Hey guys, I work at Pantheon Design in Canada as a mechanical engineer and we sell a unique industrial 3D printer.
To show off the capabilities of our printer, I’ve created an almost entirely 3D-printed gearbox using glass-fiber PA12 nylon composite, and an enclosure made in carbon-fiber PETG.
PARTS:
- Loaded Basalt Tesseract
- MBoards 12s3p Li-ion Battery Pack (21700 Molicel P42A) (Charge only BMS)
- Flipsky FSESC 6.6 Plus
- VX1 Pro Remote
- Dual Flipsky 6354 140KV 2450W Battle Hardened
- 12:25 Herringbone Helical Gear Drive
- TorqueBoards 110mm 74A Wheels
- Boardnamics 220mm Precision Hangers
- Boardnamics Split Angle Precision Baseplates
PERFORMANCE
- Top Speed: 54km/h | 33.5mph
- Range: 35-40km (Sprited Riding 4.2-3.4V)
GearBox Design
The design of the gearbox is heavily copied from @Boardnamics. Choosing a herringbone helical tooth pattern was a no-brainer to leverage the additive characteristic of 3D printing as manufacturing herringbone teeth is difficult in conventional manufacturing. The herringbone profile increases tooth strength, reduces noise, and allows for the slip-fit pinion to self-center with the spur so that the gearbox naturally runs true. Initially, I expected that I would need to press fit the pinion on top of an insert and had the idea to use a normal belt pulley like so:
But in the end, I found that using the motor shaft key worked fine. The most challenging part of the gearbox design was the fact that the walls of the housing had to be significantly thicker than an aluminum equivalent. Because the gearbox walls were so thick, it heavily reduced the ground clearance of the board forcing me to use 110mm wheels when I initially intended to use 80mm Kegels. Additionally, I can only make the spur so small because I can’t use a small tooth size for strength reasons, and I need to space the motor far enough from the hanger and baseplate. The only way I can see the gearbox being smaller in diameter at the spur section is the utilize additional idler gears between the pinion and spur.
To show off the printed gears, I had the idea to use polycarbonate as the front cover of the gearbox so that you could see inside. This polycarbonate plate was machined on a router and screwed to the gearbox housing with brass heat-set inserts. The plates are a great way to show off the gears but practically it’s much better to print part this instead as it will be stronger. The pins used to transfer torque to KEGEL core wheels are bonded into the spur using CA glue. To lubricate the gears I chose Mobilgrease 28 after finding out it’s popularity in mid-drive Ebikes with plastic gearboxes such as the ones from Bosch.
How it feels to ride + Reliability
The torque delivery of the gearbox is buttery smooth both on power and brakes. The gearbox is also virtually silent, the FOC whine of the motors and wind noise are all you hear when riding. When coasting off power you may hear a faint cogging of the gears meshing but that’s mostly the gears slapping each other due to tiny amounts of backlash in the teeth and shaft key. I have pushed the motors to the point of thermal throttling with no issues with the gearbox melting or warping.
Since the gears can’t be shock-loaded any more than heavy throttle from a stop or hard braking at top speed I can’t imagine the gears ever catastrophically failing without warning. The real question is how well the gears will stand up to wear over time. I don’t have any extreme long-term testing on the gearbox, but after riding for maybe around 500km the teeth of the gears look like they barely have any wear, in fact, for a majority of the tooth profile you can still see the layer lines. I don’t expect these gears to perform the same as steel gears, but since these gears can be printed in a couple of hours and they are so easy to swap out, I think they are a great wear component that can be swapped out every 1000km for significantly less money than a pair of machined gears.
Deck
The enclosure is printed in 3 pieces and glued together with locating pins and then bolted to the deck with countersink screws and nylock nuts. The edge of the enclosure is edged in foam tape to help seal and conform to the deck. Initially I used carbon-fiber nylon for the enclosure and glued the parts using a 3M 2 part urethane adhesive and torqued the enclosure very tight to the deck but I ran into issues with the enclosure cracking slightly near the corners. I realized that there needed to be some compliance in the enclosure so that the deck can flex (ik noobie mistake), so I reprinted the enclosure in CF-PETG for more flex, used a more flexible adhesive, and lightly torqued the nylock nuts and it hasn’t had any issues since.
Photo Dump
