Copter won't takeoff even at full throttle

My setup is T-motor F2004 1700KV motors, T4030 props, T-motor F45A 4 in 1 ESC, 4S2P 7000 mAh Li-Ion. The AUW is 900g. The motors are capable of producing the thrust required but it does not takeoff even at full throttle. The RCOU values seen in the logs suggest that Pixhawk is sending signals to the ESC. Strangely when I reduce the weight of the quad(around 200g), I have no problem in flying the quad, although it loses altitude now and then.
It appears as the ESC is limiting its output to a certain thrust. I switched the protocol from DShot to PWM, but it did not help.
Assuming the battery could be an issue, I setup the ESC on another 6S copter with Antigravity 4004 300KV motors and 10000mAh battery and AUW of 2kg. Same result.

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Post a link to the flight logs at each weight.

At 700g you’re using 70% throttle.
At 2kg I guess you’d need nearly 300% throttle…
In the 2kg log, servo outputs are hitting 2000 usec, which is your configured max in the first log.
Why did the motors move from 9-12 to 1-4 ?

As @kd0aij said at 700g you have insufficient thrust/weight (by a long shot) with an average commanded output of ~1850us (should be 1500 or less).

Even on 6S, which is what you should have assumed, with 4" props TOW should be ~450g.

I think you are way off base. 6S power and much lighter weight.

The 2kg copter is a different setup with Antigravity 4004 motors, 15" prop. The motors can produce way more thrust than required.

The 700g setup with F2004 motors and 4030 prop should not theoretically use 70% throttle. I changed motor configuration from Dshot it to PWM to see if that could solve the problem, but its the same.

In copters, you should have at least a 2:1 thrust to weight ratio for a reasonable flight, even more for efficiency purposes.

Theoratically :slight_smile: never trust the manufacturer data.
They may be right at sea level but you might be living a km above the sea level.
Do some bench tests with a thrust stand.

The communication protocol is not the issue in here unless you’re not seeing motors spinning at some reasonable RPMs.

That’s right, it will use 85% at hover on 4S power. Were you perhaps looking at the specs for the 3000kv version of that motor?