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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?
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
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
The fail safe being sold at Technobots is under 20g easy. Its very small.
Mr Stu
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?
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.
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.
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
Hi
Is the Failsafe that is built in on the electrolise rc relay switches ok for use in robots?
Regards
Ian
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.
Good Point John, We use PCM but have to be very careful upon powering up to make sure the failsafes become active. The default mode for the PCM Rx we have is upon lost of signal to stay in the last good position until the Tx updates it after a few seconds. They are the best type around because theyre in the Rx. We still use other failsafes built into the mixer/interface in case a cable becomes unplugged or the Rx battery becomes flat.
Interesting point though as when we were going into the Arena at Series 7 It failed the quick tech check because the Tx had lost it memory and returned to its default settings. It was quickly fixed and passed the second check. FRA events currently only check this once at each event! If that had not been checked at Series 7 then we would have gone into the arena without working failsafes.
Thats the strange thing with those complicated PCM systems. They have a tendency to forget theyre settings and revert to some default settings. Its not the first time ive heard about this.
The default setting usually is something you dont want for your robot. The PCM receiver we used to have in TAN actually crashed and the robot ran off because it did go on with generating servo signals.
When I started out I used a simple 40MHz set and had the problem John describes. About once per minute on average, the motors would move a fraction as the system found a valid servo signal from random radio noise.
The solution I chose was to alter the failsafe to require four valid pulses within the last second before it would move, still technically possible but extemely unlikely.
Our first Rx was a Dual conversion FM set and I should mention that the failsafe in the mixer were designed for this one.
On our mixer it has two main features for the failsafes. The first is that it effectivly integrates the in incomming signal so that any valid pulses can only change the output by a small amount so a single error would at worst case only change it by a small amount.
The second is that over a long period (100 pulses) it counts the number of in-range & out-of-range pulses and if at any point it is more than 10 pulses in error then it will enter failsafe for a minimum of 2.1 seconds. It worked well until we started using the PCM set when it effectivly overrides this.
Once it has entered failsafe mode it will not come out of it until 100 pulses are received in range. The failsafes work on a per channel basis and also have a 65mS timer so that if that channel does not receive a pulse in that time it will shut that channel down for 2.1 seconds before trying again.
The only problem (from other peoples point of view) is that its my software code running it and so far we have not had it crash but occasonally it still entered failsafe mode. There is a watchdog active that has only one timer reset function in the begining of the main program loop so if it did crash it should correct itself after a very short delay.
I dont know how other failsafes operate but I would guess its not this complex.
All in all I still would not like to approch a robot in failsafe mode as you know it only needs to pickup a valid signal (from any source) and it could activate again.
On the latest version of my radio control software I put in a 28-bit keycode. My robot wont come out of failsafe mode until this is received, so no other radio controller could activate it. Nothings perfect though, as you say, you still have to approach it with caution.
Im continously developing the ultimate rc-relay. If there exists such a thing. The hardware has christalled out nicely, but i still have to do some work on the software side. Right now it only works on one of the two channels. The most important thing to test for is the perriod between pulses. If this is too small its a bad signal.
My relays require 4 pulses to flip over the switch, both for the on-off and off-on transition. If it detects a spike it ignores the previous 3 and next 4 pulses. Failsafe detection is similar to marks system. if 4/60 pulses are bad it failsafes. It only comes out of failsafe after 60 good pulses. If the perriod between pulses becomes too long the system inmediatly goes into failsafe.
This seems to be a relyable system. Yet the most dangerous situation which can occur is when the receiver is switched off and the system is expected to failsafe. Its my experiance that if the failsafe and filtering algorithms arent good enough the relay may trigger in such a situation.
Keep your distance if you turn off your transmitter, you never know what will happen just before your system failsafes :)
yeah and i use one in mine works very well never had a problem unless i damaged it !!!
i have tried 4or 5 switches now and this is the best
I know it sometimes happens with my pcm receiver that it goes back to the default continue doing what yo are doing setting if you turn of the transmitter too quickly the first time you attempt failsafe. The answer to that is to power down the robot and rx, start tx first, start rx is it has a seperate battery pack, or the robot if it has a BEC. and allow the TX to send its settings to the RX for 30 sec to a minute to be sure.
You should always start the receiver first with PCM.
The failsafes are normally transmitted during the first 10 seconds and normally 30 seconds thereafter. If you turn the transmitter on first it will transmit before the receiver is on.
As a helpful hint, the PCM indicator flashes on the futaba screen (Field Force 6) when the parameters are transmitted.