Boosted, the electric skateboard company with the iconic orange wheels, just announced the release of a new series of the Boosted Boards. With the Boosted Mini the company is adding a smaller and cheaper version to their family of products.
At 3D Hubs we love boosted boards and decided to take a closer look at how this new board was made. We’ll review the decisions made by the designers of the Boosted Mini and we will explain to you why they selected certain technologies and materials for the new board.Representing an alternative way of transportation in highly urbanized areas, the Boosted Mini is 8 inches shorter than its predecessor and an entry level board at "only" $750.
The new deck
Since the battery and engine enclosure in the case of the Boosted Mini is spread out over the whole length of the board, it was unclear whether the Boosted Mini could offer the same flexibility and comfort as the longboard versions.
Inspired by the structure of a snowboard, the solution for the new and widened deck is a poplar wood core. Poplar wood is a less dense and a more affordable material than bamboo, the original deck material. It helps to further reduce the weight of the board, while keeping it flexible. Triaxial fiberglass and a final protective topsheet are applied to increase strength and wear resistance. Polymer sidewalls block moisture intrusion and and help the board withstand high impacts.
The new trucks
Adding a kicktail to the design improved the overall maneuverability of the board, but also led to increased forces on the board's trucks, which was the main area of concern during the design process. To avoid failure, several engineering changes were made to the production process.
Firstly, more material was added to strengthen the trucks in key areas where they are under the most stress. Additionally switching from a casting to precision CNC machining, resulted in a stronger final product, allowing for the use of high-grade aluminium alloys, unavailable for casting in earlier models. The exact material of the new trucks is a well kept secret. Boosted just refers "to use much stronger aluminum alloys", for which we can only make educated guesses about.
Aluminium A380, one of the most used aluminum alloys in casting, has a Tensile Yield Strength of 160 MPa. This might be enough for the longboard versions, mainly designed for long and straight rides on flat surfaces. For the Boosted Mini, designed for a city environment with rides over bumps and curbs, this strength level is on the critical edge.
As explained in the CNC Material Selection Guide Aluminum 6061, the the most commonly used aluminum alloy in CNC Machining, has a Tensile Yield Strength of 200-400 MPa. So, by changing the material from Aluminum A380 to 6061 they roughly doubled the Tensile Yield Strength of the part. This difference matches the companies description of trucks "almost twice as strong as the previous generation". Although CNC machining is a subtractive manufacturing solution which creates waste material, the price point of the Mini would suggest this change also led to savings when creating this part.
Is CNC machining better than casting?
In the original manufacturing process of the trucks die casting was using whereby molten aluminum is injected into a die mold where it solidifies. The process requires calibration of many variables to achieve the best product quality. To guarantee an even material structure without distortions, the injection process, as well as the cooling and shrinking phase need to be managed carefully. The wrong injection speed, an uneven material flow, different wall thicknesses or a complex shape of the part can lead to stress points and micro cracks. In a worst case scenario gas gets trapped in the material during the filling process, creating microscopic pockets of gas in the material. This grainy structure makes casted parts crack sensitive and brittle therefore vulnerable for stress failure.
Improved the overall strength and durability
The starting point of the new manufacturing process, CNC machining, is a solid block of material. These solid blocks of material are free of material imperfections. Using a variety of cutting tools, material is removed from the solid block to produce a part shaped to the requirements of the CAD model. Parts that are CNC machined have excellent and fully-isotropic physical properties and are suitable for most engineering applications. In addition, they offer excellent accuracy and repeatability and can be produced with very tight tolerances, making it ideal for mass manufacturing.
According to CEO Jeff Russkow the main objective of the new boards was to start "being a heavy-duty vehicle grade-quality [company], as opposed to electrifying something that's more of skateboard." The new way of manufacturing underlines this statement. The priorities with the design decisions have been on providing a robust product at a low price point. This can be seen in the materials used. The more affordable poplar wood used for the deck offers almost similar material properties to the previously used material bamboo but at a lower price point. The new aluminum used, Aluminum 6061, is cheaper but also dramatically increases the overall strength of the part, making the trucks almost twice as strong as before. This change in material opened the door to switching to a new manufacturing technology, CNC machining. While being more cost efficient over time, CNC machining also eliminates the risk of failure due to a porous and grainy material structure caused in the casting process. Overall the Boosted Mini showcases a more efficiently manufactured product that has reduced the cost of some key parts allowing it to be put in front of the consumer at its competitive price point.
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