# Minimum Thrust to Weight Ratio

So, I am currently flying a 650mm quad that I built. It currently weighs around 1600g. My motors are Garrt 3508 700kv motors with 1147 props on a 4S battery. According to the chart provided on the amazon page of the motors, it should provide about a maximum thrust of 1360g for each motor. So the max thrust for the entire quadshould be about 5440 grams of thrust. I am aware that the ideal thrust to weight ratio is around 3:1 or 2:1. But I am hoping to put some attachments onto my drone that would cause it to weigh around 3000 grams. I am aware that this would put it at around a 1.8:1 thrust ratio which is less then ideal. Would this still fly stably? If I remove some of the attachments on the drone such as my current FPV set up. It would be able to weigh around 2700-2850 grams putting it closer to a 2:1 ratio. But doing that would prevent me from flying FPV until I can get a smaller set up (my current one has a dedicated battery for FPV because I run 4S for the quad and my VTX can only take voltages up to a 3S so I have a 1500mah battery for my FPV, trying to fix that). So my questions are: Does the chart for the motors accurately reflect the real maximum thrust or do they exaggerate or put the max thrust in ideal stable conditions? And does having a 1.8:1 thrust to weight ratio allow me to fly the drone safely. Thanks in advance!

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Just use eCalc to determine this. I would say no way at 3000 grams with that configuration (~2000g max) . Prop up.With 14" props it looks OK and no indication of power over the limit of the motor.

As you have a flying copter, why not strap some dummy weight and fly ?.
Look for RC outs around 1500.
Post some logs here after the test flights ,for the experts to look.

For the RC out analyzing topic - I have a 600-grams copter and per logs it hovers at 1400-1500 (RCOUT) but same time ThrottleOut reports only 15-18%.
So it is not very clear - according to RCOUT it is good, but as per ThOut - it is very overpowered.

Not clear how to correctly decide if the vehicle under-powered / over powered. Should we look at RCOUTs or at Throttle Out?

Be careful using the arducopter values to derive power to weight. Many values have been compensated in the maths of the flight controller.

Imo , The best bet would be to look at MOT_THRST_HOVER. The nominal pwm range is 1000-2000. So if your hover value is ~1500, that would imply a power to weight ratio of close to 2:1. Please not my terminology is not very comittal because this method is only an approximation

Tl:Dr just use ecalc. I shoot for a 2.5:1.

Just some anecdote: the FlyKart 2.4 (https://evtol.news/news/gofly-teams-prepare-to-fly-again), a man-sized drone is at 1.3 thrust ratio. The BlackFly Opener (https://opener.aero/) is at 1.75.

So if man-carrying drones are okay with it, thenâ€¦

I dont know if the recommendations of minimum 2+ are taking into account aggressive maneuvers, orâ€¦

edit: note that these drones benefit from additional lift in forward flight. so perhaps the recommendation is purely for forward flight? but i meanâ€¦
15 deg tilt: 1/cos(15 deg) = 1.035
30 deg tilt: 1/cos(30 deg) = 1.155
45 deg tilt: 1/cos(45 deg) = 1.414

You will know when you see thrust loss errors. You are familiar with those yes?
But, here you go:
Thrust Loss

Well I guess whoever programmed the flight controller overrides physicsâ€¦

From the docs:

These warnings are the result of a motor or motors saturating at 100% throttle. Because of this saturation ArduCopter can no longer achieve the requested roll, pitch, yaw and throttle output.

So this sounds like a matter of configuration, not a guideline based on physics. A thrust ratio of 1.5 may be totally legitimate if the max rates are set accordingly. e.g. a max upward acceleration of 0.75g may cause saturation for a drone with thrust ratio 1.5, but a max upward acceleration of 0.3g may not cause saturation. That doesnt mean a ratio of 1.5 is â€śwrongâ€ť.

I guess itâ€™s a tried-and-true guide rather than a physics limit. Usually people fresh to the hobby would prefer to know that a thrust to weight ratio of 2 to 3 is going to give them what they expect.
They expect to build a quad using some relatively cheap combination of frame/motors/battery/electronics and so on. They will test the launch-to-the-moon characteristic as soon as possible, then add a go-pro, possibly a gimbal and some more electronics for telemetry, VTX with OSDâ€¦ the list goes on.
Of course the next question is â€śhow do I get more flight time?â€ť and â€śwhat does thrust loss mean?â€ť.
Weâ€™ve all been there at some stage.

You can bet those human guinea pig carrying multirotors will have super-strict limits on pitch and roll rates, and possibly some option that forces landing when wind speed approaches a limit.

The difference is: if you know your requirements and expect to have enforced rates and a limited range of suitable weather conditions, you can build and fly accordingly.
Luckily Ardupilot has all the suitable parameters for you to customise.

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So it seems like you agree; a low ratio like 1.5 is legitimate if you set the performance parameters accordinglyâ€¦ which sounds like totally reasonable statement, wouldnâ€™t you agree?

The examples you make are filled with emotion and fear. I understand you are trying to give good advice, but I am just trying to get a clear answer here.

I wouldnt be too dismissive of the FlyKart 2.4 and BlackFly Opener. The former is made by Trek Aerospace, who has been in the industry for decades working on much more impressive things. The latter is a Google-backed company, also made by people who have been in the industry for a while.

There are other forums to discuss such topics.

why? FlyKart uses Pixhawk + ArduPilot.

Read the Ardupilot Mission Statement. Itâ€™s clear, Unmanned Vehicles. As I said, Iâ€™m sure you can find a better forum if that is your interest.
Ardupilot

Another assumption. Both vehicles are primarily flown unmanned (with a man-sized payload), which makes sense for prototypesâ€¦

Are thrust ratios < 2 against the Ardupilot Mission Statement?