ADV Support Frame Project

Project Description:

We have a 2-axis motorized Velmex bislide. Each axis of the bislide is 0.5 m in length (Fig 1). Figure 2 shows a photo of 1 Velmex Bislide. These Bislides are used to traverse an ADV (Acoustic Doppler Velocimeter) which is then used to gather 3D water velocity data inside of a water channel. 

 The first iteration of this whole apparatus (shown in Fig. 3 and 4) used 1″ 80/20 framing to attach the ADV to the bislide and for overall support for the apparatus. However, it was found that it performed poorly because it was not sturdy enough. The wind and water currents in the channel caused significant shaking of the instrument.

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To design and build the mount, we took inspiration from Pete Bachant’s design. His mount was made to support a larger bislide, but we were able to adapt some parts of his design into ours, as shown below:

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Design Requirements:

  • Resist vibration from water currents and wind in the water channel
  • Overall length of mount must be 1.2 m from end to end
  • Must be able to adjust mounting point to reduce length down to 1 m to accommodate different water levels (this means that at least the part of the mount within 0.2 m of the top should be made of 80/20)
  • Horizontal distance from the vertical strut to the ADV transducer: (0.91/2 – 0.25) = 0.205 m
  • In our case, unlike in Pete Bachant’s design, the ADV transducer needs to point up. To avoid interference from the strut while measuring velocity, it also needs to be mounted some distance to the side of the strut. 
Figure 6

Figure 6 above shows a sketch of the overall frame shape and structure. Compared to Benchant’s design, our apparatus was smaller and did not consist of all the same parts Benchant’s design had. The three cross beams shown in the design sketch were inspired by Benchant’s design. Although the final apparatus did not look exactly like the design sketch it was followed closely. 

 

The design includes a top beam placed higher on the bislide supported with diagonal beams attached to the lower part of the frame. This was to provide extra overall support due to the existing large moment caused by the fluid drag on the ADV mount (because moment = force of the fluid drag x length of the vertical strut).

 

The frame was completely built using 80/20 parts ordered from Mcmaster. A small batch of 80/20 parts were ordered to begin building the skeleton of the frame and to evaluate what specific 80/20 parts were best suited for this project. 

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The frame was being built quite closely to our original design sketch. Of course, a few revisions were made given time and resources constraints but still met the specified requirements. A few challenges that arose included attaching the frame to the bislide, namely:  

 

  • Attaching the frame to the bislide
  • Missing a part that allows the vertical bislide to traverse along the top beam

At first, it was uncertain as to how the frame would attach to the bislide as the brackets and screws we had were not completely compatible with each other. This required some experimenting and out of the box thinking. Various ideas and methods were attempted to do this. It was found that the only way to make this work was to use a particular type of black brackets and screws that could successfully attach the bislide piece to the frame. 

Another challenge was to attach the top beam with the vertical bislide but also allow the vertical bislide to traverse along the top beam from side to side. In order for this to happen, a plate with custom drilled holes was required to be machined. With the custom plate, the bislide is now able to be mounted with the screws and brackets to the plate and the traversing 80/20 part (Figure 15). 

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The final touch to the design was attaching the long beam (which the ADV will be mounted on) to the bislide and adding an airfoil strut to the portion of the beam to be submerged in water, in order to reduce drag (Figure 16).

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We also used a submersible vibration sensor to measure the level of vibration of the apparatus. The completed support frame proved to be successful as there were minimal to no vibrations compared to the first iteration when submerged and subjected to water current and wind force. 

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Lastly, after looking into the Velmex bislide documentation. We were able to use MATLAB to control the Velmex Motors. This allowed us to traverse the ADV along the YZ axis. 

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