Tethers

[team_ireland]

Tethers

you can get 10ton webbing minimum. I think you can get more but I Definately know you can get 10ton. Contact Gunnebo. They are a very good company and will supply quality webbing (not the cheep chineese stuff). You can probably get away with the cheep stuff but it will not last and considering webbing is so cheep anyway (about 5euro for a 2ton 1meter web sling) your better off with the proper stuff. Also Arthur have you thought about chains?

Grabiq chain is top quality and incredibly strong.

Regards
Ian

[jamesb]

Tethers

Nevr understood this tethers thing to be honest.... Ill explain why.

a normal flipper (dantomkia for example) has 2 flipper arm attachment points. one at the hinge and one at the ram.

gravity style (gravity for example...) has 2 flipper arm attachment points. one at the hinge, and one at the movement restricting bungy cord.

Yes, I know bungy cords alone are not good enough to be tethers, but gravity runs aramid rope in addition to these to stop his flipper going 180 degrees. I would expect that similar designs cannot rely on bungy ropes for the same reason, so is it not logical to say that gravity type flippers are compromising their design by not having teathers anyway? In which case, do we need the rule?

Also, has anyone tested what happens if the arm leaves the robot with just bungy cords?

[gravity]

Tethers

I almost got whacked on my head at a live event in rijswijk, cause I only had bungees on it. The flipper arm did do the full 180 degrees, and in doing so reached to about 1 metre behind the robot... swooshing thru a spot my where my head was half a second before.

In the series 7 gravity I had 8 strings of 10mm rope each capable of holding 2500 kg... the ropes started to bend a 30x30x3mm box section... So this type of rope will do fine.

[kaideejee]

Tethers

Im having trouble picturing the three point attachment thing - Can anyone help me to visualise this? All the ones I can imagine have a single hinge, plus one or more rams. When we say 3 point - do we mean those where the flipper is physically attached to the ram, which itself pivots? Or is there more to it than that? If this is whats meant by three points, then presumably in the absence of tethers, gravity becomes a single point attached flipper whereas in this thread it keeps getting referred to as a 2 point....

Cheers

-- Kev

[Guest]

Tethers

on ours we are going to have it fixed to the flipper by a ball joint type of thing and a tether from 3 lyers of seat belt (brand new for an old jag or from a fiat panda)

[fluppet]

Tethers

Out of interest, why a ball joint? I suppose it allows the flipper to flex sideways a bit without putting pressure on the ram, but Id have thought its a relatively weak connection if youre allowing more than a narrow range of movement.

Just curious, not trying to be critical. (After all, Im not exactly expert!)

--
Fluppet

[Guest]

Tethers

@ Kev: I think a long hinge counts as two points - one at either end of the hinge. A single pivot such as that on most axes would count as one point, and can be more easily damaged by twisting forces. If the flipper is attached to the ram by a joint then that also counts as one point. It looks like Gravitys hinge counts as two points.

[jim]

Tethers

If Richards definition is correct, my next question would be: how long does a hinge have to be before it counts as two points?

[julian]

Tethers

Working towards my first CO2 flipper, I was assuming that hinging all along the edge was the way to do things.

[Guest]

Tethers

No offence, but I dont think Richards defenition is correct.

Im just guessing here, but according to what Ive heard, the defenition depends on how many pivot points you have. For example, a flipper like Dantomkia have three points, one at the bottom of the ram, one at the flipper arm, and one that connects the ram to the flipper arm.

But as the ram in Gravity is stationary, I consider that a one point flipper, with the only pivot at the top of the arm.

[maddox]

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.

[fluppet]

Tethers

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

[gravity]

Tethers

M24 Bolts.

[fluppet]

Tethers

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

[gravity]

Tethers

Right on the money, Andrew :