Why rate mode for racing, proximity flying, etc...

[joshuabardwell]

I had a light bulb moment today as to why multirotor pilots who race, fly proximity, etc... usually (always?) fly rate mode instead of angle mode. Or maybe a better way to put it is, I had a light bulb moment as to why I prefer rate mode, and I think it might apply to others. I thought I would post about it, because sometimes people ask, and maybe this answer will help them.

First, definitions.

Rate mode, also known as acro mode or "manual" mode: In this mode, moving the stick causes the copter to tilt in the indicated direction. Moving the stick further from center makes the copter tilt faster. Centering the stick causes the copter to hold its current orientation.

Angle mode: In this mode, the position of the stick corresponds to a fixed angle of tilt. So moving the stick a little bit forward causes the copter to tilt a little bit forward. Moving the stick a lot forward causes the copter to tilt a lot forward. Centering the stick causes the copter to return to level. As this suggests, angle mode includes auto-level while rate mode doesn't.

Okay, so why prefer Rate mode?

Imagine that the copter is flying straight forward, tilted at a 30 degree angle (fast forward flight). If you are in rate mode, your sticks are centered. If you are in angle mode, your stick is pushed forward. Now imagine that you need to slightly adjust your trajectory to the side. Maybe there is a crosswind, or maybe you aren't quite lined up right with that hoop you're trying to fly through. In rate mode, you nudge the stick slightly to the side, then return it to center. In angle mode, you move the stick slightly to the side and keep it there.

Notice that, in rate mode, you have the advantage of the transmitter gimbal's self-centering to prevent you from accidentally pushing the stick upwards and modifying the frontward tilt of the copter. Whereas in angle mode, it is completely dependent on your muscle control not to accidentally move the stick a little bit forward or backward while you add in that little bit of sideways input. Rate mode lets you input precise trajectory adjustments to the four cardinal directions because you are always returning the sticks to center. Angle mode requires more muscle control to make precise inputs in one axis without unintentionally disturbing the copter's attitude in another axis.

Another advantage of rate mode is that the copter's orientation is unlimited. In other words, in angle mode, full stick deflection will always map to some fixed angle of tilt, and the copter will never be allowed to go past that angle. This is why you can't flip a copter in angle mode. This matters, even if you aren't intending to do flips. Let's say that you are zipping along and suddenly realize that you want to stop, IMMEDIATELY. In rate mode, you can tilt the copter completely on its butt, so that 100% of its thrust is slowing you down. In angle mode, you are going to tilt over 45 degrees, or whatever the pre-defined maximum is, and that's the end of it. Rate mode allows for more extreme and rapid changes to the copter's velocity, by allowing the copter to tilt over as far in any direction as the pilot wants. Personally, the most common place I experience this is when I am turning to fly between two obstacles, and I realize that I am about to swing wide and hit the outside obstacle. I roll further into the turn, and sometimes end up nearly 90 degrees over, punching the throttle briefly, before coming back to level to avoid hitting the ground.

MultiWii's Horizon mode addresses this limitation (and presumably other FC's have something similar) by having the FC transition from Angle mode to Rate mode as stick deflection increases. So when the sticks are near center, you're in angle mode, but if you jam them over to the side, the copter's rotation becomes unconstrained.

Finally, rate mode works better with expo settings than angle mode. I would wager that most multirotor pilots fly with some expo on their sticks. As you probably know, expo works by making the sticks less responsive (more resolution) near the center, and more responsive (less resolution) near the ends of the stick's travel. Remember that, in rate mode, the sticks always return to center except when you are inputting changes to the copter's orientation. So this means that whenever you are inputting changes, you are starting at the high-resolution part of the expo curve. With angle mode, if you are flying forward rapidly, your stick is pushed upwards and stays there, which means you are out of the high-resolution part of the expo curve. If you want to make a small change in your copter's attitude, your expo curve is going to be working against you.

 

[FinalGlideAus]

Simply put, "all" stabilized flight modes restrict your control abilities and what you can do as well as making the flight far more jerky and bumpy which in a race actually slows you down. It also makes your videos you put on YouTube look horrible with the horizon bumping up and down while watching the play back which is one of the more annoying things watch.

So why do pilots use it? Well, it's easy to fly.... That simple. Rate mode will take longer to master but will yield far greater results when you do. Also, the longer you persist with a stabilized mode, the harder it will be to change over.

Of course there are some situations that a stabilized mode helps like hovering a camera platform and you want a super smooth stable hover. The FC can correct things far quicker and smoother than you can and that is why the DJI stuff is mainly stabilized because they are just camera platforms.

 

[Craftydan]

Seems a fair assessment to me . . . hits the high points where my preferences lie and what I've observed of others as well.

Angle/Horizon are great for FPV training, but moving upward the "assists" begin to fight you, especially in Fast Forward Flight (FFF). Acro/Rate modes are preferred when stepping up to full racing, since you set the attitude, then you fly that attitude -- any "assist" you get from your control loops work to "lock-in" the attitude, and your TX springs guide you back to "locked-in".

As for rate/expo on sticks between modes IMO, that depends on the pilot and how they're flying. The Expo settings will be custom to feel (assuming they've tuned that far). That means it's apples and oranges between flight modes, IMO, since the sticks between the three primary modes are very much different in feel -- Set to feel, means it will be set to taste. From what I've seen, Expo in rate, angle, and horizon all have it's place, and therein lies the taste of the pilot.

BTW, there is something called negative expo, and there have been times I've seen multirotor pilots use it to make it REALLLLLY touchy on center and ease off banging the sticks . . . and those pilots are generally masochists . . .

now . . . quit theorizing, go break some props and get a feel for it

 

[nextmoneypit]

Good write-up! I found this part interesting (it makes sense, but I never thought about it that way)

expo works by making the sticks less responsive (more resolution) near the center, and more responsive (less resolution) near the ends of the stick's travel. Remember that, in rate mode, the sticks always return to center except when you are inputting changes to the copter's orientation

Seems a fair assessment to me . . . hits the high points where my preferences lie and what I've observed of others as well.

Angle/Horizon are great for FPV training, but moving upward the "assists" begin to fight you, especially in Fast Forward Flight (FFF). Acro/Rate modes are preferred when stepping up to full racing, since you set the attitude, then you fly that attitude -- any "assist" you get from your control loops work to "lock-in" the attitude, and your TX springs guide you back to "locked-in".

As for rate/expo on sticks between modes IMO, that depends on the pilot and how they're flying. The Expo settings will be custom to feel (assuming they've tuned that far). That means it's apples and oranges between flight modes, IMO, since the sticks between the three primary modes are very much different in feel -- Set to feel, means it will be set to taste. From what I've seen, Expo in rate, angle, and horizon all have it's place, and therein lies the taste of the pilot.

BTW, there is something called negative expo, and there have been times I've seen multirotor pilots use it to make it REALLLLLY touchy on center and ease off banging the sticks . . . and those pilots are generally masochists . . .

now . . . quit theorizing, go break some props and get a feel for it

I used negative expo in my knuckle quad (RIP) for when I wanted to do flips and what not. BUT I tied the negative expo settings to a switch, so that when the switch was off I could just cruise and have normal (or no) expo. Flip the switch and then small stick input = big movements

 

[joshuabardwell]

I had negative expo on my quad's yaw stick before I switched to an A-tail config.

 

[FinalGlideAus]

If you are still using that horrid default PID controller on the Naze then negative expo on yaw will be your friend

 

[Mustang7302]

There is a huge amount of merit in learning and being competent in flying in rate mode, I will never disagree with that. However, it is important to fly what you're comfortable with. I learned with auto-level and naturally have a muscle memory for it. I have learned to fly rate mode, but it will take me another year of practice to be proficient at it to trust myself to use it in a race.

 

[jhitesma]

There is a huge amount of merit in learning and being competent in flying in rate mode, I will never disagree with that. However, it is important to fly what you're comfortable with. I learned with auto-level and naturally have a muscle memory for it. I have learned to fly rate mode, but it will take me another year of practice to be proficient at it to trust myself to use it in a race.

I tried learning in rate...but quickly got hooked on Horizon as a crutch. Still spent a lot of time trying to get the hang of rate but usually ended up back in Horizon.

But once I got to borrow my friends warp and them got my twitchity acro quad...and got a BIG box of props...I was suddenly no longer intimidated about crashing since I knew the frames would take it and I had plenty of props already bought and paid for. And after just a few sessions like that I found myself flying more and more rate mode and less and less horizon.

I still tend to do a lot of horizon for FPV - but that's mostly because I don't get to fly FPV very often at all and don't feel like I can trust myself in acro there yet. Still want a few more sessions with a good spotter along to build my confidence.

But for LOS flying I'm almost all rate now. I have been using horizon on my knuckle tau lately though because my current tune is too aggressive on it and it's just a hand full to fly in rate with the current settings. But on my smaller quads I pretty much only fly rate now and have horizon on my trainer switch for those times when I have to catch my breath or someone tries to talk to me and I need to devote too many brain cycles to communication and want to "park" the quad in the sky for a few seconds while I reply

I guess the point I was trying to make was I thought it would take me a lot longer to get used to rate. But I made a major effort to only fly it for just a few packs and suddenly something clicked and it made sense now I prefer it 90% of the time.

 

[joshuabardwell]

I still tend to do a lot of horizon for FPV - but that's mostly because I don't get to fly FPV very often at all and don't feel like I can trust myself in acro there yet. Still want a few more sessions with a good spotter along to build my confidence.

I learned in rate mode, but I kept horizon mode on a switch as a safety net if I started to lose it. After I became proficient at rate mode, I got rid of that setting, but just recently, my FPV antenna was loose and my video feed dropped out as I flew away from myself. I dropped the throttle and crashed the quad (no damage done, thankfully, except for a busted zip tie on a landing leg). That prompted me to put autolevel back on the switch. If I get another video dropout, I'll have the option of autolevel, so I can be reasonably sure the quad isn't running away too fast while I get my goggles off and try to land it LOS. At least with autolevel, if I have to dump it, it will probably land relatively flat.

All of which is to say that I think autolevel has its place!

 

[joshuabardwell]

I have learned to fly rate mode, but it will take me another year of practice to be proficient at it to trust myself to use it in a race.

100% agree with what you're saying about flying what you're comfortable with. I would never look down on anybody who flies in self-level mode. I do have some negative thoughts about people who only fly in GPS mode, only because they create safety issues when a flyaway happens and they don't know how to get the copter back; but accelerometers are reliable enough that a pilot who can only fly in autolevel mode probably isn't putting anybody at much extra risk.

Not wanting to have to relearn the harder mode is one of the reasons why I forced myself to learn in rate mode to start with. FWIW, I also usually play video games on the hardest setting right out the gate. I guess I'm just a glutton for punishment? No... I just want to front-load my learning curve. But I have a big tolerance for frustration. I think that technologies like SAFE are fantastic for getting people into the hobby who otherwise wouldn't have the patience to get through the learning curve. Whatever gets people flying, having fun, and being safe, I'm all for it.

 

[makattack]

These are sound points. So, based on your statement here:

I do have some negative thoughts about people who only fly in GPS mode

I should probably rethink buying a dji phantom for indoor quad racing?