pic: Just finished our pyramid. Conduit seems to work fine.

[alex334]

Originally Posted by buchanan

Good job, I was wondering if this might work. The competition pyramid has to be built to a pretty high standard, given that it has to stand up to up to three robots for many matches, but something lighter should certainly be fine for testing.



Echo that, inquiring minds really want to know - the $$ difference is about 3x.

The conduit we used had about a 1/16" wall thickness. Make of that what you will.
We built off the specs from the "Game Specific Drawings," not the team version.
We don't really mind discrepancies in pipe diameter and angles (a couple of corners are a few degrees off). If you can't build a robot to tolerate those minor differences in designs and implementations, you are really building it too precisely. As in Logomotion, many teams had very fast minibots, but the tolerances needed to get them onto the pole were just too small. We're thinking the same logic applies to this.
For those of you asking about measurements, the center of the piping in each rung is 30" vertically off the ground. The slant height is about 32"-33" if I remember correctly. Just use some simple trigonometry to figure it out precisely.

[buchanan]

Originally Posted by alex334

The conduit we used had about a 1/16" wall thickness.

This is thinwall, aka EMT. It's the less expensive stuff. It runs around a dollar a foot at my local big box home center.

[RRLedford]

Originally Posted by buchanan

...

Echo that, inquiring minds really want to know - the $$ difference is about 3x.

CORRECTION MADE. IGNORE WARNING BELOW.
WARNING FOR CHECKING POSSIBLE RADIUS VERSUS DIAMETER ERROR ON THE SUGGESTED ITEM (spherical washer)!!!

MOSTLY OFF THE SHELF H/W CAN ALLOW BOLTING YOUR CONDUIT TOGETHER & WITHOUT GUSSET PLATES NEEDED.

Here is how to save even more $$$ and time, esp. if in-house welding not so good or not available.

You can buy mostly off-the-shelf hardware from McMaster Carr to sturdily bolt your pyramid together.

The only special items are the making of (12) 1.25" OD conduit tube inserts, for which we are using 1.25" OD bar stock of 2011 aluminum (~$10/ft @speedy metals.com), which pieces then need to have two holes drilled/tapped @5/16-18 (or M8-1.25) into their OD for the assembly bolts to thread into.

Then ~1-1/4" long flanged button socket cap screws protrude out from the IDs of the horizontal tubes, first passing thru a spherical washer against the tube's ID, then going through a 5/16" hole in backside of the horiz. tube wall, then through a pair of flat-to-flat (curved ends out) nylon tube spacers that will give an ~1/2" tube spacing between the slope tube and the horizontal tube, then thru the slope tube 5/16" hole, and finally they thread into the tapped holes of the custom made aluminum inserts fitted inside & holes aligned to the slope tube.

So to have the inserts work as corner joint anchor points at each level, pairs of 5/16" holes are drilled into the slope tubes at proper angle and elevation. The 1.25" OD aluminum plug inserts (~2" long w/ pair of tapped holes) are then slid up into the slope tube and aligned with that level's pair of tube holes, and the cap screws are fitted through both tubes, along with the rest of the H/W stack to give a reasonably strong joint.

I forgot to mention that small holes are also needed on the outside of the horizontal tube for the allen wrench to fit through while tightening the joints. These can be drilled as a pilot holes in the process of doing the backside larger holes. Since this wrench hole size is so small, it doesn't affect much as far as interacting with the robot differently than a proper pyramid will, which is another reason for choosing the flanged button socket head cap screws (smaller wrench size & curved profile head top).

Keep in mind that the spacing between horiz. conduit tube and sloped tube can be adjusted wider by adding a washer or two between the pair of curved end nylon tube spacers.

Hope this assembly helps teams get their test pyramids built a little more quickly and easily than otherwise might have been possible for them.


Flanged Button Socket head bolts:
Min. length needed is ~1-1/4" and McMaster only goes to 1" on 5/16-18 so we went M8-1.25 x 30mm instead of 5/16". Other places have the longer 5/16" cap screws. Stay with button head (not socket head) or length gets too long to fit easily thru hole from inside of the horiz.tube ends.
http://www.mcmaster.com/#button-head...screws/=kztpuj


Note that the curved end nylon tube spacers are made to match a 1-1/8" OD tube size, but they should crush down and flex enough to still give decent stability of the horiz. tubes.
If we find they wobble too much, with all the money we saved, for plan B we bought a 1.5" dia. ball end mill (3/4" shank, to do some reshaping of the curved ends. We can also use larger dia, or square, nylon bar stock to make some one piece spacers with the two curved cuts in the ends made at the proper skew angle to each other, something that is not an issue with the smaller radius spec., off-the-shelf pair being able to swivel relative to each other.

http://www.mcmaster.com/#unthreaded-spacers/=kzterj


CORRECTED FOR BEST TUBE ID RADIUS MATCH => Male spherical washer with 15mm radius (gives match to 1.2" ID tube) - expensive at $1.70 each & may be cheaper elsewhere, or perhaps not even required.
CORRECTED SPEC. ID- 10.5mm OD-21mm; Note for thin wall conduit use next size up Metric washer with 17mm radius (either size will still work OK with 5/16-18 or M8 cap screws) => http://www.mcmaster.com/#98148A103

[RRLedford]

Originally Posted by buchanan

This is thinwall, aka EMT. It's the less expensive stuff. It runs around a dollar a foot at my local big box home center.

[color="Red"]

Home Depot has the 1/8" ( is this the heavy wall?) 1-1/4" conduit with a 1.51 OD spec & 1.25 ID spec. at the same <$1 a foot here in Chicago.
Online price --- http://www.homedepot.com/Electrical-...1#.UPH0rvKQk9I

-Dick Ledford

[ctccromer]

Gussets were cut out of 1/8" steel using our CNC plasma cutter.

Is Isaac Clarke on your team?

[Jeffrafa]

Dick,

Have you built a pyramid bolted together this way? It sounds appealing, but I'm curious if stability is an issue at all, like it is with FIRST's low cost design.

I had noticed comments about the low cost one twisting here, and I was looking for alternate construction methods before we sink money into materials.

For us, welding is not ideal as we would not be able to get it into or out of the room we need to use it in.

[RRLedford]

Originally Posted by Jeffrafa

Dick,

Have you built a pyramid bolted together this way? It sounds appealing, but I'm curious if stability is an issue at all, like it is with FIRST's low cost design.

I had noticed comments about the low cost one twisting here, and I was looking for alternate construction methods before we sink money into materials.

For us, welding is not ideal as we would not be able to get it into or out of the room we need to use it in.

First off, we are using the 1.51" OD by nominal 1-3/8" ID tube that is named "1-1/4" conduit" at Home Depot.

We are still machining the threaded aluminum plugs that go inside the conduit, but the initial single joint mock up with actual H/W stacked pieces shows proper contact with tube IDs and ODs to ensure no tube wall bending of the edge pipes will hppen when the horizontal rung pipes are loaded with single robot weight.
BTW, watch out for getting any dings in the conduit used for the edge tubes, as they make inserting the plugs in the edge tube nearly impossible if they are slip fit.

The dual threaded insert plugs' OD spec is 1.368" +.000/-.005 for a snug fit to the ID of the conduit that Home Depot sold (Allied brand). We know the two holes must be drilled in the edge tubes at 104.5 degrees apart going around the edge tube's OD to match up with the side to side dihedral angel, but we are still trying to calculate at how much of an angle --- skewed away from being parallel to a plane crossing the pipe plug at 90 degrees --- will these holes need the hole needs to be oriented?

Also, the rung pipes' bolt holes need to be angled downward ~22 degrees from horizontal, so that they pass through the imaginary tangent point where the edge & rung tubes would touch (without the spacers), and the angle of the rung bolt holes are thus offset down, skewed away from being at a right angle to the vertical 45 degree cuts of the pipes' mitered ends.

We are deliberately leaving extra edge pipe length at BOTH the lower and upper ends of the edge pipes until the equally spaced rung holes are all drilled. Once that is accomplished, we will then fine tune the edge tubes' 60 degree miter cuts at their bottom & top ends to get the first rung's top side elevation right at 30 inches and goal elevation at its proper height.

We drilled a 3/8" hole down the centerline of the plugs so that when the tapping drill and the tap cut in from the OD they both hit this 3/8" center hole, rather than having both holes intesecting each other asymmetrically & possibly breaking the tap.

Will update with PICs in a day or two. If anyone can CAD up the angles of these bolt hole axes relative to the pyramid pipe axes and the insert plug shape, it would be quite helpful. It would have made so much sense if these insert plugs could have been made available for purchase at kickoff day, and teams could have quickly built a sturdy metal pyramid that closely matched the welded design. The PVC design suggested by FIRST was a very bad joke to play on us.

Here is a graphic of my assembly joint concept, but angles are not exact. It is clear that the neon green nylon spacers will be thicker than the welded version's gusset plate, so if you are planning a gripper design that engages right at this spot near the edge tube, they will need to be made less thick by filing, or by making a notch in your gripper there, interference with it can be eliminated.



-Dick Ledford

[RRLedford]

We have tested our pyramid assembly concept and found it works well.
However, we are still slightly off with our angles.
Can anyone use their CAD or trig expertise to confirm What is wrong?

We are trying to drill holes in the slope pipe and rung pipe such that a hole through the center of the rung pipe follows the line that connects the center of the slope pipe's plug with the point where the two pipes would tangentially touch if they weren't spaced out by the nylon tube washers.

It is not even clear of a line through the centers of the two pipes and the tangent contact point would be in a plane that crosses either pipe at a right angle to their length axis.

We want to drill the two pipes at a right angle to their lengths. We are drilling the tapped holes in the slope tube's plug insert at 98 degrees apart and the rung tube is drilled at 22 degrees downward angle from horizontal, but the PICs show that some angle(s) is/are not right.

I suspect that the two holes in the insert plug must be drilled at a different angle separation than the 98 degree dihedral angle, and that they may need to be in a plane that does not cut the plug at a right angle to its axis.

Many teams could affordably and easily build their own pyramid, or partial pyramid with this fairly simple assembly concept

Any help would be greatly appreciated.













-Dick Ledford