YAMEB

06 March 2016

2.77 Seek And Geek #5: Hydraulic Cherry Picker

Seek And Geek #5: Hydraulic Cherry Picker

The other day I saw a Hydaulic Cherry Picker like the one above parked between Kresge and McCormick which had been used to put the "MIT 100 Years In Cambridge Celebration" posters up on Building 7.

The whole thing has a telescopic arm made of square extrusion. I couldn't get a good peek inside of the mechanism it uses to actuate the telescoping mechanism, but considering everything else on this machine is hydraulic (which is good because there is only one power source that is distributed across the whole machine) I bet this is probably actuated hydraulically, with the piston motion amplified in some way through gearing or a linkage.

Speaking of linkages, the whole thing has a "wrist" that's on a parallelogram 4-bar linkage, so it keeps the basket holding any operators parallel to the ground.

A workspace analysis found online shows off just how much reach this thing has. The wrist allows fine positioning once the big arm has been extended.

The big arm is actuated by a massive hydraulic piston in a 3-bar linkage. The forces it has to exert to hold the arm in place change given the angle of the arm, and the horizontal configuration requires it to bear the highest load. Luckily, static force holding is something inherently free in hydraulic systems!

You can see the cable/hose carrier, bringing both electronic cables and hydraulic hoses up the arm to the the pistons located near the basket.

The wheels are hydraulic! Both drive and steering are achieved through hydraulic actuators. This thing is really slow when driving, no more than 15MPH, but at least no additional forms of power are needed. The same hydraulic power unit is used to move the arm, the basket, steer, and drive the wheels.

There are two pistons that orient the basket! One is coupled to the 4-bar parallelogram linkage, and the other will simply change the angle of the entire basket with respect to the arm. This is probably coupled to the motion of the arm's beefy main piston near its base, so the basket is always oriented horizontally.

There also is a left-right rotational joint at the basket's wrist, also hydraulically actuated.

27 February 2016

2.77 PUPS #4: Kinematic Coupling

PUPS #4: Kinematic Coupling

Turns out this is a 3D version of my PUPS#2 Planar Coupling. I'm using these projects to test concepts for my final project.

ADD SPREADSHEET PREDICTION OF PERFORMANCE:

I haven't used a mill in a while, let alone a fly cutter. It's good to smell like machine oil once again!

There are two pieces of Aluminum stock, one will be the "robot" part, the other the "fuselage". I will make the Fuselage part first, and iterate through concepts for the robot fixturing using the spreadsheet and given the rest of my design work and eventually settle on one.

I have founded Chip City!

I left the 0.25x0.5" shoulder where the 45-degree taper of the "fuselage stringer" will go.

Chamfer endmill!

And the finished fuselage section. This was a great exercise in learning the conversational mode on the Makerworks ProtoTrack.

Here's the real 787 Fuselage for comparison. My Aluminum model is 1:6 scale.

(Aside: The waterjet works again! The pressure sensors on this have been dropping like flies. This one is Serial Number 2, one of the oldest, if not THE oldest Omax still existing.)

I have a confession to make: I'm using my lab's 3D printer in order to test various concepts. I suppose my project is different in that the entire machine must kinematically couple with respect to the airframe, perform several operations, and then be moved to the next set of holes along the airframe.

This ends up fitting quite well! The hole was for a screw to thread through and clamp the Robot down, but its position was arbitrary in this model. This position is currently unstable and pulls the robot away from its coupling location. When the clamping force is in line with at least one of the Kinematic Coupling contacts, ideally more, the clamp will be more stable.

The Big Robot will preload the Fastening Robot by applying both forces and torques against the frame, then the robot will clamp itself to the frame, and the Big Bot will let go. The Fastening Robot can then perform its operation, confident that it is localized with respect to the airframe where it must perform fastening operations.

TODO WHEN ROBOT DESIGN IS FINALIZED:
Test angular repeatability with a laser in a hallway, Test accuracy with a dial indicator mounted on a mill, Use spreadsheet to modify design and modify if needed.