pic: Pyramid Problems

1511 is having problems building our pyramids, they insist on twisting and torquing. Has anybody else had this problem and solved it? We really would like some advice, we will need these pyramids for our week 0 event.

Had a little bit of that. Not nearly as drastic. We used some pipe clamps under the rung to hold it level, then started tacking things in place. You need to get someone (or multiple people) to hold the twist out of it while it’s being tack welded. We worked from he bottom up. I wouldn’t try to do the whole thing at once.

We use 8 packing straps attached to the top corners and adjacent lower corners and the tighten them up carefully with the ratchets. It makes the tower pretty firm.

Remove the chairs and step to the right. That will fix your problem.

Bolt the top joints together. That should fix your issue somewhat.

There is nothing wrong with there joints. All you need to do is step right one step and remove the chairs

I see it corectly, we built it similar to theirs. We had the same issue. Put some bolts through the top inserts and that fixed it.

Cut the corners at 45 degrees instead of butting them up against each other

What bolts?

The bolts are mounted on the gusset plates, and basically what we do is drill a hole in the leg, and put a bolt through it and there is a nut welded to the gusset that holds it there, and it keeps the levels of the rungs consistant.

Check out this other thread for internally bolting your pyramid with mostly off-the-shelf H/W and one custom part => threaded internal sliding donut

The holes in the threaded aluminum donut plug inside the rung pipe were mistakenly drilled at the 98 degree dihedral angle, instead of the correct 90 degrees, which accounts for the miter gap and the spacer stack skewing over in this initial test assembly. The nylon “curved end tube spacers” are the key to the whole concept working. We may need to glue their flat ends together with the curves rotated to the proper tube angle offset to each other to further improve joint stiffness

-Dick Ledford

We also had some twisty-turny stuff.

We made plywood gussets for the corners, serving the same function as the nylon spacers shown above, and that tamed the pyramid.

We used Lots of different sized Jigs to hold things in place. also, as mentioned above, clamping under where the squares rest (to hold them up) and then measuring, tacking, measuring, cussing, cutting, and welding it up. ours turned out fine though. One thing that helped was putting a small but tall welding table in the middle and welding up things (and holding the top box up and twisting it.)

If you make a big X out of the metal pipes (not in the original design), and weld the legs diagonally to it, it shouldn’t twist as much, but there may be problems with your robot driving over it, since it’d be flat on the ground…

We made a full welded pyramid and had the same problems. After a lot of struggle some local welders helped us out for free. Thanks welders!

After we posted this we did some more investigation into why it was twisting and how to correct it.

Really the issue we were facing was that the angle of the legs relative to the four corners on the top of the pyramid were off. We did not constrain the angle so the legs were free to twist relative to the top of the pyramid. Another issue not helping us was that the weight on the top of the pyramid was making it hard to straighten out the pyramid. So based on these two major issues we tried a new approach.

The new approach:

  • We flipped the top of the pyramid upside down and placed it on the ground.
  • Next we put in the inserts that interface the top of the pyramid to the legs.
  • We adjusted each leg so that it was at the correct angle relative to the corners of the top of the pyramid (now upside down on the ground). This was done by eye just making sure the legs opposite each other where in line.
  • Once they were at the correct angle we pinned the angle of the inserts in the top of the pyramid.
  • We then removed the pipes from the newly pinned inserts.
  • Then we placed the middle and lower rung levels around the top of the pyramid (yes still upside down).
  • We then inserted the poles in the gusset plates on the low level followed by the mid and then finally onto the inserts now pinned on the top level. By just holding the angle of the inserts and ultimately the legs it stopped the twisting issue.
  • We then used a jig to set the gap between levels and set the mid level relative to the top level.
  • Then once the middle was set we set the distance to the low level.
  • Once all levels were set relative to the top we flipped it over and tripped off the excess pipe to get the low level to the 30 inches.

Not sure if this will help anyone but it certainly helped us based on our pyramid design.