I know what you’re asking, Doug, What’s your big esk8 project for this winter after last year you skated through the whole winter producing nothing more exciting than runflat Nova’s?
Well, the smoke finally cleared from the summer projects and Halloween’s madness is behind me so notwithstanding Thanksgiving (yes, I’ll be esk8ing in beautiful warm San Jose CA) I’m finally getting back to . . . The Mountain Board!
Yes, I got spoiled by having a board with a suspension (the Propel Endeavor) I wanted to try my hand at a suspension board. But I don’t think the shocks are necessary and indeed are just a heavy distraction from what your feet should be doing. So I decided to try a suspension made of nothing but spring steel.
Probably ill advised but those who know me know I’m not too bright and am loathe to accept the status quo.
Which is obviously just a 3D printed proof of concept test fit, but it seems to hold water as a design, so I’m going to go ahead and cut out the aluminum pieces and order some thicker spring steel.
But the problem with suspension boards is powering them. Either you have to hang the motors off the unspring wheels or you have to have some sort of actual drivetrain involving driveshafts and such…
Or you could cannibalize the hub motors off a stupidly heavy Ecomobl which has been holding my house down for at least a year.
Just a suggestion, adding some spreader plates top and bottom, might mitigate any stress concentration around the screws, perhaps even add a rounded chamfer to the axle blocks and spreader plates where the leaf spring exits the sandwich.
What comes to mind with this idea is that you’d need to stay inside the elastic deformation region of steel, otherwise you’d fatigue the material quickly. FEA tools can help you calculate the required thickness for that, but the thing with FEA is that you need to know the shock loads that the board will see to spec it well which is just something I don’t have any data for.
@A-damW You are correct, 0.15 cover plates are on the agenda for those connections top and bottom.
@Dinnye Yes, I have a plan to “distribute” the flex via the shape of the inside connection points. I can’t remember what the name of the curve is but it’s the one that gets progressively tighter as it comes in, like a snail. That will basically act as a progressive bump stop. I’ll post a picture when I get it worked out but I need to actually see the deflection by jumping up and down on the thing before I can figure it out. And that requires the final thickness spring steel to get here. Which I just ordered it. (I know it’s the final because it’s the thickest I can get at Online Metals )
I figure I don’t have to worry about speed wobbles on a mountain board. But the truth is I never have to worry about speed wobbles because I’m just slow
What about using composite/fiberglass leaf springs? Also, you may be able to put an elastomer between the leaf springs to help tube the compression and rebound.
which means the only thing between me and a spring steel eMTB suspension is a whole lot of time in front of a manual mill. The downside is that this steel is too thick to cut on the Barbie Saw that I was using to cut the samples.
So I’ll have to load up a chopsaw with a metal cutting blade to get through them which will make a lot of noise and a lot of sparks. And make the shop smell funny.
I found a new way to burn down the house. What you do is put a metal cutting blade on your chopsaw, attach the Shopvac to it and then try to cut spring steel. The sparks, see, they go straight into a large bin full of sawdust and plastic dust amidst a flurry of high speed air.
OK, well re-learning is I guess the best reinforcement. In the back of my head I already knew how to cut hard metals, but it has a downside. Which is better than not working at all.
The chopsaw got really hot and melted the plastic parts of the saw itself, so that was a non-starter. Then I decided that the blade does fit in the table saw so I cut the first piece on the table saw which went reasonably well, but what happened is that it glazed the blade and it wouldn’t cut anymore without undue force, which is about as dangerous a thing as you can do on a table saw.
The problem of course is that it doesn’t cut particularly straight (or I don’t), so I had to follow up with some edge grinding but in the end I now have the pieces to the correct dimensions with almost no goofs.
Now, how to drill holes in them. I suspect I’ll burn through several bits before I’m done.
Waterjet is the obvious solution here except that I don’t want to take all the time to go up to the Makerspace, fire the thing up and run them. I really want to do it in house so I can make quick changes/adjustments, fine tune etc.
Awesome idea. Looking forward to see how it turns out. Yea, spring steel is nasty to work with, super hard stuff to saw and drill.
I wonder if hanger arm twisting is gonna be an issue.
And I got a good start on the stub axles. They are mild steel, I hope that’s strong enough, it’s all I had in stock aside from 6061 which definitely isn’t.
Yes, those are 3D printed hold downs. They work amazingly well. If you look closely you can see that they have a bit of flex engineered into them. Of course you want to orient them so the side is the bottom while printing.
It’s a full inch higher than the rear so I’ll need to adjust that before testing, and the pre-load on the turn-springs is too low so I’ll need to fix that.
And I feel like the sheet springs are just a little too stiff so I’m going to swap out the upper spring for some thinner spring steel.
Then wait a really long time for the trails to be dry enough to try it out.
)
