Motor KV vs Speed

[RobTHighDFPV]

I can't help but notice that the kv on the motor doesn't reflect the actual in game speed. At the top of the page in the workshop, two of the fastest motors in the game, the 2600kv super fast, and the Hypetrain 2450kv motors, are the same speed. Then some 2650kv motors like le drib's 2650 is slower than both the motors I mentioned above, despite it having a higher kv.

It appears to me, the process was sort of a guess. Or the dev's are just to lazy to fix it. It would be nice if the motor KV reflected the speed, but it roughly does not.

[Tomodaore]

Hi RobTHighDFPV!

The speed indicator is calculated using all the forces acting on the quad. The motor are taken into account through dynamic thrust.

Now, it is right to say that an unloaded motor with higher Kv will spin faster with the same voltage. But things get more complicated once you are talking about loaded motor, and when you consider dynamic thrust instead of RPM.

With a loaded motor:

- There are losses proportional to the internal resistance of the motor (negligible without load, this is data we get from manufacturers that can really differ from motor to motor);
- Depending on the load and the battery, you can also get in a situation where you reach the motor max power (data from manufacturer) which in Liftoff results in "saturation". In real-life it could end up burning the motors.
- In some conditions, consequent part of the propeller could reach supersonic speed (think high kv, 6S, 6inch), then things get complicated, the interaction between propeller and air is different (IRL most propellers would break, motor/battery burn etc...). In Liftoff this results in saturation as well.

When you consider dynamic thrust:

- Saturation also happens when reaching pitch speed. So let's say a 2300kv at full throttle reaches 34500RPM which makes your drone move vertically exactly at its propeller's pitch speed, then a 2600kv motor with same resistance might give you 39000RPM, but it will not make the drone any faster as pitch speed has already been reached meaning the propeller cannot "scoop air" any faster.

So when you are comparing the impact of 2 different motors on a build, the build you choose matters. Maybe one motor is performing at its max "performance" while the other saturates. Maybe the internal resistance from data we get from manufacturers are very different for these 2 motors reflecting difference in build quality and material used.

Going from motor + propeller to maximum dynamic thrust is a complicated matter. We use different models and a lot of data from motor manufacturers.

Of course, the elements I give here are greatly simplified and is not an exhaustive list, it's just for the sake of giving some insight.

P.S: LuGus Studios has no lazy dev, we are doing our best :D

[Bipolar Weasel]

Wow. Tomodaore must build drones IRL because this is exactly what the advanced drone builders research before selecting motors. In fact, you have to take into account the weight of all of your parts (including frame, screws, standoffs, solder and wiring and other parts), the pitch of the motors and then check the manufacturer data to see how the motors would perform on your build. Literally motors and props are the last thing I buy when building a quad.