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Loren Zimmer
Washington, DC
Post #: 10
As a reference this is the motor I'm using.

Here are the stats copied from the HK Site:
Model: NTM Prop Drive Series 28-26A 1200kv
Kv: 1200rpm/v
Max current: 18A
Max Power:200W @ 12v (3S) / 250W @ 15v (4S)
Shaft: 3mm
Weight: 57.6g
ESC: 20A
Cell count: 3s~4s Lipoly
Bolt holes: 16mm & 19mm
Bolt thread: M3
Connection: 3.5mm Bullet-connector

Prop Tests:
7x6E - 11.1v - 90W - 8A
7x6E - 14.8v - 192W - 13A
8x4E - 11.1v - 100W - 9A
8x4E - 14.8v - 222W - 15A
8x6E - 11.1v - 145w - 13A

Questions about the eCalc site:

KV (w/o torque): I assume 1200rpm/v for my motor.
no-load Current: Is this measured at the supply to the ESC? At Hover RPM???
Limit (up to 15s): What needs to go here?
Resistance: Where is this measured between legs on the supply?
# mag. Poles: guessing 4?? but not sure?
Christopher Vo
Washington, DC
Post #: 310
Kv is the motor velocity constant, measured in rpm/V. Represents the rotational speed of the motor at a given voltage when there is no load. For your motor, it will be 1200 rpm/V

No-load current: The amount of current that the motor draws at a given voltage, with no load (e.g. no prop attached). Charge your battery to something in-between its nominal voltage and full. Calibrate your ESC if necessary. To measure, spin the motor at expected operating RPM for hover (try 50% throttle if you don't know, think of it as "planned operating RPM") and record both the voltage and amps. It is acceptable to use the supply to the ESC to measure this voltage.

Limit: The maximum power (in watts) that your motor can handle. Usually provided by the motor spec sheet, but it's not a big deal --- this value is just so that eCalc can warn you if your motor is drawing more power than it is rated for. On your spec sheet it looks like 200W @ 12V (3S) and 250W @ 15V (4S).

Resistance: The resistances are really small. Instead of just hooking it into your meter, you need to use Ohm's law, measure voltage and current and use that to calculate resistance. However, putting a voltage into your motor directly is dangerous and the windings would vaporize. You need to put another resistor (call it "R2") in series, one that can handle the watts. Use two multimeters, one measuring voltage, one measuring current. Calculate the resistance, subtract the resistance of the R2 (measured seprately) and you have the internal resistance of the motor. Do each of the three possible pairs and verify.

Motor poles: Just count them. The number of permanent magnets on the rotor.
Jonathan R
user 61079222
Washington, DC
Post #: 28
Chris gave an excellent reply in terms of helping to understand what all these specs mean in the world of physics, but if you don't have all the equipment, you can go to the same website you listed for the motors: http://www.hobbyking....­ and look at the pictures of their test data to the resistance

For resistance, V = I*R. On graph 2 & 3, V is constant, I changes linearly. Reality check passed. calculate R. this number should be very small (0.something)

For no-load current, that I don't know a nice mathematical solution. This number usually comes as a spec by the manufacturer

hope that helps a little
Christopher Vo
Washington, DC
Post #: 312
Someone like HobbyKing needs to sell a cheap-as-dirt motor test rig thing that you can clamp to your desk and plug into your PC via USB. Open the software, follow the on-screen instructions, and it will run an automated test of your motor to produce all the static and dynamic measurements in a standardized file format so you can share it with others..... sigh, more thing that never going to happen
Loren Zimmer
Washington, DC
Post #: 14
Ok so the transformation is nearly complete. My question is that this thing weighs almost 5lbs. Will it even get off the ground?



user 118695272
Washington, DC
Post #: 3
Just reading about your landing gear - there is a long legged one available(google "tall landing skids") that gives loads of clearance. Something like http://www.google.com...­

Loren Zimmer
Washington, DC
Post #: 18
Hello Everyone,

The X8 is progressing nicely. I think the next step is tuning a little more. I was able to get out yesterday and get some footage for a project that I'm working on for my church:


All of this video was done with me flying manually. I would love to do shoots like this autonomously to get smoother shots. One of the issues that I face is that when I tried to put my quad into loiter yesterday it would dart to the right. It seems like I have to input stick movements for it to hover and hold still. Would the going through the "save trim" process be a good first step in getting to loiter correctly?

Once I can get it to loiter correctly would the next step be an autonomous flight?

Thanks again for all of the help guys!


Gustavo Zastrow
user 56452902
Mc Lean, VA
Post #: 205
Want to try this super cheap landing gear?
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