Failsafes (specifically in Feathers)

[kaideejee]

All,

Ive had a read through the rules and Im just wondering how people have managed to tackle the failsafe requirement? Im aware of the RC switches that are available but Id be after a low tech or at least self build low cost approach ideally. Is there any established way of adding a failsafe - specifically with featherweights in mind or am I limited to using an extra channel for an expensive RC switch?

[s8nsmum]

see the thread entitled

Safety Discussions » High Powered Feather Flippers

there are a few suggestions there but my advice would be to get the fs1 from technobots

[kaideejee]

OK so Ive been to technobots and seen the new failsafe which it appears can be used with servos, ESCs and I presume RC relays (tho theres a built in one on those too)

Does anyone have its weight to hand?

Cheers

-- Kev

[stu]

The fail safe being sold at Technobots is under 20g easy. Its very small.

Mr Stu

[kaideejee]

Just to revive an old thread, Ive begun detailed planning of parts for my developing feather, and along with removable links and LEDs and stuff, Ive come across the issue of how to failsafe the whole machine.

Basically, the whole thing will be run with servos hitting microswitches or actuator levers, or with RC relays. If I put a single high power relay in my circuit between battery and everything else, and trigger that relay with a servo controlled microswitch or with an RC relay, and just put a single failsafe between Rx and that servo/switch, would that be considered safe enough? Or do I have to have an explicit failsafe on each active channel?

If I can use this approach and I used an electronize RC switch to control the relay, would I need an extra failsafe or are the ones in the switches completely reliable? (seems a bit of a waste to control one relay with a 2 or 4 contact switch but its almost as cheap as an FS1 and certainly cheaper than FS1 + servo + microswitch).

Cheers all

-- Kev

p.s. does anyone know the coil power rating of some of the seriously high power relays e.g. 180Amp versions?

[maddox]

yes
Albrights use about 8W on the 24V coils, unless asked for faster or stronger ones. But experience learned me that the coils can take a lot more.On 36V my 24V coils dont even get warm after 5 minutes, and the higher the driving voltage,the faster they react.And thats good.

[jim]

Hi Kev,

I think you will comply with the rules by doing what you state above, although I would put failsafes on the other channels as well to make it less likely that your robot will go out of control due to a single component failure. I would strongly recommend RC relays over servos and microswitches.

[kaideejee]

Thanks for the info Mario - I was just checking what sort of contact rating Id need on whatever I used to drive the big relay.

Jim : It would be good to use RC relays (e.g electronize) but at £20 each it makes the servo/microswitch approach a cheaper way of starting out for the driving at least - Ill probably invest in one for the failsafe if I do as described above - important that that one doesnt fail after all. Its all down to cost - for example I could get rid of a huge rats nest of wires if I invested in a pair of electronize speedos but thats 80 quid that can go much further elsewhere.

Would you put a failsafe between Rx and RC-switch - e.g. the electronize 2x12A switch which claims to fail safe anyway?

Are there any cheaper, single contact RC switches out there? After all, I only need a single contact so two is just a waste, unless I decide to put power cutoff on one and some sort of light on the other to indicate explicit power kill.

Cheers

-- Kev

[terrorhurtz]

Note that the only really effective failsafes are the ones built into PCM receivers. OK, maybe not so relevant to a featherweight perhaps, but I would not consider operating a heavyweight without PCM.

All an external failsafe can do is check that the signal is within a valid range. If you get some interferance, but the bad signal is still within range, then the failsafe will happily let it through, firing the axe or whatever. Next to useless.

A PCM reviever can generally detect that the signal is invalid and block it.