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Member postings for Allan Bennett

Here is a list of all the postings Allan Bennett has made in our forums. Click on a thread name to jump to the thread.

Thread: And now for something completely different
11/03/2018 08:49:17

While I was learning I hovered in "normal" mode, with a throttle curve that went from 0 to about 65% in the first step, and then increased gradually to about 75% over the remaining steps (7-step curve with my particular transmitter). That gave me the safety net of being able to shut off the motor by banging the throttle stick to zero (more instinctive for me, as a fixed-wing flyer) rather than having to find the correct motor-cut switch. I also used a pitch curve which went from -3 to +10 or so degrees. I found the negative pitch was necessary to counter momentary wind gusts which caused unwanted lift.

As for what is likely to break: In my experience it was always main blades, usually main gear stripped of a few teeth, and sometimes boom bent. With torque-tube tail drive you will also strip the bevel gears whenever the tail rotor touches the ground. Strangely I never damaged a main shaft or feathering shaft, which other people seem to have problems with. Maybe those on my 500 are more robust than some other models.

10/03/2018 21:16:54

I wonder why the design of the lower gear set and its M2 nut and bolt differs so much from those on my T-Rex 500 and 550. In each case the gear hub has a deep nut-shaped recess so that one simply puts the nut into the recess, then holds it there with one finger while inserting the bolt from the other side with a hex-driver.

Thread: FrSky & Helicopters
04/03/2018 07:21:43

I have flybarred and fbl helis (TRex 500 and 550) running with Taranis and OpenTX. Fbl were easy to set up because all the clever programming is in the fbl controller (BeastX in my case); flybarred was a bit more involved, but not a big problem.

If you've already got a Taranis, I would say go for it. I use X4R receivers in my fbl helis and, I think, an X8R in the flybarred (away from home for a couple of days, so can't check).

Thread: Foamy repair?
24/02/2018 13:30:55

So long as it's the modern slightly-rubbery foam, such as Multiplex's "elapor" then boiling water or steam will restore its shape to a certain extent. But it will also give it goose-pimples which can be sanded down if you're fussy.

Thread: HS 2
24/02/2018 13:24:12
Posted by Martin McIntosh on 23/02/2018 20:45:55:

Now hang on a moment. The London undergrounds run every one to three minutes apart, so why does there need to be such a long gap between overground trains? The tracks do not exactly seem to be over used to me. If it is a power supply problem then this could easily be overcome. If they can allow aircraft to take off and land with a 45 second gap then why not trains?

Good point! Mainline trains can, and do, run at one-minute intervals under favourable conditions: Speed must be the same, speed needs to be high enough that the first train can get 2 or 3 signals ahead of the following one (i.e. over about 90mph in the area I live), acceleration capabilities need to be similar, no stopping or slower trains in the way, no trains crossing the track to go onto a branch line, etc.

Underground trains can run at short intervals because they run at much slower speeds than mainline ones and they're equally matched for speed, acceleration, and braking.

Aircraft can take off at short intervals because they're not usually following the same track after they get off the runway, so won't bump into each other.

Thread: Wing Tubes
23/02/2018 08:19:53

If the wing was originally designed as a one-piece, there's presumably enough strength in the main spar to stop it from folding. The length of wing joiner you need is therefore basically determined by the strength of the inner and outer tubes (so that one won't punch through the other), how tight the inner tube is in the outer one (to avoid slop), and what length you need to accomodate the retaining screw. The outer tube, of course, needs to be firmly attached to the main spar, in which case the strength of the ribs in that location is probably of little importance.

Thread: HS 2
23/02/2018 07:55:11

Having been involved in the construction of HS1, I would like to point out that reducing journey times is not the only aim of HS2: Most of the UK's conventional rail network is already overcrowded, with very little scope for the addition of extra trains. To run extra trains, extra tracks will be needed, so they might as well be "HS" tracks. And while we're at it, they might as well be built to European loading gauge so they can accomodate their larger carriages.

Hence HS2's oft-unappreciated objective is to free up the West Coast Main Line (and others) so that more stopping trains can be run on them. Whether or not it's still value for money I'll leave to others to debate . . .

Thread: Seagull P40 - weak bulkhead / poor design
17/02/2018 07:39:51

I haven't owned that model but, from other stories I've read, I'm not too surprised by the design/build quality of an ARTF.

But what does intrigue me though, is what on earth would cause the spinner bolt to shear? Presumably the prop stayed attached, but was it perhaps a bit loose so that a backfire would have caused it to slip? Doesn't explain the spinner bolt, even if that is the case.

Thread: A Question for the Electric Cognoscenti.
13/02/2018 06:54:46

I think that lvc is a bit of a red herring: Even if lvc wasn't active, or it was an incorrect value, the motor would simply have stopped producing any useful power long before there was any danger of the BEC failing to supply the receiver. Unless, of course, the BEC itself is faulty.

My suggestion is that the pilot hadn't realised the motor was no longer producing power (prop windmilling freely so it looks like it's running well), and too low airspeed resulted in a fatal stall. Motor failure could have been aided and abetted in this by a momentary wind swirl or direction change.

12/02/2018 09:47:53

As others have pointed out, letting the battery to run down to lvc, or even lower, should not result in the receiver losing its power from the BEC.

Asuuming that it was Ludovic who handled the take off, and you had no input until the fateful landing attempt, there's a possibility of some setup error in the buddy system. Did you check all surfaces moved in the correct direction, from both transmitters, before take off?

Thread: Lipo and LiFePO4 - resting voltage following charge
20/01/2018 07:51:36
Posted by Gordon Whitehead 1 on 19/01/2018 16:16:48:

. . . . In case guys don't know, it is possible to solder to the aluminium cases using normal lead solder and resin flux so you can readily make up packs to whatever configuration you want. . . .

My experience with A123 cells harvested from DeWalt battery packs was that they were quite easy to solder with a suitably large iron. They didn't need constant scraping like when I tried to solder to regular Nixx packs, which led me to believe their end caps are not aluminium. Checking with a magnet showed some attraction, which would seem to confirm this.

When harvesting from a batter pack you'll probably find that the cells all have spot-welded connecting bars anyway, which look like tin-plate, and are certainly easy to solder to.

Thread: Repair of crashed model
11/01/2018 20:36:23

In the picture I see two plywood side pieces, faced on their outsides with balsa. But the balsa extends further forward than the plywood. Will the firewall be attached to the plywood pieces, with excess balsa to be cut off? Or is the balsa the structural element, and the ply pieces are simply to hold it in alignment while you glue it?

With a brand-new front end like that it would be a shame not to make a new firewall. Maybe you can scrounge some suitable ply from a clubmate? Apart from having to drill new holes for the engine mount, and maybe for the fuel tank lines, there may be a problem with the glue if the old one has too much fuel soaked into it.

Thread: Considering going electric - advice rplease
11/01/2018 16:36:48

I started electric flight on 35MHz with brushed motors. My first conversion was a Flair Magnatilla, with a geared Speed 700 motor and 12 NiMh cells. While on 35MHz I found the most reliable way to avoid interference problems was to use a genuine opto ESC -- not the no-BEC ESCs that are often described as "opto" these days -- and a separate 4-cell NiMh battery for the receiver. The opto ESC isolates the receiver from all the "noise" generated by the ESC and motor.

Apart from that, I simply observed all the other good practices mentioned already by others, such as keeping receiver, antenna, and servo wires as far as possible from ESC, motor, and battery, and their connecting "power" wires. My equipment at the time was Jeti opto ESCs and Futaba standard 35MHz receivers.

Since going over to 2.4GHz I've simply replaced the NiMh Rx packs with stand-alone BECs, which get their power from the main flight pack.

Thread: Help needed with logic switches please
10/01/2018 16:10:15

Everything sorted. Thank you gentlemen.

I added extra channels to verify that they work in iNAV, and they do. Despite extra channels now being available, I've configured channel 7's down position to do what I want, with SH as the safety.

10/01/2018 08:51:58

Thank you Mike, that explains why channel 8 is wandering aimlessly, and unresponsive to any control, when displayed in iNAV configurator. I'll "unlock" the other channels this afternoon, and then maybe use Bob's configuration on another pair of switches so I can leave channel 7's switch as it is at the moment.

09/01/2018 20:42:48

Why can't I edit my previous post?

Just to say that your latest suggestion DOES WORK Bob! I'd forgotten to click the "ON" boxes against the SFs. Thank you very much.

And thank you to the others for suggestions. I'll certainly be looking to see if I can get more active channels, even though I've now got my "safety switch" working.

09/01/2018 19:44:21

Ahh, I've mis-read those instructions and set the transmitter channels to 8 frown

Apart from mis-reading, I didn't (still don't) understand the first statement about 8 channels by SBUS to UART2. So, how do channels 9 - 16 communicate with the flight controller?

Anyway, I'll try that tomorrow thank you. And, as I've mentioned a couple of posts above, I've also got a Plan B which doesn't require the switch override.

Bob, I may be misunderstanding a fundamental here: I've got ch7 specified as SE 100% in the Inputs screen and in the Mixes screen, and nothing in the Outputs screen. I've then programmed Special Functions and Logical Switches as you suggest, and SE is still able to move channel 7 to all three positions in simulation, irrespective of the position of SB.

09/01/2018 14:38:15
Posted by Frank Skilbeck on 08/01/2018 22:37:06:

Allan, can't help on your logic switch question, but aren't all Frsky Rxs 16 channels as the serial (SBus) port, can't you use this to map more channels to the flight controller?

Also is another way to do this is to use flight mode/phases and fixed values on channel 7 which change depending on the position of the flight phase switches.

Edited By Frank Skilbeck on 08/01/2018 22:40:45

This particular receiver is integrated into a multicopter flight controller board, FrSky XMPF3E F3EVO, and it's only got eight channels available. Unfortunately mine seems to be faulty because channel 8 doesn't work (I've double-checked that I've configured it as 8-channel in the OpenTX setup screen), but just floats around aimlessly when displayed in the iNAV configurator.

Bob, I've tried your Logic Switch + Special Function setup, but SB still doesn't have any impact on the 3-position action of SE. That probably means I've implemented it wrongly. The idea of setting up a couple of flight modes did cross my mind, but even after watching Open TX University videos on this, I still can't figure how to implement it.

I'm still interested in solving my problem, but in the meantime I've got another cunning plan: My arming switch is 3-position SG, with the up position being "armed", and the other two "disarmed". So I can use the middle position of its channel to activate the "Reset home" function. Ok, it won't have the two-switch safety functionality that I was trying to achieve, but once airborne I never use the arm/disarm switch so I'm unlikely to reset the home position by mistake. This way "home" will always be the location at which I arm the quad, rather than the location at which I power it up, which is the default situation.

08/01/2018 20:18:52

Thanks for those replies. Bob, yours does almost what I want, and if it doesn't it's because I don't know how to apply the logic result to the channel outputs correctly. I've assigned SE and your L1 to channel 7 in the mixes screen, but with SB in the up position SE stays at "off" when I it's in the upper or middle position, and goes to 50% when I switch to the down position. Then switching SB "on" (i.e. L1) SE goes to 100%. But your and Attilio's replies have given me a better insight into the functioning of the logic switches screen, so I think I'll be able to get where I want now. I had been bamboozled by the thee columns to the right of the ones we're using.

Just to unveil the mystery, this is for a quadcopter with GPS. SwE at the moment is "off" in the up position, and "Barometer hold altitude" in the mid and down positions. Another 3-position switch is "off" in the up position and gives me "GPS Hold position" in the mid position, and "GPS Return to home" in the down position.

"Home" is normally defined automatically as the position the model is when it's powered up, but there's a facility in the flight controller to re-set the home position to wherever the model is at the time. I want to take advantage of that, but want to ensure that it needs two simultaneous switches to avoid any accidents. I want to use the "down" position of SwE for this function, with spring-loaded SwB as the "safety". The problem is I've got no more spare channels available in my receiver, so I need to use the same channel (#7) that SwE is controlling.

08/01/2018 16:28:10

I wish to program a safety feature so that nothing happens when switch E is moved to the fully down position, unless switch B is also fully down. With both of them in the down position I want switch E to be able to act as normal in all three positions, but without switch B down I want switch E to be restricted to the up position and the middle position only.

Can someone please help me achieve this. I'm sure it's quite simple, but I still can't get my head around the logic programming page in OpenTX Companion.

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