This build log is gonna contain plenty of pictures and will be updated throughout the following year. The build took a bit longer than anticipated but its finally rideable.
So a few months after building my first budget esk8 i decided that i don’t want to be constrained by road quality or lack of it.
Last year I build budget esk8 and got instantly hooked on the fun. That board was single motor, 8S3P with 100mm MSB wheels. The board is still going strong after 500+ km but i need to carefully plan my route to avoid bad roads, and as many sidewalks and other obstacles.
I wanted to build a board that would ride over any potholes, tram tracks and even some light grass or pebbles so that I can ride wherever. It was time to build AT board. Half trough the process of parts searching i decided i want full off-road board, so here we go.
- Trampa short kiteboard deck (suspect low ply 13?)
- MBS fivestars with 3D printed pulleys
- Scrub trucks (yep, your read that correctly)
- Rithblu motor mounts (one of the first iterations)
- 3D printed baterry and electronics eclosure with LEDs
- 10S6P 30Q with AliExpress 60A discharge BMS
- 2X Fatjay 6374 170KV 2880W motors
- 2X 4.12 Flipsky ESC
1. Board and powertrain
I bought used old trampa from @Acido. The price of the whole board and motor mounts was less than just used Trampa deck so it was quite a bargain. The board was not in the best shape so i cleaned, painted and replaced rusted and broken parts.
After sanding and clear coat
Bushings were worn out and i decided to buy a Trampa Kingpin refresh kit, but after few measurements i found out that these arent Infinity trucks but rather Scrub trucks that are discontinued and i wasn’t able to find replacement bushings. I printed replacement bushings in PETG but they started to creak fairly soon so i replaced them with nylon ones.
I suppose these mounts were designed for Infinity or Vertigo trucks as they didn’t quite fit on these trucks. Grub screw holes on mounts are drilled perpendicular on mount not on trucks and so they did little to stabilize mounts. But printer to the save again. I printed clamp adapters and screwed them together on trucks. Works fine for now, but I will probably CNC new ones in near future. Also i printed 72t gears for the wheels. Motor pulley is 17t which gives me top speed of cca 50km/h.
For the battery i was indecisive between 12S5P and 10S6P. I opted for the latter because of the 4.12 ESC not being reliable with higher voltages. Since this is a eMTB build, space was not limiting factor (at least not in my case) i decided to use 18650 holders instead of just gluing the cells together. I spot welded one 7x0.2mm nickel strips for parallel connections and doubled them for series. So the current of one cell goes trough 7x0.4mm strip which is 2.8mm^2 for 15A on less than 18mm of lenght. The battery is 650Wh and theoretically should get me 30km of range.
BMS is generic AliExpress with 10A charge and 60A discharge. I soldered connectors to the pack so i could replace the BMS in the future if needed. Charge port is fused with 10A fuse while charger is 5A.
I placed NTC thermistors on the 3 of the battery cells to monitor battery temperature (4 pin connector on the pictures). For the charging i DC barrel jack is used which seems to be at its limit at 5A charging current.
For the ESC im using Flipsky 4.12 FSESC and running FOC with following parameters:
Motor current 50A, braking motor current -40A per motor
Battery current for both motors together 40A, battery regen current -30A. This setup gives me 1.6kW of power on full charge. I plan on increasing current limits when i get a bit more comfortable on the board.
4. Enclosures and cosmetics
For VESC enclosures i didn’t want just a box so i tried a few shapes and settled for this one. As any other project it wouldn’t be good if there was no LEDs so i laser cut acrylic glass and placed WS2811 on the inside. The second iteration of enclosure will have waterproof glands instead of just holes for battery and motor wires and with white acrylic glass in place of transparent one. The enclosure is fitted on the deck with truck bolts.
Battery enclosure is as simple as it gets. It has opening for battery wires, XT90S and charging port, attached to deck with industrial velcro. M5 heat inserts are melted in both enclosures. As water sealant around wires i used butane tape aka sticky.
I also printed some concave pads from thingiverse designed by Johnny1983 link
Front and backlight will be controlled with MCU, which is connected to hte UART of VESC, and 2nd channel of receiver. MCU will also monitor and display battery temperature from NTC thermistors. A switch to turn on/off lights, change VESC mode (250W,1000W, 2kW…) and some other misc functions.
Backlight: custom PCB with WS2811 leds, need to print enclosure and wire it up
TODO list and upgrades:
Enclosure and buck converter for display and lights.
Power wires management.
First ride impressions:
WOW. The power on this board is absolutely amazing. No more kick starting and waiting 10-15 seconds to reach top speed. I’m running FOC on this board and the difference vs BLDC is on another level. So smooth even on hill from standstill. Never going back to BLDC again. Didnt push top speed yet since i haven’t installed dampas on the back so speed wobbles appear at around 30-35km/h.
Some more pictures