Links vs. Switches - How to Choose!
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- เผยแพร่เมื่อ 2 พ.ค. 2020
- Links and switches. What are they, how do you use them, and which is the best choice for your design? In this video, I discuss everything you wanted to know about links and switches (and more!).
Fingertech Robotics: www.fingertechrobotics.com/
Team Whyachi Switches: www.teamwhyachi.com/switches.html
If you're new to Combat Robots, check out my getting started guide: • Combat Robot Resource ...
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Good video, though as you guessed people are going to weigh in, so here I go! I will preface and say I'm in the UK and we have to use Links!
- Main point for me is you can clearly identify when a machine is dead when using a link as you hold the thing that will arm the robot in your had. Power lights can fail/be damaged and short of putting the Allen key back into a switch and turning it, you can't tell at a glance if a machine is dead or not.
- The last point on 'having to hold the robot to put in a link'... if someone is doing that they haven't mounted their Link properly. We have 4 links to put in on our Middleweight, and 2 on each of our FW's and we don't have to hold the robot to do it.
- I know people comment about G-Forces being able to dislodge Links due to the shocks involved. Again, you can avoid this by keeping the mass of your link to a minimum, and having pairs of links for the same system if needed. In Robotwars, Smash was launched completely across the arena and also into the ceiling before dropping into the trench... no links were lost and in the second scenario there was 8 links in the robot! (4 Top, 4 Bottom).
All of this said, most of this is a mute point on both sides. The most dangerous time is when you are Arming your robot, and the fact that I've seen teams in the US/China arm up standing next to their machine just makes me cringe. Link or Switch, you should arm up over a barrier/wall. If its in the arena and its locked, your safe. If you're pulling the link out that should mean it was safe to approach and disarm, again this should be over a wall unless the machine is immobile.
On a more comical note, but no less true... you can't lose a switch :-P The number of times I've had to scramble around trying to find a link, despite bringing 10 of the things and only needing 2... yep, that is a problem Switches don't have. Unless you misplace the Allen key...
Feel free to question my logic. I genuinely like having these tricky conversations if it helps us find better solutions!
One factor not discussed is space necessities. In the insect classes, specifically antweights, spare room is at a premium. With those little finertech switches you can put them in a tiny nook or cranny. Plugs will fit too, but then you have to have space for your fat fingers to reach in. The best space saving plug I've ever seen the guy used a JTS plug and needed a pair of micro needle nose pliers to put in on or take it off.
it's also worth noting that over here in the UK, switches are only banned in classes above 150g, and we don't run a 1lb class at all, with beetle being the next class up (where space isn't at such a premium). In our 150g class, slide switches that can be used with one hand are allowed and are used very commonly and effectively, and if placed with some thought, generally have little to no issues outside of taking a direct spinner impact.
This is a very fair breakdown and, while its fun to watch things get heated and I do have quite a long-standing opinion on which I prefer, its good to feel like there's scope for a proper discussion.
I have no choice but to run links, but even if I did have the choice I would use them anyway. Maybe if I had started building in the US and was used to using switches, I would think the opposite, and I don't see a big gap between the two in all but the most extreme/unlikely circumstances. I really value the fact that I don't need a tool to power down (the fact that anybody can walk over and pull the link post fight keeps things moving nice and quickly at events) and the low cost (an insectweight switch isn't hugely expensive if you're doing a competitive build but could easily be more than 10% the cost of a low budget first robot). I also worry about the much greater potential for serious external damage to make a switch inaccessible, which I realise is one of many fringe-cases that many people might choose to not worry about but having had an incident like that with an antweight (where we do allow switches) its something I'd like to avoid simply because it annoyed the EO.
Your point about emergency situations is completely valid, but I do think that links can offer a small advantage when it comes to dealing with issues on startup - if you're activating and, for whatever reason, the robot starts up you are going to get your hand out of there as fast as you can and bringing the link with you. This isn't a common situation and not one that would really make you pick one or the other, but a nice bonus if links are your choice. Your point about how people sometimes power up with a link is also valid and I like the idea of being able to turn a switch with one hand and no actual contact with the robot. As is, I trust my link placement, my weapon lock, and my own ability to follow a good startup procedure to combine and keep me safe, but if I were dealing with something bigger than a beetle that could easily become a persuasive enough concern.
Overall, I think the real elephant in the room when it comes to links is the fact that so many link failures are surely avoidable. Even as a total newcomer, I've never had a link come out in a fight and that's not for a lack of powerful opponents and big hits. People seem to make the link an afterthought and then view losing fights because of it as an inherent problem with the system rather than a consequence of their design choice. It feels like the fact we have an accepted, 'good enough' solution to making a link in the UK has stopped people trying to make it better, and the only people I've seen try to innovate was an international team who approached the problem with fresh eyes and found a new (and IMO better) solution. Whilst I can see why people are against adding an extra failure point to a robot,I honestly believe that if more people started using them we would quickly see new solutions developed which drastically reduced the amount of failures we see.
I feel cheated, you didn’t once discuss how much current these device make using a thermometer to show us. The debate lives on!
Hi, Robert! Yeah, you're right! I didn't see any bananas for scale, either...
these devices dont make current. they literally just turn on and off. Switches are very slightly resistive but its only on for 3 minutes tops. This is not at all an issue with them.
while watching this video, I liked the fact that both the Whyachi switch and links can be inspected for pitted (high resistance) contacts.
All very fair and sensible. Thanks, Robert!
General disclaimer: please note - the following Comment relates primarily to HEAVYWEIGHT bots. I have no experience with the lighter weight classes.
I think that links gained a following in Britain during the Robot Wars era because they were cheap, simple, and the machines lacked the lethality of today's kinetic terror-bots. Any studio-floor safety-guy could kill any bot bare-handed - no tools required.
One nice point about a link is that you can SEE when a bot's safe. A switch could be left on - slightly - or the switch itself could come loose, making it very hard to kill a bot without either some wire-cutters or a bucket of custard.
Having said that, it's hard to imagine any situation where rushing up to try and disable a bot gone berserk would be better than simply keeping clear till it died of natural causes.
Remember Deep Six in the BattleBots test box?
(It's kinda like men who claim that they need a really powerful car 'to accelerate out of trouble'. Tosh. More speed and charging ahead won't help. Unless you're robbing a bank, just hang back, slow down or stop. If overtaking is risky or dangerous, don't overtake. Nobody'll die. If too much testosterone and machismo keeps getting you into dangerous situations, maybe it's time to sell the car and get on the bus.)
When I built my first bot [1987 in England] we used links. Ant-weight, beetle-weight, and other teeny-weight robots didn't exist; it was all crude, heavyweight stuff back then. Weapon motors were so feeble that you could stall and stop them with a bundle of rags or the sole of a heavy boot - yes, really - so disabling an old-school bot with a spinning weapon was laughably easy. Links could then be yanked out even if the whole darn robot was on fire.
If the drive wheels were running flat out, you just let the bot run into the nearest wall and then jumped on it to grab the link. Pneumatic flippers sounded scary up close, but links were always at the other end of the bot and still good enough to make them safe.
As bots improved, quite a few Robot Wars fights were spoiled by links falling out (well, actually they were jolted out with some force, but the end result was the same). Radios weren't 'smart' and didn't have a fail-safe function, either. The programme producers didn't keep up with the times; I think sticking with links was a mistake. But... it was the BBC after all, so no big surprises there.
For today's larger bots, I think switches are more practical. True, it's easy to not-quite turn off a bot, and it's also impossible to be certain what state it's in if the LEDs stop working, but today's machines are frighteningly powerful; the physics involved is astonishing, and a properly-mounted [sic] switch is more resilient than a loose link considering the G-forces involved.
Note: this means that 'the show goes on' at the expense of 'whoops, the silly old bot's accidentally turned itself off'. If safety comes second to stopping a fight prematurely, using switches becomes more of a money i$$ue than a safety issue.
But... Cars have ignition switches. Racing cars also have emergency kill buttons (like the big red button on body-mangling workshop machinery) which is more of a link than a switch. Maybe there's a case for using both switches AND links in today's bots.
I can see links still working with some of the smaller weight classes, but I like the idea of having a standardised switch for heavyweights. One size fits all. One tool fits all, like a drum-tuning key. As Robert says, if a bot like Copperhead or Cobalt is out of control in the arena, don't make it angry - just stand back until its batteries run flat. Sure, it'll mess up the TV filming schedule, but that's better than losing digits, limbs, or even a life. No need for any heroics.
I've no idea how reliable a switch's on/off lights are, though. That's important in the pits and that's where a link has the advantage: if it's hanging on a hook you know that the bot's definitely dead.
I like having all my links on a carabiner when not in use. Means I can't loose them! :-P
If there's batteries in the bot then you treat it as if it's live. Same as pneumatics. The switch is only there (in the pits) for long enough to button or unbutton the bot.
One minor point on the links side; for our low-end uni comp, we went with a standardised link as the spec, and confiscated the links during the competition itself so people had to request them from the EO if they wanted to power up their robot for any reason. Obviously they're not hard to fabricate on the fly, but it adds a layer of control. Also, correct me if I'm wrong, but I feel you should generally power up prior to removing the weapon lockout, and the weapon lockout then should be removable without touching the robot? That way you can verify it's under control before making it dangerous.
I am DEEPLY offended that you did not discuss something. lol
I watched the entire video and forgot to take a nap. Thanks for all you do and sharing your knowledge.
I mentor FRC robotics and every few years the team decides to put the cutoff switch in a "convenient place", and as is my nature, I walk by and drop a ball on it. It's moved 10 min later.
i prefer switches but i think both should be allowed. i used a link when i was in the uk with no issues but would have preferred to use a switch.
Personally, i think the issue you raise with turning on a robot is correct in that as a tech checker i would feel extremely uncomfortable with a robot that can not be armed up whilst sitting on the floor. Also yeh, never touch an out of control robot.
Personally, all of my robots can be armed up with 1 hand. In fact as a solo roboteer i frequently do this as it means i do not need to place the Tx on the floor. All my robots use a different method for keeping the link secure, and it really depends on what i am working with as to what method i use. I think the only robot i have where i place my hand on the robot itself after arming up is Resistance, which has a little door to keep the link secure thats turned by a finger (though in most fights i have not used it).
One method that works surprisingly well is just have a really long wire that i can pull outside the robot to attach the link, then tuck it back in after arming up. The low mass of the link means it just rattles around in there and doesnt really pull out because the whole wires not mounted to anything (thus no transfer of shock). Thats a stupidly low skill method to secure a link - though luckily the robots i use that on have a load of space.
I totally agree with you on people reinforcing the link - you shouldnt zip tie it etc. You can get some locking style connectors which are great if thats what you really need, but really the best way to lock a link is by using its positioning within the robot. Ive showed people before how my HW has a link which turns 45 degrees when not being pulled by a rip chord, and that locks the link nicely under some bodywork and any shocks need to go through 2 axis simultaneously to make that fail. Whilst that needs a hand inside the robot to set up, you remove both hands before actually putting the link in.
Anyway, the personal issues i have with switches are the following scenarios.
1) Switches are more likely to fuse on, and have in the past - i realise you covered this. But i have had to "defuse" a robot before by taking the battery out, and honestly that was the single most concerned i have been in doing safety tasks on a robot.
2) Switches require a key, should key be lost the robot cannot be disarmed. - i realise most Switches are standard, but theres nothing stopping someone building their own switch.
3) Should a link get knocked, it comes out and thus fail safes. Should a switch get knocked, it may not line up with its hole any more and thus the robot cannot be switched off - hence fail kill.
4) Switches by direct hit can potentially become unturnable, links are more likely to either fail-safe or remain usable. - not the biggest issue, but ive seen it where the surrounding plastic took a hit and its a consideration.
5) In an emergency situation, links are quicker to use than switches. - Note i dont mean if your trying to catch an out of control robot. But say theres a fire and we need to turn all the robots off, switches can be quite a few seconds
6) Links can be used by anyone, switches require the operator or someone with similar key
7) Should robot fail on startup, switches require a second and for the key to be inserted to switch back off. Links effectively tether a robot to within a certain distance of the operator (and in smaller classes some would pop straight out if the robot drove away) but also the operator naturally removes the link in the process of removing their hand from the area of the robot under fail conditions. - As a note, ive had it where the Tx accidentally had the weapon on as i armed up. In my panic as i jumped back, i naturally pulled the link out.
8) Should the power lights fail, links provide an easier visual inspection for a marshall to note wether a bot is deactivated or not.
9) Similarly, even when not in view of the robot a link provides a visual identification for the deactivation of the robot - whereas a switch requires the roboteers word. - there was once an incident in the UK where a switched robot was left on in the pits and scarred people when the roboteer used another robot at the arena. Its highly unlikely people forget their link inside the robot.
Overall, i dont think Switches are "Dangerous". I just dont think they are the best option, and given how crucial the power cut off is inside a robot - i dont feel we should be accepting of 2nd best. Now if someone in a developing country that was looking to run a safe event asked if they could use Switches - yes certainly, you have bigger issues to worry about. But somewhere we have been doing it a long time and should really be ironing out the small problems that could have potential consequences - i dont see the value in the risk. I think for things smaller than 1kg a switch does make a better solution, as we start to introduce some safety concerns with the link (the robots so light you may need to place a hand on it, etc). Its just for things over 1kg, maybe BWs have a good debate but i dont see any reason above that.
For some reason, I kinda miss Brobert... Excellent video as always!
one thing I notice you didn't mention, in effectiveness (outside the inrush current issue), is a potential shortcoming inherent in using a screw. Namely that threads can snag, or heads can strip or shear if overtightened or otherwise mistreated. In this case, the failure mode could be much more severe than a link, in that the failure mode could quite easily leave the robot powered up. Granted failsafe check should help in this scenario, but it still means someone has to open up the bot and pull the wire to shut it down.
Personally on big bots I use switches for the obvious performance advantage of not having the bot turning off in the middle of a match.
But there are two safety related scenarios where switches are worse:
1. The switch coming loose in the bot, I've seen this happen, taking apart a live robot (with the weapon lock in) in the middle of the arena.
2. Knowing for sure a robot is off and can't come back on. A switch like the Whyachi ones could easily be left in a not all the way on, not all the way off position. Or could be just left on when a bot is pulled out of the area, say the power indicator light has failed, the bot isn't responsive to control input, but is still powered on. Also note power indicator lights are not required by Battlebots and last season they had arena staff turn off bots.
Obviously there are other safety measure that we have, but similar to fire arms relying on the fail safe isn't the right mindset.
As far as only having 5 minutes worth of battery goes, certainly not the case in the couple times I've seen this in person. Just spinning full speed is pretty low load compared to an actual fight and bots have run for a long long long time without running out of power. If leaving the bot there spinning the safest answer sure. And events have time tables they need to follow. Should there be another solution to a human going into the arena absolutely yes.
did invader (megabyte) fail and had to wait a long time for it too spin down, ?
To be honest i think the main reason links have a reputation of turning off mid fight is because there is no commercial solution. If there was a $10 "mount this in and forget about it" solution like a switch with whyachi, then Links are no less failure prone really. Personally only time my link has failed is when i done something stupid (i once used the wrong link for example), but i take time to design them and make them work - others just put a link in and pray.
Personally, if everyone had to make their own switches - we would be seeing alot of failures from people who dont factor in the requirements correctly.
A little concerned, that lacking an example of of a wiring harness, someone is going to plug a link into their battery. Don't do this boys and girls!
Darwinism at its best lol
I've been more strongly pro-link in the past, and myself have never had one fail, but I've heard a few insights recently that have brought me more towards the center.
I think links have more of a bad reputation due to how much easier it is for a poorly designed one to fail, as well as how obvious it is when it's the failing component. There are tricks I use to protect my links (mostly out of reach of other robots, spreading the pins inside to make it a tighter fit etc.), but there are a lot of people who see them as afterthoughts. The standard "connector" link seems to have been one of those things where something quick and convenient was made the standard, but it doesn't really have to be. The main requirement of a link is that it must be easily accessible, and removable without the use of tools. Many links pop out when a linear force is applied to them in one direction, and designing your link in areas where it''s unlikely to receive these forces already increases success rates greatly. If you were to design a link that required two simultaneous forces in different directions to remove that didn't short out until removed completely, you'd have something just as reliable as a switch with all the safety of a regular link. It feels like the European scene is one brainstorming session away from having the "Fingertech switch" of links available if you absolutely need 100% reliability, though I'm still personally OK when using regular old XT60's with the usual tricks done with them.
I do believe that most bots have links that can be removed without touching the machine in dangerous positions, but I acknowledge that this is a bigger problem in insectweights where it's likely that you could support the entire machine on the link. I think that the better debate to have for safety is that of methods of arming and disarming of bots. I remember seeing some very dodgy arming of bots while watching Motorama this year (no locking bars, body parts in the arena etc.). I believe that that's the area where things are the most dangerous, and I'd like to see more standardization of arming bots over a bull pen, removing locking bars last, and where there are consequences for those who break these rules often.
hi i nead your help ... you made a video on a
Plugable USB 2.0 Digital Microscope .. i am starting a small electronics hobby using small electronic circuits boards do you still recommended? appreciate you help.. wish you well and stay safe
You seem to only have experience of bad link designs. In my BW I can insert the link one handed, from over the barrier with ease while the locking bar is in. I've never had a link fall out because I design it so there needs to be two perpendicular forces to remove the link. I also disagree, I think switches are a lot easier to design in, a link requires a lot of thought and space to do properly. But I do prefer them, I've heard of switches being broken because there's no indication they've made or broken the connection, and yes, of the contacts welding together. I also like the fact that if the link is in my hands I know the robot is deactivated.
But it was a good video and thanks for being fairly balanced!
I prefer the epic shootout
Is it possible to design/make our own custom killswitch?
Yuvraj Ghorpade Yes
As far as I'm aware the FRA (european) rules don't allow switches, and at some events you may have to hand over the link beforehand so no one can power up their robot without the organizers knowing about it. Personally, I prefer to have a separate "starter key" to my robot rather than a switch, so i can be 100% sure that it's powered down when i'm working on it.
Or at least while I take the top panel off so I can disconnect the battery.
i have lost a link once in 5 years and i lost it cause a vert launched it and regardless if it was a switch or a link it would have lost cause the whole set up left the bot
overall i prefer links as it is a visual check
I have always thought that with links it would be good practice not to use the same connector as your battery to avoid the link connected to battery accident. One solution to this is to make the link the same sex as what is on the battery (generally female). Oh and you are right of course switches are the right way to go. I have done the insert 4 links into a 250lber on TV thinking and then spending 3 minutes just hoping that one of them did not come out. Give me a set of switches with inrush protection any day.
If you have a helicopter ESC running your weapon, it will actually set to 30-50 percent when it loses connection to the radio. This is to prevent helicopters from falling quickly, but it makes them very dangerous for combat robots. My antweight thankfully had a weapon lock whenever I discovered this, and my fingertech switch was able to power it off without putting myself at risk.
in a lot of competitions this 30-50% throttle failsafe would actually fail the pre-competition safety inspections, just so you are aware. Most escs or Tx/rx's will have a way to change the failsafe value to zero. Worth looking into?
Provided your weapon lock is good, which if you're building a spinner it damn well should be, and you've followed a sensible procedure for arming up this really isn't a situation where your choice of link or switch is impacting your safety. If your lock had failed or you hadn't followed a good procedure and the weapon had spun up, you then shouldn't approach the robot - meaning that your choice of link or switch still isn't impacting your safety.
Crediting the switch or link for helping in this situation would be like surviving a lightning strike and thanking the fact you were wearing a green shirt. What is saving you here is the thick rubber soles of your arming/disarming procedure.
Spot on Robert. One thing that you didn’t mention is the reason why this is a debate in the first place. In most countries builders can choose whichever method they prefer. However the UK has banned switches, so any bots wanting to travel there are required to modify their bots to accommodate a link. UK builders will tell you that is trivial, but if your bot was designed for a switch you don’t have a large cavity big enough to get your fingers into designed into the body.
I use only links because switches are illeagal in Europe. What I like about links is that when you turn the robot off you have something in your hands. With switches the only thing indicating if the robot is on is the LED and if this is broken for some reason you have no way to see if the robot is turned on.
I usually screw the female connector of the link down in my robots so i can plug the link in without touching the robot.
Where's the commercial plug ??? :D
Motor make spin spin!
I have always preferred a switch cause I think a wire outside of the robot is stupid
A link doesnt need to be outside of the robot. In pretty much every case it isnt
When it comes to safety I don't believe the cost should be a deciding factor. Maybe a conscious choice due to budget but I wouldn't use it as a reason to choose one over another if both options are viable. Overall these parts are one of the lower cost components in general, which is a conclusion made in the video.
I personally would suggest a switch to a new builder as off the self components are easier to start building with than making custom parts. It depends on an individuals learning curve and experience, a link can be a learning aid and you will have to build connectors at some point anyway. Suggesting a switch is one less thing to build and easy to explain when you have new builders who often ask for lists of parts/suppliers. The complexity of implementing them into robots can be equal to links as more than often (in the UK) these are mounted also.
I've cringed during many live streams and events all over the world where people have mishandled their robots during power up/down regardless of the link vs. switch debate. I feel that is more down to robot design, safety knowledge, attention to your surroundings and the events procedures.
I'm not saying that this is important enough to be considered as part of the link/switch decision making process, but I believe that the fact that a link requires a little bit of thought and fabrication is potentially a useful barrier to entry. Making a link is as simple as mounting a connector and soldering a wire across two terminals, so if this is prohibitively difficult for a new builder they most likely won't be making it to the arena anyway. Its a part of the build process that often leads to new builders reaching out to the community for advice, which is advantageous as it then leads to them getting further support (and a little bit of oversight) which can make it more likely that their first experience of competing is a positive one.
Again, this isn't something I would suggest as a reason for mandating the use of links, but its a nice side-effect where that decision has been made.
It's defiantly not part of the link vs. switch debate as to which is better, it was more of a digress in the conversation. Additionally I didn't want to express an alternative opinion without explanation. That's exactly what I mean when I said a link can be a learning aid, something to hone skills and learn about electronics and engineering. A switch is something premade and tested that would allow a new starter to focus on other aspects of the build process.
We all see the posts online "I used to watch Robot Wars and been given an old electric wheelchair, how do I build a robot?", sadly I think while there are a lot of helpful people in the community I don't see a lot of support for these types of questions because they come up frequently and often don't materialise into anything. For these people I feel it's easier to suggest set components, often that's all people ask for. If someone came to an event and asked the same question the response would be different, maybe you can show them things first hand. No one wants to feel like they've wasted their time explaining the same things over and over on the internet.
If there was a widely accepted, used and approved "link kit" that included the link as either pre-made or self assemble kit including a universal mount and instructions then I'd recommend that. We are lucky to have companies like Fingertech Robotics and Team Whyachi LLC otherwise everyone would have to design and build their own switches, while not impossible, it's a lot more involved and complicated than a link mechanically.
Wholeheartedly agree it's not really in keeping with the subject of the video above, but still a good conversation to have. Thank you.
@@mrrants I can understand your view on community support - we can't always ensure people get the quality of advice and guidance we would like - but I still believe that a majority of people who do touch base in that way are better off for it. This is especially true for the people who come in assuming they can just build whatever they want, however they want, and get a bit of a reality check - even if they don't enjoy that! I don't like to over-generalise but, to generalise massively, the people with the ability to ask good questions are the ones that get good help. Those who can't/don't are probably going to need a lot more than a link to a part anyway.
Its funny that you mention a link kit - Bristol Bot Builders just released exactly that for UK Beetleweights. Their kit includes an LED, fuse wire, heat shrink, and a mountable xt60 - it strikes a good balance between being an off-the-shelf solution but still requiring assembly, with the added bonus of the whole thing being cheaper than the smallest pack of XT60s I can find. I would be very surprised if it didn't become our go-to, and I'm amazed that somebody didn't produce it sooner!
This is as close as I would want to get to an off-the-shelf solution because, as you say, just buying the part and moving on allows a new builder to focus on other parts of the build when surely we want the safety requirements to be a big part of their focus.
Deja Vu.
I have been in this place before.
I'm furious at links now!
AS YOU SHOULD BE!
Personally, I am too cheap to use a switch. But I understand that the removable links in all my robots do reduce the safety of those robots.
No it doesnt?
Angry Comment
the way i see it is just follow the rules of the event if you come to the uk for an event beetle weight to heavy weight your going to be required to use a link just accept it. same is if an american event requires a switch then use a switch
Do any US events actually require a switch? As far as I can tell links are typically allowed, and in many cases preferred, but rarely chosen. That's certainly the case for Battlebots.
Plus, there's no harm in questioning rules/accepted ways of working if you believe they can be improved.
Links are allowed everywhere. Links are a type of switch.
Using switches on my bots 🙃