Thrust Units

Firmware/software/electronics/mechanics
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anandbala1597
Beginner
Posts: 1
Joined: Wed Mar 09, 2016 4:40 am

Thrust Units

Post by anandbala1597 »

Hey,

The documentation says that the thrust can range between 0 - 60000. What are the units of this thrust range?

Also, I read a post that says that these map to a PWM output. I was wondering if someone could help me with that.

Thanks a lot!
kristoffer
Bitcraze
Posts: 479
Joined: Tue Jun 30, 2015 7:47 am

Re: Thrust Units

Post by kristoffer »

Hi and welcome to the forum!

The thrust is set by a 16 bit integer (0 - 65535) and the unit is slightly undefined in connection to the physical reality. 0 means no thrust, wile 65535 is full thrust. In the range you get a proportional amount of thrust, so 32767 would give you 50%. The thrust value is used to control the pulse width of the square wave that is fed to the motors. Since the amplitude of the wave is simply the voltage from the battery, there is also logic that tries to compensate for battery power changes by adjusting the pulse width.

There is also some inoformation on the wiki that might be of interest https://wiki.bitcraze.io/misc:investigations:thrust
CrazyGuy
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Posts: 27
Joined: Fri May 02, 2014 6:03 pm

Re: Thrust Units

Post by CrazyGuy »

Nice to know. That's exaclty what I was looking for. I have a CF 1.0 and will try this battery compensation with the CF 2.0 parameters. Do you know if there are any thrust vs volt analysis for the CF 1.0 too?
kristoffer
Bitcraze
Posts: 479
Joined: Tue Jun 30, 2015 7:47 am

Re: Thrust Units

Post by kristoffer »

There is no complete analyses for CF1 as far as I know, but I found a function describing an estimate of the lift force that might be helpful.

u is the raw thrust in the range 0 − 65535
f ≈ 1.6648 × 10−6u − 0.011772

If you add compensation for battery power for CF1, a contribution to the code base would be most welcome!
CrazyGuy
Beginner
Posts: 27
Joined: Fri May 02, 2014 6:03 pm

Re: Thrust Units

Post by CrazyGuy »

The battery compensation for the CF 2.0 works for my CF 1.0 too. Now my regulator is able to hold the cf at the same altitude even with low battery, although it's too much thrust (for my model) now. I set the target point at an altitude of 0.5m but my regulator hold the cf at about 0.8m. So I think I will do some adjustments. Either on the battery compensation code or on the parameters of my quadcopter model.
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