Zero metal EMC antenna tripod - Page 1
Forum section: electronics / rf-microwave

author: dazz1
author_rank: Frequent Contributor
timestamp: January 31, 2025, 11:34:01 pm
content: HiI have been developing a DIY Biconic antenna for a few years. You can track progress at this link:https://www.eevblog.com/forum/rf-microwave/diy-rf-emc-biconic-antenna/I need a zero metal tripod to hold the the antenna. Zero, or near zero, metal tripods are usually obscenely expensive, or more than I want to pay.I decided to develop an all plastic tripod specifically for emc testing.The tripod is to be made of 3D printed components. The legs are to be made of PVC electrical conduit. An all plastic tripodThe first part to be developed is the hinge between each leg and the tripod head. The hinge will be printed in place. The design would be impossible to manufacture as separate parts, then assembled.I have been designing, printing and then destructively testing prototypes. The aim being to find the weakest points and strengthen those. The result is a material efficient design.The hinges allow a limited rotation to fold in/out each leg. The hinge is basically a splined shaft engaging in very loose splined bore. This works by spreading the torsional load across multiple points. The splines are divided along their lengths to similarly spread radial weight to different parts of the hinge. So the effect is that both redial and axial loads are spread throughout the structure of the hinge unit.So attached are photos of the load test setup. I apply torque with what starts as an empty plastic bucket. I fill the bucket with measured water quantity until the hinge fails.The hinges have not failed before the conduit sockets. I fitted cable ties to try and strengthen the sockets enough to shift the weakest points to the hinge.For prototype development, the 3D hinge is printed with 2 layers. The hinges are weaker than they can be. Adequate for prototype destructive testing.The sockets failed at 10N.m. The hinges flex quite a bit before failure. This is considered a good thing because it will reduce the risk of over-stressing the hinges in service.Next step is to incorporate the hinges into the design of the head.

author: coppercone2
author_rank: Super Contributor
timestamp: January 31, 2025, 11:40:32 pm
content: I put mine on a wooden chair for testing lolthe next test was going to be wooden stool on top of wooden chair

author: dazz1
author_rank: Frequent Contributor
timestamp: January 31, 2025, 11:53:55 pm
content: Quote from: coppercone2 on January 31, 2025, 11:40:32 pmI used a plastic basket, but it doesn't look impressive enough.

author: Kean
author_rank: Unknown
timestamp: February 01, 2025, 12:22:18 am
content: Curious to see how this goes.I've generally just used some wooden dowel stuck into whatever was handy, plus cable ties as needed. I've considered buying a used surveyors tripod (wood or fiberglass), but don't really use my BicoLOG antenna often.In my experience most PVC electrical conduit is too flimsy, but I guess you can put some wooden dowel or thinner conduit up the center.FDM 3D printed parts are also a bit weak unless you really bulk them up, and the weakness moves depending on the orientation of the layers during printing. I now pay for MJF Nylon 3D prints once I finish the design review with ABS FDM. The MJF Nylon don't really have layer lines, thus reducing potential weak spots.

author: dazz1
author_rank: Frequent Contributor
timestamp: February 01, 2025, 01:33:22 am
content: HiMy tripod is intended for occasional use.PVC conduit is strong enough, but it does sag with time and load. This tripod is intended to be put up, used and put away.When folded, the tripod will be low profile so it can be easily stored with the associated biconic. This will require a non-standard layout of the head.The folded length of the tripod will be limited by the dismantled length of the biconic. I think the tripod will be able to hoist an antenna to about 1.5m off the ground.For the most part, the tripod will be non-repairable. If I break it, I will just print off another. Some assembly required.Current plan is to use 20mm/25mm conduit, but if I need greater strength I will upscale to 25mm/32mm conduit.

author: Kean
author_rank: Unknown
timestamp: February 01, 2025, 08:57:36 am
content: You might want to consider PVC pressure pipe. Thicker walls, so a lot more rigid at a modest increase in cost and weight.Of course, it uses different dimensional standards. I don't imagine it would be too hard to adjust your 3D design to suit.

author: coppercone2
author_rank: Super Contributor
timestamp: February 01, 2025, 05:48:32 pm
content: I have been thinking how to make one using fiberglass poles. The hinges you made make it into a real tripod, but I had something in mind that the poles support each other and go into a plank with some holes in it.the kind of tripod has difficulty being on unlevel ground thoughI think a metal chain might work toofiberglass poles for paint brushes and such are ridiculously strongand if you can tolerate a tiny amount of metal, you could put threaded inserts embedded in a base plate made of fiberglass and resin (might be tricky to build) that basically turns in into deploy able furniture (or some hard wood)then it would get screwed together upside down and flipped to make a tripod shelf thingI wonder if iron-wood can be threaded to make a receptacle for a paint brush thread that is strong enoughfor precise leveling I imagined mechanism that is like putting a sphere in a sandwich with 4 nylon threaded rods to adjust the angle of the top platform precisely.

author: A.Z.
author_rank: Super Contributor
timestamp: February 02, 2025, 06:58:54 am
content: https://www.bsatroop1424.com/skills/scouting-skills-tripod-lashing/

author: Gyro
author_rank: Super Contributor
timestamp: February 02, 2025, 10:46:01 am
content: Another vote for wood. it's going to be more rigid than tubular plastic. You can cut simple finger joints for hinges - hinge pins being easily replaceable nylon bolts or wooden dowels. You can then make a simple removable wooden spider half way down the legs to provide stability, resist twisting and set their angle. Modern plastic materials can't really compete for something like this.

author: coppercone2
author_rank: Super Contributor
timestamp: February 02, 2025, 12:52:36 pm
content: that survival tripod can seat a sphere on top to adjust angle. Actually I wonder if you can just put notches in wood, and tighten it down over the sphere at 'level'. So long the object is light, it might be stable enough to get reasonable angles. That could be a stone age surveyor tool, if you get the friction right

author: A.Z.
author_rank: Super Contributor
timestamp: February 02, 2025, 02:12:46 pm
content: Quote from: coppercone2 on February 02, 2025, 12:52:36 pmtoo complex, just hang a pipe with a weight at bottom and it will stay vertical

author: A.Z.
author_rank: Super Contributor
timestamp: February 02, 2025, 02:13:50 pm
content: don't use a pressurized pen when a pencil will do the job

author: tszaboo
author_rank: Super Contributor
timestamp: February 02, 2025, 02:21:45 pm
content: Quote from: Gyro on February 02, 2025, 10:46:01 amI've been in a million EUR anechoic chamber, where the DUT was placed on a wooden desk that looked like what my great grandmother used to have. I see no reason, why OP couldn't just chop off a broom handle and use that to hold the antenna. It's the "once you have a 3D printer, you make plastic hammers for every nail" issue.

author: coppercone2
author_rank: Super Contributor
timestamp: February 02, 2025, 02:34:41 pm
content: how unprofessionalI think you ran into a real bullshit artist, thats just a way to try to look cost effective after someone blew a gasket over EMC chamber costs.suddenly it meets a metric of having successful cost reduction applied. what would it be like 2000/1000000?next they wrote a memo about double sided printing and started rationing the tetleywhy not steal some traffic cones too?

author: Kasper
author_rank: Frequent Contributor
timestamp: February 02, 2025, 04:27:52 pm
content: I had some picky tripod requirements to fulfill and made this.I'd use plumbing pvc and couplings to make a non metal version. Glue a few 45s together to make the base.

author: tszaboo
author_rank: Super Contributor
timestamp: February 02, 2025, 05:19:41 pm
content: Quote from: coppercone2 on February 02, 2025, 02:34:41 pmWhy? I gets the job done.You can buy a new wooden desk as well, would that be better?https://theemcshop.com/anechoic-chambers/emc-emi-test-setup/all-wood-non-conducting-emc-test-table/

author: Kean
author_rank: Unknown
timestamp: February 02, 2025, 06:48:49 pm
content: Quote from: tszaboo on February 02, 2025, 02:21:45 pmSeen the same in a couple of EMC chambers here in Sydney, particularly when doing conducted emissions. I think they like using really old wooden desks as they use proper joinery and little to no nails/screws.Large "styrofoam" (expanded polystyrene) blocks are also popular for placing the DUT when doing radiated emissions or immunity. They also get beaten up over time.

author: Gyro
author_rank: Super Contributor
timestamp: February 02, 2025, 07:20:51 pm
content: Yes, nothing wrong with old properly jointed wooden tables, especially when you consider the variety and weight of some of the DUTs that get dumped on them. More or less standard equipment in the test houses I've been to.EDIT: Looking again at the modern table that tszaboo linked in reply #15, I see no proper through tenon joints, just lots of glue blocks. A veneered chipboard top too.

author: coppercone2
author_rank: Super Contributor
timestamp: February 03, 2025, 08:19:04 am
content: I think there is nothing wrong if its a DIY effort but nothing makes the... lab workers.. embarrassed more then barncraftIts like sad, the managers can spec out 2000$ steelcase chairs and exhorbant standing desks and stuff, then your playing macguyver in the lab with bushcraft fixturingthat kind of stuff is awesome privately but at work it ends up feeling like your getting scammedWhat I am thinking though is to make those parts into molds and make it out of a engineering polymer (prototype part epoxy)... I feel like those parts are good, improving them any further just seems like you are fighting with the 3d printer material, I think the design of those joints is commercial qualityhttps://specialtyresin.com/products/tough-cast-65dI never tried it because its PU