Thought I’d share a little project that I’ve been working on for about 6 months just to first kinda show off this cool design and maybe get a bit of feedback from people who’ve tried similar builds before (or even concerns from people who haven’t, I’ll post my main concerns and why I think they won’t be an issue or why I can live with it).
Anyways, before I bore you with the specifics, here’s a quick render of the build, with a screenshot of the CAD model. (the front truck is not mine and is just there to look nice. I’ll just use an off the shelf longboard truck and deck):
Anyways, I’ll quickly go over the components:
_The biggest component here is the battery pack. I really wanted to keep them hotswapable (because I’m kinda international-ish, and I have no idea where I’ll be after university so I’d like to be able to bring all the batteries with me so I went with 18650 battery holders (didn’t want to go with lipo pouches, though now that I think about it that might have been safer than soldering my own pack together), that will be holding 40 LGHE2 (or HE4, I forget), giving me a 10s4p, 37V nominal 10Ah capacity pack. This cost about $200 and is the most expensive “component” of the board _Next we have the ESC, cheapest (new) VESC I could find was the 4.12 version from diyelectricskateboards for $99.99 _Then to power my wheel I’m going to order a Turnigy SK3 168kv motor from hobbyking for about $80 _I’ll be using a 10s bms to charge all the batteries (at only 2A, the highest small-ish power supply that was 42v), which should charge ii in about 5 hours. It’s only used for charging and balancing though, couldn’t find one that would handle the high currents without costing significantly more. About $20 for both the BMS and power supply. _I’m using a Fuzion 110mm kick scooter wheel (was supposed to be 100mm, ordered the wrong one, but the design allowed for switching if I wanted a bit more speed instead of torque). With a 3:1 gear ratio using HTD5 16mm found on ebay (36T:12T). The wheel uses the original bearings and the gear is mounted directly to the wheel, There’s a picture of a 3d printed gear lower in this post, but the gear shattered when I dropped it two seconds after taking the picture, I’ll be machining the aluminum one. Total for both the wheel and the gears and belts ~$45. _The shaft holding the wheel was actually the biggest issue. With mechanical parts such as the wheel, I wanted as big a factor of safety as possible (anything below 7 static FOS kinda worries me considering how fast this board can go, that it’s carrying me, and that I have to take fatigue into account as well as vibrations), which actually was causing really big issues when running FEA in solidworks. The stainless steel 8mm shaft was failing (not failing failing, but way too low FOS, can’t remember exactly, but it was maybe around 2.5-4 for only half my weight). So that had me kinda worried but luckily, they make 8mm tungsten carbide shafts meant for mills or some kind of machining equipment which gave me a factor of safety of 9! That was only $20 shipped from Israel too so that was cool. _ The mounts are plain old 6061 aluminum, FOS on that was like 20 so I’m not even worried, the only thing I had to change is make little stainless steel inserts to distribute the load from the shaft over a greater area, but those will be tiny steel parts, also machined in the university shop, not sure what the steel stock would cost, but the aluminum was only $35 and is big enough to allow me to mess up once. _The motor mount is kinda boring, the nice thing about the three wheel design is the motor can be mounted directly to the board, which is really nice for clearance and looks. I tried 3D printing a mount and it turned out pretty nice, but I have no way of adjusting the belt and I might have to make a new part just for that.
Not sure exactly how much this would cost from scratch but my spreadsheet says around $650-$700 with all parts including board and controller ect.
Anyways, here’s a picture of how big the holder is, and a rough idea how the other components will be layed out (still waiting on my VESC and have yet to order the motor):
Speed: _Because I’m getting 6200rpm, with a 3:1 gear ratio and a 110mm wheel, this means I should be getting up to 26mph on this board. And if I need any more speed down the road (which I really think I won’t, I enjoy not dying) I can always switch the 12T for a 16T which gives me a lower gear ratio and 35mph max speed. Range: _Using the 14Wh/mile approximation gives me 26 miles (37V*10Ah/(14Wh/mile)).
My main concerns: _The first one was my biggest concern, which is stability. This is a completely different design and could cause instability and wobble. However, after thinking about it, and seeing videos of other people’s builds on youtube, I think that having a static wheel in the back might be the same as having a ridiculously tight back truck (like tighter than is possible probably), which means that stability should actually be better, especially at higher speeds. So I’ll test it unpowered first, and hopefully it performs fine. _My second concern is with the batteries, I’ve tested the resistance of the holders and seen people use the same holders for their electric scooters, but they’re gonna be seeing a lot of current. I soldered copper wire as close to the contact point on the holder as possible (it’s on top actually, so maybe 1mm of strip + contact resistance). I’m just slightly worried that my batteries might get hot. I’ll test it and it it can’t handle the current I guess I’ll have to make packs (can you bring custom made packs on a plane?) _Finally, my last concern is whether the board will twist since there’s less support in the back. I know most of my weight will be in the front but I could see the whole board twisting and I’m not sure how that would affect it. If it looks too bendy though I’ll just add aluminum square tubes or something, but that’ll make it soo heavy. Anyways, I’d love some insight on that, otherwise I guess we’ll see when I finish it.
I would really appreciate feedback and any concerns that you may have that I wouldn’t have thought about!