Thanks a ton!
All of the sandwich panels will need a bit of sanding to fit them up before I can tack them in place with filler, but hopefully I can get that done today after I get back from work. Reinforcing all the joints with carbon will take at least another day after that.
All I got done this afternoon was cleaning up the ends and cutting out the drop through slots with my rotary tool. As usual, I forgot to factor in how little skill I have in using a rotary tool.
I’m glad I took all the time I needed though, because carbon dust and splinters are no joke.
Following with great interest! It’s refreshing to see some true and innovative DIY here and I appreciate the lengths you’re going to to make the process accessible for the rest of us mugs. Were you as nervous as I was when you first aid stood on the Tüüb? 
…and will the cocaine feature in later episodes then? 
Thanks! Yep, I was totally nervous putting my voice out there for the first time.
Correct, the Not Cocaine™ will feature heavily in the next segment.
Sorry, just saw the typo. I meant were you nervous when you first stood on the Tüüb?
Oh yeah. If it made a snapping noise at any point that means it’s junk.
No visible progress today, but I deburred and fit up all of the panels for the foot pads, which hopefully should be pretty much the last sucky part of the build. Joinery begins tomorrow.
It finally looks like the finished product! Got the panels glued up today. None of the joints are structural yet, but it will be ready for carbon reinforcement tomorrow when the epoxy is cured. For reference, that is a 37-in long cutting mat.
After a breif intermission caused by me not realizing I was running out of epoxy because the container was heavy so I thought that I had more…
I finished the main structure of the deck last night and took it out for a spin at my local park in analog mode today, did a few miles and took it up to around 20 mph downhill (EDIT: GPS says 27mph 
). It was my first time ever seriously riding a board, but I think I picked it up pretty okay. I got relatively comfortable doing gentle carves and foot braking. I’m still not super steady in turns and especially not in low speed ones, but I love the handling of the board. Super smooth and predictable.
I think I got the width of the foot pads spot on, I can just hang either side of my foot over the edge a little bit if I want to. The concave was okay I think, I wasn’t pushing it very hard in the turns but I still never felt like I was in danger of slipping off, even though there isn’t any grip on the deck yet. No complaints about the wheelbase, it’s a little long for analog pushing but feels super steady while coasting, and the foot placement feels totally natural to me when going downhill in a tuck.
The trucks have a lot of lean in them right now, which is definitely going to result in motor bite. I have a lot of headroom in the tail of the board to carve out clearance for the motors, and I can also look at flush mounting the rear truck. Plus I can just get bushings that limit the lean more, so I’m optimistic.
Spent the past couple of days building all of the battery modules. I’ll start on the weight shift control system next.
These strain gauges are easily the trickiest thing I’ve had to solder. Why did I sign myself up for this 
(Banana for scale)
I finished installing all of the strain gauges, and I wired up the first of the amplifier circuits to test if it works.
It is responsive to my weight, but even with the gain turned all the way up the response is only a few millivolts, so I have to figure out why that’s happening.
Are you sure they’re installed in the right orientation? I’m not sure how much deflection you’d actually get with them installed that way
Based on my calculations, (sorry about all of the clutter in the equation list, weight transfer is controlled by the Xcg parameter in line 18) putting all of my weight on one pad like that should result in 0.25% strain on both the top and bottom surfaces, strain gauges typically have a maximum of 2%, so it should definitely be within range. Using the 5V supply of the amplifier it should result in a change of 100mV, which of course should only need a gain of 20 or so to boost it back into the 5V range. The deflection of the deck under load is in line with my calculations, so at least that part’s not wrong. But there’s a lot of other stuff to check.
Hmm yeah in my experience thus far tiny strain gauges like these are so picky sometimes
So turns out I get readings in the single digit volts as desired if I jump on the deck. This makes me think I’m not getting the strain being transmitted to the site of the gauges? Like the footpads could be stopping that area from flexing enough. I tried to design the pads to be bending compliant, but who knows.
Did you take into account the weave direction of the carbon fiber of the footpads?
Maybe you could try a foot pad with a unidirectional weave so it can flex along the length of the deck?
Edit: I lowkey didn’t watch the video, so I will make sure to do that before giving more feedback lo
Haha, you made me paranoid so I rewatched the video too. I aligned the unidirectional fibers in the same direction as the tube. It would have made them more bending compliant to make them perpendicular to the tube, but honestly I don’t think that’s the big issue here. I noticed very little change when I stand with my weight on the foot pads like I normally would while riding, and a larger change (still small) if I put all of my weight in the center, on the tube. The bending stress might be flowing around the perimeter of the footpads through the vertical braces, and I chose a bad location to glue all of the string gauges to.
Yeah that’s what I was talking about. I would have noticed if I watched it first haha
I mean yeah, way more load is applied in this fashion because of the moment arm.
Yeah I think you’re exactly right, I didn’t realize you built it as a box. I bet most of the load is going around the outside there. If you have some extra ones you could try gluing them to the center of the outer sidewalls and seeing if you experience more flex there. I still think it will be minimal though
Another thing is that the amplifier output is like 79mV at zero load. It should be zero, which makes me wonder if I just wired something wrong.
