New link design

I have a new link design on my robot Cayenne. Due to space problems I cant fit the normal 175A connectors in, so Ive come up with my own solution which is shown on my profile.
The link is a piece of flat copper bar which clips into place between the battery terminals. The links are removed by pulling the cord. They are easier to pull out than a 175A connector.

To fit with the rules on battery terminal insulation, the link will be covered by tough fabric (seatbelt material) which is held on by velcro. The cord will protrude from under the battery insulation, so the insulation and link can be removed in one action.

There are two links - Cayenne has always had two - which the rules allow, but they do have to be adjacent. Theyre about 50cm apart on Cayenne - do you think this counts as adjacent? Also, any other comments you have on the design would be useful - better to find out now than at Magna.

There are some bigger pictures at :
http://mode7.srimech.com/gallery/newlinks/http://mode7.srimech.com/gallery/newlinks/

Its a link like any other kind of links I have seen. So if it does what the rules ask, you can use it.According to me.

But do you need to pull the 2 links to shut down completely?

Hi Jim.

2 things. First, it looks a bugger to arm. I dont fancy putting that lot together, lidding it up and then fighting it. It doesnt look simple nor easy to arm.

Second, not sure about having to have 2 links in a machine before it will disarm and be deemed to be safe.

Other than that, nice work.

Mike.

Only one pointer to make and that is contact resistance. You will find a temperature rise at the wiping connections which will be transferred into the Hawkers which will complain! I remember using a solid copper link between two Hawkers once which very slightly worked loose - the M5 bolts still were too tight to undo with your fingers. This contact resistance caused the copper to heat up, the Hawker case to melt and one cell to fail.

So unless you can guarantee a very low contact resistance (remembering greasy fingers on the key causing tarnishing etc.) that does not worsen in service, I would look for another solution.

Paul

Cant you put a 175A connector flat, and have the access from the side/back? How do you access the link if the robot is inverted?

How about using a 50A connector? These are much smaller than a 175A one.

We use 1 with no problems, although it did burn out the contacts after a years worth of use (caused by initial charging of the capacitors rather than current loading). We run upto a peak current of 300A and its never been a problem.

Thanks for your responses, all good points...

Mike: The links just push in, like a normal link. The bolts you can see in the picture are static, you dont need to tighten them or anything when arming.

Paul - a good point which I will need to think about. I use a PCB cleaning block to shine up the link before using it, which may be enough, I havent noticed it getting warm yet. However, dangers of heating up batteries notwithstanding, performance and damage to components are secondary to safety.

Alan and Mario have perhaps the most important points. It does require both links to be pulled to make the robot safe, and I think this is where most disagreement will occur. The reason there are two links is because its very nearly a clusterbot . The front and the back are just bolted together at the moment, theres no or mechanical or electrical connection between them and both can run independently. Once I sort out a mechanism to disconnect them, it will be a true clusterbot, but I would still like to run it as a joined up unit if possible. Id really like to keep the two sides independent and that means not running cables between them.

RE inversion - yes, its going to be difficult to remove the links if it gets flipped over, but I think this is true of quite a few robots.

Jim.

We have an example in history. Stinger.

In theory you must be able to disarm the whole machine with 1 link.On the other side, I believe that the rules are not put into cast iron.
Not that I will accept a multiple parallel link in machines that could be builded with 1.
Multiple series mounted links for added safety is no problem.

Also, we have run Tough As Nails with the Anderson minipowerpoles. Normaly accepted to 45A, but more than capable to survive 5 minute uses over a 100.
So, if this alternative link doesnt satisfy, the miniandersons are an option.

Weve replaced those with normal 50A andersons ages ago, suspecting them of problems. Weve never used minipowerpoles as a link.

We also use the small Anderson connectors but now use 2 in parallel, but bolted together. Dont forget the the current rating is for the connect/disconnect rating only and will handle far more. Think of them like Relays where they have 2 current ratings, Swithcing current and max on current.

Mark, not so sure thats correct. The rating is also based on the temperature rise. They have a max operating temp of 105 deg C. For example, a 50A connector can officially handle 100A for 16 seconds if you use 10mm2 cable (the bigger the cable the better as it acts as a heatsink) whereas the 175A connector can handle 400A for the same period.

Looking at thier datasheet:

http://www.andersonpower.com/products/pdf/DS-SB50REV01.pdfhttp://www.andersonpower.com/product...-SB50REV01.pdf

It does state that there max continous current is 50Amp for a 20C Temperature rise with 6AWG (13mm sq) wire, but their figures dont seem to add up.

At the full 50A it states a voltage drop of 10mV, hence 0.5W of power lost in heat. For this to be true then the connector + wire must act like a heatsink of 40C/W and that seems too high with such thick wire.

I did a bit of work in the garage last night and managed to cut down one of the 175A connectors so that it would fit in. This still leaves the issue of multiple links, however.

Jim, as I understood it, if you have 2 seperate electrical circuits then 2 seperate links are OK (with 2 seperate power lights) but weather they have to be together (or just near to each other) is a little unclear, and I suspect that if the robot design does not allow them to be together then it should be accepted by the event Organiser anyway. After all to make a Co2 robot safe you have to both pull the link and turn off the Gas and they are not always together so I dont see much difference.

My feather has 3links. One for drive, one for weapon and another for the rx. All 3 are near each other. So i would not expect a problem.

Regards
Ian

I think it should be indicated clearly to the arena crew that there are multiple links because in case of emergency they are the ones who must pull the links out.

At Roaming Robots Events our arena man Pete always watches how machines are turned on so he knows what to turn off.

Mr Stu

Tie all your links together with cable tie or string so that the crew will always pull all the links out, no error possible in the heat of the moment.

Unfortunately, the only way I could do that with my robot would be have the string going round the outside of the robot - it would be very easy to catch during a battle.

we have a feather in holland wich could be interpreted as 2 robots bolted into 1. so, 2 receivers, 2 batterypacks, 2 removable links, 2 power leds. The links are not in the same place so you do have to de-link one side first and then the other. No way around that. I have allowed this robot in the competitions. If other Tech checkers have a problem with it i would appreciate another solution, but i honestly dont see how else to do it.

I was half expecting the response to be dont built it like that, then!

I think just in case I will take a link extension cable which plugs into one link and provides the link contacts on the other end of the link, right next to the other link. It would lengthen the battery leads (not good) but is better than being sent home.

Id be interested in knowing more about this featherweight, Leo - do they have a website?

It just happens to be mine :)
It works on the stinger principal. most of the weight is in the wheels, about 8 Kg. So the motors/batteries/etc spin round the axle. Newton says if you spin the wheels one way with a certain force, the axe goes the other way with the same force.
On the down side.. each wheel has to have its own batteries, reciever, link, etc.

http://www.dutchrobotgames.nl/cgi-bin/robots/49http://www.dutchrobotgames.nl/cgi-bin/robots/49
http://www.bugs.nl/media/album/index.php?path=L3Byb2plY3RzL2Z6bjEvhttp://www.bugs.nl/media/album/index...plY3RzL2Z6bjEv
http://www.bugs.nl/media/album/view.php?&path=L3J3L2Fob3kyMDA0L25sLWNhcmxpam4vSFB JTTA3NTkuSlBHhttp://www.bugs.nl/media/album/view....LWNhcmxpam4vSF BJTTA3NTkuSlBH
http://www.bugs.nl/media/album/view.php?&path=L3J3L2Fob3kyMDA0L25sLWxlby9JTUdfMDA xNi5KUEc=http://www.bugs.nl/media/album/view....LWxlby9JTUdfMD AxNi5KUEc=

Apart from having two links in our robots, I see we also both use bicycle chainrings and read Douglas Adams :) Nice work.

Those nylon drill gears dont look too happy though :)

Just thinking that usually all battery terminals and areas that could short must be covered. Judging from the photos this doesnt seem to be the case with your robot. In battle something could easily link the power back up to the robot.

I covered that in my first post.

Jim ......... I personally cannot see a problem with you having two seperate links, as you say it is very nearly a cluster bot so it two independant robots joined at the hip so to speak .. therefore I as Roaming Robots ARENA MARSHALL would be treating you as two robots which means i would expect to pull two links to disarm you......... Speaking from past expiriences so long as you and the arena staff ie myself or whoever is in charge of the arena at the time are aware of your arming and disarming procedures i have had little or no problems. AND DONT FORSEE ANY IN THE FUTURE ... PETE(ROAMING ROBOTS ARENA MARSHALL)

Good news, thanks for the feedback Pete.

For future reference...

Paul was entirely correct. One of our links did overheat, despite soaking them in phosphoric acid solution before our fight. We intended to fit the Anderson connectors but ran out of time before Magna. Luckily, our Hawkers survived to fight another day.