e-longboard build

makepeace

10 mW
Joined
Sep 25, 2014
Messages
34
Sup folks

New here, name is Jono and I'm from Cape Town - South Africa, studying electro-mechanical engineering at UCT.

Anyway, I've been bitten by this bug since sometime last year and have been lurking on this forum and others since then, but I've finally decided to dive in and build my first e-board. It's mostly going to be for travelling to and from uni (about a 6 km return trip), but also for just cruising around to friends etc. I'm keen on at least 15 km range once I'm done tinkering. Been ordering parts the last few days (much to the displeasure of my wallet). Here's what's on the list so far:

2 x 250mm (axle measurement) eBay clone trucks, they're kind of Randal looking
4 x 90mm 78a Abec 11 Flywheel eBay clone wheels (come with bearings and spacers)
Some Blood Orange barrel and cone bushing sets to play around with
2 x NTM Prop Drive 50-60 270 KV motors
1 x Alien Power Systems 120A 2-8S Car ESC BEC Twin
8 x 5.8 Ah 25C single cells

I then ran out of money. I planned (and eventually plan) on getting 16 of them 5.8 Ah cells to make a 11.6 Ah 8S2P 25C pack. That should do me way more than enough run time, but I'm sure 5.8 Ah will be plenty for now.

Anyway, will most probably buy some "proper" trucks, wheels, bearings etc anew once I've managed to stockpile some more cash.

So the plan is to go for the diagonal drive arrangement with a 1:2.5 RR for the moment, so probably 12T -> 30T which should give me about 38 km/h (being quite conservative), and enough torque with 2 motors for some decent climbing capability (my uni is at the base of Table mountain, quite a bit higher than where I stay). Will see what happens as I get a bit braver.

Still need to order a drive pulleys and belts. Probably going HT5, 9 mm wide. Also need some fasteners, and perhaps some risers - will see.

I'm going to take the frugal option and get as many of my other parts laser cut from alu-alloy plate, which I'll design myself. These include motor mounts, truck clamp brackets, driven pulleys + guides and any additional parts for the wheel attachment to the driven pulley. Also going to take a frugal approach on the deck, which I will make myself. It's probably going to be a birch + maple veneer ply with some alu-alloy reinforcement. Going to base it on the Landyachtz Tomahawk (if anyone knows of any similar decks, please let me know - need inspiration). Probably about 995 long, 240 wide, 605 WB and about 16mm thick.

I plan on doing something a little different with the battery arrangement, hence the 136 x 50 x 10 mm single cell batteries. I want to rout cavities in the deck on either side of the centerline from the bottom, to house the 10 mm batteries in the deck. I'll then clad it on either side with (quite thin, probably 2 mm) alu-alloy panels, one of them being easily removable to get to the batteries. I'm not 100% sure about how this will turn out, and I may fiddle with this idea a bit. It's mostly for protection, but also to look a bit more polished.

Thoughts, comments, crits all welcome

:mrgreen:
 
So I've been obsessing quite hard over this, being my first electric skateboard (and skateboard in fact). Whenever I drive to campus I can't help imagine cruising along on the pavement instead. I can't wait! So here are a couple of things that I've bought:

image.jpg
57_1.jpg
22036_main.jpg

Trucks: $20.20 ; Wheel kit: $28.75 ; Motors: 2 x EU28

18562_3.jpg
20131213_151249_FILEminimizer.jpg

Batteries (5.8Ah, 1S): 8 x EU 11 ; Alien 120A Twin ESC: P 99

57_2.jpg
KGr_Hq_J_lw_FI34_N1dk2_BSOW_Vn_F_g_60_57.jpg

12T XL 8mm bore pulley: 2 x $8.48 ; 10" 10mm belt: 2 x $4.11

Things that will still cost + estimates:
Radio control stuff: $30
Board wood: $70
Machined parts $100
Another set of batteries: EU88

For a total of about $715.77 or R 8,026.13 (my local currency). This is about as much as an above average mountain bike (which you have to pedal to move).

Anyway, as I've run out of cash, the only thing to be done is some designing while I wait for parts to arrive. Threw this together on Solidworks yesterday evening:

render_5.png

render_7.png

render_6.png


Designed the board myself, and I think it's turned out ok. Will work on sourcing some ply sheets and make a press from some hardwood. Should be relatively easy to approximate the shape I've drawn up with hopefully not too much work. The ply sheets will be pre-lasered to the outer shape +5mm (to rout off), and the top couple of sheets will have slots on either side of the "stringer" for the batteries. This will leave about 5mm of wood between the batteries and the bottom of the board, and the top of the board will be clad with 2mm (or so) aluminium plate that screws in from the top.

render_8_2.png


All of the fabricated parts will be laser cut aluminium alloy (not sure what exactly, depends on what I can get my hands on). Mostly 1mm, 4mm, 5mm and 10mm, stacked up where necessary for some extra strength. The reason for this is that machining here is generally quite expensive and unreliable - we don't have many CNC places.. So this will work out to be a way cheaper option, provided I'll be able to design around any inefficiencies due to the compromises of having to work with 2D profiles.

render_9.png


Did some strength calculations for the critical parts (clamp, motor mount etc), however I'm slightly worried about those small button head screws for the clamp. Best I could do without overspeccing the clamp bracket thickness wise, and they check out with a safety factor of two on the estimated torques and belt tensions. Might go up to 12mm thick and M6 depending on the quotes that I get for the laser cutting just in case, as it doesn't look right.

render_10.png


Included a motor guard 4mm thick. Will leave it aluminium as I don't mind it or the motor mount being slightly sacrificial in the case of a prang.. better R200s worth of aluminium than the motor.. I think I've managed to keep the motor raised up enough (about 5cm from the ground) without compromising on the boards overall height - which would mean bad things for stability.

I've ordered a 12T 8mm bore pulley and a 254mm belt, 10mm wide, and have designed accordingly. Kept the pulleys small to reduce weight, which I've been religious about wherever I could be. I've settled on the XL profile, as it seems to be more widely available than the HTD. Will sacrifice a bit in terms of power transmission, but as there are two motors and 10mm belts, I should be ok. The driven pulley is cogged at 30T, which gives me an RR of 2.5:1 which by my calcs should allow for about 43 km/h, way more than enough I think. Torque calc says I should get about 0.855 Nm (net, at 43 km/h incl. effects of drag, rolling friction etc) up a 15 deg incline with the two motors. This is a bit of an unrealistic calculation, but it proves that if I can accelerate up a 15 deg hill at top speed, then I should be ok generally.

Still got quite a bit more fiddling to do till I'm happy, but for a night's work I'm pretty stoked!
 
Nice motor mounts!

I would suggest if your going to laser cut your sheets over size, and then route the edges to skip the laser cutting. Just get some rectangle shape pieces glue them together, throw it in the press and route it all out at once. That's what I did with mine.

Also, I would stay away from the XL pulleys. I had those before HTD 5M pulleys and belts. The HTD ones are much stronger, and reliable. I broke several sets of XL belts, they stretch, they climb the teeth and skip, and they break. I am still on my original set of HTD belts.
 
Hmmm. You have a good point about the pulleys.. I think I'll try out the XLs first since I've ordered them and the belts, and since HTD brings with it some complications.. I am splitting the torque over two, so maybe it will work out. Will do some calcs to see if I need to do anything drastic. But I hear you! Will see how it goes.

In terms of the laser cutting ply sheets, it's pretty cheap for me to get it done, and it's kind of necessary at least for the inner cavities - don't trust myself with a router to get my complicated deck shapes right. And I only have a hand router with a pretty makeshift table that I made so I'd like to do as little of that as possible..

I wish I had a laser cutter! I'm not going to be doing any of the laser cutting, going to get a shop to do it for me. They have a cnc bending set up, so they'll bend those motor guards for me too.
 
Update time.

Ok so I've ended up going with HTD 5, 9mm belt in the end. Everything else was either too expensive or not strong enough to be durable. Ordered two of them from SDP, waiting on those. Also, I've settled on an RR of 2.5:1. This should get me crazy torque with the two motors and 8s and still offer some pretty good speed. Will see how I feel after a few rides.

I received my ESC from APS which I'm quite excited about, and I also ordered an Arduino pro-mini and UART serial link. Have tested it out and loaded the wiiciever code (thanks austindavid again for the dev work on this, looks awesome!).

IMG_20141103_202934.jpg


In the meantime I've been doing some more design work and have refined my deck to what I think is a bit of a work of art (if I do say so myself).

image.png

image.png

image.png

image.png

image.png

image.png

image.png


It's got it all: symmetry, microdrop and flares for keeping feet stuck in, kickers, W-C-W concave, slightly angled truck platforms to increase truck angle by about 2-3 deg, wheel arches and some nice camber. It'll be 5 sheets of 3mm bendy ply - so about 15mm thick, +1 or 2mm for the plate.

Also modeled the pockets for the batteries and an alu plate for the cover. Looks like so:

image.png


If there's anything you can see that you think needs improving, please let me know!

Still waiting for:
Motors
Batteries
Nunchuck
Wheels
Trucks
Pulleys

Stuff to get locally:
Pulley belts
Random electrical bits like wire etc.

Will send off the drawings to the laser-cutter as soon as the stuff starts coming in so I can check the measurements. After my last exam on Monday, I'll be getting to work making up a cement press for the deck, getting some 3mm bendy ply, laser-cutting the profiles and pressing it out. Will then hit it with the router to smooth off the edges. Next is getting the alu plate laser-cut and glassing the bottom of the board. By then hopefully all of the other stuff would have arrived and I can start putting everything together.

Anyway, hopefully I can get going on this in the next week or two.
 
Your solidworks skills are amazing.
Great job.
I love how each new build brings new skills to the forums..
 
Looks like you're going to have a sweet board! :) Nice motor guard too. The circles make a nice pattern.

Random question, but since it's relevant to the mock-up: Does anyone know how much (if at all) the integrity of a deck is compromised when routed? Can't really think of an application besides sinking the wires for a split enclosure layout. Or adding EL tape into the top.
 
drmacgyver said:
Looks like you're going to have a sweet board! :) Nice motor guard too. The circles make a nice pattern.

Random question, but since it's relevant to the mock-up: Does anyone know how much (if at all) the integrity of a deck is compromised when routed? Can't really think of an application besides sinking the wires for a split enclosure layout. Or adding EL tape into the top.

We'll if you remove too much. I would assume that area would be pretty flexible. Evolve seems to have about 1/2" routed on their carbon decks to fit part of the battery. I would think it would be fine with a 9 ply but some 7 ply decks are pretty flexy. I think 1" is a safe size for the height of an enclosure. Been thinking about routing a rectangle in the deck though.
 
Thanks for the comments.

I've been using Solidworks for about 3 years, but mostly on and off for Uni assignments. Every time an idea props into my head I like to model it to see what it looks like so I've become pretty good.

Regarding the putting the batteries where I intend to okp, why would you suggest I don't do that? There is going to be a 2mm sheet of aluminium between the grip and the batteries, and about 8mm of wood between the batteries and the bottom of the deck, so I don't really see the problem. I really don't like the way the batteries stick out of the bottom of most of the boards I've seen. The enclosures make them look a bit better, but I still find it a bit garish. Also, more protection this way.. From some videos I've seen, you really don't want to get a puncture with these batteries..

In terms of routing and how it affects the structural integrity of the deck, this is a very broad question. The answer (as expected) is that it depends, but the result hinges on the fact that you are removing material that would otherwise be stressed, which means the material that is still there becomes more stressed. Bending stress increases towards the center of the board from the two supports (the trucks), so the centre of the board (along its length) needs to be the strongest, unless you want some flex. In that case you would need to consider how much flex you can get before you reach the yield point of your material. Corners and things also introduce stress concentrations.

You need to either analyse the design from a solid mechanics point of view (using traditional approaches or FEA - finite element analysis - which you can do on programs like Solidworks, but you need to know what you're doing) or make a couple of simplifications and assumptions ie a normal flexy deck is 12mm thick, if I cut 5mm out of that, i need to increase the overall thickness to 17mm. This is not a very certain approach and will probably require a lot of testing to get an adequate result.

I tried to get a couple of screen grabs of my FEA, but the model isn't meshing since I've made some changes.

edit: here's a screen grab of the displacement (amount by which any element moves as a result of application of force) for a 150 kg mass in the centre of the board (which is what i deem to be the worst case scenario for this board - i weigh about 80 kg).

displacement.png


it's about 0.5 mm, which i think should be ok. it's probably not very accurate anyway, but an indication that it will probably be strong enough.

here's the stress:

stress.png


i would compare these values to the material properties in order to work out if the material might yield. seems pretty safe here as the yield stress in bending for 18 mm birch ply is about 40MPa, the max on the birch sections is about 6-10MPa. the yield stress for the aluminium is about 120MPa and I have max at about 15MPa. might actually reduce the thickness to 1mm now that I think about it.
 
Would like a bit of comments/criticism on my idea for battery connections.

From what I've read the safest and best (in terms of longevity) way to charge LiPos is in parallel. In my case, I'm making my own "custom" battery setup using single cells. I need 8s, so I will use 8 cells in series. I want to make up a plug type of thing that has a block off plug to put them in series and enable the + and negative - outputs to the rest of the circuit, whilst still being able to charge in parallel. I don't want to use a balance charger as it's another expense and adds complication. Also, the way my board is designed, I would prefer it if the batteries could stay in the board while charging.

What I've come up with is (very roughly) as follows:

2014_11_061_1.jpg


Obviously I will need to optimize the wiring paths and orientations of the batteries.

With this in mind, even if it's optimized for the least possible wire length, my concern is that I will end up having a lot of wire and the associated problems with this. For those with experience, is this necessarily a huge problem that can't be catered for by using higher gauge wire (without getting ridiculous)?
 
Will you charge it as a 1s 46,4Ah battery? I assume that would take really long or quite high amps while charging. That is quite some time to sit next to the lipo and watch it charging.

What king of connectors do you have in mind? Don't you have to at least use xt60 or something that size? Could get quite a big block then.

Having wired a few board, I always calculated too little space for the wires and had to pack everything very close later on. Especially if you have wires for each scell instead of the cells linked internally in the pack it could get real messy. My small board got 3x2s zippy compacts in series and I just used the presoldered bullet connectors to connect them which ended up suing about 1x2x14cm just for wires and plugs. I don't know exactly how the electronic magic happens, but won't yoou need at least 12 to 10awg wire for all the battery wires? If you are referring to voltage ripple or higher resistance with many wires, I can't really tell if the wire lenght will cause problems there. If in doubt, add a cap like some here on the forum described.

Interested to see how this works out, keep us updated :)
 
In terms of wire gauge, I think I calculated about 8 AWG a while back to be super safe, so yeah I guess I'll have to make provision for that mechanically.

Yeah I'd be charging it like that, but the max charging rate is theoretically 2C. As they are in parallel, if I do 1C, I can theoretically charge them at 46.4 A for an hour charge. I'll probably go for 30A which would mean that it would take about 1.5 hours to charge, right? That seems reasonable. Will probably design a circuit around two parallel CSR1504 adjustable regulators for 30A.

Also, I think I'm going to put a little controller in it that can watch the amps, volts and keep time. Will also put it on a wallplug timer and make sure I'm in the room (there's no ways I'm physically going to watch it charge, is that what you guys do?!).

Probably not going to use those connectors you mentioned as another 6 week wait for hobbyking will kill me. Will probably try find something local, but yea I expect it will end up to be quite big. Can deal with about 80 x 15 mm if it comes to that :p.
 
8 AWG might really be overkill, I don't think anyone used something thicker than 10 on a board yet, so you could go with 10 for more flexibility and better fitment to the connectors. 10AWG fits the 5mm (or was it 5.5mm?) perfectly.

If you can build a matching charger by yourself, that is great! I was assuming you would use an rc one which would be quite expensive for high amps I think. Seems like you will get a really nice charge time, I like the method! I can watch my battery charging cause I got a small living room, but I wasn't being literal :)

You don't need to use the connectors I mentioned, was just for reference of size. For your parallel/series setup, I think there was a link somewhere on this forum to some kind of click system for connectors which basically allowed you to click single ones together for a connector for your needs, so no awkward glueing them together or so. Lego with connectors :)
 
Nou toe nou. Groete uit Gauteng!

It is a bit too late now, but I found a local shop that sells hobbyking stuff. Junctionhobbies.biz they are in Pretoria. They don't stock parts individually, they sell kits. I called they recon I can order and they can bring in if I don't mind waiting. Have mailed the wishlist on Wednesday for pricing but heard nothing yet. Don't have high hopes the only 2 google reviews they have are negative.

I am also looking for pulleys and belts. I wondered about the belt and pulleys in belt sanders since there are enough aftersales services for them to be freely available and cheap. They also look like about 1:2 RR but have not counted teeth numbers yet. I think they should be tough enough. Having worked a lot with belt sanders, and in my irresponsible youth ridden an 800w Hitachi for about 1.5m before I fell off:D.

If the above two suggestions for sourcing parts locally is not going to work, we are at the mercy of the exchange rate and high courier cost to South Africa. Since Marikana never been favourable :oops:
 
howzit ek se!

Yeah I checked them out before I ordered a while back and they look a bit suspect. Also, the stuff in their kits isn't entirely what we need :/ so would most likely have to get them to bring it in, but it would probably be quicker (and cheaper) to bring it in yourself. It's been a long wait for me so far (ordered about 6 weeks ago) but I think it's probably due to the post strike we had a while back. Apparently they've got about 2 months worth of back up. Normally HK orders take about 2-4 weeks (past experience) to get here.

That's an interesting thought about using belt sander stuff. Let me know if you have any luck! I doubt that this will be my last board :p. If you don't come right, have a look at RS components:

http://za.rs-online.com/web/c/?searchTerm=htd+5mm&sra=oss&r=t

They have excellent service and super fast delivery, and they're pretty reasonably priced. I decided to order from SDP/SI so I didn't have to pay for post machining since they already come with a fastening solution, and I had to wait for the other stuff anyway. Plus the ones I got are plastic to save weight. As far as I remember RS only had steel ones in the size I needed.

I have no problem in getting stuff from elsewhere. I've had loads of experience in the past as I've done some other projects like building a valve guitar amp, fixing electronics etc and you just can't get a lot of specialized stuff here and when you can it's majorly marked up in any case. Importers also have to pay for shipping and duties.

WRT our currency, something tells me it's far more complicated than an isolated incident of "police brutality" (the dubbing is debatable in any case).. It's way more systemic than that. These types of things are happening all over the world, often usually far worse. The US is a case in point. But lets not go there. We have a beautiful country with (mostly) beautiful people and that's all that really matters. Anyway, money is just a distracting illusory construction and in a country as awesome as this who really gives a #$&@!

Belt sander racing sounds really fun! Think I had a deprived childhood.
 
Was fun. Until my mom found out.

Thanks for the leads. Will follow your build with keen interest
 
A work of art you say? Maybe for a piddly little program like solidworks :twisted: , wait until you try a fully surface capable program like creo! This is one of my recent decks, got the works - flares, microdrops, boob drop and more, pressed from 8 ply plus glass. Hopefully picking up some graphics to press a few more this weekend. But that motor housing looks neat, you did it as an assembly of with the guard a sheetmetal part? Shouldn't be a problem sending people the cad to cut it for you then. CNC benders are awesome... Interesting charge method though, my chargers all top out at around 8 amps so wouldn't work for me, but it is a great way to balance charge easily!

0


edit


edit


edit


So from the top image I cnc routed a mdf mould, finish it with a 3mm ply cover glued on, lay some 3mm rubber then press the deck veneers onto the top with a pneumatic press, about 45psi. With the ply and rubber it gives me a good enough surface to use for a fibreglass finish. Seeing as you are making your own deck, if you want layup/pressing advice give me a yell.


Edit: Screw it, can't get the images to work, try here through drive: https://drive.google.com/open?id=0B_1V_UsOd8XLcnZrb3NCdC00enM&authuser=0
 
Please please please fix those photo BBs, really keen to check yours out!

Yeah I've just been using Solidworks cause it's what my uni provides for us. I haven't had any experience with other packages, but as a piece of software its VERY rough around the edges. I'm pretty keen to try out some other modelling software, but trying to learn another package is a bit daunting. Will give it a go at some stage. Yeah I made the guard sheetmetal, planned on just sending them a flat pattern and get them to bend it up. I've been reconsidering it though.. I actually don't even think it's necessary as my motors are going to be pretty high up.

Anyway, new update. I've just bought some Caliber I trucks that were on special here, so I won't be using those trashy fake Randals anymore :D
 
bandaro said:
Edit: Screw it, can't get the images to work, try here through drive:
The GD page doesnt' work either; why not just upload them directly to the forum as attachments to your post? ;)
 
The GD page doesnt' work either; why not just upload them directly to the forum as attachments to your post? ;)

Guess I will, that gd should be searchable on the open web, so not sure why it's not working... but here, some screen shots - pretty renders may come later, but I generally don't bother.

1.jpg

2.jpg

4.jpg

5.jpg
 
Back
Top