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Old Dec 21, 2014, 12:12 PM
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Changed from 3S to 4S and WOW

So, today I hanged my battery pack from 3S to 4S. The system has tons of power now and works well, the only thing is that it seems to be quite erratic on the motor speed. What I mean is that when I apply or reduce power flight becomes quite unstable and difficult or impossible to control.

Are there and PID adjustments that are made when making a shift from 3 to 4 cells.
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Old Dec 21, 2014, 01:16 PM
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United States, VA, Richmond
Joined Dec 2013
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Your motors have an RPM "rating" that is a function of the applied voltage.

If you have a 1000 Kv motor, it will spin at 1000 RPM for every volt you give it. With a 3S cell that comes out to around 11,400 RPM max. If you take that same motor and use a 4 S cell the max RPM jumps up to 14,800..

Go back to 3S cells. Live long and prosper....
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Old Dec 21, 2014, 03:06 PM
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United States, NJ, Hamilton Township
Joined Jan 2013
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Throttle curve on your TX or FC may help a bit. It takes a few batteries to get used to the difference in responsiveness. If your getting oscillations you may have to dumb down the PIDs a tiny bit. The same throttle travel equals a larger variation in RPM as mentioned by Oldgazer.
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Old Dec 21, 2014, 08:09 PM
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Quote:
Originally Posted by lockwood View Post
Throttle curve on your TX or FC may help a bit. It takes a few batteries to get used to the difference in responsiveness. If your getting oscillations you may have to dumb down the PIDs a tiny bit. The same throttle travel equals a larger variation in RPM as mentioned by Oldgazer.
Multirotors do not use throttle or pitch curves. In fact, when you set up a multirotor flight controller, you set the model type in the TX to ARCO (Airplane). The FC takes 4 input signals (Aileron, Elevator, Rudder, and Throttle) and mixes them into control signals to send to the individual ESCs.

Also, it is common knowledge within the heli community that when you run larger packs, it is better to change the motor pinion than it is to run the motor at a lower RPM by tweaking the throttle curve. The main concern is for the ESC, in that the output FETs will dissipate more power as heat than they would if the motor was running at a higher RPM.

As an example, when I converted to a multi-blade head, I went from 3S packs and a 4000 Kv motor with a 13t pinion to 4S packs, 2700 Kv motor and 12t pinion. I started out with a 13t pinion, but the head speed was way to high for the head, and tweaking the throttle curve to bring the HS down made the ESC trip on over temperature....

One other thing you need to look at is the cell rating of your motors and ESCs. if they are not rated for use above 3S, then you could be looking at some rather spectacular, all be it brief flying....
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Old Dec 21, 2014, 08:39 PM
Mildly Awesome
The Netherlands, LI, Brunssum
Joined Mar 2011
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It's pretty common with mini's to move from 3S to 4S. You just have to keep the RPM down. Those that swap cell count move down from 2300kv to 1900-2000kv and usually a taller motor for the extra heat. 2204 to 2206 or 8. All with the same prop.

If the kV is too high for the combo or the ESC cannot handle the extra rpm you will get jitter which can smoke a motor/ ESC. I know from personal experience.
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Old Dec 21, 2014, 09:02 PM
Team WarpSquad
United States, PA, Doylestown
Joined Jan 2014
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My one quad I run 3S and 4S requires slightly lower pitch & roll 'P' values else it oscillates on 4S.
I also run slightly less RC rate and a little more RC expo in the MultiWii FC else it gets away from me too easy.
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