EMTB Build Log | Custom gear drives | Stormcore | 12S6P P42A | Haero Bro |

I thought I would create a build log for my new electric mountain board, it will hopefully be informative for other people and I’m sure I will need help from you folks along the way too.

Feedback welcome!

Aim of the build

For this build I want at least 20km of range and enough power to tackle the mountain bike trails around me which can be quite hilly. Finally, the board must be rugged and light enough to handle jumping, potential hard landings and muddy conditions in winter.

Parts list

  • Deck: Haero Bro 2021 (purchased)
  • Trucks: MBS Metal Matrix II black (purchased)
  • Hubs: MBS Rockstar II black (purchased)
  • Tires: MBS T1 Tire - 8" (purchased)
  • Bindings: MBS F5 Bindings & Heel Straps
  • Gear drives: Archer EMTB gear drives (in development)
  • Battery: DIY 12S6P Molicel P42A with LLT Power smart Bluetooth BMS
  • Battery enclosure: Top mount Peli 1200 Protector Case (purchased)
  • ESC: Stormcore 60D+
  • Remote: Flipsky VX2 Pro
  • ESC Enclosure: New IDEA ESC enclosure black anodised (purchased)
  • Motors: Flipsky Battle Hardened 6384 170KV (purchased)

Firsts steps

I’ve finished designing the first iteration of my EMTB gear drive, just waiting for the CNC metal parts to arrive now, hopefully everything will be here by the end of the month. In the meantime, I will be ordering parts, building my battery, and cracking on with the rest of the build. More updates to come shortly.


Update! Mountain board build and mounting the ESC and battery enclosures

The great guys at ATBShop delivered my trucks and wheels on Friday, so I went ahead and assembled the gravity mountain board, that will be the foundation of this project. I love the combination of the Matrix II trucks and Haero Bro deck, it feels great to stand on and has the perfect amount of flex (the guys at Haero Boards recommended the stiff deck for me as I weigh 87kg). I must say I am very impressed with quality of the Haero Bro deck, there has been a lot of attention to detail and thought gone into the design, I really like the nut inserts for the bindings and wide foot bed (I have very long feet lol).

I won’t go into details about mounting the black anodised ESC enclosure from @IDEA , its super easy to do and he gave me plenty of infromation on FB messenger to make sure I assembled it correctly. I really recommend this enclosure its very well made and sturdy, although import duty to the UK was a bit pricy (Brexit :roll_eyes:).

Most of the work went into mounting the battery box (Peli 1200). I decided to attach the case using three M8 bolts and 15mm high longboard bushings to create some clearance between the deck and Peli case. I felt like this would be the most secure method and I think the clearance will be necessary when the deck flexes whilst jumping for example.

First, I cut off the 4 feet flush with the 4 protruding channels using a multitool then sanded them smooth to tidy them up, this will give more clearance between the deck and Peli case. Then I drilled 3 holes 70mm apart in the bottom of the Peli case along the centre line.

The next job was to drill 3 corresponding holes along the centreline of the deck, I hated doing this to such a beautify crafted deck. I am using counter sunk bolts, so I chamfered all the holes so the bolts world would sit flat.

Finally, I bolted the Peli case to the deck, I used some large washers on the inside of the Peli case as the plastic isn’t that thick and this helps spread the load.

The next job is to 3D print platform to go in the bottom of the Peli case to cover the metal nuts and washers, so my battery is properly isolated and protected. But I’ll will have to wait for my TPU foot pads to finish printing first as they take around 25 hours each :sweat_smile:


i want to see these gear drives : P

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I’m hoping to receive all the metal parts for my first functional gear drive prototype by the end of the month, I can’t wait to test them :grinning:

I made a 3D printed mock up of the gear drive already, you can check it out here if your interested.

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Update! Footpad design and print + fitting the bindings and heal straps

I didn’t want to rout the power cables from the Peli case through the rear binding and into the ESC enclosure, so I designed a footpad with cable groove so the cables could be routed more discreetly through the footpad.

I 3D printed the foot pads out of eSUN black TPU with 20% gyroid infill at a print speed of 20mm/s, and they took ages to print (~25 hours) . The footpads turned out to be quite flexible but firm, which is good because you don’t want to feel those cables under your feet. I finished them off by applying skateboard grip tape to the top surface. The front footpad is an identical mirror to the rear footpad but without the cable groove.

I’m still waiting for my battery smart BMS and gear drive protype to arrive, so I think I will work on preparing the battery box next by adding a loop key, cable gland entries and a base for the battery to sit on.

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Starting with a really solid base! Great choice of parts. You’ll definitely enjoy it. The Bro + Matrix combo is pure magic.

I’m in the midst of tuning a very similar build, and I’m a similar weight, so let me know when you get there if i can help.

What hardness shock blocks are you running? The stock orange may not be enough. At the least i highly highly suggest adding a second nut to the matrix kingpins - they are notorious for coming loose and creating speed wobbles when you least expect.

I’d be very surprised if your final board weight comes in under 20kg, but maybe you have stronger legs than i do!

I have similar footpads in 100% infill. I’m curious about your feedback on these

gyroid ftw


@sleepless Thanks for the advice dude.

Thanks mate, I’ll definitely take you up on that offer when I get to the tuning stage! Can’t wait, it’s going to be so much fun to ride! Really digging your modular jumper build at the moment!

I’m running the standard orange hard shock blocks, they do feel very loose at the moment but haven’t tried adjusting them yet, may have to move up to the red hardest shock blocks. Good to know about the kingpins, that would be super sketchy if the nut came loose whilst riding!

The board feels nice and light now, but I can imagine after the gear drives, motors and batteries are attached it’s ganna be a chonka. Might have to make a smaller jump pack battery.

I actually got the idea to make the TPU footpads from your build! I was going to laser cut the pads out of foam originally. The shore hardness of eSUN TPU is good for this application, I printed the pads with 4 perimeters and 5 bottom and top layers and the pads hardly compress at all under load. Time will tell to see how durable they are, but looks good so far.

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There’s a bunch you can probably do before you need to switch blocks. I’ve currently got orange front, red rear, and they’re quite carvey. I’m no pro, but search around. #1 is making sure the kingpin is tight.

@Venom121212 just posted this awesome reference:

He’s a Matrix whisperer that may provide some guidance.

I would also recommend starting without the heel straps installed. Get some good mileage in getting a feel for the board (and bailing / jumping in and out) and figure out how loose you like the main straps.

What remote are you going with? I didn’t see it mentioned.


For sure!

My top tip is to preload the bushings about 1mm or 2mm like in that bottom photo. This takes a lot of the center slop away and makes it feel less like a slack line.

I am a big fan of running a harder shockblock in the rear. It makes the turning more divey but controlled. I imagine I’d only use the same bushing front and back on a board I was riding switch all the time like a gravity boarder.

Make sure that kingpin is cranked down tight so there is almost no wiggle in your hanger if you grab both your tires like a steering wheel and try to turn it. Throw an extra locking nut on the kingpin and it won’t come loose for half a year or so if you send it :call_me_hand:


imo weight doesn’t have as huge of impact on jump-ability. i find atleast i can easily jump my daily 19kg board the same if not better then a 14kg board i’ve just built. (comes down to comfort on what you ride tbh).

this^ hard rear,soft front. i only run the same strength if it something i’d ride both ways (gravity board/4wd)

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Can you link the esc enclosure?

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I’ve got the Flipsky VX2 Pro, forgot to add it to the list of components, I was tempted to try out the new VX4 but wasn’t sure if was worth the extra money.

Whoa! you are the Matrix whisperer! Thanks for all the advice man, I will be ordering a red shock block for the rear and adding that additional kingpin nut :slight_smile:

That’s good to know dude, I thought it should still be good for jumping as I’ve seen other people using 12s6p packs. Have you jumped your Iron Giant board, how heavy is it?

You can contact @IDEA on this forum or Facebook, for more details about the enclosure. He was very quick to respond to me on Facebook and sent me additional infromation and pictures.


my daily runs a 12s6p p42a pack. i have run a 12s 5ah lipo , but i find it’s too much effort to switch them out.
i have jumped the mock up of iron giant and was surprise how easy it was. heaviest i have jumped while riding was mud monster at 32kg it was small jump up a curb but still counts

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Update! battery box preparation

Sup homies!

I finished preparing my Peli 1200 case and now it’s ready for the 12S6P battery to be fitted :zap:

The first thing I did was change the mounting hardware that attaches my battery box to my deck, I am now using M8 countersunk barrel nuts on the deck side and low profile M8 bolts on the inside of the case. This gives more room for the battery, the M8 Nyloc nuts I had in the bottom of case before took up 5.5mm of dept, whereas the heads of the low profile M8 bolts only take up 2.8mm.

Next, I designed and 3D printed a loop key and corresponding socket that’s mounted on the lid of the case, so I can disconnect power form the system when required. I 3D printed these parts out of ASA, as this is supposed be more weather resistant compared to ABS and bonded the socket to the case using Araldite.

To rout the power cables out of the Peli case to the ESC, I 3D printed a custom cable Grommet out of TPU and glued it to the case using Araldite. I’m happy with the how the 3D print turned out but not with the performance of the Araldite (it fails when things flex), if the bond fails I might switch to a mechanical nut a bolt mounting method or find a permanently flexible adhesive.

I placed closed cell foam in the bottom and lid of the Peli case to hold my battery it in place and cushion it a bit. I also had to chisel away some of the Peli case internal features to get my battery to fit properly. I might add thin vertical strips of foam around the sides of the battery to lock it place and protect it further.

I haven’t been able to build my battery yet; I have borrowed a spot welder, bought my cells and designed and 3D printed a custom cell and BMS holder, but the battery building supplies (nickel strip, 21700 insulator rings and fish paper) haven’t arrived yet. This is kind of annoying as I ordered them from a UK seller on the 29th May thinking they would provide good quality components and fast delivery. I got tired of waiting yesterday, so I ordered from an alternative supplier so hopefully I will be able to crack on with the battery build soon :crossed_fingers:

I’ve been testing the assembly of my prototype gear drives, more updates to come shortly about installing them on my board :gear:


i love me some countersunk barrel nuts (use them on my boards). put the foam in, better it be extra safe then have a chance of damaging the battery

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Ya I think that is a big benefito running bindings, you can put more leverage into the turning.
running no bindings you need to run softies and be more on point with the tuning to get to get decent turning out of it while still having it stable at higher speeds.


I love these things :grinning: can’t believe I didn’t discover them until recently!

I’ve taken @sleepless’ and @Venom121212’s advice about putting a red shock blocks in the back truck, this should keep the board stable at high speeds and the bindings should hopefully allow me to really lean into turns. On my street board I enjoy using double kingpins they are super carvey and surprisingly stable, but it seems like once you exceed a certain speed threshold (~25MPH) the death wobbles come out of nowhere. I like your boards! I bet MBS trucks are great on street board too :metal:

I’m going to use my torquiest gear ratio (5.29) option for this build, I prefer high torque for blitzing up hills rather than high top speed.


Update! Installing the gear drives.

Installing the gear drives went pretty smoothly :sunglasses:

First, I stuck on the self-adhesive cover and truck clamp gaskets, this was a real ball ache to align, and hence it doesn’t look very neat around the seams of the gear drive when fully assembled. For the next version of the gear drive I will try out non adhesive gaskets.

I set the position of the motors using the truck clamp, to give as much ground clearance as possible without clashing with the trucks. Thanks to @sleepless for the multiple mounting hole idea, they can be adjusted in 9° increments.

Once I was happy with the motor position, I attached the pinion to the motor shaft using Loctite 648 retaining compound. One cool thing about this gear drive is that you can still remove the motor after the pinion has been glued on, as the hole in the motor mount plate is large enough for the pinion to fit though. It also prevents clashing with some motor’s circlips. I think this idea came from @glyphiks and @sleepless . With other gear drives the motor pinion prevents you from removing the motor which isn’t good for maintenance.

I lubed up the gears with Lucas Red and Tacky grease, this stuff is great, it really is tacky and stays where it should do and makes the gears run real smooth.

After adjusting the backlash of the gears so both left and right gear drives were the same and optimal, I assembled the rest of the drive. All the bolts are secured using Loctite 243 thread locker.

The wheel hub coupling idea that @Linesflag had works great! I got the tolerances just right, there is a nice positive click when you push the wheel hub in or pull it out. I think it will be really hard wearing compared to other approaches that I’ve seen such a threaded bolts in holes.

Overall, I’m really happy with how the assembly process went, there were no issues apart from the self-adhesive gasket alignment. I can’t wait to test the gear drives out, so far I’ve only free rolled the board down a hill :joy: I need to get cracking and finish building my battery!


looks great! excited to hear how they sound!

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Update! Building the battery pack

Turns out its quite hard to fit a 12S6P 21700 battery pack inside a Peli 1200 case, so this was more work than I expected. I was going to use standard hexagon 21700 cell holders, but it was impossible to fit the cells inside the case using this configuration, so I had to design and 3D print a custom cell holder.

The cell holder consists of two 3D printed end caps and is held together using hexagonal M4 stand-offs and M4 screws. The LLT Smart BMS is mounted to the side of the battery pack, and there is free space next to it for the for the output/charging wires and connectors. I’m quite pleased with how this turned out, all the cells are mechanically secured and don’t rely on the spot-welded nickel strip to hold them in place :slight_smile: The 3D printed end caps are 10mm thick and 3D printed out of durable ASA plastic and the M4 metal standoffs have heat-shrink around them to insulate them in case of malfunction.

Before I began spot welding the cells together, I double checked that the cell holder assembly fitted into the Peli-case, it was very snug :sweat_smile:

First, I attached self-adhesive fish paper rings to all the positive cell terminals and measured the voltage of each cell, they were all 3.54V ±0.01V. I then proceeded to insert all the cells into the holder and bolted the cell holder assembly together using Loctite thread locker, and then spot-welded all the parallel groups.

The next step was to spot-weld all the series connections. At the positive and negative terminals at the end of the battery pack there are 10AWG cables soldered the entire length of the P group, unfortunately I forgot to take pictures of this process. I used 0.2mm nickel strip throughout this build.

All the nickel strip that is not located in a deep recess had its corners rounded, so doesn’t cut through anything and the BMS wires are soldered onto the balance wire tabs.

Finally, the top, bottom and sides of the battery pack were lined with fish paper and secured with fibreglass tape. The Smart BMS Bluetooth module is secured to the top of the battery, you can see it blue status light glowing through the tape.

I was planning on heat shrinking the entire pack but the charging and discharge cable positions kind of stopped me from doing this, and there isn’t enough room in the Peli case to have the wires easily protrude out of the end of the pack. So, I opted to heat-shrink the pack in two sections with a gap in between them where the cables come out. The pack output has an anti-spark XT90 connector and the charging is done via an XT60 connector.

Currently you must open the Peli ase to charge the battery, I might add an external charging port in the future, but not sure if it’s worth it.

I would like to say big thankyou to @Halbj613 for setting up the spot-welder lending group, that Flipsky spot-welder worked real good and borrowing instead of buying saved me a lot of cash :grinning: