Need help limiting the end point of my throttle.

[MonkeysPunk]

Hi guys I was wondering if anyone can point me in the right direction. I have the ER9X on my transmitter and all works very well but recently I have built another multirotor and have used more powerful motors than I needed for the size of the airframe (all i had in the shed lol). The thing I need to do is limit the max throttle to something like 70% as this will then calm it down, but I cant seem to work out how to do it. I did play around with the limits menu but ended up creating a dead band below 3/4 throttle then it went full power almost like expo. What I want really is full stick movement but spread over a smaller amount of throttle (ch3) if that makes sense.

[Kilrah]

The easiest thing is to use a curve on your throttle mix, as it's simple to visualise. Limits would work too, but less straightforward. Basically, reduce the upper side, then set offset to the middle (if your throttle channel limits are -100/+60, you'd want to set offset to -20).

[MonkeysPunk]

When you say curve would this stop me hitting full throttle regardless of stick position. Sorry to come across a dumb but programming curves and mixes is all new to me.

[kaos]

yes, it will. I am running a 3800kv motor on a heli only need 2700kv.. my max throttle curve is 80 to limit my head spd under 3K. just make the curve linear(if that is what you want) from -100 to 80.
The curve is, like Kilrah says, easy to do.

[MonkeysPunk]

Thanks for that. Will try tonight.

[MonkeysPunk]

Ok so in curves I have gone to channel 3 (my throttle) and pressed menu. That has sent me to the curve graph screen where I have set -100 the bottom is 75 and all in between make a straight line. Then exit back to curve screen that shows the new curve I have on channel 3.
Is that it or do I need to calibrate again ?

[Kilrah]

I supposed you edited the curve on the CURVES screen. These have nothing to do with channels, they're just freely definable curves that can be referenced anywhere, so at this point it's not assigned to anything. You now need to go to the MIXER screen, select the entry you have for your throttle, press menu long on there to go to the EDIT MIX page, and on the "Curve" line choose the curve you've set. You can then also press menu long to directly edit it from there.

http://openrcforums.com/wiki/index.php/ ... e#Edit_Mix

[MonkeysPunk]

Ah that's perfect. Good I could also long press to edit direct as this confirmed I had selected the correct mix. Cheers all done now I think.

[MonkeysPunk]

I have used it a few times now since doing the curve and I don't actually think is has slowed it down at all. I even dropped the bottom point to 50 and it still was no different. When I long press the menu button it shows that the curve I created is selected so I know it's in there but just doesn't seem to do what I was hoping.

[Kilrah]

Can you post a screenshot of your curve?

Sent via mobile

[kaos]

for 70% of max throttle you need to limit your highest curve value to 40. -100 - 40

er9x throttle is -100 to 100 not 0 to 100. so -100 is 0 throttle, 0 is 50% throttle, 40 is 70% throttle.
your mid throttle point after limited to 70% max will be 35% and that is -30 in your curve.

I know this is very Nerdy. Took me 2 wks to figure this out when I started using er9x.

[MonkeysPunk]

Thanks for that good explanation mate. It has made it much simpler to get into my head the way you put it. I will try the method you discribed above and take a screenshot of my current curve to try and find out what it did wrong maybe.

[MonkeysPunk]

This is the settings I had set that didnt seem to change anything

And this is what it is set to now, but cant test as Receiver has stopped working

[Kilrah]

Both look good. It would be nice to know what multicontroller setup you're using.

[MonkeysPunk]

I run the APM 2 with Simon K flashed speedos. 1100kv motors x4 3s lipo

[Kilrah]

OK, I don't know that platform.
BUT, most advanced multicopter boards don't just pass the radio's signal to the ESCs, they do a lot of processing on it, so you usually can't just solve that kind of issues simply on the radio.
A multicopter board sends speed orders to the motors based on its own calculations, so even if you limit throttle it might still give full power in some situations.

Best would be to start over. What's your problem? Current too high for the esc/motor capabilities? Hover throttle too low? Simply too nervous? In most cases the adjustments should be done on the controller board, not on the radio.

[MonkeysPunk]

Think the main problem is the motors are to powerful for the weight of the frame so giving to much thrust with little movements of the stick.
I am using Mission Planner with Arducopter software.

[Kilrah]

You could replace the props with smaller ones.

[jhsa]

I think that's the best option..

[sgofferj]

That would cost him dearly in the endurance part... I'd tend to increase the weight of the copter by putting ridiculous big batteries in it . Solves the touchiness AND gives more endurance.

[jhsa]

I think it would be the other way round.. the motors would draw less amps..

[sgofferj]

Are you sure? I would assume that a motor running on 100% RPM pulls much more amps than a motor running on - let's say - 70% RPM. Even with a smaller prop.

[jhsa]

As far as I know, a motor without load (prop in this case) spins at max speed and draws less amps.
Get this program and use several combinations of props and motors

http://www.drivecalc.de/

[sgofferj]

I have been using the ecalc tool a lot recently because I want to build a copter too . You are right if you compare load and no load. But we are talking about big prop at 70%rpm and (little bit) smaller prop at 100% rpm. But this probably warrants a detailed calculation with the whole setup of the threadstarter .

[jhsa]

I don't understand, 70% from what?? following the way you're thinking then 100% is acheived without load (prop)
You can only compare performance between 2 props if all the other factors remain the same.. Voltage, ESC, etc..
So, for the same voltage, let's suppose that is full throttle, the bigger prop will lower the RPM compared to the other prop and increase the current draw.. but not necessarily more thrust..

[Kilrah]

Are you sure? I would assume that a motor running on 100% RPM pulls much more amps than a motor running on - let's say - 70% RPM. Even with a smaller prop.

Oh no, it's by far the opposite.
A simple idea - remove the prop, set your throttle to 100% - your motor uses very little

ESCs adjust speed by quickly switching motor windings on and off. By changing the on/off ratio, the average voltage varies, and that's what adjusts speed. BUT, you should always remember that the windings get either nothing, or the full battery voltage.
So if the voltage, Kv and prop combination results in excessive current at full throttle, it will also result in excessive current during the ON periods. If you measure the average current with a multimeter it will seem OK, but in reality it's composed of short spikes that exceed the rating.

And the thing is, heat losses in a motor are proportional to the square of the current (P=RxI^2) (simplified a bit, but the principle is right). Consider 2 scenarios where you give the same electrical power to the motor, once with a prop that is correctly sized, and once with one that is too big.
In the first case, you have a full throttle current of 20A. In the second, you get a full throttle current of 30A. To get the same electrical power in, you'll throttle down the 2nd motor to 2/3 power.
So in the first case you have 20A all the time. In the 2nd you get 30A (1.5x more current) 2/3rds of the time, which is the same in terms of input (3/2 x 2/3). But now remember the heat losses go with the square of the current. The 2nd case has 1.5x more current, and thus has 2.25x more losses. These only are there during 2/3rds of the time, so we multiply by that - 1.5x more losses.
So, we have the same electrical power supplied to the motor, but we have 1.5x more losses -> efficiency is lower.

So, you'll always want to design for full power.
If your setup is too powerful, you'd better adjsut it to have jsut what you need at full power instead of reducing throttle.

Now on a multicopter, you'll want if possible to first reduce the prop's pitch , then diameter only if you can't find what you need. A large prop with little pitch is more efficient than a small prop with big pitch.

[kaos]

I think the best approach may be changing the motor with the proper Kv and wattage. I did run my motor with modified/reduced curve, but ESC and motor got hot, although it should draw less amp. but after about 20 fly, the ESC burned out. Can't say for sure it is from the reduced curve that ESC had been sitting there for 2yrs doing nothing (was good). The motor is designed with its speced kv/wattage. running at lower rpm is less efficient although drawing less amp. Brushess motor run most efficient at full rpm. properly matched motor/prop would be a better way.

[jhsa]

exactly what I said but better explained In drive calc you can see the efficiency curve..

[jhsa]

in his case, with smaller props (pitch and/or diameter), he will reduce the thrust, which is what he wants, get more flight time from the battery (less amps), and the response in acceleration from the motors for stabilization might even improve.. with less load the motors will change speed faster..

Kaos, as far as I understrand his copter is overpowered. So, the props might even match the motors but this setup might make a rocket out of it

He doesn't want his copter to get into orbit before he reaches the throttle stick to bring it down.. of course he can always sit on it to add some weight but won't save on the amps and flight time

[sgofferj]

Ok, my head just exploded and I need to take a pencil and a paper and try to folllow your explanation step by step . Because it somewhat is completely opposite to what I have heard/read/concluded before.