Thread: Pyramid Dimension Contradiction
View Single Post
  #15   Spotlight this post!  
Unread 08-01-2013, 20:14
Retired Starman Retired Starman is offline
Registered User
FRC #3573 (Ohms)
Team Role: Mentor
  
Join Date: Jan 2009
Rookie Year: 2003
Location: Stone Mountain, GA
Posts: 159
Retired Starman has much to be proud ofRetired Starman has much to be proud ofRetired Starman has much to be proud ofRetired Starman has much to be proud ofRetired Starman has much to be proud ofRetired Starman has much to be proud ofRetired Starman has much to be proud ofRetired Starman has much to be proud of
Re: Pyramid Dimension Contradiction
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.
Reply With Quote