Pyramid Dimension Contradiction

[CalTran]

I was looking at the Autodesk Inventor one and all the angles I could measure all measured out at 68.9...which is a new measurment.

[Undertones]

I'm having troubles visualizing what the problem with the specs are. Can someone explain in a way that I am likely to understand?

[misterli]

Is it possible to purchase the pyramid from FIRST?

[cgmv123]

Originally Posted by misterli

Is it possible to purchase the pyramid from FIRST?

No.

[Retired Starman]

I built one of the pyramids according to the plans for the competition field for the Peachtree Kickoff. It should be part-for-part interchangeable with the ones FIRST has built.

There is a 60 degree angle between the legs and the floor. That is, if you start at the top of one leg, go to the floor, draw a line to the diagonal leg, the angle made between the leg and the floor is 60 degrees.

If you start at the top of one leg and go to the floor, then to either of the adjacent legs, I measure an angle of about 67-69 degrees. I was using a very small protractor, however, so I'm not sure of the exact angle, but it is in this range. Looking at the pyramid from the side, the side view or view you get by projecting the vertical image on a flat surface gives a base angle, according to the plans, of pretty close to 68 degrees.

The outside dimensions of the rungs, going vertex to vertex of the rungs is

Middle Rung = 50.63 in.
Lower Rung = 75.13 in.

This assumes the weld adds nothing to the length, that is, the weld is ground down to the original tube dimensions at the corners. On my pyramid, I haven't ground down the weld and don't intend to, so our lengths are somewhat longer.

I'll have to wait until we assemble the pyramid again to get an accurate dimension on the rung heights. We are painting the pyramid now.

Remember that the pyramids are made of tubing, not pipe. Pipe is sized by internal dimensions, tubing is sized by outside dimension. The DOM tubing used in the official pyramids has an OD of 1.50 in.

If you are building a pyramid from the Team Built plans, be careful. Team built plans call for 1 1/4 in. water pipe which has an outside diameter of 1.66 in. If your robot design depends on clamping or hooking the tubing, be aware that the diameters will be different.

I would suggest that teams building a pyramid use EWR tubing which is "good enough". The finish isn't quite as smooth, there is a weld up the length (which may create a bump inside the tube, but the cost is much more reasonable.

Dr. Bob

Chairman's Award is not about building the robot. Every team builds a robot.

[Aren Siekmeier]

The Pro/E version of the field appears to have the correct pyramid geometry.

http://www.chiefdelphi.com/forums/sh...80#post1212082

[dcarr]

Originally Posted by misterli

Is it possible to purchase the pyramid from FIRST?

http://www.youtube.com/watch?v=7KiVR9rmEgc

In this video, Andy says that AndyMark may offer one for purchase - could be an option if you are unable to build one yourself.

[slijin]

Originally Posted by CalTran

I was looking at the Autodesk Inventor one and all the angles I could measure all measured out at 68.9...which is a new measurment.

I'm not sure where you're getting 68.9, but that's approximately the angle between the diagonal and the rung when measuring in the plane of a face of the pyramid.

The 60 comes from measuring the angle between the diagonal and the floor (or a plane determined by a set of rungs); the 68 (IIRC, 67.72) comes from projecting that angle onto a vertical plane parallel to an edge of the pyramid base.

[CalTran]

Originally Posted by slijin

I'm not sure where you're getting 68.9, but that's approximately the angle between the diagonal and the rung when measuring in the plane of a face of the pyramid.

The 60 comes from measuring the angle between the diagonal and the floor (or a plane determined by a set of rungs); the 68 (IIRC, 67.72) comes from projecting that angle onto a vertical plane parallel to an edge of the pyramid base.

I measured from the diagonal to the pyramid base plate

[slijin]

Originally Posted by CalTran

I measured from the diagonal to the pyramid base plate

Did you measure to the plane of the base plate, or a line in the base plate? There is a distinction.

[Aren Siekmeier]

This same issue being discussed across a few threads now...

http://www.chiefdelphi.com/forums/sh...85#post1210885
http://www.chiefdelphi.com/forums/sh...64#post1210364

Does anyone know if this issue is also present in the Pro/E version of the field?