Designing and building a custom electric longboard for commuting.
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The caliber hanger profile is a rectangle, with one rounded edge. Sounds simple right? All I need to do is take some measurements.
Unfortunately, not all trucks are built the same. Since I don't have access to the technical drawings for the caliber trucks, I cannot tell the tolerances on the hanger dimensions so I will take reference from a few sources.
Also, the profile appears to be thicker towards the centre than at each end, so I need to take this into account too.
|Source||a (mm)||b (mm)||x (mm)|
|Front truck left||14.0||18.8||18.0|
|Front truck right||14.0||19.2||18.0|
|Rear truck left||13.8||19.0||18.0|
|Rear truck right||14.3||19.3||18.2|
|ESK8 forum post||16.6||20.7||18.2|
The inconsistencies in my measurements may be explained not just by manufacturing variations, but also from measuring at different points along the hanger.
I have assumed that Caliber II trucks have the same profile as Caliber III trucks, but what's interesting is that the two Caliber II sources have a value of a which is 1.4 - 2.8 mm longer. The width of the profile, i.e. x, seems to be consistent at around 18 mm, and the height, b, varies within a 1.9 mm range.
I could validate my results by asking other caliber truck owners to measure their hanger profiles, or even by contacting the manufacturers themselves to find out, however I'm impatient and this is just a hobby project so this should suffice.
I will proceed with the following nominal dimensions:
|a (mm)||b (mm)||x (mm)|
Any variation in these values will be accounted for in the design of the clamping mechanism.
Truth be told, I'm incredibly proud of this. After a few hours in Fusion 360 I have what feels like a no-compromise design. however, before my head stops fitting through the door, I need to do some physical testing and receive feedback from the ESK8 community to validate it. As with any product, I'm sure there will be plenty of revisions to come.
I will not provide a detailed explanation of every design choice, dimension and fastener length, however here are some of the main considerations.
Firstly, you may notice that the clamping mechanism is not a direct copy of the Boardnamics motor mount. This is to reduce the number of parts, therefore theoretically reducing the number of things that can go wrong and hopefully providing a more stable solution. My only concern with this is that the displacement of the adjustable holes when the clamp is tightened may prevent the screws from aligning with the holes in the "arm".
This brings me onto my next point, which is that the motor position is adjustable unlike the Boardnamics mount. It is worth noting that the idler will only fit if the motor is in the outermost position from the trucks. I can modify this by increasing the arm length, however I intend to keep this design as compact as possible to prevent the mount from contacting the ground or underside of the deck.
Throughout the design I have intended to minimise the number of manufacturing operations. I have opted to produce this via waterjet cutting, with no milling required whatsoever. This should allow the design to be manufactured at a lower cost than the Boardnamics one, as the channel around the screws which join the clamp to the arm has been redacted.
Originally, I had the idler slot perpendicular to the length of the motor mounting arm. However, I found that by angling it like the Boardnamics one, it allowed me to reduce the arm length without the idler interfering with the motor or wheel. It is fascinating how you only come to understand seemingly meaningless design decisions when you explore the product from the ground up yourself. Or maybe I'm just tipsy.
My research (window shopping) has shown me that high quality motor mounts, the ones which are not likely to vibrate off mid-journey, are either ridiculously expensive or sold out. What separates a high quality mount from a low quality one in my eyes is a mounting profile specific for the brand of trucks used.
For example, the image above depicts the most common, low cost design sold by Chinese manufacturers. It features a round profile with grub screws used to clamp down on the truck. This is not a robust mechanism by any means, as the grub screws provide very little contact with the hanger, can be loosened easily by vibration, and if the grub screws are worn down, there is no means of constraining the motor mount to the hanger in the lateral plane.
As a degree apprentice, luckily I have access (provided I sweet talk the technicians...) to my Uni's CNC machinery including a waterjet cutter. Theoretically this should allow me to design my ideal motor mount for a low cost. Time to design!
The motor mount must fulfil the following criteria:
Some optional features I'd also like to include are:
"There is no such thing as an original idea. Only improved versions of their predecessors"
(Paraphrased from a source I cannot remember)
Essentially, my plan here is not to start from scratch, but to draw inspiration from (i.e. strategic copying) existing designs born from the ESK8 community.
I'm sure...Read more »
Whilst I was waiting for my new Caliber trucks to arrive, I wanted to produce a CAD model of the board to help visualise the overall assembly.
I began by importing the pictures of the deck from here into Fusion 360. This gave me a basis to sketch from:
I then extruded the base sketch to produce a blank of the board, that I cut to shape by intersecting the top-view:
I then added holes and chamfers as appropriate. It's worth noting that the holes are not perfect - the tops/bottoms are not flat as I used splines to model the deck. This makes them difficult to assemble components to accurately. I could have gone to the hassle of getting it perfect which would allow me to design parts like the electronics enclosure more accurately in CAD.
However I think there's something satisfying about getting more hands-on from time to time. As a mechanical engineer, and someone who spends more time modifying their 3D printers than they do actually using them, I tend to turn into a bit of a CAD monkey sometimes. This can lead to mistakes which may easily be avoided by simply measuring things in real life, or producing cardboard templates and taking some hand tools into the equation, because in the real world dimensions are not perfect and tolerances come into play.
Anyway, the deck is now modelled up. Like I said, this CAD model will serve more as a visual aid for the proportions of the board and component placement than it will as a detailed design record.
I will hold my hands up and admit I cheated a little here. I found this model on GrabCAD for 50 degree Caliber trucks. These are slightly different to the ones I will be using, which use a 44 degree baseplate and raked hanger, but the model will suffice.
I extended the hanger width to 184mm, painted all the parts in pretty colours, and assembled them with the correct constraints.
These were tougher to model. I started with a revolve which included all of the small chamfers and main surfaces:
In hindisght this makes it harder to manage the relationships between different constraints, and modify dimensions without moving other aspects of the sketch. But, it worked I guess.
I added a few extra dress-up features where needed, and then drew the cut out for the ABEC-style mounting holes. This was then extruded through, and patterned around the centre.
With all of the components of the basic deck ready to go, I chucked all the models into a soup, threw in some herbs and spices and nuts and bolts, and out came this:
At least now this project has a nice cover photo to use!
The drivetrain (at least, by my definition) includes the mechanical components which move the skateboard forwards. This is the most important part of the build, and will drive the requirements for the electronics. The drivetrain consists of the following:
These components structurally and functionally support, or are supported by the following:
Before exploring my options for each of these, I want to make it clear that I am hoping to reuse as much of the original setup as possible, only swapping out components which would require irreversible modifications. This is for a few reasons: firstly, to preserve the overall look and feel of the board. Secondly, to keep cost down; and thirdly to add some challenge to the build. intuitively this means hopefully reusing the trucks, but not the wheels as they would need modifying. Also, this means I will be using a belt-drive rather than hub motors or direct-drive motors.
ESK8 wheels come in a range of shapes and sizes, depending on the use case. They can even resemble tiny bike wheels for mountainboarding! This guide is, as far as I can tell, fully comprehensive and incredibly useful. As I will only be powering one side of the board, I'd like the driven to resemble the existing ones as closely as possible. The current wheels can be defined as follows:
It is important to note however, that a and b are not always the same. Offset wheels (such as my existing ones) and side-set wheels (bearing flush with surface) change the weight distribution across the wheel such that the lateral centreline through the bearings is not coincident with that of the wheel.
|a - b (mm)||5mm|
I have toyed with the idea of casting my own hard-cored polyurethane wheels with a 3D printed mould. However, my humble Ender 6 is currently a Frankenstein's monster of r/redneckengineering material due to half-assedly modifying and developing it over the course of the last year. As it currently stands, I don't trust it to produce consistent prints, let alone with more engineering-grade materials which will be safety critical and under significant load. I don't want to have my wheel cores shatter at 20mph downhill! In future I may carry out a project to rectify this.
The closest wheels I can find to these which are commonly available and relatively affordable are the Orangatang Kegel 83a wheels. these have the same hardness and are only 5mm larger in diameter.
Unfortunately they only come in this unnecessarily garish lime green and purple combo which doesn't fit the aesthetic of my board. Therefore I need to look for an alternative.
I briefly explored various buy & sell groups, and a selection of different UK/EU ESK8 vendors but struggled to find components. As the ESK8 market is still in infancy, especially outside of the US it seems, most sellers and vendors offer full setups or conversion kits as these appeal to a larger audience. I caved in, and decided to visit AliExpress, where I came across these:
Though not particularly exciting, these wheels match my requirements almost perfectly. They are black, only 8 mm larger in diameter than the stock globe wheels, have a hardness of 80A and have an ABEC style core. They are also very cheap, at only £6.81 per wheel at the time of writing this. I am aware that by limiting the outer diameter of the wheel, which is relatively small in terms of ESK8 wheels, I am trading stability and "momentum" for nimble handling and acceleration - this is driven by the focus on aesthetics. Whether this comes back to bite me or not in future we shall see! I hold some concerns about the quality of the wheel also, as this is an unknown vendor. However, given that I am not planning to use the setup in harsh environments or offroad, these should suffice.
For bearings, I will use the tried and tested...Read more »
It's August 2022 near London...
The sun beats down on your face, whilst you painstakingly push a 3.7kg slab of wood up 45m of elevation, with only 3m of downhill, over 4.8km.
The gradient varies by 0-3% throughout the journey. Although this is mostly flat, you're on your way back from work, exhausted and drained with a 4.5kg backpack. You weigh approximately 70kg. It only takes you 15 minutes on the way into work, but the way back is almost half an hour!
Sweat rolls down your cheeks, drenches your back, and floods your nethers in the 32°C heat. You think to yourself - "if only this longboard was electric! That way, I could still enjoy skating to work, without dreading the journey home."
As you may have already guessed, this person is me. As a skateboarder, I have previously had an elitist mindset against longboards. God forbid electric ones, how could you let such a heinous display of consumerised technology take the spotlight of a classically skillful and dangerous sport?
However, since owning my (now beloved) Globe Byron Bay 43" setup in Ebony/Nightshade, after being shown the joys of downhill longboarding (yes I'm aware this is not a downhill setup!) my mindset has changed.
This Surf-inspired squash tail longboard has a Mellow concave, with kicktail made of Ebony wood + Resin-8 hard rock maple. It features 150mm Slant reverse kingpin trucks and 70mm 83a wheels. I would do unspeakable things to this beauty.
Research & Specification
I performed some basic research into electric longboards to develop a basic understanding of what components I will need. This involved binging builds on YouTube instead of working from home, scouring ESK8 forums and scrolling through Reddit.
From this, I can break this project down into a few major categories:
The following project logs will delve deeper into each.
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