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First Build won't take off

Bobert1892

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I'm just getting into FPV and recently completed my first build. The goggles connect to the camera and my receiver responds to the transmitter in beta-flight. The motors all spin the correct direction when tested at low rpms in beta-flight. But when I tried to do my first hover, I couldn't get off the ground. The motors would arm and the quad would respond to little nudges of pitch and roll. When I throttled up, the motors would spin faster and faster until right before lift off, then everything shut down. The flight controller went dark and the motors stopped. The battery was still plugged in, but the quad was completely unresponsive. This happened every time I tried to fly.
The motors would cut at about a throttle of 1200 (1000-2000) in betaflight.
I am running the mamba f722 mini stack with a 100c 1500mah 4s battery. I have 2205-1800kv motors from Race Day Quads, a FrSky XM+ Receiver, and a taranis x7 transmitter.
Also I built my own lego frame, which is not the best frame, but it should still fly right? It does mean that the drone is heavy, about 540g with the battery.
 

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1ikhan

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I'm just getting into FPV and recently completed my first build. The goggles connect to the camera and my receiver responds to the transmitter in beta-flight. The motors all spin the correct direction when tested at low rpms in beta-flight. But when I tried to do my first hover, I couldn't get off the ground. The motors would arm and the quad would respond to little nudges of pitch and roll. When I throttled up, the motors would spin faster and faster until right before lift off, then everything shut down. The flight controller went dark and the motors stopped. The battery was still plugged in, but the quad was completely unresponsive. This happened every time I tried to fly.
The motors would cut at about a throttle of 1200 (1000-2000) in betaflight.
I am running the mamba f722 mini stack with a 100c 1500mah 4s battery. I have 2205-1800kv motors from Race Day Quads, a FrSky XM+ Receiver, and a taranis x7 transmitter.
Also I built my own lego frame, which is not the best frame, but it should still fly right? It does mean that the drone is heavy, about 540g with the battery.
2205 @ 1800kv 4s with a weight of 540g might be too little, not sure. At 4s I think you have to be at much higher kv motors to get good enough lift. Are you certain that your escs can output enough amps? It can also be that your motors being underpowered spin to the max pulling a lot of amps but being unable to fly trips something in your power delivery process. Talking out of my *** really, someone will provide more pragmatic solutions.
 
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Bobert1892

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2205 @ 1800kv 4s with a weight of 540g might be too little, not sure. At 4s I think you have to be at much higher kv motors to get good enough lift. Are you certain that your escs can output enough amps? It can also be that your motors being underpowered spin to the max pulling a lot of amps but being unable to fly trips something in your power delivery process. Talking out of my *** really, someone will provide more pragmatic solutions.
Thanks for your response. How big of motors would you suggest? Also my esc specs says a max continuous current of 30A, does that seem adequate?
 

1ikhan

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Thanks for your response. How big of motors would you suggest? Also my esc specs says a max continuous current of 30A, does that seem adequate?
Hmm, 30a should do. I'm familiar with 2xx6 and greater stator heights, so I can recommend xing-e 2207 2450kv. Cheap and good. But before making a purchase, wait for others to chime in of course. Also, man if you crash with a Lego frame won't it just fall apart? I mean you can fly it but like just hitting a wall at low speeds might just break things.
 

rtkDarling

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@1ikhan is right about the motors, 1800 kv is better suited to 6s, but I bet your ESCs are only 4s rated.

This exact thing happened on one of my very first builds and it was a semi-cold solder. That means that power could flow though it, but not enough to fly. I wasn't knowledgeable enough to track it down at the time, I ended up taking it apart and putting it back together. I'm sure it was a wire from a motor to an ESC. Are you an experienced solderer?

Lego frame is gonna be a tough first build. You can get a carbon frame for $30, it's worth it to protect your components when you crash. Otherwise, you're likely to break your electronics.

When it shuts off does the FC reset and beep? Maybe some video would help, we can tell a lot from the sound of the motors when they're spinning up.

What kind of battery? If it's a low C rated battery it won't get off the ground
 

Bobert1892

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@1ikhan is right about the motors, 1800 kv is better suited to 6s, but I bet your ESCs are only 4s rated.

This exact thing happened on one of my very first builds and it was a semi-cold solder. That means that power could flow though it, but not enough to fly. I wasn't knowledgeable enough to track it down at the time, I ended up taking it apart and putting it back together. I'm sure it was a wire from a motor to an ESC. Are you an experienced solderer?

Lego frame is gonna be a tough first build. You can get a carbon frame for $30, it's worth it to protect your components when you crash. Otherwise, you're likely to break your electronics.

When it shuts off does the FC reset and beep? Maybe some video would help, we can tell a lot from the sound of the motors when they're spinning up.

What kind of battery? If it's a low C rated battery it won't get off the ground
I'm not an experienced solderer, so that could be the problem. Is there a good way to identify a semi-cold solder or do i just have to redo them all? (I'll post a pic of my motor solders.)
Here is a video of it running from betaflight. It seemed to run longer before shutting down without the props on. I can also post a video of a real attempted flight if that helps.
I have a 4s 100C 1500mah battery
 

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Bobert1892

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Hmm, 30a should do. I'm familiar with 2xx6 and greater stator heights, so I can recommend xing-e 2207 2450kv. Cheap and good. But before making a purchase, wait for others to chime in of course. Also, man if you crash with a Lego frame won't it just fall apart? I mean you can fly it but like just hitting a wall at low speeds might just break things.
Thanks for your help!
 

rtkDarling

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Battery numbers are good.
Cold solders look cloudy instead of shiny, they come off easier. If you have a flux pen you can hit the joints with a little flux then reheat them and they'll settle.

When you wind up off betaflight, does it make the startup chimes after it shuts off? Plugged in to the computer it won't reset because it has USB power

[Edit]
Have you checked your ESC settings in BlHeli? If you're out of options you might try updating the firmware on your ESCs and updating betaflight just in case. It's not science I know, but it's the equivalent of restarting a computer when it's acting up, sometimes it just works 🤷🏻‍♂️.

Be sure to use the right firmware for your Flight Controller if you decide to update betaflight.
 
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