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49” flexible 8s15p direct drive 100km cruiser

Engineering the esk8 of my dreams, from the drawing sowftware to the road in 6 month; a picture story:

  1. Specs
  2. How
  3. Let’s build
  4. Testing

I will provide all files I made and product links I used.

1. Specs:

I am a junior mechatronics engineer and also love to esk8. It so happened that I had 2000EUR to blow, so here it comes! I have already built 2 smaller boards but this time I want to go all out, over the winter there shell be no compromises, take time and money it takes.

I want my dream esk8 to be like:

  • comfortable to ride
  • reliable
  • at least 45"
  • last 100km on a full charge at good conditions
  • charge to 80% under 2h
  • fully programmable
  • 40km/h top speed for cruising efficiently

2. How:

Find a drive solution, find a controller, estimate power consumption, calculate a battery capacity, choose the cells. Based on that lay out the pack and simultaneously choose the deck.

In favor of reliability I chose a direct drive. Torque Boards DD was my best bet but I found Boundmotor who offers a similar solution for half the prize, they were really nice in their customer service so I got their DD. The drives gives me 40km/h on an 8s setup so this is preferred. To drive them I went with the Flipsky vESC DUAL 6.6 since it checks all the marks on my list. Power consumption was estimated to be 10Wh/km with the help of experiences from r/ElectricSkateboarding (spoiler: it turned out to be pretty accurate). I needed roughly 1kWh of energy to go 100km, after extensive testing different cells (see the cell test sheet I linked at the end of the post) I settled on 120 NCR18650B cells. Now I know the deck would have to be large. Therefore I got the largest I could find, after I had roughly calculated that the battery pack can fit on it if I give my best at packing them tight.

Once everything mentioned arrived I stated laying out a CAD design with evolved into this:

one half of the battery enclosure the controller box

Cooling the components to keep them reliable for long runs was a key thought my build revolved around, I see so many DIY boards that just treat a heatsink on a controller like it was not even there this always makes me cringe. Therefore I have the controller mounted with the heatsink exposed to airflow, but protected by the underside of the deck. Also the battery is air cooled, more on this later! The other though was vibration dampening. The 4 circular mounting points at the battery and the 3 smaller ones on the controller are for rubber-metal-dampers. Those are the key to mount everything in a flexible way to keep the deck flexy and in the same way dampen vibrations on the enclosures. Once I had that idea I was especially excited to make it reality!

The battery blocks are pressfitted in the enclosure. This is made possible by exact CAD construction and 3mm thick thermal pads in between the battery and the covers of the enclosure. The heat of the cells is transferred through the pads, into a 2mm thick aluminum sheet and then to heatsinks mounted externally.

3. Let’s build

testing the fit for the controller heatsink

putting the nuts inside the 3D print for the cover screws

combining the shells

printing the covers and mounting the aluminum heat spreaders

welding and soldering the battery

mounting the controller and the drives

mounting the bumpers

test fitting the enclosures

finalizing the battery pack

getting the battery in

mounting the thermal pads

compressing

charging her up

adding dust covers

4. Testing:

6 month of busy work flew by and its spring!! Time to go for a test run, or 2, or 500km of riding! All I can say is I am happy, all the goals were met, 100km can be achieved on a flat route with no wind. The deck is flexy and smooth the motors have power for days and the battery is just massive! Everything stays cool and nothing moves. I will post more once I have new findings.

Please ask questions! The biggest honor for me would be if someday a second one this board live somewhere out there!

This files:

3D files, cell test and parts list

4 Likes

The Evolve trucks on a direct drive, never seen that before. Are they stable?

They come with the Boundmotor DD! Yes they are smooth and stable, I had to tighten them 5 turns in the deck sided and 5 turns on the street sided bushing from the stock setting which is the nut flush with the bolt. For me (60kg) the stock bushings are very good, turning feels good and also stable at higher speeds. But I ‘only’ went 40km/h with it. Initially I was worried about stability since the deck is also very flexy but it turned out to be just fine.

I like that you are thinking about cooling the battery, this is not so common to see at the moment in DIY, but i think its actually very worthwhile in order to maximize battery health.

1 Like

Yes! In my other build I meassured battery temps up to 70°C, after 4 years and likely not more than 3000km, battery life is down to 70% even though I only cycled between 3V and 4V. Never had any overheating issues with this design, the battery did not even get any hotter than 2°C above ambiant.

1 Like

Yeah, i’m sort of surprise more people aren’t toying with this idea. I suppose if you have a really massive over engineered pack the heat build up might not be such an issue. But i do believe heat is one of the biggest issues for battery health / longevity… Especially if battery is in same enclosure as ESC

Meh I did.

  • some SS enclosure

  • insulated from the deck like heaven to hell,

  • some thermal paste and wallah!

  • or fill the thing with oil.

but personally for me it’s just basic battery safety and planned obsolescence