031 Multirotor Tips

by FliteTest | June 17, 2014 | (12) Posted in Podcasts

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We discuss new Rotor Bones series updates, quad copters we have been flying lately and how to dial in or lock in your multirotor.

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COMMENTS

alexcunningham55 on June 17, 2014
this will make my drive home so much more enjoyable. the best part about tuesdays are listening to FT podcast during my commute
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Eddy Current on June 17, 2014
+1 Sir.
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carsonpauli on June 20, 2014
+2 to you
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Freaky_1 on June 18, 2014
"Less of our nonsense and more about rc" (paraphrased in quotes, lol).
Anyway, nooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo × a sideways 8 squared. Nonsense is a very important part of the hobby and more importantly the community y'all have fostered if not built.

Lastly, give JB back his "clicky thing"! :D
Thanks for much fun for many days may we all know many more. Thanks as well for sharing with the bigger family.

Frank
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Freaky_1 on June 18, 2014
Forgot something.

For dt750 motors and others that mount the same, a single TINY drop of loctite 640 to one side of the mount surface (not the set/grub screw, but adjacent) will settle things nicely for motors you don't intend to dismount often. Removal may take the touch of a soldering iron close to the drop from outside.

For motors dismounted more often, loctite 222 is wonderful. Removal is simple, but the dot may need reapplied after a hard wreck or ten.

Again, not for bolt/screw threads, but rather flat to flat contact of the mount to the "hub" and only a tiny dot is needed unless you acquire a very loose fitting one.

Frank
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Freaky_1 on June 19, 2014
It was brought to my attention that I should mention this is in addition to blue loctite on the grub/set screw rather than in place of.

Frank
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andre on June 18, 2014
Josh I had a DT750 motor come off my tricopter. Lost a set screw so I will use locktight and a friend suggested a ziptie as well to keep the screw in place.

Andre



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toolone on June 18, 2014
Hi guys,
I believe that the so-called "nonsense" is what gives the podcasts the human factor. The podcast at least in my opinion is the equivalent of being able to sit at that table with you guys. Sometimes conversations get off topic. But thats what happens when friends are enjoying each others company.

Many thanks for all that you do
Randy
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Neilusx8 on June 19, 2014
Hey guys, Love the podcasts, look forward to it every week. Josh mentioned about the new Wizard in APM 2.O with the new compass calibration window. I have downloaded the latest version I think (v 2.0.10) it doesn't have the wizard. I have seen 3D robotics demo it but cant seem to find it anywhere. Any pointers on where to find it? Thanks again for all your great work I love the "live" feel with your podcasts, feels like I am right there with you ,car alarms included, just love it.
Cheers
Neil.
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danallen82 on June 19, 2014
That tip about shaving off a flat area on the DT700 & DT750 was great Josh! I didn't notice how much slop was there because to the set screws. Now my rig should be a lot stiffer.
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Captain Crash on June 19, 2014
is it Paul Baxter from rtf quads thats helping you guys with the electro hub

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sixshooterstang on June 19, 2014
I kindly ask you.... Please stop plugging paul baxter from RTF Quads. His customer service and the time it takes him to ship items is worse than Hobbyking by 10 fold. He took two weeks to ship me a broken APM board and wouldnt answer calls or emails asking for a return. Several friends of mine had similar issues with shipping and one of them got different ESCs than they ordered.
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stay-fun on June 19, 2014
Hi guys,

I love your podcast! Talking about multirotors will definitely help people get their multirotor dialed in, you guys are great!

I'd like to give my opinion about 'heading hold', 'locked in', and I'll try to explain what P and I gains do. I hope this will give you a little bit more understanding, because I hear that you guys have trouble explaining it. I'd like to think I understand what all this means, and I'll try to give an explanation for it. I hope I can find the right words to explain it well.

I'd like to note that I have a background experience with mainly helicopters, so bear with me if I sometimes refer to that ;).

Heading Hold
What I understand from Josh is that heading hold is the same as autolevel. This is not true. Heading hold was first introduced in tail gyros for helicopters. Before that, there was only rate mode. The difference is the following: in rate mode, if the gyro detects motion, it will counteract that, until the motion is gone. Heading hold knows where the heading is (say, it is at 0 degrees). If the tail gets deflected, it will counteract and also put it back to the 0 degrees, whereas the rate mode would only counteract and bring it to a stop (at a different location than 0 degrees).
Translating this to a multirotor, it means that the control board wants whichever axis (for example, roll axis) to be at a certain position, and it will keep it there. If the multirotor gets deflected, the board will adjust, give inputs to the motors, to get back the the position. This is NOT autolevel. Autolevel simply means that the control board wants a different postion relative to the stick inputs on your transmitter.
As far as I know, multirotos don't have rate mode. This is something from the past, when heading hold in gyro's wasn't invented yet.

Locked In
Locked in means, that (in acro mode) you put the multirotor (or helicopter, sorry I can't resist ;) ) in a certain attitude and it stays there without moving/being squirrly. For example, you put the aircraft perfectly level, and it stays perfectly level. Sure it may start drifting with the wind, but the attitude of the aircraft remains the same. In my opinion, this is what's called 'locked in'.
As Alex says, this can apply to both docile and acrobatic aircrafts. Also in autolevel, an aircraft can be locked in. For example, if you keep your aileron stick at the same position, your aircraft should also stay at the same bank angle.

PI gains
Ok, the hard part. Let's start with P gain.
In these explanations, you need to have the perspective of the control board, NOT the input of the transmitter. Let's assume 1 arm of the multirotor, with motor attached. The board wants to have this arm at a certain heading, we will call this heading 0. Now as the arm gets deflected by an outside force (like wind), the board needs to correct. So say the arm drops a little, 1 degree. P gain tells the board how STRONG the motor needs to respond. So for example, with 1 degree drop, the motor has to increase thrust by 5%. In this case, a 2 degree drop will increase the thrust by 10% (this need not be linear though, but for sake of simplicity, let's stick with this). If you increase your gain, the motor will respond more strongly, so in case of a 1 degree drop it will now increase by e.g. 7%. 2 degrees of drop will result in 14% increase in thrust, and so on.
Now as the arm is rising due to the increase in thrust, the thrust will decrease. So it's going from 2 degrees (14%) to 1 degree (7%) to 0 degrees (0%). (note, again, this is 0% extra thrust, so there is still thrust to hover your multirotor).

So if your gain is too low, the motor won't give enough trust to compensate for the deflection, and your multirotor will feel sluggish. Not 'locked in', as described above. The other extreme is too high gain: the arm is being forced back with so much force, that there is an overshoot! As the arm gets too high, the motor will decrease too much power, so the arm will drop too fast, and motor power is increased again, but too much, etc. so this causes oscillation. Typically, you increase your gain until you find this oscillation, and then you back off your gain a little and that's it!

So that is P gain. All great. But what is I gain? That's a little harder.
Let's assume you've set up your P gain pretty well as described above. Now inertia and response time of your motor/prop comes into play. We'll take the same example as above: your arm is lower than where the control board wants it to be, and it's giving the motor extra power to get back to 0 degrees. Now, as your arm is rising to neutral, 0 degrees, the motor will hit 0% extra thrust at exactly 0 degrees. But the arm still has momentum moving up, and additionally the motor is still in the course of slowing down to neutral thrust (0%). So the arm is going to overshoot. Hmm but didn't we just correct for that by backing off the P gain a little? Yes and no, that'll come later.
This is where the I gain comes in. The control board is going to give the command to the motor to slow down to 0% slightly ahead of time, before the arm actually reaches 0 degrees, to offset the slowness in response of the motor/prop. How strongly it does this, depends on the I gain. If you increase the I gain, it'll give the command for 0% very early. So if you have a motor/prop/ESC combo that responds slow to control inputs, you need to increase your I gain.

You will find, that as you find the optimum I gain, you'll be able to increase the P gain ever so little, because now there is less overshoot, which caused you to decrease the P gain.

Geez, this has become quite a response...
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stay-fun on June 19, 2014
PS sorry to correct you bro, with "not true" I mean to say incorrect, ofc :)
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theteeheeguy123 on June 19, 2014
Hey, I'm a beginner in this hobby, and when i say beginner, i quite literally mean BEGINNER.
I haven't flown a single multirotor, but have flown those $20 3ch helis.

Is there a setup or a certain scratch build (ish?) tri/quad setup that you would recommend to a beginner?

Thanks.
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Epitaph on June 22, 2014
I know you guys like honesty, so I'll be honest. I'm sorry, but I didn't like this podcast so much. Those people that say "less nonsense, more RC" are probably the same kind of people that say about how much they like the garage feel to FT, which I see as a contradiction. I'm sorry, but it was starting to feel like the type of podcast Hobbyking would make, pure on products and nothing of a personal touch, and I think that is exactly the type of talking head style you need to avoid and have done well to do so up until now.

I especially noticed it right at the beginning with the car alarm... before that would have been at least 5 minutes of joke cracking and stuff that make us smile and enjoy the podcasts. But in this case it was more like Josh sweating buckets getting nervoius because of it being off topic, trying to ignore the happenings at the same time as just appologizing. Please, lighten up... that seriousness and nervousness, and the attempt to eliminate random randomness is exactly what I for one was hoping would never happen to you guys. I could tell you wern't feeling comfortable with this recording, that it was more stressful. If people want pure talking heads giving facts with no humanity whatsoever, they should listen to the RCG podcasts instead!

I prefere a 2 hour podcasts with half facts and half antics and mayhem than an hour podcast of just pure facts dished out in a nervious fashion... what those complainers don't realise is that they probably got the same amount of pure RC stuff out of this podcast as they would have gotten out of one of your more fun and subsequently longer podcasts, which is much more enjoyable to listen to...

I know you guys are reading feedback because for you the community is important, but let me tell you: the feedback was VERY wrong in this case

I still love you lots though guys!
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031 Multirotor Tips