I was rocking with unprotected lipos on one of my builds for years before it got hit by a car…
they were more robust than I thought.
I recommend covering everything up. 
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@lowGuido No lie man, I actually thought of this build of yours when I was originally typing that statement! Also, I like seeing that I’m not the only one here still using Dean’s Ultra connectors 
Since @dinodave is riding off road, a flying rock, stick, or any other piece of debris could puncture the casing. We all know what happens next! LiPos are great and seemingly very sturdy until something hits them or they are damaged. I fear for anyone who has a punctured LiPo and doesn’t know it!
I’m just going from the dozens of quadcopter crashes I’ve had with these LiPos, unprotected on-board. Direct hits at high speed into rocks/trees/everything, and my carbon fiber frames got dinged up or an arm broken, propellors disintegrated, screws snapped, motor shafts bent, but never a battery explosion. I did bang one up enough that I decided to discharge it and dispose of it, but seriously, they need a sharp thing delivered with force. I don’t think even a loose nail flying at 50km/h is a threat.
On the extremely unlikely chance I do hit something very sharp that is sticking out of the ground more than 5 inches at just the right angle and it manages to puncture a battery, I’ll jump off when I see the flames and enjoy the show 
Something that is a serious threat which I think hasn’t been talked about enough in this community is explosions while charging. That I’m very careful about, always double checking cell voltages and balance charging every time. If you over-charge a cell you’re going to have a bad time.
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The irony is that was a well protected ESC catching fire, not an unprotected battery!
But yeah, enjoyable fireworks 
UGH! man I don’t know what my problem is with drilling straight holes. I use a hole punch, line everything up perfectly, tripple check, then I press down and actually see the drill bit bend out sideways and go off in its own direction as I slowly press down. Not sure if it’s my drill press or the drill bits or what, but something is broken! Time for a bunch of googling.
Anyway, I was having a major problem with my plywood truck wedges, the screws coming down through the deck were working their way back out. They had come out almost 1cm the past couple of rides, so it’s only a matter of time before the whole wheel axle falls off while riding!
That aint ideal, so I got to work a couple of days ago making aluminium truck wedges. I have some 1/4 inch by 2 inch aluminium bars and some 1/2 inch by 2 inch bars. I would use two 1/4 inch thin plates, top and bottom to spread the load on the deck and trucks, and two 1/2 inch thick plates on the sides, so I could comfortably drill 5mm holes in them edgeways.
So I actually drew this out first. It was a very good idea, my first 2 designs would have failed. But this was looking pretty good:
The front (left in that pic) screw that comes down through the deck has to go into a threaded hole in the side plates, which I don’t really like, but I don’t know if there is a way I could secure a nylock nut there, given it is one of the last screws to go in.
Luckily tapping went very smoothly. I have read a few horror stories about that, but I used the drill press, winded the tap down slowly and everything worked out great there.
The top and bottom plates were relatively easy too (would have been even easier if my drill press would behave). But the wedges were a bit tricky, I got out protractors and stuff I haven’t seen in 20 years to try to figure it all out. I cut the 1/2inch thick aluminium with a hacksaw, that wasn’t as bad as anticipated. the wedge that needed cutting out was done by drilling a bunch of holes, cutting down to the holes on either side with a hacksaw, then using a hammer/wrench to knock out the waste, files to tidy it up.
It sucked having to make two of them though. And I am yet to make a whole nother set of these damn things for the rear truck.
Anyway. The one truck mount that was coming loose is now looking pretty solid. Tomorrow I’ll probably wake up with a renewed enthusiasm to work on the other one. But for now… What a pain in the ass that was. I hope I can ride this board OK with different angles and heights front and back, I’m dying to get out there again!
Here’s how it looks pretty much done:
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They look like the ones I made for my Urban Beast build
If you want a cnced set let me know.
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I did see yours, they actually helped give me the idea to do it this way, so thanks! Sorry, I should have credited you really.
Good idea with the rubber spacers, I might do something similar too, can see how it might damage the deck.
Cheers!
I completed the other mount. Much easier than the first, my drill press issues were just a combination of small errors, issues with clamping properly, my hole punch was too sharp, and wasn’t creating big enough round enough holes, and I wasn’t taking enough time to triple check everything was lined up correctly.
I might end up replacing the drive train if these belts wear out too fast, otherwise I’m probably going to go all in and make a 4WD build next.
Either way, it’s been a blast, and I’m super happy with how this board performs as a first build. I’m calling this done for now, am working on a better ride video, learning how to ride better. Thanks everyone for your suggestions and feedback along the way.
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Hey anyone know where too get tires that go to higher speeds with these? Mine wobble around 15mph
My pulley is balanced too it is actually my back wheels that wobble. Front wheel drive a/t board
I haven’t even built my mountainboard yet, but I can already tell how our of balance the wheels are. Could you just get some stick on weights that they use for auto wheels? That’s what I’m going to try.
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Hmm, I haven’t noticed any problems with wheel wobble at those speeds, maybe I just got lucky. They’re definitely not well balanced, but it doesn’t seem to be a problem for me.
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Yeah I was thinking of that for sure I definitely am going to look into goped tires too and see if those may work
Had my first major failure with the motor mounts, both of the zinc brackets cracked and fell apart. It is still ridable, but the mounts are now jiggling all over the place, not ideal!
I also have had plenty of belt skipping while braking heavily, and have decided it’s time to go with 15mm HTD pulleys, with shorter belts and new mounts.
I ordered a set of 72t and 17t aluminium pulleys, with 84t belts from sdp-si.
Those big aluminium pulleys are beautiful. Shame I had to destroy them! Used a hole saw in the drill press to cut out the inner part. Was a bit worried, but it was OK. Just took it slow, and make sure you remove the grub screws first, they worked their way out and caused trouble.
I measured up the radius of the MBS hub screws again, and calculated where all the holes needed to be. Have learned a few things since the last try! I used this calculator to figure out the lengths between points and used digital calipers to mark them.
Fitting nicely. Next up is the new mounts.
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Just to follow up, I got the mounts done, and it’s working great. I actually did a separate thread detailing the mount design/build.
I ended up having to replace the M4 bolts I had used to fit the pulleys to the wheels with longer ones, which was kind of a nasty job, but necessary to pad the wheel pulley out further and make sure the motor pulley didn’t rub against the wheel.
It’s a lot better with the new belts. There is less flex/give in the whole drive train, so everything feels tighter, and more responsive. There is no belt skipping while braking with the belts much looser than before, so I think it actually rolls more freely now, should be more efficient.
I’ll probably round off the mounts to fit the motor profile to make them look nicer and a bit safer.
Here’s a couple of pics of the new mounts.
Here’s a video I forgot to post in this thread of the build in action, however it is with the old belts/pulleys/mounts.
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Any updates?
Really nice build log… with lots of photos and comments… I like that
Seems like you have gone through a lot… while making it possible
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I have not posted my build pictures yet… still quite a lot of things to improve (from visual side)… though Im already looking into building a more compact deck / board… the one I’ve got now is just a monster… 
it is about 42.5’’ in lenght, +/- the motor mount,
got to measure the original lenght of the board.
So - looking at your somewhat compact board was a treat to me… though… looks like I’ll have to make some sort of wedges too… if the stock ones does not fit the new deck I’'ll get.
Hi, nothing new to share really. I’ve still been enjoying riding it, and haven’t had any more technical issues. My problem right now is that it’s still currently drying out after I accidentally rode through a pretty horrific pile of cow shit, and got it splattered all over the underside! Maybe a case for the ESCs/batteries isn’t such a bad idea after all, just to make cleaning easier.
I’m finding the lack of torque with the new pulleys a little annoying too. 17:72 is really not as good a fit as 16:78. I even went up to 2x5S batteries but found it didn’t make enough difference. The top speed is mental now too, I haven’t had the guts to go full throttle on the flat yet.
I’ll probably try a new build next year with some Trampa trucks/wheels, but for now this is going great.
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I am working on a mountain board too but with single drive only, The problem that I am running into is with the xl belt and pully system. XL 10mm wide is causing the gears to slip. I might Chang it to dual drive. Can you post a picture of the motor mount.
I might change the gear and belt system to htd5m with 12 to 15mm wide.
It may be your belt tension is too low. Those gears are massive and engage a whole lot of area and presumably teeth, seems odd it would slip unless it’s under a lot of load.