Bungees for Full-pressure Flippers

[jeremy_cuss]

I have a 100mm full pressure ram with a 140mm stroke. It powers the flipper. I intend to use bungees to restrain it, and bring it back down. I intend to mount these on either side of the ram. These will be backed up by a seatbelt harness to stop the flipper going round more than 180° if the bungees fail.

I would like some advice on the number of bungees needed, and whether they should be pre-tensioned with the ram at rest. The flipper weighs 14kg. The vertical distance between the bungee mounting points on the robot base and on the flipper arm is about 200mm.

Jeremy

[maddox]

You want a bit of pre-tension. About 50 kg. This is to avoid an open flipper when ended on a side.
This can be done with 2 bundles of 4 sturdy bungees.

You also want the bungees as long as possible to avoid snapped bungees.

The seatbelt harness will have to take the full force of the arm, and this again to avoid snapped bungees. 14 kg of moving arm with high speed is a lot of force.

[jeremy_cuss]

Thanks for that information, Mario. I will build in as many bungees as I can.

Jeremy

[tunna]

Why not just attach the cylinder rod end to the flipper arm ,,no woories then!!

[maddox]

Moving weight. Inertia. Speed*mass is force.

All the force that acts on the rod must be absorved. The more moving mass interlocked with each other, the stronger, and heavier everything has to be build.
So, going the classical way gives you a weight disadvantage.

[tunna]

Some roboteer once told me that it is the responsibility of every roboteer to ensure that he and everyone else should be safe from the potential danger of his Robot!!!!!However----
(when you are up to your arse in alligators it is difficult to remind yourself that the initial
objective was to drain the swamp). :

Bulldog Boyz

[jeremy_cuss]

Thanks for your thoughts. My design follows the trend towards a fixed bottom location for the ram and a sliding bearer on the flipper arm. So I couldnt restrain the arm by connection to the cylinder rod end. However I am also very aware of the extra load that I would put on the end of the cylinder by stopping very quickly a 12kg flipper arm - as Mario said in his response -even if the design permitted this solution.

Jeremy

[tunna]

simply fit a nylon or hard rubber shim inside the cyls, to cushion the end of stroke impact,!

Bulldog Boyz

[jeremy_cuss]

Well.... On my last machine there was a 16barg supply and an 80mm diameter double acting ram with an 8kg flipper arm. The arm was fixed to the ram. I used the maximum cushioning at the end of the travel and still bent the body upwards around the lower mounting point. This time the arm is heavier and the forces are an order of magnitude higher. I dont want to rupture the ram or damage the body. That is why I am sticking to bungees to decelerate the flipper arm.

Jeremy

[beast]

I have a spring which pulls the ram back down

mind you its broke lol so need to get a new one
as i only use hydralic rams made of steel
still need a lighter one as it weighs 15kg
mario need your help yet again lol