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Yeah. That’s what this guy from NGS said. Back then they had no harness or safety belts. Just climb and do what needed to be done.
Those old marks are exciting to find. The thought of doing what they did and accomplished is amazing with the equipment. Now we can never leave the office and ties every CORS together across the country. I was doing some work at a naval facility which has an old NGS mon which was not called NGS then. They built a look out tower over it and it’s still accessible but I was trying to tie it with gps but couldn’t. It is a mark that has several azimuth to some industry smoke stack features along the Potomac. . I ended up tying to it conventional. I rigged up a long plumb bob and dropped it from the look out tower to transfer the mark up. They had an old digital transit 20” gun laying around. So for fun I went up set up wrapped the angles to my points and all the old azimuth marks the transit was way out but just to get a feel for the historical significance of what they accomplished. Makes me appreciate the technology today most times. However when I see companies that have the technology but still use it like it’s 1980 all the standards and processes to accomplish something it makes me wonder Why am I doing something for 8 hrs when in 2 hours I can get the same results and same quality. Doesn’t make since to my brain.
This presentation is interesting, on the NGS site, I only see the optical theodolite method, but this presentation mentions approval of an edm total station method also:
https://docplayer.net/63170299-Ngs-river-valley-crossing-procedures.html#download_tab_content
docplayer.net
NGS River/Valley Crossing Procedures - PDF Free Download
NGS River/Valley Crossing Procedures Iowa ASCE Meeting Ames, IA October 19, 2016 by Dave Zenk NGS Northern Plains Regional Advisor Team Members Kendall Fancher, Team Leader, Instrumentation Branch Chief
I will have to make a phone call. See if they have the edm one out yet. I will have to take out the trash and do extra honey do’s to get on the wife’s good side. The guy who did a lot of work on that use to borrow my trailer once in a while to fetch hay for his horses. Great guy. I honestly haven’t met anyone I disliked from NGS including the wife. lol. They are a great group of folks and honestly all want to provide us with the best they can.
Hey I got kudos for telling you about that presentation. The wife loves when she gets to hear from outside the agency that surveyors are reading and such the products they put out. I am very blessed she is a good woman and hard worker. I think that must be a Trimble S9 in that presentation. Which on the optical side is rare at NGS historically.
@OleManRiver 👍😀<div>
Thinking about making a couple of prism holders that can be installed in the main shaft of the tripod, so they sit directly under the centre trunnion axis of the total station. A slight variation on methodology, but same principle.
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I never cease to be amazed at the ability of humans to come up with clever ways to solve problems. Cool looking bit of kit.
Man you are innovative. That’s what it is all about. Seeing a problem making a solution and test and verification of that solution. Keep it up. I think you get it all worked out you should patten that.
You mention the error tolerance displayed at the end of a scan. That is just how far out of level the instrument got during the scan. It’s not a measure of stability of the scan. If the tripod isn’t stable enough, it won’t even scan. This is because the instrument vibrates a bit while scanning and when warning up to scan.
@OleManRiver , @lukenz Thanks for your encouragement 👍
The SX12 has a field calibration routine for level, when we first level the instrument, we level it within an arcsecond, then rotate it 360 and check it remains within an arcsecond of level, sometimes it can be 6 arcseconds or more out, so if we were to use it like this, the level compensator would be compensating for a non-level condition, so we run the calibration routine, after that, it’s always within an arcsecond. Following this procedure, if it goes out of level during scanning by more than the preset alarm value, by default 8 arcseconds, it will notify us, I’ve asked Trimble if they would add a similar alarm to normal operation, not just scanning. So far only high-quality properly adjusted timber tripods pass this test, even high-quality fibreglass tripods fail it every time. Hopefully it will pass, we will know soon, if it exceeds the alarm, I’ll report how much it moves and we’ll try to figure out how to improve it.
This is what motivated us to design the new tripod, the noise in the background is a conveyor, there’s no ground movement, there’s a breeze, we’ve tensioned some nylon chord in an attempt to stabilize the tripod, this is a quality brand name elevating tripod, with no load other than a tribrach and prism.
I was thinking about you today. At the ball field watching my daughter play softball. I was talking with the wife and telling her what you were doing. She then reminded me at the office where she works they had all sorts of tool and die and other machines and tools. They use to make everything they could right there for various situations to adapt items. For leveling to triangulation GPS. One of the men that worked there back the last time they positioned the Washington Monument he went up and made some measurements and went back there to Corbin and built a adapter to be able to set the gps antenna and such on it for the survey. Good old fashioned ingenuity. No one makes what you need fine build it yourself. Keep it up. If you need a silent investor let me know .
Thanks @OleManRiver appreciated, testing will help us understand if the tripod is viable.
We have some very interesting results from our first test today.
As @RobertUSA mentioned the SX12 has internal movements that may cause vibrations.
The tripod has clips at the top that hold the legs at 45 degrees and 27 degrees (approx), when these clips were engaged, and we were adjusting the tripod level, it caused the legs to bow and when this happened, the vibrations resonated through the tripod and prevented it from scanning.
So we lowered the tripod and released the clips that hold the legs, with clips released they were in simple compression, no bending forces to bow the legs. The clips are useful to hold the tripod in position when setting up, but clearly need to be released. Also we were careful to free the upper legs while levelling the tripod, and then applying a slight compressive load to the upper leg after levelling, this also allowed some fine adjustment of level, with most of the adjustment performed while the upper leg was free to extend or contract, without load. There was however still some resonance detectable in the upper legs, gently touching one leg about 1/3 the way up (the legs were slightly different lengths due to slope), completely resolved the vibration and the SX12 had no problem scanning. However we didn’t manage to complete the scan, as the instrument ran out of battery before it finished transferring the scan to the controller, @rover83 definitely has a point regarding the external battery.
This means we didn’t have the opportunity to test the scan level alarm today, so we’ll be out again Tomorrow to test that function. The construction is typical of Scanner tripods, we found the glue used to attach the aluminum to carbon fiber isn’t flexible enough and some of the bonds failed, when we applied tensile load, we repaired the failed bonds with Sikaflex 252 high strength structural adhesive, which remains flexible and is a lot stronger than original adhesive used.
Regarding upper leg resonance, I think we need some small cross braces between the upper and lower legs, with rubber dampers surrounding the top leg, to change the resonant frequency of the upper legs, so they don’t coincide with vibrations generated by the SX12. Holding one of the top legs gently between two fingers 1/3 the way up eliminated the vibrations completely, holding the leg the same way in the middle didn’t resolve the vibrations which is typical of resonance.
I’ll provide a progress update tomorrow.
- This reply was modified 1 week, 2 days ago by pfirmst. Reason: typo
Some more tests this morning, I found a parasol umbrella, with spring and rubber clamp, this alone was sufficient to eliminate the resonance. It looks like it’ll need some small rubber mounted mass dampers to prevent resonance.
Results are similar to a quality fiberglass survey tripod (non-elevating, just a typical brand name survey tripod), in that I have so far only avoided scanning tilt errors using a high-quality timber tripod. It was sitting on grass this morning, and the feet aren’t designed to push in, this would be the cause, so I’ll try again later on concrete again. It could be the case, that the properties of carbon fibre are just similar to fibreglass.
I could brace the upper legs, roughly halfway, which would result in a fourfold increase in their buckling strength, although I can’t see it by eye, it’s likely that slight buckling of the upper legs is responsible for changes in level.
It is very difficult to get the tripod level, I have however changed my technique for levelling, by releasing the upper leg, then adjusting the lower leg, then applying the turnbuckle on the upper leg, when the latter occurs, due to the turnbuckle screw clamp design, it changes the level slightly as it closes. What I probably need is a fine screw thread on both upper and lower legs to adjust level perfectly.
I have no doubt you are going to figure it out. So as my small brain sits here staring at the picture. What would happen if the middle pole came all the way to the point. Sorta like a gps fixed height set up. Even with a Topo foot type contraption at the bottom to give direct support at the vertical directly under the weight. It could maybe be something that expanded straight down. No need for a tip as setting directly over a point is not necessary. Would that relieve some stress maybe
Hmm, a center leg with foot, that’s a relatively simple addition, so everything else becomes stabilizing outriggers. That’s probably worth trying before adding additional braces. The funny thing is, I could put a big old point on the end, the tube ends are threaded, saves making a ball foot, then we’d know instrument height exactly and it would always be the same.
Crazy how that parasol umbrella stops the vibration.
Another video from this afternoon, seems fairly consistent, there are some level changes during operation, in this case 17 arcseconds.
- This reply was modified 1 week, 1 day ago by pfirmst. Reason: add level deviation, not legible in video
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