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Cedar Rapids, Iowa | I acquired a broken AutoSense and finally decided to open it up to see whats inside. It was a challenge to get open. The case is made from two pieces of aluminum with an o-ring to make a waterproof seal. Once that was open I discovered the whole thing has been 'potted' in a black epoxy. Potting a circuit board is somewhat common in the electronics world for several reasons. Common reasons for potting a board are: to protect the board from being physically damaged, waterproofing, or to obscure the design so it is much harder to reverse-engineer. However, in this case I suspect it is mainly to make a very solid connection between the gyro and the case. Eliminating any possible vibration or movement is necessary for a high accuracy gyro.
The top of the gyro sensor was visible, the name on the top is Silicon Sensing Systems. That company specializes in MEMS gyros. I had once heard that the AutoPilot/AutoSense used a Ring Laser Gyro, but I guess that's not the case. This appears to be either the CRS03 or CRS43 MEMS gyro. Cost of that one part alone is $125-260 depending on accuracy.
https://www.siliconsensing.com/products/gyroscopes/crs03/
I then cut the case around the connector so that I could get the whole black epoxy brick out of the aluminum. Luckily the epoxy was not adhered to the aluminum, so it separated relatively easily. This revealed a circuit board. There are 4 pins on one side for the connection out of the case, and three pins on the other side that go to the gyro. It looks like this board simply translates the analog gyro signal to a digital signal to go to the NAV2.
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Near Intersection of I-35 & I-90 Southern Mn. | Interesting. Looks well built internally. Too bad, the connector stub to the outside world wasn't more durable. Whenever I had problems, it was always the stub cable.
The unit worked well but I still don't understand how it worked. I realize that a gyro resists change which could be measured but I don't understand how the system "knows" which way my tractor wheels are pointing when it is first started after sitting. |
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South Georgia | It actually doesn't 'know' until you start moving. Then it figures it out. If you look at the voltage in the diagnostics page, it's all over the place until you start moving. Still, how does it translate it into a direction? I haven't the foggiest idea.
Adrian |
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North Dakota | I was told at a school once that the black box was filled with P.F.M. No one in the class wanted to seem unknowledgeable and ask what P.F.M. was. I understand that they are just electronics but being filled with "Pure FINE Magic" seems more appropriate. I looked it up after class. You have to replace the fine with your favorite epithet that starts with an f to make it sound correct.
From what I understand it sends a digital signal back to the NAV and when the unit is moving and has a GPS heading and speed it uses an algorithm to calculate the difference between the NAV and the autosense. Unit has to be moving greater than .75 MPH to get a reliable reading. |
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roaming | tedbear - 1/7/2018 04:50
Interesting. Looks well built internally. Too bad, the connector stub to the outside world wasn't more durable. Whenever I had problems, it was always the stub cable.
The unit worked well but I still don't understand how it worked. I realize that a gyro resists change which could be measured but I don't understand how the system "knows" which way my tractor wheels are pointing when it is first started after sitting.
+1 on the connector/cable.
Autosense MUST be used with a GPS-based guidance system, because Autosense itself has no clue (and doesn't care) about heading. It is only measuring amount of change in heading, and (I think) rate of change in heading. In other words, it's providing a relative heading (the heading has changed D degrees at R rate since the last measurements) rather than an absolute heading.
In addition to the gyro Lance described, I think there is also an accelerometer, although maybe Trimble uses more PFM to calculate rate of change from multiple filtered gyro measurements.
Autosense can't be used with feeler systems, or laser systems, or optical systems, unless there is also a GPS receiver present to provide heading info to the system. |
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Near Intersection of I-35 & I-90 Southern Mn. | That makes sense. When I was attending electronic tech school and a topic came up that we didn't understand the term FM was used. It did not stand for Frequency Modulation such as in radio. You might guess what FM stood for. |
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| Yeah - we use FM all the time for explanations for things that just work, but we don't know exactly how... funny that it's not just the group of guys I work with. |
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Inside a Trimble AutoSense (Pics)
