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Posts to stop the model flying away (restraints and safe practice)


Mitchell Howard
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On 07/05/2021 at 19:26, Don Fry said:

Arrrrrrrrrrrrrrrr, Matty. But the point is, is the setup stable, throttle on or off. It’s got nothing to do with if the problem is vibration, or electronic.

If it leaves the ground, it has to be landed. It has to be checked.

 

Not sure I fully understand your post above tbh, but in summary:

  1. I am not disagreeing we should always do a range test for a new model, and periodically at least every few sessions too
  2. I am not disagreeing that the failsafe should be tested on the ground before flight
  3. I am only wondering whether there is a need anymore for the range test and failsafe test to be carried out with the motor on for brushless electric models guided by 2.4 GHz radio.

Rationale for point 3:

  • I have seen plenty of instances where and IC model or (brushed) electric models on 35MHz exhibited a loss of range/control issues in the range test with the power source running. However I have never seen that in ~10 years of flying and watching brushless electrics on 2.4GHz.
  • For the failsafe test on an electric model using spread spectrum radio you are not proving anything additional by testing with the motor running vs. not. If the failsafe is set wrong the motor will jump into life irrelevent of what it was doing before the signal was lost. Similarly if the motor was off before and the failsafe is set correctly it will stay off, and only the flying surfaces will move to their pre-set positions.

I can understand the average club safety officer will feel more comfortable seeing a motor running and then cut under failsafe, especially given they will also be checking IC models where you need to see the engine will cut fully under failsafe. For that reason I'm happy to demonstrate it that way when required, but when flying on my own (which I do a fair amount) I feel there are more dangers in range testing and failsafe checking motor on than doing so motor off and relying that it more on the telelmetry (which I now have in all my models).

 

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Whilst I personally always do a range check for every model at the start of a flying session the handbook says that it is only necessary if changes have been made since the last session or range issues have been experienced.

 

Regarding the failsafe and in particular IC engines, I don’t believe that they have to fully cut, in fact it makes far more sense for them to go to tickover thus giving you chance to recover control if the signal is recovered.

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1 minute ago, Ron Gray said:

Whilst I personally always do a range check for every model at the start of a flying session the handbook says that it is only necessary if changes have been made since the last session or range issues have been experienced.

 

Regarding the failsafe and in particular IC engines, I don’t believe that they have to fully cut, in fact it makes far more sense for them to go to tickover thus giving you chance to recover control if the signal is recovered.

I agree Ron,

Electrics cut completely and ICs to a reliable tickover for the exact reason you said.

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6 minutes ago, Gary Manuel said:

I agree Ron,

Electrics cut completely and ICs to a reliable tickover for the exact reason you said.

 

I tend to agree, but have seen several safety officers who were of the opposite opinion and were not prepared to negotiate on the point!

Edited by MattyB
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30 minutes ago, MattyB said:

 

I tend to agree, but have seen several safety officers who were of the opposite opinion and were not prepared to negotiate on the point!

 

That might be due to local club rules Matty, which of course any club is entitled to apply. They may have taken the view that if a member of the public is going to be hit on the head by an out of control model, it would be better if the engine wasn't running. I can see both sides of the argument but I believe that recovering the situation by allowing the engine to carry on running and avoid the impact is the way to go (it's also the officially prescribed way).

 

The BMFA Handbook (citing CAP658) states that:

For All Model Aircraft

Any powered model aircraft fitted with a receiver capable of operating in failsafe mode (i.e. PCM receivers, Digital Signal Processing (DSP) receivers or 2.4 GHz equipment) must have the failsafe set, as a minimum, to reduce the engine(s) speed to idle on loss or corruption of signal.

This means that you will have to carefully consider what type of receiver you are using in ANY i/c or electric powered model, even the smallest.

 

It then goes on to clarify (and emphasise the difference between IC and Electric models!

Electric Model Failsafes

The setting of the failsafe to, as a minimum, reduce the engine(s) speed to idle, obviously applies to all electric models too. However, given the ability to re-start the motor(s) at will, it makes sense to have the failsafe cut the motor(s) completely. This will give you the desired ‘minimum power’ situation and will avoid you having to decide on what idle speed you might need to set.

Edited by Gary Manuel
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Matty B, re your post of two hours ago, and a slight argument with Andy 48, my rationale motor on, motor off, is the parameters are different and must be explored. I agree modern equipment had better interference rejection, but I have not seen a written guarantee that it will not care if the motor is on or off, therfore I will test it before launching it, electric or IC, rather than relying on telemetry to tell me I have a problem after the wheels leave the ground.
Is that not standard engineering practice, minimize the unknowns. 

If I’m being a bit OCD, so be it, but a simple statement that you haven’t seen this in 10 years has no relevance when the bite end of a statistical distribution curve, savages the backside.

I haven’t used quote, entry would get too long. 

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42 minutes ago, john stones 1 Moderator said:

 

? Elaborate please.


Just that the Officers in question expected all motors (even IC) to  cut during a failsafe event, presumably for the reasons suggested by Gary above.

 

Edited by MattyB
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4 hours ago, Don Fry said:

Matty B, re your post of two hours ago, and a slight argument with Andy 48, my rationale motor on, motor off, is the parameters are different and must be explored. I agree modern equipment had better interference rejection, but I have not seen a written guarantee that it will not care if the motor is on or off, therfore I will test it before launching it, electric or IC, rather than relying on telemetry to tell me I have a problem after the wheels leave the ground.
Is that not standard engineering practice, minimize the unknowns. 

If I’m being a bit OCD, so be it, but a simple statement that you haven’t seen this in 10 years has no relevance when the bite end of a statistical distribution curve, savages the backside.

I haven’t used quote, entry would get too long. 

Basically,  you are suggesting that your crude ground range test with motor running and not running is better than a standard range test followed by monitoring and recording the signal strength every part second of several test flights going out in every direction and at all sorts of different heights as far as one is able to fly. On top of that you are suggesting that your ground range test is better than getting a signal strength warning on every flight long before a loss of signal?  I don't need a written guarantee from elsewhere, I have one instantly from the telemetry of every single flight I've made.

 

Going onto your minimizing the unknowns, components in a receiver can begin to fail in time, or even after a hard landing and  component values can drift. On the OCD scale one should do a range test before every flying day for this reason. However, telemetry is constantly monitoring that on mine and an unexpected low signal strength indicator gives an early warning of this. I have actually had this after a hard landing, the loss of signal strength being not enough to really show up on a range test, but enough to affect overall range. Better safe than sorry and the receiver got binned.

 

Your crude range test still has plenty of unknowns, and walking 30 metres is far far less than the 130 metres I range test to, even though my transmitter reduces the signal by the same amount as others on range test. At one time it was the best we had. Today we have far better. Our flying site has a microwave link running directly across it. Would you like to tell me how your ground test ensures that you still have an effective signal strength flying through it? I sometimes get a low signal strength warning when I fly through it. I have to be exactly at the right height to do this, as it appears to be a narrow beam. I can look back at the telemetry and see these low peaks and just how low they get. Thankfully they never get anywhere low enough to lose the signal, but they certainly did with 35MHz gear, and my first Spekrum radio.

 

Incidentally if I do get a low signal strength warning, I can double that distance away from me before the plane will go into failsafe. That is quite some safety margin. I know my system and trust it.

 

 

Edited by Andy48
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On 07/05/2021 at 20:18, Gary Manuel said:

I have test flown models for other people a number of times. On at least two occasions, when I have done the fail-safe test the engine has revved up to full throttle rather than cutting. Thank goodness for model restraints is all I can say!

 

The cause of this was a simple mistake. Binding with the throttle channel initially reversed, then reversing the channel to correct it, but failing to rebind in order to reset the failsafe.

 

On the other hand, I once almost had a very nasty accident due to use of a large version of the type of restraint linked in the second post. I had been doing some work on the tail wheel of "Dusty" as per my Avatar image, with the tailplane resting on top of the restraint to allow the tail wheel to dangle in mid air. Some time later, it was time to have a fly, so I flicked the DLE55 into life, the model moved slowly forwards, but instead of being restrained, the tail dropped off the restraint. The spinning propeller was now heading directly towards me! I managed to jump backwards without instinctively putting my hand in the prop and finished up in a sitting position with the propeller heading towards my meat and two veg! I managed to get one foot onto one wing's leading edge and the other foot on the other. My manhood was safe but there was a problem. I couldn't quite reach the transmitter because I had jumped backwards away from it.  All I could do was shout for a fellow modeller to pass me my tranny (or wait for it to run out of fuel), so that I could hit the kill switch. A day I wont forget I can tell you.

 

Sounds like this should be in a 'tales from the flying field' ebook! For helping learners, collated for educational purposes by the BMFA of course!

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I believe that an electric motor should be running for a failsafe test, certainly with some makes of radio, because one of the failsafe options is for the receiver to stop sending pulses on loss of signal.

I have ESCs which, in this scenario, will carry on driving the motor at whatever speed they were running when pulses disappeared. 

So rather than identify which combinations of RX and ESC fall into this trap, it's much easier to test every setup. 

Restrain model, open the throttle a little then switch off the Tx. 

For me, only then do I have confidence that the complete setup will do as I expect. 

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I usually set up my electric model fail-safe in my workshop with the model restrained on my model stand (usually without a propeller fitted but not necessarily).   As Chris says I run the motor as well as hold controls at some extreme position before switching off the transmitter (my Horus hates that because it 'knows' there's a receiver still connected and I have to insist!).  My usual fail-safe condition is all controls neutral and motor off.  It's an easy and quick check and well worthwhile doing.  I choose the neutral control option because it offers the best chance of recovery from a brief signal loss though, I've never experienced a problem in actual operation ... so far .

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TBF his question was answered within 4 replies but as he also mentioned he was going to take his A test associated information re failsafe and range testing have crept in which may, or may not have been better in a separate thread.

Edited by Ron Gray
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16 hours ago, Ron Gray said:

Where's the harm in the range test that Don is suggesting? 


There’s no harm in a power on range test, some of us are just not convinced it really adds anything vs a power off test if you are using brushless power and 2.4Ghz with signal strength telemetry. Of course I will demonstrate it that way if flying at a new site to comply with any local rules, but don’t use that method normally as a) it’s tricky on your own with a model without an undercarriage which most of mine are, b) like Andy I have telemetry in every model, and c) I’ve never had an instance when a brushless setup controlled by spread spectrum radio showed reduced range power on.
 

@Chris Bott - Moderator’s point is a good one though - I had forgotten the “zero pulses” option was available as I have only very recently started to play with the odd multirotor (which is the only model type I’m aware of where that is the recommended setting). If zero pulses is set it’s correct the motor could continue to run, but you would still pick that up in a motor off test because none of the other surfaces would move when it went into failsafe. If seeing that motor stop makes you more comfortable though by all means do it that way - tbh I may change back to that now I have a few models setup with the zero pulse option ?.
 

PS - How do you restrain a 1.5” Tiny Whoop multirotor for the failsafe test please?!! ?
 

Edited by MattyB
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28 minutes ago, Andy48 said:

Tent peg.?

That would certainly stop a flyaway...! I did see someone with a Phantom once bungeeing it to a table to test, ‘’twas quite amusing to watch as they kept twanging free but he did get there in the end!

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