5A at 5V and the battery will see 5A at 10V. Each motor will use 25 Watts. Parallel gives more power per motor at the cost of a bigger battery.

RE: Electric power question
 

Forget it. I'm wrong I guess.

RE: Electric power question
 

Hmmm - seems like going from 8 to 16 cells is a bigger battery to me. Hey Matt, lighten up.

RE: Electric power question
 

What on earth are you talking about? Lighten up?

RE: Electric power question
 

The biggest problem with putting motors in series is that the cell count oftens exceeds the ESC limit for use with BEC. This means more weight and cost by using either an Rx. battery pack or an Ultimate BEC device.

The 16 cells of 1000mAh HECELL or KAN1050 NiMH that deliver 10amps will rougly weigh a similar amount to 8-cells of 1900SCR or 1950mAh FAUP NiMH that deliver 20amps. Overall, the lower cell count is cheaper and will weigh less with progressive technologies like Lithium Polymer.

So, in summary, keep it simple! Use the motors in parallel with a single ESC on less cells.

Good luck!

RE: Electric power question
 

Folks, 20V is bigger than 10V even if the pack is similar in size and weight. 200 Watts is bigger than 50W even if the size and weight are similar. Matt, if you don't know what I mean by lighten up, you have a bigger problem than I thought.