Alright alright I’m ready to throw in:
Stella is my lightweight jumper and she came in at 30lbs exactly.
Flexy bro deck is 2.1kg
I’m using 6369 motors from when it was my daily and had a bigger battery. Definitely could go smaller.
Matrix 2s all metal are a bit heavier too.
Belt drive but the motor mounts are the evolve ones iirc and definitely on the thicker side.
But my 10s3p P42a pack should be lighter.
Light boards are so fun… While the battery lasts
This is impressive!
Bro medium flex is 2.1kg, and stiff is 2.3kg. Which one are you riding?
At what point is it worthwhile just considering a limited lifetime on your pullys?
Accepting faster wear in favor of weight savings.
2 years of life is pretty good life span for saving 60+ grams.
I’m not sure I’d do it but it’s interesting to think how you can go the absolute lightest.
Mine is the medium flex. Thanks for the info.
I’m not sure where to put these but just for reference in the future I guess.
HD SRB truck (normal) and HD SRB truck with the reverse/front bracket
We can classify weight in two Static categories, sprung and unsprung weight. Sprung weight is load carried at the pivot center of the hanger. Unsprung weight is hanger weight with any components (wheels, motors, and on) that are attatched to and move with hanger articulation.
For steering recovery and performance. Removing Unsprung Weight will yeild the most in performance gains. Balancing front to rear Sprung Weight would be second. Thirdly reducing is lateral G pushback ( non static weight. Last would be removing weight from the deck, battery, chassis.
Lateral G is a non static force measured between lateral forces above the pivot center with the lateral G forces below the pivot center.
Reducing motor, wheel, gearing and hardware weights from the hanger would be where to look first.
The thread below is a few years old, but it would be good to bring it back to life as it’s probably the best place for those pics.
I made some revisions to the ultralight build.
We’re down to 11.2kg (24.8 lbs)
Compromises include range (realistic 15 miles on this pack) and tires are light duty MBS T1 tires.
This imaginary board is also quite powerful, (40mph top speed, 650 Newtons @ 100a/motor)
| Bro - ultralight | weight | count | total weight | |
|---|---|---|---|---|
| Bro med. Flex | 2100 | 1 | 2100 | |
| 18s2p battery (583wh) | 2790 | 1 | 2790 | |
| radium motor mount | 160 | 2 | 320 | |
| 15t pulley - aluminum | 18 | 2 | 36 | |
| radium belt | 33 | 2 | 66 | |
| MBS 72t pulley | 99 | 2 | 198 | |
| newbee rtkp | 751 | 2 | 1502 | |
| Flipsky 6354 140kv motors | 460 | 2 | 920 | |
| MBS T1 tires | 220 | 4 | 880 | |
| inner tubes | 80 | 4 | 320 | |
| MBS rockstar ii | 165 | 4 | 660 | |
| Junction Box (case) | 400 | 1 | 400 | |
| mbs f5 bindings + heel straps | 580 | 1 | 580 | |
| Bearings | 20 | 8 | 160 | |
| ESC | 330 | 1 | 330 | |
| 11.3 | Kg | |||
| 24.8 | Lbs |
If you stuck in a 16s3p, with more acceptable range of ~20 miles max, you’d be just shy of 30lbs.
Battery is really the limiting factor here. It’s basically impossible to make a lightweight board with what I’d call good range (>25 miles), on pneumatic tires.
And this is how I ended up with a 108 battery cell emtb and a 30 battery cell emtb 
I have watched the evolution of bicycle technology starting in 1991. So many changes have occurred which may be applicable to ESK8.
If we were to look at 3-link truck, a hollow steel or aluminum hanger combined with steel axles might work. Higher quality cromoly steels could allow for less material to be used. Carbon fiber motor mount plates with carbon fiber tubes going from plate to plate.
Steel/titanium/aluminum pulleys that are machined to remove un-necessary material. Motors could have hollow shafts to save weight too. A larger hollow shaft could also allow for the use of a lighter pulley. I would be interesting to chat with a manufacturer like Flipsky or Reacher to see how much weight could be removed.
As for wheels, maybe we could try to use spokes. It sure saves a lot of weight on bicycles. I still like the thermoplastic idea. Maybe carbon fiber reinforced nylon. Tubeless wheels could potentially save weight too.
Decks/enclosures could be made ultra-light with optimized carbon fiber construction. It is not uncommon to find bicycle frames that are 700g. Carbon fiber forks are pretty damn light too.
Ultra-light acoustic bikes dont have massive heavy batteries. They also don’t need to be built to handle more than ~500W (the max a person can put through the drivetrain). Not saying we cant learn anything from them, just saying that the design constraints are very different, and the marginal benefits of cutting weight throughout the esk8 might not make much of an impact compared to the battery pack. It would be a lot of extra cost to still have a pretty heavy board by the end.
I emphasized this in one of my previous posts. It does not have to be a lot of extra cost. Focus on the areas what will give you the biggest bang for your buck. Thermoplastic fiber reinforced wheels is a good example. Regardless of whether you make a chunky wheel or not, the mold is going to cost the same. A more optimized design will retain all the mechanical properties you need and eliminate the material that is not contributing to anything.
After the lunar new year holiday is over, I will try to chat with both Flipsky and Reacher to see if there is any way weight reduction can be achieved and how much it would cost.
My point is not “every weight savings has to cost a lot.” My point is that I dont think many people care that much about saving 100g off a 25,000g board, where most of that weight comes from the battery (which isnt going to get any lighter per Wh anytime soon) and the drivetrain (which can get lighter, but strength and cost become much larger factors).
Plastic wheels exist, and will continue to be purchased. Them being both cheaper and lighter is a big plus for lots of people. But that’s the low-hanging fruit of the board. There are not many other parts of the board which can be cheaply and easily weight-reduced without serious downsides.
i think u still need to add misc. for all the screws / nuts / washer u gonna have…just to make it as accurate as possible
a pic of board on scale after u build the final version then compare to ur table would tell how “off” the estimated numbers are
If there is any opportunity for weight saving in motors, I’d be interested in hearing more about it.
My hobbyist level experience thinks probably not, since magnets, iron, and copper are all heavy materials that are critical to a high power motor.
Like @BenjaminF we do have some good lightweight wheel options made out of nylon from MBS, Tomiboi, and trampa.
The place with the biggest opportunity I see to save weight is the deck. The lightest deck available is 2.1kg. I think with some creative bamboo/CF work you could cut that in half.
I’m also making that up from absolutely no experience, so it could be totally wrong 
The other place we’ll see improvements over time is battery energy density, but we don’t really have any control over that. For now we’re stuck building small packs if we want light weight.
Not until a switch to pouch cells (not necessarily LiPo) is done and the right shape/size of cells are found to maximize pack fitting to the enclosure. I don’t have any recommendations now but would love to see it happen.
Yes, pouch cells are more fragile. But IMO the metal can protection of round cells really isn’t needed with a decent enclosure. Anything that smashes the enclosure would probably zap a round cell pack too. This is debatable, certainly, but I feel that pouch cells could be used, especially if “standard” Li-Ion chemistry (NMC or NCA).
what if…u make ur own mtb deck with 600 layers of carbon fiber 
I just found a reasonable Li-NCM pouch cell to compare and it appears the wh/kg is worse than a p45b cell.
1000wh pouch cell = 6.35kg
1000wh p45b = 4.32kg
Maybe I’m looking at the wrong kind of pouch cell. Can you point me in the right direction?
Sorry, no. As I mentioned I don’t have any recommendations, just the memory of the paper that ran the math.
You definitely need to use a very good (high energy density) pouch cell though. The “everyday” China cells aren’t going to work out…as you calculated. 
You also have to factor in how much more Ah can fit into an enclosure if using pouch cells of the right size. Round cells have dead air spaces around them and there are empty spaces in an enclosure that need to be factored in.
We can compare W/kg or W/L (or other volume) and would need to have numbers for both. I was referring only to Wh/L (volumetric efficiency) but I realize that weight (gravimetric efficiency) is an issue too.
I should add that I am totally open to being wrong now as I read that article in 2021 IIRC and the energy density of round cells has gone up considerably since then. In hindsight I should have considered that more before my post.
Still thinking that inter-cell and enclosure air spaces for round cells add up to a lot more than we think though, making a great pouch cell a good idea. No time to dive deep into this, would love to. 
