What: A good frame material for new teams is ½ inch PVC pipe and fittings. Intermediate teams may want to move to creating their frame from HDPE (high-density Polyethylene) cut into strips and fastened together. Advanced teams often custom cut and shape HDPE, aluminum, or 3D print plastics to create a frame or attachment points.
Who: MATE Staff
ROV System: Frame
Competition Class: ALL
When: Any time
Pros: Lighter weight, more construction options
Cons: More difficult construction, more expensive and potentially harder to find
MATE Insights: The frame material you use should depend on the construction skills of the team, the tools available to the team, and funds on hand to construct the vehicle. For some missions, the physical properties of the materials might be important as well.
Most teams starting out use PVC pipe for their ROV frames. PVC is ideal as it is readily available, inexpensive, and easy to cut. The same PVC pieces can be reused for many years, although users should note that PVC can become brittle if left in the sun for long periods of time. However, PVC does not paint well, and although colored PVC is available, it is costly. PVC with water inside the pipe also adds a lot of mass to the ROV.
Here are some other options we've seen competitors use through the years:
HDPE: HDPE (high-density polyethylene - think your plastic kitchen cutting board). HDPE is naturally buoyant and can be bent if it is heated with a heat gun. HDPE can also be easily cut and drilled by hand. HDPE requires mechanical fasteners (pan head machine screws with lock nuts or rivets work well) to connect one piece to another. Don’t use glues, epoxy, or paint on HDPE. These will not adhere to the plastic. The “stick built” HDPE frame is an easy way for teams to starting building HDPE frames and only requires a hand drill. The “stick built” method involves a ¼ inch thick HDPE sheet precut into ½ wide strips of various lengths (45, 35, 30,and 20 centimeters). Teams can bolt together the sticks to make their frame. HDPE can typically be purchased at local plastic stores. It might also be available at sign stores. Finding HDPE sheets locally can be more economical than purchasing HDPE off the web and paying shipping costs. Often local plastic stores have scrap pieces that they will sell you by the pound.
If you have intermediate to advanced building skills and tools, HDPE may be a good option for your frame. You can use hand tools or even a C-N-C machine to cut HDPE sheets into the required shapes. Some frames are constructed from a single piece of HDPE and bent with heat. This reduces the number of fasteners needed to construct the frame. One common error when using HDPE is cutting the plas4tic too thick (over ½ inches wide). This may result in a heavier frame.
Aluminum: Aluminum is light, strong, inexpensive, and readily available. Typically “U channel” or angle aluminum is used, though one clever team used aluminum tent poles with 3D printed connectors. Think creatively! One potential issue is that aluminum frames can be more difficult to manufacture and modify. Often, aluminum frames are limited to rectangular shapes. Aluminum frames typically weigh less than HDPE frames.
3D Printing: 3D printing the entire frame out of PLA (polylactic acid – 3D printing filament) means you can create your frame to any size and shape. Some 3D printed frames incorporate their waterproof housing and other system connections as a structural component. 3D printed ROVs tend to be compact and nimble.
Additional Tip: MATE does not recommend construction a frame out of acrylic (plexiglass). Acrylic can shatter if it is dropped or if it is roughly handled during travel or shipping.
References: Technical reports: Northern Ozaukee HIgh School, Aptos High School, Drexel University
Search Terms: HDPE Brands - Seaboard, Starboard, Marine Board
Fun Idea: Need a frame for a mini ROV? Use 1/4 inch plastic irrigation drip line
Compiled by: Jim McDonnell, P.E., MATE Engineering Instructor