Nov 09, 2015, 04:32 PM
Free Falling
Discussion

# ecalc - dual escs-motors, computed amps for one or two? Thrust values vs auw

I can't seem to find a real answer on some of these things.. I took a look at the help and other places..

I have a ts2, dual D2830-11's and 9x5e props (counter rotating).. all on a 3S 5200mah 35C power system, weighing 73oz..on 30 amp x 2 esc's..

If i put the closest value i can find for battery (5000) into the system and choose the 60 amp max? or should that be 30, is it counting two at once or "per esc"?).. i get computed values for "full" charge and 43 on wing area..

Motor Max: 14.81 amps (in my real world test, i show a pull of about 20.5 amps for the two motors combined, so would this calculation be for the two motors combined as well)?

Motor max wattage: 169..

For propeller, i see thrust at 30.1 oz (again, is this for both motors combined, i also put in 2 props).. if so, i guess my understanding of the thrust value is off, as if the weight is 73, it wouldnt go anywhere (which it does, though not screaming fast upward but it goes up "ok").

Mixed flight time shows 12.6.. i know some people with the same motors/weight that can crank out as much as 32 (at altitude with tailwind), obviously this is just a closer flying/more throttle approximation i'm sure.

So mainly i'm trying to (for the sake of science, knowing real world is very different) understand what the calculation numbers are supposed to be representing.. ie: two motor max amps or one etc (and if you set the value to the total of the two combined at 60)?

 Nov 09, 2015, 04:40 PM Registered User Enter in the specs for each individual PART (i.e. for a single motor, single propeller, single cell, single ESC). The fact that there are two ESCs and two motors running off the same battery will be accounted for in the "# of motors" field. eCalc assumes one ESC for every motor. eCalc also assumes one propeller per motor (no gang driving!). Motor and propeller stats are for individuals in the system. Total Drive, Airplane, and Battery specs are for the whole system. For example, if you have two motors/propellers that draw 10A each and and each produce a thrust of 1kg, then the battery C-rating will be calculated using 20A and the thrust to weight ratio will be calculated using 2kg thrust. Does that answer your question? It was a bit difficult to follow all your specifics (plus my laziness) Last edited by DKNguyen; Nov 09, 2015 at 04:53 PM.
 Nov 09, 2015, 04:50 PM homo ludens modellisticus And 5200mAh 35C = 2 x 2600mAh 35C C value does not change. Vriendelijke groeten Ron
 Nov 09, 2015, 04:55 PM Registered User I have tried using ecalc on numerous occassions. It is never accurate, most times not even close.
Nov 09, 2015, 05:12 PM
Free Falling
Quote:
 Originally Posted by DKNguyen Enter in the specs for each individual PART (i.e. for a single motor, single propeller, single cell, single ESC). The fact that there are two ESCs and two motors running off the same battery will be accounted for in the "# of motors" field. eCalc assumes one ESC for every motor. eCalc also assumes one propeller per motor (no gang driving!). Motor and propeller stats are for individuals in the system. Total Drive, Airplane, and Battery specs are for the whole system. For example, if you have two motors/propellers that draw 10A each and and each produce a thrust of 1kg, then the battery C-rating will be calculated using 20A and the thrust to weight ratio will be calculated using 2kg thrust. Does that answer your question? It was a bit difficult to follow all your specifics (plus my laziness)

Ok, so i choose 30 amps as the total.. put in # of motors as two? And put the weight of the system at 73oz (total)..

The computed values for amp draw are then counting the sum of two motors? When i do this, the computed value seems to be "way off" compared to the actual amp readout on the amp meter (say 11 vs 20) and less than if i set motors to 1 and multiplied by 2 (7.95x2=~15)

The thrust ratio of say 0.68 to 1 (basically less thrust than the weight) is calculated over two motors? (and how does that work exactly, ie: less thrust than weight and still get airborne). I'm assuming other factors like the airfoil of the craft must come into play to overcome the less than 1:1 ratio of thrust/weight through lift, which overcomes weight (reduces).
Last edited by markm75; Nov 09, 2015 at 05:18 PM.
Nov 09, 2015, 05:23 PM
Registered User
Quote:
 Originally Posted by markm75 Ok, so i choose 30 amps as the total.. put in # of motors as two? And put the weight of the system at 73oz (total).. If you have two ESCS and two motors and each ESC is 30A. The computed values for amp draw are then counting the sum of two motors? When i do this, the computed value seems to be "way off" compared to the actual amp readout on the amp meter (say 11 vs 20) and less than if i set motors to 1 and multiplied by 2 (7.95x2=~15) Under the motor specs column, it is per motor. Under the battery specs column, it is for everything. The thrust ratio of say 0.68 to 1 (basically less thrust than the weight) is calculated over two motors? Thrust-to-weight ratio are under the total drive column so it is for both motors together. (and how does that work exactly, ie: less thrust than weight and still get airborne). I'm assuming other factors like the airfoil of the craft must come into play to overcome the less than 1:1 ratio of thrust/weight through lift, which overcomes weight (reduces). Only a aircraft that need to fly on the prop/rotor need a thrust equal to the weight to stay aloft such as helicopters, 3D planes that prop hang, and fixed wing aircraft that do vertical climbs like fighter jets which actually need a thrust greater than the weight. Remember that wings are what pushes an airplane up during normal flight, not the propeller. The propeller thrust's main job is to move the airplane horizontally and moves the wings through the air. The propeller thrust also assists in a climb along with the net lift of the wings exceeding the weight. You could technically stay aloft, however precarious, if your propeller had just enough thrust to overcome the drag at stall speed. All the thrust beyond that is used for things like accelerating on the ground (takeoff), accelerating to speed, and climbing. Furthermore, in flight thrust is different than static thrust anyways. A unstalled propeller produces less and less thrust in faster and faster moving air until the thrust reaches zero at pitchspeed, above which speed the propeller begins to windmill. This means that an airplane can never actually reach pitch speed under its own power unless the airframe has zero drag.
See bold responses above,.
Last edited by DKNguyen; Nov 09, 2015 at 05:34 PM.
Nov 09, 2015, 05:31 PM
Free Falling
Quote:
 Originally Posted by DKNguyen See bold responses above,.
Yep that makes sense..

So for the computed values, just to confirm, the current reported would be per motor, so if it said 11 amps, means 22 amps for the motors combined (plus props)...

Under battery the only value shown is 4.7C so thats 23.5 amps on a 5000 amp battery i think.. makes more sense, still about 3 amps too high actually, but very close (the whole 25% margin i guess)

Thanks for the clarification on all this.
Nov 09, 2015, 05:35 PM
Registered User
Quote:
 Originally Posted by markm75 Yep that makes sense.. So for the computed values, just to confirm, the current reported would be per motor, so if it said 11 amps, means 22 amps for the motors combined (plus props)... Under battery the only value shown is 4.7C so thats 23.5 amps on a 5000 amp battery i think.. makes more sense, still about 3 amps too high actually, but very close (the whole 25% margin i guess) Thanks for the clarification on all this.
Yes.