Rigging A Failsafe

hi im very new to the robot world although i have really been into robot wars with all the videos and stuff anyway, im planning on building my first robot (heavyweight), buying tools that i havnt got and then buying motors, speedos, batterys and build the chassis so i get an idea of the right size.

Anyway what im wanting to know is the best way of rigging up a failsafe system. as i have no idea. ive read other threads on this but get confused, can any of you give me an idea of the best way?

If possible i want to build my own failsafe, as i am quite skilled at electronics.

Cheers
Danny

Failsafes are not a particularly expensive component, so I imagine youre doing this because you find it an interesting project or the existing systems dont meet your needs.

First, do you know what sort of speed controllers you will be using? Some have failsafes built in, and different types have different input signals. Most types need an interface to connect to a 40MHz remote control system - and this interface may have a built in failsafe.

Failsafes are simple devices and standard ones are available from model shops. These type just plug in between your Rx and speed controller/servo. Some speed controllers such as Vantecs and Robotechs have them built in so you dont need them on the drive. If you use a seperate Rx channel for your weapon then you may need one, but Rx relays such as the Electrolise (have a look at http://www.technobots.co.ukhttp://www.technobots.co.uk). If you are skilled at electronics then building one of these which simply switch a relay on with an Rx channel would be where to start. I built one with a MOSFET in place of the relay although I dont use it on any of our robots.

I use PIC chips for the bulk of my stuff.

I would be glad to help but I suggest you get yourself to a live event before you purchase anything and have a talk with roboteers. Thats the best way to learn and aviod making the same mistakes as we all have done while building.

Tip for the forum: Dont visit the Power Light thread :) Its enough to confuse anyone

Just looked at your website, and noticed you are planning on getting the Pro 120 speed controllers *at this point everyone else knows what Im thinking about saying* but just for your benifit I would be careful in your choice as Ive learnt the hard way. I sent 3 off to be fixed last month and we have 3 in our robot and have 4 spares just in case. Some people dont have any problems with them but whatever the reason we do. Having said that we are still using them.

Im assuming the interface/mixer you are talking about is the 4QD one. Is this the one that requires servos to move pots? If so Id aviod that one, there are much better ones out there. I built my own and this provides the failsafes.

are you saying the 4qd controllers are crap, what have you learnt the hard way.
danny

On average one breaks every 2 meets. If we get say 8 fights in a meet then thats an average life of 4 hours per controller. It might just be our setup that causes it. Other people have gone years without troble. Its your choice as to what to get. They are cheap and if you can afford a better controller then it will be worth it.

Our first robot used 4 of them back at Series 5 and we simply reused them in the new design. One thing we did throw away was the 2 DCI-111(?) Mixer boards we had as they kept setting one of the speed controllers to full speed every now and then. Instead we used Derick Foxwells mixer boards until I made one. Still got 2 of them somewhere but I took the Opto-isolators off one to use on something else. We only used these twice at series 5 and have been in a drawer since.

If we knew what trouble we were going to have then we would have choosen something else, but its kind of hard for us to change now as the robot was built around them. What 4QD say is that they will last alot longer if we dont turn the acceleration/decel setting to minimum. Maybe we will try that one day and suffer with slower response.

Yep they are crap

urmmm,
1, if 4qds are cr*p why are so many peaple using them.
2 what other speed controllers are ther, no way can i afford vantecs.
i need cheap, im only 15 years old and dont work full time.

Taken from Techobots web site.

4QD pro 120s £130 Each + 4QD mixer £42.53
Total: £302.53
RoboTech £395.95

What isnt clear is if you need failsafes for the 4QD mixer and this is the cheapest configuration that will work.

So for just an extra 23% cost you get the best out there so far. Its simple to wire up, only one box + Rx and has builtin failsafes and more functions than any other contoller out there. Oh and its lighter!

Your choice. If you want really cheap then you could even make your own (check out OSMC in google) but if it doesnt work first time it will probably end up costing more.

Also Keep your eye out for second hand Vantec speed controllers on this fourm so far i have brought 2 one for £350 and one for £250. I personally think they are still one of the best controllers available but i havent tried the Robotec of course.

The Vantec and Robotec both include failsafes and mixers so they can be pluged straight into your Reciever.

i really would like the robotec but if you get an axe thru it or it fails thats 400 quid down the drain,

The three 4QDs we had fixed cost us just sort of 100 pounds. Dont know how much it costs for the robotech though. You would have to find someone whos had one fixed. If you dont want an axe through it put some extra armour around it :)

If you are thinking of designing your own failsafe, have a look at one of my webpages all about the subject:

http://homepages.which.net/~paul.hills/Circuits/Failsafe/Failsafe.htmlhttp://homepages.which.net/~paul.hil.../Failsafe.html

It describes how to make circuits that do fail safe. This includes what happens when transistors and other components fail. Failsafes that cannot cope with any single component failure in their circuit contradict their names!

This is where it gets confusing :). Failsafes for robots dont have to failsafe! Well, at least in the sense that if they go faulty they dont. There purpose is to stop the robot when there is a loss of rx signal when all the other electrics are working correctly so failsafe is really a bad name for them.

The ultimate system would be as in pauls web site that would bypass everything and cut main power. You could simplify the RC detector circuit using multiple micros. I did make a RC to 0-5V circuit using opamps to drive a 4QD a while ago that worked on a pulse by pulse basis using an integrator, sample & hold circuit. It could be used to detect out of range pulses by 2 comparators on the outputs and could be modiifed to act as a true failsafe circuit but it would be complex.

Another point that didnt really affect big nipper but since we started with feathers noticed the delay in some failsafes / controllers. For Axes, Flippers and other fast weapons Ideally when we press the button on the Tx we want it to fire the weapon instantly. On the other hand if a single interfenece pulse appears this would also fire the weapon and no one wants that. So in practice the RC Relay will count a number of pulses from the Rx and if they all say fire then it will fire. This can add a significant delay by which time your opponent has moved out of the way. If you use a PCM Tx & Rx then it has its own error checking and failsafe (which they dont publish tech details of) which dont introduce much of a delay and you can reduce the number of pulses before the weapon activates. Its all trade offs and in some cases safety is reduced so we have to be careful.

Some good points there Mark. My site describes the maximum lengths you can go to. It is possible to do less of course.

As your last paragraph points out, unless you have a PCM radio set, or use one of the 459MHz telemetry modules, youre going to have to live with delays if you want a fully safe system.