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First build, Octagon, DIY NKP 3-Link

Thanks to everyone for all the info posted on this forum. It’s been 32 years since I rode a skateboard but I decided a few months ago to try and build a long board for my son who is 14. I built a CNC machine in my garage a few yeas ago and bought a 3D printer as this build progressed. A big part of the fun for me is making the various components, hopefully without failing :slightly_smiling_face: What a fun rabbit hole to go down!

Particular thanks to @MoeStooge, @Winfly, and several of the battery builders for sharing your ideas with this forum!

I wanted to try and make a NKP 3-Link since they seem extremely stable at high speeds. I don’t anticipate my son racing with this board, but stability is a great thing and I experienced enough speed wobbles in my teens to never want that to happen with this build. I don’t own a lathe, which seems like an essential tool to making the NKP 3-Link. So that was a big challenge. I used telescoping steel tubes over a 8mm steel threaded rod. The main center heim joint is a 1/2" ID and the steel tube I’m using has the following dimensions: Chrome/Moly Tube - Round: 1/2" O.D. x .065" wall, Chrome/Moly Tube - Round: 5/8" O.D. x .049" wall. So if you do the math you get 0.027" spacing between the tubes. With the tolerances for manufacturing, it’s a pretty nice fit. I named it Octagon because the coupling surrounding the steel tubing is octagonal in shape. This coupling helps keep the steel tube on center and provides the pressure when secured to push the washers up against the center heim joint bushing. I went with an octagonal shape coupling so the smaller heim joint rods will have a flush surface to mate with and ensure full movement of the heim joint itself while allowing some adjustment for the vertical angles of the rods. In actuality, this does limit the positions of the rods, essentially one vertical and one horizontal, but between those two positions and different durometer bushings I think we have enough adjustability for the ride of the board. I made bushings with 80a, 90a, and 95a durometer ratings. Looks like we’re going with 95a in the back and 90a in the front to start. I was pretty surprised how much of a difference the different stiffness of the bushings made. If I make a board for my younger daughter, I may use some combo of the 90a and 80a…

I cut out a temporary plywood deck just to see if my trucks worked. Overall, they seem great at this point, but the testing was limited to push speeds and I didn’t use any Loctite or lock washers at that point. The temp board also let me test the bushings. The center main 1/2 heim joint did twist a little on the temp deck, so I’ve got some Nord-Lock wedge lock washers and permanent Loctite for those threads which will hopefully prevent any twisting on the final board. With the heim joint rods in a more horizontal position and 95a durometer bushings, I could barely get the board to turn and I’m 220 pounds… I don’t think we’ll ever use the heim joint rods in the horizontal position, just too hard to turn the board. But we’ll see.

This was also my first time milling aluminum on my CNC. I’m using a Bosch 1617 EVS router, so I’ve learned the best feeds and speeds for aluminum. Mostly 0.02 depth of cut and 50 Inches per minute, so milling the various parts takes several days. The deck itself is milled from 1" thick HDPE. It’s pretty smooth so I’m going to have to figure out some type of grip tape usage in the end or maybe some glass fris… The Base Plate, Base Plate extension and Center Piece support are all milled 6061 aluminum. Takes a while and doesn’t have the mirror finish (I’m dry cutting) but it looks pretty good.

I milled the 36T kegal for the 110mm wheels from Delrin (acetal homopolymer) which was a fun challenge. Needed to buy some 0.1" diameter endmills with the ability for deep cuts to make the 3mm radius cuts for the pulley. Found them at Kodiak Cutting Tools and made in the USA which was nice since everything else for ESK8 seems to be made in China…

I’m using Fusion 360 with the hobbyist license. Have really enjoyed the McMaster-Carr components to add and then order. Makes getting various supplies really easy. I’m in Charlotte NC and McMaster is in Atlanta so it’s always next day shipping for me. Still need to buy some hardware as you’ll see in the photos, some of the button head bolts are too long…

I used the compression design from @Winfly for the battery holders to avoid buying a spot welder. I milled the holders from Delrin on the CNC instead of 3D Printing them since I had plenty of DElrin leftover from the pulleys. I made one change, added a flat set screw above both terminals and tapped the holes. The set screws help put pressure on the braided wire directly at the terminals. I wasn’t sure if the nylon threaded rods would put enough downward pressure on the braided wire with the 3D Printed node in the @Winfly design. Haven’t seen much discussion so perhaps his change was unnecessary. Not sure if I need loctite on those flat threaded screws yet. We’ll see. They seem pretty secure.

I went with 10mm ceramic bearings as I have a 8mm ID / 10mm OD compression sleeve around the 8mm threaded rod. Wow are they smooth, so much better than the bearings I used 32 years ago.

The motor plate is 10mm thick aluminum (all the aluminum is 6061) to match the typical 10mm spacers. I am making one change and that’s to add a belt tensioner to the motor plate. Bought some 8mm ceramic bearings for the tensioner. Haven’t milled the new plates yet.

I’m using reclaimed Panasonic ncr18650bd batteries. We’ll see how that goes - I’ll start them at 5 Amps with a 12S6P configuration. If my son needs more power / speed I’ll probably jump on a future Molicel group buy.
Other items:
Flipsky 6374 190 KV Motors with their controller and Dual FSESC6.6 VESC
13S 48V 20A Li-ion Cell 18650 Battery Protection BMS PCB Board with Balance Function from Amazon…
Not sure what charger I will use yet…
I plan to 3D Print some type of enclosure for the battery / BMS / VESC… probably modify one of the shared Thingiverse designs folks on this forum have posted…

Any suggestions or comments are appreciated.

Thanks!

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Wow what an accomplishment! Beautiful build and great parenting :+1:

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Wow really cool man, must be fun to ride

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I have been admiring the photos you have been posting and it is wonderful to read about your creation. Very impressive first build!

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That’s the sexyest deck i’ve ever seen ! Amazing

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That’s a heck of a first build.

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You had the machinery to make your own pulley, and you went with such a low tooth count? :laughing:

The board looks incredible. Hands down, contender for build of the year. So freaking cool!

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When you don’t know what you’re doing :grinning_face_with_smiling_eyes:… figuring out the CAD for that was a total PITA! But certainly can end up on the “now I know” to do list. So just curious, what difference do the teeth count make?

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Changes the gearing. For big wheels like that folks here usually use ~44T pulleys. With a larger pulley, you’d get more torque (but less speed), but assuming your son isn’t a speed demon, that probably isn’t an issue. And a ratio with more torque will be easier for the motors to drive, so more efficient, leading to increased range.

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Haha once you get the concept of cad down for HTD belt pullies it’s a breeze

Involute tooth gears on the other hand… Yeah those are fun.

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Getting closer to finishing… The 3D printing for the enclosure has been a train wreck… Can’t seem to figure out bed adhesion. Bought a glass bed, tried the Elmer’s glue stick, blue painters tape, etc. can’t get the PETG to adhere to the bed… only have one piece left of the enclosure to make… slathered a bunch of CA glue and activator to connect the parts for the enclosure and seemed to work. Need to paint it with epoxy and then paint it black eventually.

Still need to buy the correct hardware and I think I need an anti-spark power switch as I don’t think the Flipsky VESC has that built in… if anyone has recommendations I’m all ears. But otherwise I think I have everything I need to get it running. Haven’t used the permanent Loctitie yet on the center heim connection. Want to see if the blue Loctite provides enough stability and get this thing running before doing anything permanent :slight_smile:

But the motor mount, belts, motors seem to fit well so that’s nice…! The board has some decent flexure to it - thought with the aluminum center piece it might be too stiff, but that’s not the case. Goal is to get it riding by the end of the month! Fingers crossed.

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That’s pretty good… for a first build I guess

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Beginners :yawning_face:

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AWESOME WORK DOOOOOOOD! :smiling_face_with_three_hearts:

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would be cool to hear a sound/vibration comparison with and without that urethane riser.

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Absolutely phenomenal build! :heart_eyes: Definitely a build of the year contender, imo. All the parts fit so seamlessly together and this thing really looks like a serious machine. Seems almost a shame to cover up the bottom details with an enclosure, but I guess the electronics have to go somewhere. Looking forward to seeing this thing complete and in action.

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This thing is awesome :star_struck: why didn’t you go with a cool aluminum enclosure to add to your wonderful metal fab :thinking:
But I still love everything about this build :heart_eyes:

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Thanks guys! Most of my answers are “because I’m new at this” :grinning_face_with_smiling_eyes:

Frankly, I still have no idea how this will do at a decent speed. I did make a basic plywood deck and it was very smooth, but I think that is mostly due to the ceramic bearings… those didn’t exist back when I was riding a board…

It’s so cool to have this forum! I didn’t know what a VESC was, I didn’t know what a BMS was, never even considered a NKP 3-Link or heard of it, and then there are pucks, Dave(forgot the acronym but it provides ride info), battery reviews - who would ever know WTF a Molicel was ? On and on…

Crazy to think a skateboard can be stable at 35 mph and have a range of 30 miles… makes me want to get back in the garage and keep improving…

If I can get away from this 3D printer I will! :grinning_face_with_smiling_eyes:

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You may have tried this already, but I struggled with bed adhesion on a glass plate too. Get an accurate thermometer and measure the top of the plate! My actual temp was off by ~6 C from the set/read temp.

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Too hot or too cold? My PETG roll says 210-240 but everything online says to do PETG at 250? My next “guess” is to lower the nozzle temp…

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