Tethers

Actualy, the only pivot in the Gravity system(actualy, Hammerhead had the first of those, with Flip as second)is at the back of the flipperarm, not on the ram whatsoever.
And in Gravity the hinges are based around M20 bolts.

Weve got another one of those threads where everyone assumes what everyone else means, havent we? Im beginning to think it might be handy to have a forum glossary somewhere; even if the definitions arent scientifically accurate, it would be nice if everybody knew what everyone else meant in the context of this forum. (Translational spinner would be another good one to add.)

Jim: Going off Richards definition, I suspect the points in question are of the mathematical infinitely small variety used in two elephants connected by light inextensible string examples (as much of my maths A-level was).

That is, a single point connection doesnt constrain movement to a single axis - its a ball and socket joint. Put two ball and socket joints on the flipper and you have the equivalent of a conventional hinge. So its a double point so long as it constrains the axis of rotation of the flipper.

But, to be honest, I have no idea what Im talking about. It depends whether were talking about the flipper in three dimensions, or a two-dimensional diagram of it in the plane of its motion. Christian seems to be going with the latter interpretation, Richard with the former. The numbers are plausible either way around.

(I got called an anorak on LBC radio recently. Youd never guess...)

--
Fluppet

M24 Bolts.

WJ: Slightly off-topic, but how *does* Gravitys ram activate the flipper? Is it just mounted vertically under it, and pushes it (and presumably slides along it a bit)? Just making sure that my assumptions are correct.

Ta,

--
Fluppet

Right on the money, Andrew :

http://httpd.chello.nl/~wj.dijkstra/...s/grav3003.jpg

Aha! Thanks!

(Whoohoo, I got something right for once. :-)

--
Fluppet

anderw you read me wrong i meant for the end of the ram so it runs smoothly
and the tether will be below the ram fixing point but can some one send me an ilistration of the 3 point i cant picture it

i also ment to say it will be in a gap between 2 1 squaire bars and that will limit sideways movement i think lol

I will try to put up an illistration under my profile later tonight. Note that it will be my version of it, and it may not be 100% correct.

thanks

Fred - no, I think I understood: flipper attached to robot by normal hinge, ram hinged at the bottom, ram attached to hinge by a ball joint, yes?

I just wondered why a ball joint. With my limited knowledge of mechanics, they would appear to be less strong (per unit weight) than a traditional hinge - from the point of view of the flipper being pulled away from the ram, at least. Presumably your ram moves only in the same plane as the hinge and ram anyway, so theres no benefit to allowing it to move the other way (unless you want to avoid twisting your ram as the flipper bends). Id have thought a hinge where the ram meets the flipper would help reinforce the main flipper hinge, too.

Presumably tension on your flipper isnt an enormous problem (because you have a tether - see? back on topic! mind you, if the tether is supposed to be a safety device then you may not want it to be stressed under normal conditions...) but I was just curious at the choice. Im not quite sure how this helps it run smoothly.

Not being critical, just trying to learn a bit of engineering!

btw, do you know how hard it is for someone with my user name to type flipper? (A bit unfortunate, given my plans for pneumatics.) Ive managed to type flupper and flippet several times in the course of this post. Possibly I need some sleep.

--
Fluppet

Dont know if its needed any more, but the picture is under my profile. Not one of my best drawings (as Ewan can testify), but I think youll understand.

The top one is a three point flipper, like Dantomkia (each black circle is one point). The lower one is a one point flipper, like Gravity.

So theoretically, there is no two point flipper.

My understanding relates to how many points the flipper attaches to the body / chassis and not the ram base to the chassis. A three point is one for the ram and two for the pivots.

Paul

So strickly speaking as long as you have one or two points on the flipper and a teather (or three points on the flipper arm) the RAM does not have to have any fixing points :) to comply with the rules.

I think most is common sense, but been board at work I thought Id say something stupid.

Have you noticed how quiet the forum is today?

Fightingrobots.co.uk is down at the moment - see the thread in General - which explains why its quiet.

Already been there, I hope its sorted soon or we will all have big problems.

anderw i got the wrong eng of the stick yeah a seious hinge on flipper to bot an ram hinged
the balljoint was the best way i could see but i would take any advice any one has

Fred: You type how I feel (bad cold, spent all day in the A2 traffic jam in a car with the heater stuck on, got to work 6:30pm...) :-)

Thanks, glad I understood. Dont think theres anything *wrong* with your approach, I just wondered if you had a reason for it!

Id be interested to know what everyone else does. I presume most are normal hinges at the top (need to dig out some tapes and check, but since I spent last week moving house [no, I hadnt lost the forum when the links went down, the blissful silence was for another reason] it may be difficult) with the exception of the Gravity push-linked variants. Am I mis-presuming?

--
Fluppet

how does every one elst fasten there ram to there flipper

Im planning to have a round silver-steel bar running laterally across the underside of the flipper, with the clevis on the end of the ram attached around this bar. Fairly standard I think, but please feel free to correct me anyone?

Not sure how Ill fasten the *bar* to the flipper yet tho.

-- Kev

Hi

I was just wondering what would be considered addiquate as a tether for a lp featherweight running at 8-12bar with a 50mm bore 110stroke ram.

Thanks
Regards
Ian

Would a piece of bungy be ok? Simular to that used by Dantomkia to retract their ram.

Regards
Ian

Dantomkia does the retraction with low pressure CO2.
Gravity used 4 times 3/8 arimide rope for tether, and several loops of heavy duty bungeecord for retracting the huge ram.

A bungee should be fine to retract your L.P. ram.

Things are a little different with an untethered arm and a H.P. Ram...as stated above by Mario..

Please note guys, the ram is low pressure retracted but it is not directly connected to the flipping arm. I assume though that bungy will be ok for to retract it?

Regards
Ian

Rope to stop the arm ....bungee to retract it.

Would a steel bike brake cable be to sufficient to act as a tether on a LP featherweight axe? I know a couple of people building them at the moment, and neither of them are 100% sure on what would be reliable and lightweight.

The only way to know that is to test it. But in theory it counts as a tether, as the rule dont state it has to be this or that , or capable within these parameters.

Brake wire has a very high tensile strenght, so it should do.

Grant I would imagine so as THz uses a similar cable for the size and weight of the axe.
PS can get you some if you need. (well wanye i assume)

Yer that would be great thanks Ed. Were hoping it will be finished this weekend ready for Robots Live!. If you could pass it onto Dave when he gives you your DX6 that would be great cheers.

Will do, should see him before the weekend. But am having problems at home this week so cant say for sure.

Ok thanks Ed, much appreciated.

Who of the FRA do I have to ask for teather questions?

I not sure that it comes under pneumatics so, I would address any questions over the rule itself to Geoff Smith (his email is on the contact page).

Or post here.

Grant- Ed has his DX6 and i have your steel cable.

Ill bring it to the factory when my Hardox arrives.