Any Electronics Gurus Out There?

[wvgca]

a 'scope can read usb data, but data + and data - lines must both be read, requiring a dual channel [or better] 'scope for it to work..
usb uses uses a differential transmission pair for data. This is encoded using NRZI and is bit stuffed to ensure adequate transitions in the data stream.
the 'scope ground should be hooked up to the usb ground ..

 

[npalen]

How big of a job would it be for an electronics guru to design and spec all the components required for this system?

 

[quicksandfarmer]

How big of a job would it be for an electronics guru to design and spec all the components required for this system?

Here's how I would approach it. There's basically three parts: reading in the setting, controlling the blade movement, and the logic to connect the reading to the controlling. I would use a small microprocessor like an Arduino or a Raspberry Pi.

Reading: if the signal between the receiver and the remote is a standard protocol, both Arduino and Raspberry Pi have built-in processors for USB, RS232, I2C and other protocols. Reading the data is just a matter of connecting the right pins on the receiver plug to the right pins on the microprocessor board.

Controlling: Two ways of controlling the blade have been proposed, either using an electric hydraulic valve or using a power-steering type valve with a DC motor. The electric valve is not difficult, it just needs to be attached to one output pin of the microprocessor for up and another output for down. If the current or voltage requirements of the valve are different from what the pins can provide there needs to be an appropriate relay. Controlling the power-steering type valve is done by controlling the speed of a DC motor. This is commonly done by a technique called pulse width modulation, where pulses of electricity are sent to the motor, the longer the pulse the higher the speed. This requires attaching a single output pin of the microprocessor to the motor. Again, if the voltage or current requirement of the motor can't be met by the microprocessor pin a relay is necessary. If you were to take a course in using Arduinos or Raspberry Pi this is all stuff you would learn in the first month.


The third part is the control logic, this is a program that runs on the microprocessor. This is the big wildcard. It could be as simple as "once a second, read the blade height. If it's too low raise it, if it's too high lower it. Repeat." Or it could be that you need to keep track of the history of the blade height and the history of commands you've given and adjust your response based on what's working. Or maybe you need the user to input some information about the hardness of the soil. Or maybe you need another sensor to tell you the speed of the tractor.

The control logic will take some trial and error, a lot of time just driving across fields and watching what happens. The reason I'd prefer Raspberry Pi for this, even though I have more experience with Arduino, is the RP has more capability for things like logging data and giving a display while it's working. If you were to do this with Arduino you'd probably have to have a laptop on the tractor with you while debugging log what's happening. I've also done projects like this where I had an Arduino-like device attached to the USB port of a smartphone and the phone provided the display and logging.

 

[npalen]

Thanks again for your extensive input! I don't have the knowledge but I'm sure that you and a couple others who have been responding are more than capable of making this work.

I see some advantage in the DC motor approach. The rpm could be controlled as needed depending on how far from the target as well as acceleration and deceleration for smooth operation. I keep thinking that PID could be utilized as well for "learning on the go" but may just add unnecessary complexity. Just about every closeup I see of the control box on the tractor has a sensitivity knob and I suspect this is in response to ground speed. With that said, I still feel that a solenoid valve could be made to work

I don't believe, in my mind at least, that the hardness and type of soil would be needed inputs. The height needs to be adjusted if the receiver is showing off grade and the operator needs to adjust tractor speed to that which the control system and sensitivity adjustment can consistently respond well.

 

[npalen]

I've noticed that some of the ATV pulled small box blades use 12 VDC linear actuators to raise and lower the cutting edge. That would take a level of complexity out of this project but doubt whether a "normal" alternator and battery would come close to powering a BB of any size in an auto grading app. I'm guessing that an oversized alternator and battery combo might work but not sure. Anyone have experience along those lines?

Many of the linear actuators have built-in limit switches. Duty cycle might be another consideration, I'm guessing.

 

[Industrial Toys]

I am sure that the duty cycle would come into question. That could be going up and down constantly appoaching grade.

 

[quicksandfarmer]

I've noticed that some of the ATV pulled small box blades use 12 VDC linear actuators to raise and lower the cutting edge. That would take a level of complexity out of this project but doubt whether a "normal" alternator and battery would come close to powering a BB of any size in an auto grading app. I'm guessing that an oversized alternator and battery combo might work but not sure. Anyone have experience along those lines?

Many of the linear actuators have built-in limit switches. Duty cycle might be another consideration, I'm guessing.

The reason tractors use hydraulics is that hydraulic has the advantage when you need to transmit a lot of power. Transmitting 1 HP for a hydraulic system is easy. For a 12V electric system you need about 60 amps to do that. That would require a #6 wire, but also in the windings of the motor or actuator. That would be a big, heavy, expensive item -- if your tractor electrical system could handle it. Electric is good for moving small items around but not something like a box blade.

 

[npalen]

Thank you. Points taken.

Thinking about the linear actuator got me going again. I have a linear actuator mounted on the box blade as shown in the pics with up, down, speed control and remote readout on the tractor. The idea is to take grid readings of the elevation of a work site prior to grading. This is to calculate cut and fill and finished grade elevation and it would be a manual process by moving the rig to the next location on the grid, raising or lowering the receiver to take a laser "hit" and then recording the reading on the remote readout at that location. Then rinse and repeat.

With an automated setup for grading the same electronics that control the blade height could be switched to and used to automate the surveying process mentioned above. The process would be driving to each grid location with the linear actuator energized by the auto control so it would elevate to follow the laser beam. The blade height would be clearing the ground by several inches and the cylinder wouldn't move during this process, only the actuator which is DC motor driven.

The digital readout I have mounted on the linear actuator would give the continually changing elevations to the operator's remote while driving and could be recorded statically at each grid point. The GPS coordinates could also be recorded at that point but that's another story.

 

[quicksandfarmer]

I've been experimenting with differential GPS. The idea is that GPS is accurate to within about 20 feet at best. For the most part the error in GPS is due to variation in atmospheric conditions, so if you put two GPS receivers side by side they will both read the same. With differential GPS you use two receivers, and put one of them at a fixed location. By subtracting the reported location of the fixed one from its known position you get the local error. You then add the local error to the reported position of the mobile one. If all you care about is relative position you don't even have to know the actual location of the fixed unit.

This is the unit I've been using: C94-M8P | u-blox The units are $400 each and you need two. I've found that I can typically get accuracy to within a half inch with these. The hitch is that there has to be good GPS reception, which means line of sight to the entire sky. Trees or buildings blocking the sky degrade the results.

I could see a couple of ways of using these in conjunction with the laser level. The first is mapping. Drive around the field and every few seconds log your location and elevation. The second would be in creating more complex contours. You could draw out a contour map of how you want the land to look. Then as you drive around the GPS tells the computer the current location, the computer looks up the desired elevation, reads the current elevation off of the blade, and adjusts the blade accordingly.

Next step would be to eliminate the operator altogether...

 

[npalen]

That is very interesting stuff! The farmers are using RTK, as I'm sure you know, for sub inch auto steer accuracy, but it comes at a much higher price than $400/$800. One of the local RTK installations (Real Time Kinetics) has the base station mounted atop the local "high rise" grain elevator to cover a large portion of the valley. The good thing is that several farmers can share one base to minimize cost for auto steer and other GPS apps . I think there is a pending market for consumer grade auto steer for lawn mowers and fertilizer spreaders. (Not sure how the robo mowers work) A GPS controlled lawn fertilizer applicator with auto shut off is not far fetched, in my opinion.

I'm an old machinist who became acquainted with NC (Numerical Control) back in the late sixties in a machining environment. We used punched tape to control the milling and drilling of holes etc as there were no micro computers back then. It later morphed into CNC (Computer Numberical Control) and prices stated dropping dramatically to the point where hobbyists could afford it. CNC wood routers are common today and I have used mine extensively for producing components for the Palen Archtop Guitars shown at the link below. (Shameless plug but I actually quit building them in 2012.)

What I'm getting at is there seems to be a corollary between the CNC and GPS that keeps popping up for me as time goes on. You mentioned "Drive around the field and every few seconds log your location and elevation" and that is basically what I did to one of my hand carved archtop back and top plates to get it into electronic format. The archtop plates start out about 1" thick and end up as a carved contour about 3/16" thick. Digitizing the carved plate (spruce or maple) involved mounting an electronic probe into the spindle of the CNC router and traversing the entire surface in a grid of points about 1/16" to 1/4" apart and taking elevation readings at each. This created an electronic file that could be read into the PC creating a point cloud and generating a surface in turn. This surface could then be viewed on the screen and tweaked as desired and even a solid model could be created.

Sorry to ramble but but it seems that there is a tremendous opportunity out there for consumer grade GPS apps.

Edit: Forgot to mention that the CNC router could then be used to machine subsequent parts eliminating much of the labor intensive hand carving.