I know what you’re asking, Doug, radio silence, WTF? What’s your big esk8 project for this winter?
Well, I had one, it was truly ambitious, involving upgrading the mountain board to independent suspension, adding 4WD via 2 crazy huge (and really heavy) 63100’s going through RC car differentials.
I was going to upgrade from the current Unity to a MakerX D100 and go from 10S5P to 12S5P and add onboard BMS.
I was even going to embed the Sk8n Sasquash into the deck and have an edgelit PNW Esk8 logo on the side of the BMS box.
It was going to be awesome.
But then reality struck, adulting had to happen, blah blah blah and I’ve tuned the project down to 4 basic tasks for now.
upgrade to 12S5P (including latest design of the battery packs) (boring!)
onboard BMS (boring!)
MakerX D100 (boring!)
Independent suspension on the (unpowered) front only as a testbed. (wait, what?)
So this build log will be fairly spartan at the beginning while I do all the upgrades, but when I get serious about the independent suspension I’ll post more details here.
But it’s evolved a bit since then. I’m not exactly versed in suspension design so it’s going to be a lot of field testing and breaking shit.
Please correct me if I’m wrong, but I think I will be the first person to try to create a DIY independent suspension. If anyone else has done it or has skills or suggestions (or is, you know, an actual mechanical engineer) I’m happy to take input.
when the stock upgrades are complete it will look almost exactly like FS2 (same boxes for driver and BMS with blindingly expensive CF covers, upgraded charge port, etc. But it won’t have the display, just a V meter.
But the way the front and rear (front for now) are put together will change a lot. There will likely be an upper and lower extruded rail, something like this:
A couple of piccies of the mock-up. I don’t think this suspension’s going to work in this form, but I want to get the steering figured out before I go back and re-work the whole thing.
Below is the camber action of the tires which with these flat profile tires would be a blocking problem, but the Mountainboard tires are round profile so might actually be advantageous in terms of wear. Plus hopefully will dig in a bit on turns.
Well, I’ve been fighting with this thing for quite a while now and I’m not getting some key details on how these suspensions work. The problem is that any time the suspension moves up or down by definition the tires toe in or toe out. I haven’t been able to find a geometry that allows for tilting of the board to input steering but for up down motion not to. So I’m going to take a break on that front. Here is a picture of the latest prototype of the arms and suspension.
but as you can imagine when the suspension compresses the tires will tend to toe out. Since they’ve shipped these boards I assume it’s not that big of a deal because you’re in dirt anyway, but on my design the toe was pretty significant so I wasn’t too happy.
The other method is to tilt the whole suspension such that it mimics the function of a standard truck.
The problem with this is that the pivot points appear to need to be near the center. I’m going to test this but the problem with this is that I want the motors to be un-sprung and this doesn’t give me much useful space in the center of the board to install pulleys and driveshafts.
So I’m still noodling on this.
On the upside I did get a friend to cut out some cool Sasquatch feet for the blue deck.
Before I get into that, though, I did try the tilted suspension and as I suspected, if you don’t hinge them in the middle you won’t get much turning action.
However, I have this crazy idea about how to handle the regular A-arm suspension and in a fortuitous combination of availability of a waterjet cutter and my likely need to actually start road testing designs I found myself in front of this magnificent machine (hopefully the video comes through):
and cut myself out enough A arms for both the front and rear.
The nice thing was that after a bit of training I got to run the machine by myself, so hence forth if I need waterjet parts I can just pay the relatively inexpensive machine fee and go to town.
I’ll post more about my idea for the steering system once I figure out whether it will work or not. It’s not exactly traditional design. Even if it doesn’t work I’m just turning the corner to where I think I understand the subject well enough to put something together that works and won’t try to kill me first time out. However it’s unlikely I’d ever let @Yeahthatperson get ahold of it
In other news I did put down my wookie feet on the dyed deck but I don’t particularly like it.
I think I’m going to cut out another deck and cut the feet out of black grip tape next time. I will likely lighten up the dye job on the next deck so the feet pop just a bit more but not as much as they do here.
I don’t know if any of you have realized this but Baltic Birch is no longer available because of the Russian invasion of Ukraine. Fortunately I had enough in stock to cut 4 decks.
I did a little playing with dye temperatures and times and have found that at just under boiling (plus the time it takes to carry a large pot of scalding death from the kitchen to the shop without spilling it) for 20 minutes is a little too dark, but the second dunking, still 20 minutes, but the water has had time to cool off - seems to give me about the shade I’m after.
No, I’ve not managed to figure out the exact geometry of the suspension, but I’m getting closer and, honestly, I’m taking a little break from it because I’m waiting for my brain to come up with the perfect solution and it’s taking its time.
All of this is to say that I got distracted and I haven’t made much actual progress on the MTB.
After spending a lot of time and (3D printer filament) playing around with the suspension I came to realize that I needed a little help. I have a friend who is a mechanical genius so I asked him to help under the guise of “learning Fusion” which was on his agenda so it was kind of a win-win.
The first thing he said is that you really need to have longer arms. I’m leaving the final design up to him but I am still trying out different configurations. The latest one is this, with 2040 extruded rail in a vertical/horizontal configuration.
Just for the record, in case anyone else is playing with contact based battery packs, here are the changes I made to the latest run of the PCB’s.
instead of standard 1.6mm FR4 I went to the thicker 2mm to give it more rigidity against the pressure of the spring contacts
I moved the copper fill on the top and bottom out away from the center screw mount. Originally if there was enough vibration I think it would be possible for the metal screw to rub through the solder mask and cause a short circuit across the 2 sides of the board (Yellow)
for whatever weird reason the balance contacts on the earlier board were backwards, where the contact for the positive side was on the negative terminal and vice versa. (Blue) I fixed that.
Well, the full suspension thing got put on the back burner while I spent a surprising amount of time bringing Farkasszem (F1) up to the same spec as F2, which meant full rebuild of the battery pack, new deck, end caps, all new 3D printed enclosures, a complete re-wire tip to tail, onboard BMS, etc. Basically everything except the frame.
Oh wait, I had to lengthen the frame. You know how these things go, it turned into a complete rebuild.
So here’s some pron about that in no particular order.
Then I made some wood blocks for my honorary grand niece (I sort of adopted a niece, and she got married and had a baby). No paint on them yet, but they are carved out of Cocobolo ends
But the other day I had a trip planned and I knew of a certain trail along the way that was perfect for a mountain board, so I put the old Mountboard back together, oiled the chain and took it out as is.
Man I love that board - it’s so well behaved. There was a steep switchback climb and it just took it. I couldn’t quite make the sharp corners, but it ate up the rest of it, until I reached the limits of my skill.
Something about those mountainboard spring-based trucks, it’s just a totally different feel. I have to get used to it every time but once I get it the board is sublimely nimble (notwithstanding the crap turning radius)
I’m just coming back to that project now, though. But I think it’s going to be a 4th board (5th if you include the Sand Runner) rather than a rebuild of the original eMTB. My mechanical genius friend also got distracted and I don’t think he’s going to get back to this, but I began thinking that I really only need an inch or maybe 1.5 inches of suspension travel, so with the new longer A arms across that small of a range even I should be able to figure out the steering dynamics.
