Quote from: Lee Jay on 03/17/2017 11:12 amQuote from: meekGee on 03/17/2017 02:33 amQuote from: Lee Jay on 03/16/2017 11:46 pmBased on the sketches, the thing is going to prevent lateral movement by putting hydraulic or pneumatic rams in bending while at full extension?That would be, ummm..., shocking.I don't think so. I think the Roomba is strictly a "pull down" device. It increases the force on the four legs, compressing the suspension, ...That would be even worse.Why?Stage walking and stage sliding is a result of too little reaction force on the legs.If a stage is doing that, you run under it and pull it down to stop it. Not push up, since that will reduce the force in the legs.The pulldown chains did the same trick. The jacks the stage was pulled into didn't lift the stage, they just limited how far down the stage was winched down.The robot does both things with a single set of jacks.
Quote from: meekGee on 03/17/2017 02:33 amQuote from: Lee Jay on 03/16/2017 11:46 pmBased on the sketches, the thing is going to prevent lateral movement by putting hydraulic or pneumatic rams in bending while at full extension?That would be, ummm..., shocking.I don't think so. I think the Roomba is strictly a "pull down" device. It increases the force on the four legs, compressing the suspension, ...That would be even worse.
Quote from: Lee Jay on 03/16/2017 11:46 pmBased on the sketches, the thing is going to prevent lateral movement by putting hydraulic or pneumatic rams in bending while at full extension?That would be, ummm..., shocking.I don't think so. I think the Roomba is strictly a "pull down" device. It increases the force on the four legs, compressing the suspension, ...
Based on the sketches, the thing is going to prevent lateral movement by putting hydraulic or pneumatic rams in bending while at full extension?That would be, ummm..., shocking.
Quote from: meekGee on 03/17/2017 02:12 pmQuote from: Lee Jay on 03/17/2017 11:12 amQuote from: meekGee on 03/17/2017 02:33 amQuote from: Lee Jay on 03/16/2017 11:46 pmBased on the sketches, the thing is going to prevent lateral movement by putting hydraulic or pneumatic rams in bending while at full extension?That would be, ummm..., shocking.I don't think so. I think the Roomba is strictly a "pull down" device. It increases the force on the four legs, compressing the suspension, ...That would be even worse.Why?Stage walking and stage sliding is a result of too little reaction force on the legs.If a stage is doing that, you run under it and pull it down to stop it. Not push up, since that will reduce the force in the legs.The pulldown chains did the same trick. The jacks the stage was pulled into didn't lift the stage, they just limited how far down the stage was winched down.The robot does both things with a single set of jacks.Why? Because they want to optimize the legs for landing, not for standing during transit.They are extended by gas pressure, then locked in place. They don't keep enough gas for the trip back to port, and they can't or don't want to rely on the locking mechanisms, so they have to remove the weight from the legs. Now it is a manual operation at sea, with significant risks. So they build a machine to remove the weight from the legs and hold the rocket to the deck, either brute force with mass or with some way to attach to the deck.
Holding it down from inside a 3.5 m base won't do it.
Quote from: meekGee on 03/17/2017 02:26 pmHolding it down from inside a 3.5 m base won't do it.Then how does it stand on the launch pad? Especially during a static firing.
Quote from: Jim on 03/17/2017 03:12 pmQuote from: meekGee on 03/17/2017 02:26 pmHolding it down from inside a 3.5 m base won't do it.Then how does it stand on the launch pad? Especially during a static firing.Because the launch pad is anchored to th ground.The robot, from what we hear, is mobile.If we hear about stud welding, and lots of it (more than would have been required at the feet) then maybe.But holding a rocket by the thrust structure, in waves, would required a very strong torque-carrying connection to the deck.
Or, big electromagnets powered by an onboard generator & cables to match.
Quote from: meekGee on 03/17/2017 03:18 pmQuote from: Jim on 03/17/2017 03:12 pmQuote from: meekGee on 03/17/2017 02:26 pmHolding it down from inside a 3.5 m base won't do it.Then how does it stand on the launch pad? Especially during a static firing.Because the launch pad is anchored to th ground.The robot, from what we hear, is mobile.If we hear about stud welding, and lots of it (more than would have been required at the feet) then maybe.But holding a rocket by the thrust structure, in waves, would required a very strong torque-carrying connection to the deck.What if the Roomba had extendable outrigger feet? Many types of cranes, lifts, construction equipment, and even firetrucks have these. It is very much off the shelf equipment.Yes, I know this is added complexity, but it does mean that the main body and its attachment points do not need to have a large footprint.
Why does the roomba need to pull down? It needs to attach securely to the thrust frame and use its mass to increase the normal force static friction so the stage doesn't walk. No need to add many tons of force stress to the legs.
Quote from: AAPSkylab on 03/17/2017 03:28 pmQuote from: meekGee on 03/17/2017 03:18 pmQuote from: Jim on 03/17/2017 03:12 pmQuote from: meekGee on 03/17/2017 02:26 pmHolding it down from inside a 3.5 m base won't do it.Then how does it stand on the launch pad? Especially during a static firing.Because the launch pad is anchored to th ground.The robot, from what we hear, is mobile.If we hear about stud welding, and lots of it (more than would have been required at the feet) then maybe.But holding a rocket by the thrust structure, in waves, would required a very strong torque-carrying connection to the deck.What if the Roomba had extendable outrigger feet? Many types of cranes, lifts, construction equipment, and even firetrucks have these. It is very much off the shelf equipment.Yes, I know this is added complexity, but it does mean that the main body and its attachment points do not need to have a large footprint.How wide? Regular outriggers add a bit of width, but mostly take out the suspension and tires. (And conform to the ground)
Quote from: philw1776 on 03/17/2017 03:34 pmWhy does the roomba need to pull down? It needs to attach securely to the thrust frame and use its mass to increase the normal force static friction so the stage doesn't walk. No need to add many tons of force stress to the legs.It might, but then the up arms will be working in bending.The main problem IMO was stage walking, not sliding.During to dynamic tilting, the normal force on one or two legs would decrease, and they would move a bit. Then the tilt would go the other way, and they'd move.Cinching it down solves everything, and I don't think the legs are anywhere near their load limits.If the legs are both unlocked and losing pressure, the only remedy is to pump them up. Might as well suppose they installed the piping to allow the robot to do that.
The legs are built to carry the landing impact, so are strong enough.If a leg didn't lock, those tiny jacks and stands would never hold the overturning moment during wave action. They'd buckle out of the way in a second.If a leg isn't locked, they need to pump it up actively to make up for any gas lost.Holding it down from inside a 3.5 m base won't do it.
Quote from: meekGee on 03/17/2017 02:26 pmThe legs are built to carry the landing impact, so are strong enough.If a leg didn't lock, those tiny jacks and stands would never hold the overturning moment during wave action. They'd buckle out of the way in a second.If a leg isn't locked, they need to pump it up actively to make up for any gas lost.Holding it down from inside a 3.5 m base won't do it.The legs are supplied with a crush core to protect the stage from damage upon landing. Once the cushion is used in a hard landing, leg loads go directly into the side of the stage/tank. In waves, with even a little asymmetry in the landing gear, this will hammer the stage for a few days before unloading.The legs, with the crush core intact, are designed to take one impact, after that any loads on the air frame where it is not strongest are undesirable. SpaceX would not employ jacks if they deemed the stage tough enough to just ratchet it down to the deck.Dragging those aircraft jacks around on a rolling deck is no picnic, why would they be doing that if they don't need to?Matthew
Quote from: Lee Jay on 03/17/2017 11:12 amQuote from: meekGee on 03/17/2017 02:33 amQuote from: Lee Jay on 03/16/2017 11:46 pmBased on the sketches, the thing is going to prevent lateral movement by putting hydraulic or pneumatic rams in bending while at full extension?That would be, ummm..., shocking.I don't think so. I think the Roomba is strictly a "pull down" device. It increases the force on the four legs, compressing the suspension, ...That would be even worse.Why?
Unless you somehow anchor to the deck, lifting up makes the stage less stable.
Why does this device need to provide either up or down force? Seems to me that if it merely snugs up the slack, it then serves to impede any up or down motion. By avoiding said motion, the walking and any subsequent weakening of the legs would be prevented.
Quote from: meekGee on 03/17/2017 04:19 pmUnless you somehow anchor to the deck, lifting up makes the stage less stable.No, the base device could be heavier than the stage, and it could have a higher frictional coefficient with the barge deck (i.e. rubber). If properly attached to the stage, it could therefore add an enormous amount of lateral resistance to movement that the stage needs to keep from moving around. It doesn't need over-turning stability, but if lifted the device would have to provide that as well. An easy way to do that would be the way the stage does it - with outriggers (called legs on the stage).Crushing the legs down against the deck sounds like the worst of all worlds to me - even worse than putting rams in bending (which is a total no-no).