{"id":11492,"date":"2025-10-13T22:37:05","date_gmt":"2025-10-13T21:37:05","guid":{"rendered":"https:\/\/dronesonen.usn.no\/?p=11492"},"modified":"2025-10-13T22:48:01","modified_gmt":"2025-10-13T21:48:01","slug":"hydrawlics-week-8","status":"publish","type":"post","link":"https:\/\/dronesonen.usn.no\/?p=11492","title":{"rendered":"Hydrawlics – Week 8:"},"content":{"rendered":"\n


Hello and welcome back!\ud83d\udc4b<\/p>\n\n\n\n

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This week marked another milestone for the Hydrawlics team. We completed our midterm presentation, and it went really well! With Sprint 3 now behind us, we\u2019re starting to see more and more of the arm come to life; both physically and digitally.<\/p>\n\n\n\n

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Here\u2019s what the team has been working on this week \ud83d\udc47<\/p>\n\n\n\n

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Fredrik:<\/h2>\n\n\n\n

This week we completed sprint 3. From the mechanical side, our goal was to have a prototype of the arm structure. I was responsible for the arm segments, joints and end effector prototype.<\/p>\n\n\n\n

To achieve this, the layout first needed to be defined. I have played around with different arm segment lengths and cylinder placements for a couple of weeks now, to see how it would affect the drawing area and shape of the arm. The layout I landed on gives a large drawing area, but might demand too much from the hydraulic system. This will need to be tested when this is possible. The tentative layout is shown in the picture below. (The picture is for visualizing distances only, and is not a technical drawing)
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Seeing as what we are currently developing is a prototype, I think it would be beneficial to design it with the ability to be disassembled. Earlier in this course, while working on the hydraulic cylinder, I fastened parts to each other by pressfit, without the ability to remove them again. This turned out to be a nuisance. Therefor, I wanted another non permanent way to fasten components, and turned to 3d-printed bolts. This is something I have wanted to learn how to do for a long time, and thought now would be the perfect opportunity. I watched some YouTube videos and tested for myself, and it worked great. It opened the door for secure fastening, with easy assembly and disassembly. 
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While the arm segments would be made out of lasercut material, I decided that the joint should be made out of 3d-printed components. In the design, the two lasercut plates are separated with a bushing in between to prevent them from rubbing against each other. That would lead to a lot of friction, and variable friction area based on the position of the segments. PLA has relatively low friction against PLA, so I design the bushing and joint shaft accordingly. Finally, a bolt on each side to hold everything in place. I choose inner threads and a bolt over outer threads and a nut because I think it would be easier to print, and easier to assemble.<\/p>\n\n\n\n

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I have included images of the 3d-model of the joint below. I included notches in the interface with the lasercut plates, to lock their rotation to each joint component. Now the inner plate rotates with the bushing, and the outer plate rotates with the joint shaft. This ensures that all rotation takes place between the PLA components, and not the lasercut plates. Locking the outer plate to the joint shaft also ensures that the bolt’s rotation is always the same as the plate directly below it, greatly reducing the risk of it loosening during operation.<\/p>\n\n\n\n

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The arm segments was lasercut at school from mdf plates. After a couple of mishaps, the results looked promising. The plates seemed strong enough, and it was really cool to see the true scale of the arm segments. The printed parts fit together with the lasercut parts perfectly, and the joint system worked as intended. After successfully combining my design of the arm segments with Erlings design of the base, the arm structure was complete. This meant that we now need to finish designing and start implementing the hydraulic system, before we can run our first real tests.<\/p>\n\n\n\n

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Finished arm structure, including Erling’s base design<\/figcaption><\/figure>\n\n\n\n

I didn’t have the time to include the end effector prototype in the physical model this week, but the 3d-model is shown below. It fits only one type of marker, but is fastened with bolts to enable easy swap for other designs. This design holds the marker down to the holder by elastic rubber band, which should at least be good enough for a prototype.<\/p>\n\n\n\n

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The valves we ordered arrived this week, and need some attachment module for our tubes. Me and Erling was thinking of using push-in fittings, but realized this would cost around 500-600 NOK. We are therefor looking into alternatives. The valve has 1\/8 inch taper pipe threads, so I am looking into 3d-printing threads to match this. Using online resources to calculate the diameter and thread pitch, I managed to print an attachment that fit the valve surprisingly well. Safe to say I have learned a lot about threads this week. I think making sure it does not leak will be a challenge moving forward, but this is a good start.<\/p>\n\n\n\n

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Lisa:<\/h2>\n\n\n\n

After a week away, I\u2019m finally back in full swing and ready to continue developing.
This week, we successfully held our midterm presentation, which I think went really well! After the presentation, I continued focusing on my task, which was to extrapolate the angle of the potentiometer<\/strong> used to measure the rotation of one of our hydraulic joints (J-2), as shown in the figure below.
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Overview<\/figcaption><\/figure>\n\n\n\n
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Understanding the challenge<\/strong>
A potentiometer provides an analog voltage signal that varies as it rotates. The Arduino reads this signal as a number between 0 and 1023, this is also known as the ADC (Analog-to-Digital Conversion) value. However, this raw number doesn\u2019t directly tell us the joint\u2019s angle in degrees. To make the data useful, it had to be converted into a physical angle that matches the actual movement of the joint.<\/p>\n\n\n\n

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Establishing the ADC angle<\/strong>
To obtain specific and accurate angle values from the potentiometer, I first needed to calibrate the system<\/strong>. A potentiometer only gives raw analog readings (0\u20131023), so to make these meaningful, I had to map them to the actual physical angles of the joint.<\/p>\n\n\n\n

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  1. Turned the potentiometer to its minimum position<\/strong> and recorded the lowest ADC value (a_min<\/em>).<\/li>\n\n\n\n
  2. Rotated it to the maximum position<\/strong> and recorded the highest ADC value (a_max<\/em>).<\/li>\n<\/ol>\n\n\n\n

    From simulations, we know that J-2 moves between 54\u00b0 (min)<\/strong> and 98.2\u00b0 (max)<\/strong>.<\/p>\n\n\n\n

    With these two known points, we can describe a linear relationship between ADC readings (a<\/em>) and the corresponding angle (\u03c6<\/em>):<\/p>\n\n\n\n

    \u03c6<\/em>=m\u22c5a+b<\/p>\n\n\n\n

    where;
    m: <\/strong> is the slope (degrees per ADC step)
    b: <\/strong> is the offset ensuring the output starts at the correct base angle.
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    This means that each ADC step corresponds to roughly 0.043\u00b0<\/strong> of rotation.

    Implementation <\/strong><\/p>\n\n\n\n

    Once calibrated, I implemented the formula in code and connected a LCD display<\/strong> to visualize the live angle values. The screen now shows the current angle in degrees<\/strong>, along with a progress bar<\/strong> that moves as the joint rotates. When the potentiometer reaches its limits, the display clearly indicates \u201cMIN\u201d<\/strong> or \u201cMAX\u201d<\/strong>.<\/p>\n\n\n\n

    This small addition turned out to be incredibly useful, and it gave a nice, interactive feel to the setup.<\/p>\n\n\n\n