Electric Mountainboard Build Part 8: Summary
It has been an incredible journey getting the board built, from the initial planning months ago to the relatively quick build time within last month. Almost everything deviated from the original plan at some point, so it is important to always be flexible and adapt to new information and situations.
All Previous Parts:
Part 1: Planning/Initial Design
Part 4: Drivetrain and Layout Work
Part 5: Powertrain and Enclosures Work
Part 6: Final Assembly/VESC Programming
Part 7: First Ride/Observations
Spec Breakdown
So how does this board stack up? It certainly isn't the most powerful, or fastest DIY board out there, but even then it punches way above its price class.
Trucks: 16" MBS Matrix II Channel Trucks
Wheels: 8" MBS Rockstars with T1 tires
Battery: 12S1P 14Ah 622Wh, up to 350A discharge (limited to 100A by XT90 connector)
Motors: Dual 6374 7000W Total, Unbottlenecked
VESC Version: VESC 75V/300A
Range: 20mi (Assumes 20Wh/km)
Drive Ratio: 1:6.2
Top Speed: 22mph (Assumes 30% drivetrain losses, 32mph max theoretical)
Built in Bluetooth connectivity
Modular, revert to gravity board in <5 minutes
The result is an off road oriented board with tons of torque, which beats out every prebuilt board in the same price bracket. The channel trucks are stronger, 33% longer, and more controllable than the DKP trucks used in prebuilt AT boards. The motors aren't bottlenecked by the ESC or battery, and can make full use of its 7000W at 75A if necessary. Top speed is currently limited by gearing, but the motor sprocket is a standard 8mm #25 chain sprocket, so I can easily swap it out for a 12 tooth or even 15 tooth to up the top speed to 34mph, at the cost of torque.
It is also a board with plenty of upgrade pathways in the future. Matrix II is a standard for MTB trucks, so it's easy to find different motor mounts or gear drives for them. Same with the MBS hub bolt pattern. The Spintend uBox can take up to 18S batteries, which leaves considerable headroom for larger batteries and more power. The motors can be replaced with larger motors that follow the same mounting pattern, and the truck width allows for some truly long motors, like 63100s. The modularity of the battery enclosure allows a larger box to be easily stuck on to accommodate a larger battery.
Cost Breakdown
This is the part that everyone seems to be interested about, so here it is. This is the raw list of literally all the purchases that went onto the board
All in all, the entire board cost me nearly $1200 to build. All parts were purchased brand new over the course of two months from October 31, 2020 to January 3, 2021. This played an instrumental role in keeping costs down, as I could take advantage of the multitude of 11.11, Black Friday, and Holiday sales. Purchasing during the holidays saved me well over $150 on the board and motors alone. If you noticed the notes above, many of them contained more than I needed. While purchasing singular units of some stuff like bolts would have been cheaper, the shipping costs would have offset the gains and ultimately it was more convenient and faster to just order from Amazon. The total cost of shipping for everything was $75, which was mostly kept down because of Amazon's Prime shipping.
In addition, there were a few extra tools I had to buy to complete this build. I needed a center punch and step drill bits, so I got those off Harbor Freight. That adds an extra $20, although if you had the tools already it's not that bad. I also got a larger LiPo fireproof storage bag for the two batteries, and while it's not really part of the board itself, it was an extra cost. I already had a LiPo charger, but no charge leads for XT90, so that was another purchase I had to make.
There were a few things I already had lying around the house. I already had a 3D printer, so printing the panel mounts was free to me, and only cost a few cents for the plastic. Same with the silicone caulk, as it was left over from some bathroom project many years ago. I salvaged an XT90 male connector from the spare series harness, since I removed the loopkey requirement as the batteries had AS connectors already, which saved money. The wire gauge was wrong anyways, so it wasn't particularly useful by itself. As I mentioned earlier, I also had a LiPo balance charger, so I didn't need to get a new charger or BMS.
As always, all of these parts could be replaced with a multitude of parts, unlike a prebuilt. The Flipsky motors were affordable and good quality, but there are cheaper 6374s out there for the budget conscious, or larger motors like 6384 or even 63100 for those who want more power. Chain drive could be swapped out with a more traditional belt drive, or upgraded to a gear drive. The battery box can be replaced with a larger box, and carry 18650 or 21700 packs instead of a LiPo pouch, or go smaller for a lighter, more jumpable board. The nice thing about DIY is all of this can be fine tuned to your own unique requirements. This can serve as a guide if you're building your own, but don't take it as the only combination.
Future Improvements
Since this will be my flagship board for a while, I am expecting to add some upgrades to it in the future as it becomes necessary. While it is a working board, improvements can always be made.
The first addition I would like to do is attach lights on it for better visibility. During the design phase, I had thought about adding a rear light to the back of the ESC enclosure, as it was higher off the ground and not occluded by the motors. I'm still going with that plan, but I will need to either drill a hole or design some kind of mounting mechanism to attach my light onto it. For the front light, I am thinking about either a top mount light, which has the best throw and protection, or a truck mounted design, which takes less space. I tried a mockup with my current flashlight mounts though, and they're too tall to allow for movement up front. This segues perfectly to my next change.
A solution for deck bite is to not have any deck at all for the parts to hit. The rear had some issues with the motor mounts, and the fronts will have issues with truck mounted lights. I haven't run into any issues so far with the bite interfering with normal use, but you bet there's some dents in the back where they hit. Thus, I am seriously considering trimming the deck tips to fix that. I've got the tools to do it, so I may end up doing this at some point in the near future.
The board is by no means light, so rolling it around like a suitcase is the easiest way to move it around. However, thanks to the outboard mounted motors, I can only drag it from the rear. The truck works, but the motors and mounts are sort of in the way. Thus, I'd like to add some crossbars to the end of the mount that not only doubles as a handle, but also stiffens the drivetrain. The mounting holes are already on the mount, I just need to figure out a good way to utilize them.
Lastly, I'd like to experiment with more tires. The current T1 knobblies are good all rounders, but tend to wear quickly on pavement. I'd like to try more street oriented slicks, which should last longer and provide better grip on the road. I would save the current knobblies for mixed use. Conversely, on the off road side I'd like to try out 9" tires at some point. This would necessitate some new hubs like the MBS Fivestar, as the Rockstar hubs only support 8" tires. This should provide even better clearance, although handling might be diminished somewhat from the heavier weight of the tires.
Conclusion
Is it a pretty board? Eh not really. But it's much more capable than a prebuilt at the same price, while leaving lots of headroom for upgradeability in the future. Even if you can't find all the parts on sale, it still is a compelling option for those who like to customize their own board and don't like any of the prebuilt options out there. It's also simple enough as a first build, as everything was more or less plug and play, and could be completed within a week. It didn't require a bunch of specialized tools to build, nor did it require a particularly powerful soldering iron, which isn't always the case for 10AWG. I learned quite a bit from this build, especially on the materials and soldering, and I can totally translate the knowledge gained to future projects. I'm looking forward to all the new projects this will open up!
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