soft start vs throttle curve vs throttle hold

[Pete550]

With my new T-Rex 550E (AR7200BX, Talon 90 in gov mode), I noticed it takes a very long time (flight log says 8 sec) to do a soft start. There's nothing fundamentally bad about that when actually starting the heli, but I'm concerned about the possibility of this happening in mid-air. With my current setup, it could happen, because my normal throttle curve looks something like 0% - 93% - 93% - 93% - 93% (93% = 1700 RPM in my particular setup).

So if I accidentally lower the throttle stick to 0 while in normal mode, I get a soft-start and the heli will drop. Of course one can argue that this will not happen in practice, but I'm just worried about the possibility of any single button or stick on my remote sending the heli into certain doom. Also when doing a session in trainer mode, if the slave lowers throttle to 0 by accident, I won't be able to save it anymore.

How are people dealing with this? I can think of several ways using mixes on some of the other switches, but then I also want to keep things as simple as possible.

In summary here's what I'm trying to achieve:

1) soft start when starting my flight
2) no possibility to go into a soft start situation via the throttle stick
3) no possibility to go into a soft start situation via throttle hold
4) set up throttle hold for fast auto-rotation recovery (i.e. throttle hold needs to be at something like 17% in my case)

So requirement 4) defines my hold curve, and this also fixes 3). 2) implies that the low-stick value of my normal throttle curve must be 17% or higher. I assume that 1) happens by default, because when the Talon gets armed, it sees 0%, so it will do a soft start mode when throttle is increased for the first time. So the only remaining question is how to arm the Talon. I can configure the AR7200BX to arm it while initializing, but then I might have a problem with the fail safe position (see bonus question below). So if it doesn't arm through the AR7200BX, the only possibility I see is to set up an 'arm' switch on my remote, which mixes into throttle, subtracting 17% when activated. So I'd have to toggle that arm switch once before I can start.

Alternatively, I could use a throttle curve of '0% - 73% - 73% - 73% - 73%' for example, and have a switch that adds 20% to the throttle. So during spool up I would flip that switch, lifting the normal throttle values to 93%, and lifting the low value to a safe 20%.

Any thoughts or comments? How are people dealing with this? Or are you just trying not to lower throttle to 0 while flying?

Bonus question: thinking about this more, I also don't like the possibility of a brown out setting my heli into soft start mode. How are people dealing with this? Is it wise to program the fail safe throttle position to the fast auto recovery value (17% in my case)?

[pgkevet]

Without thinking about this too much (cos it's not a setup i have) how about starting your throttle curve at 20% and using TH - which you should be using anyway as you go to the flight line.

[parksy]

Sounds like you are over thinking this! I don't use governor so I might be talking balls so bear with me! In normal you are only taking off/ landing, once you're up you switch to idle up 1 or 2 and have a flat (v) line at 80, 90,or 100% Do you think you'll remember what combination of switches you gonna have to hit if you 'accidentally' switch from idle 1 or 2 back to normal at zero throttle? Might be better off learning autos on the sim. I should really have a go meself hahaha. You might also want to check that it will actually go into soft start after initial start up, I thought once initialized you have direct throttle response, once again I could be wrong. Even if it does go to soft start, remember your blades will be spinning at least hover speed so even soft start will give enough to land safely, unless you're inverted funnel or some mad sh*t

[tomatwalden]

How are people dealing with this? I can think of several ways using mixes on some of the other switches, but then I also want to keep things as simple as possible.

For one, don't fly around in normal mode. I did that recently with my Goblin, then flipped it inverted ... can you guess what happened!?

4) set up throttle hold for fast auto-rotation recovery (i.e. throttle hold needs to be at something like 17% in my case)

This one! Use this. It's easy to setup and is designed for exactly the situation that you are describing (ie. bailout of throttle hold).

[Pete550]

Thanks a lot for your comments. You're right actually, I could just change my normal throttle curve so it doesn't go down to 0 and then release throttle hold to start. No need for any mixes. Only problem with that is I won't be able to soft-start again after landing until disconnecting and reconnecting the battery (remember my throttle hold only goes down to 17%, for fast auto bailouts).

Sure if worst comes to worst I could try to auto. Unfortunately the area I'm flying over is not really suitable for auto landings, even a normal landing without tipping over would be difficult I reckon. So I'd rather avoid having to do that. I've tried soft start recovery close to the ground and found it would take 8 seconds after dipping throttle to 0 until the heli lifts off the ground again. So that's about how long the heli would be in auto (or near-auto) if you do a soft start mid-air. Pretty sure it would be hitting the ground during that time.

About not flying in normal mode in the first place, I've currently set up my normal mode for low-ish RPM cruising, idle up 1 for sport / light 3d and idle up 2 for max power. I like flying low RPM from time to time, and like being able to switch modes while in the air. But maybe I should restrict myself to two modes (like, idle up 1 for low rpm and idle up 2 for light 3d) and only really use normal mode for start and landing as you say. Then set up a second model on my remote for different idle up curves. But then I'd have to rebind all the time when switching models, which is annoying. So instead I could use a mix on a switch to turn my idle up 2 from 'sport' to 'max power 3d'.


So the one question remaining is how to best program the fail safe throttle position. I've currently set it to the minimum throttle value my Talon 90 would accept, which I think is how it's supposed to be set up (because it makes the AR7200BX arm the Talon on initialization). But it also means a brown out would result in a soft start, which I think is not desirable. Does anyone have an opinion on this?...

[tomatwalden]

Thanks a lot for your comments. You're right actually, I could just change my normal throttle curve so it doesn't go down to 0 and then release throttle hold to start. No need for any mixes. Only problem with that is I won't be able to soft-start again after landing until disconnecting and reconnecting the battery (remember my throttle hold only goes down to 17%, for fast auto bailouts). ...

I've got my curves for normal set to 0,30,30,30,30 with TH set to 14%. So, throttle hold cuts the motor, but allows fast spool up. If I land however in throttle hold, I switch back to normal mode, lower the stick and switch out of throttle hold. The ESC then sees a zero and re-enables soft-start.

BTW : I've got 30% because I use governor mode. So the 30% isn't really a throttle value - it just enables the first governed head speed.

[Downdraft]

Seems to me your way over thinking a problem that may never occur (not meaning to offend).

If auto bailout is high on your priority list for esc functions I'd suggest you change the esc for one with this feature, for example Kontronic has the facility and I seem to recall so do the castle Ice2 esc's.
Take warning though that if you allow the head speed to decay so badly that it can no longer create lift, flicking out of throttle hold back to full motor power may well strip the main gear and cause even more damage than a hard landing from incerficiant head speed.