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.
The first lot of photographs, when we were having trouble with vibration. Last image with arrow, showing leg clips that hold legs at an angle.
Scan completed after releasing leg clips, these were causing legs to bow due to legs bending past the clips restraining angle.
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.
