I wanted to share this if anyone is out there considering GPS/LPS. Just a quick reference to what I am talking about if your not savvy to the lingo. LPS uses a total station and a prism for machine control. GPS uses satellite guidance for machine control. I have a TOPCON LPS (LN 150) on a Sharp Grade 128 blade being pushed by a CASE DL550 Minitour. We have finished 3 projects with this set up now. This last one is the one which is most impressive. We pulled out the Massacre Rocks State Park parking lot in Southern Idaho. The lot was replaced and expanded. The total SF was about 65K. It was paved last week by a Depatco crew out of Boise. According to the paving crew and checked by us through out, except for one small spot, the entire parking lot was graded to within .25 of an inch the final base material was 3/4 road base. The spot that was just outside of that I think was due to a bad data conversion. We struggled with that location during the prep. We ended up 6 tons under what the paving crew estimated for the bid. Our spot checking showed a couple spots that were 3/8 out. The system is not totally dialed in yet. Topcon is coming out to look over a connection issue we have at times. However, the accuracy is incredible. We had zero issues with distance and the LPS system. It covered the entire project without a problem. The one issue with LPS is if anything gets in the way of the total station and the prism breaks the connection and has to gain the prism to continue to track. That sucks. We learned just to work the pad in a way that prevented that as much as possible. GPS has its advantages over LPS for sure, and later in the year I will be able to switch back and forth from LPS to GPS. However, I was frankly really surprised that over such a large area we could average grade as close as this. I have a lot more I could talk about, but I leave it here. If anyone has any thoughts, I can elaborate more.
Amazing technology and it's got to make you feel good about your investment after the results at Massacre Rock! The line-of-sight issue with LPS prevents us from using it, but I would assume the tolerance is more a result of how well the machine can use the data rather than purity of the data. Also how well the operator understands what works the best. When we use our rover with GPS the data collector displays the current tolerance, and will not allow measurement when the accuracy is out of tolerance. That however is a snapshot in time. When machine controls use the information it is more of an average all the snapshots, and the accuracy is pretty amazing. It still is curious to me that we tend to have satellite issues mid-afternoon more than other times of the day. We work in canyons and amongst trees often though and rarely have any issues when out in the open. Your process must be very good to end up with the results you achieved, specifically how you handle water, compaction, cut to finish, etc. Also, the aggregate out of the Pocatello sources is quite different than the IF stuff, that can add a bit of a learning curve. Thanks for sharing info on LPS. It is neat to here about it.
So would trees and light poles disrupt the LPS system? or is it only if there's a larger building around. And then if there is a building in the way, can you move the base and re set up? or does that throw the system off?
Funny you mentioned the Pocatello sourced pitrun and road base Oxbow. What a mess it was. I don't know if everyone's material is the same down there, but Depatco's material was very hard to get compaction on. IF material we can hit compaction easy with anyone's material, that is not the case down south apparently. We figured out a method to feed material and water and compact by keeping all of that on the outside of the grader and Total Station, its a pain to do it that way. The State had taken a ton of data points, so due to that it made the data very accurate. Why that one spot was problem, that I don't get. The process I used was this, we cut it a half inch above grade for compaction on 4" of 3/4 road base. We compacted it and got it passed compaction testing. We then cut it again at 2.75 below top of finish grade asphalt grade and recompacted it. This allowed for the 3" of asphalt. It was a bit of guess honestly, and it took some time, but the 11' blade made it go pretty quick. The results were worth the effort. Crane, a light pole isn't an issue, but about anything else would be. For us, it was the wheel loader, and roller that were the most problematic. IF you stop right when the object breaks the view its not a big deal. IF you keep going, the TS has to start searching and that takes a minute to find you again. Yes if you have a building or something like that in work area, you need to reset up the TS to hit that area. Its not a big deal, the LN150 is quick to set up. I feel really good about it. I will feel even better when Topcon dials in a couple things. We went LPS for the accuracy and we got accuracy. When I have time, I will do a write up on the Sharp Grade 128 and the Minitour.
Ha, I was wondering how you made out with the Poky stuff. It's kind of like the difference between Swan Valley material and Driggs/Victor material. They are pretty close to each other, but one side of Pine Cr. is quite different than the other.
Same here. GPS gives us the tolerances we need .10' +/- over an expansive area. The LPS system can deliver much tighter tolerances over GPS. Depends on what your scope of work is.
Lps is super accurate in my set up as well, as for line of sight I wish that they would offer an active prism. It would be a much quicker pick up if the search window was guided by the prism like some other manufacturers do. The more expensive total station they offer rotates much faster than the LN (quicker through the search window), but in my opinion the LN is tough to beat for the money.
I have told them the same thing on an active prism. The method that LN uses to search is not the best in my opinion. We have a Geo Max Total Station and its method of search is much faster. Watts what do you the LN on?
I use it on a 85-7 Kobelco with swing boom, to be honest I normally use the LN as a layout tool. I work busy commercial sites and line of sight is a nightmare. As you stated the search function is not all that rapid so if you lose contact it can be time consuming to get back. I have found in trenching applications that layout with a total station followed by trenching with 2d laser to work very well.
Similar to what we do. Use the GPS for layout and dual slope laser for pipe laying. We get our models with line work for rough trenching but we still like the accuracy of the laser for flow line. Doing a fair amount of roof drains on a larger project now and the building interferes with the GPS as well.
I work with Trimble UTS same technology line of sight and very accurate to 1/8. must have for airports and athletic fields. To get the most out of this type of system you need a 2nd total station and prism to check grade while working. how are you checking grade behind machine while machine is running off of the total station on your set up? UTS runs an active prism. setting search window to a smaller area helps when you loose line of sight.
Just saw this, we have two total stations. The Topcon system to run the machine and a Geo Max we use to check grade.
I went ahead and liked all of you alls posts....even though your speaking french
Have used Trimble UTS on many rd jobs on a grader. Most jobs have +\- .04 so it’s very accurate. I’m my experience your set up will dictate how your day goes. Dump trucks, rollers, telephone poles even your own cab could block your line of sight so you have to put a little thought in it and plan your set up. Some projects such as PENNDOT requires you to use the UTS instead of GPS.