Hello everyone, I’m new at this forum. I heard about electric longboarding and, as I need to figure out if I want to continue learning electrical engineering (and also getting an electric longboard of my own), I decided I wanted to build my own. I’m a student going to university (if anyone else goes to UMass Amherst, hi) so I have pretty specific needs, namely that I will prioritize weight and cost over top speed and range. I would be happy with a top speed of 15 mph–anything higher and I would be a danger to myself and my classmates. Furthermore, there is one hill on campus notorious for how steep it is, so I also want to prioritize hill climbing abilities.

My ultimate goal is to convert my foldable boardup longboard into an electric version.

----- Parts -----

I did a lot of research and wanted to get feedback on whether the parts I want to use.

Although I don’t have much experience, I want to create my own battery. I wish to use these cells in a 6s3p combination with this BMS. https://eu.nkon.nl/rechargeable/li-ion/18650-size/samsung-inr-18650-30q-3000mah.html

I also want to use two of these motors. I found it really cheap on taobao. Here’s the link but it’s in Chinese, so I translated and copy and pasted the specs here. https://item.taobao.com/item.htm?spm=a1z0d.7625083.1998302264.5.5c5f4e69kk4ENj&id=558189099368 6354 Dimensions: Output shaft diameter: 10mm Shaft: Flat shaft output shaft length: 30mm weight: 554g KV: 180KV Power: 1500W Voltage: 24V No-load speed: 4350 rpm No-load current: 1.1A Number of Poles: 14 Torque: 4N / m

I’m assuming that this truck would be able to fit two of these motors in a dual motor setup. https://www.amazon.com/Caliber-Trucks-Cal-44°-Longboard/dp/B00NY426YW

I plan to use this charger https:///collections/battery-chargers/products/6s-epower-pack-4a-charger#description

My VESC will be two of these. I know lots of people use dual ESCs, but I’m afraid I’ll burn one out by accident, so this kinda gives me two chances at screwing up rather than one.

Although there are a few more parts I need to decide on, I figure these are the biggest ones and the ones that I should be most concerned about.

----- Questions -----

My first biggest question (apologizes if this was already answered, I just had to make sure), is selecting the right current for the BMS. I read somewhere that the BMS should have be rated at half the maximum discharge rate of the battery so the battery doesn’t wear down fast, so considering three Samsung 30q batteries with a discharge rate of 15A each, that adds up to 45A total discharge rate, meaning that my BMS should be rated at around 20A. Is that correct?

Second, different 6354 BLDC motors have ratings between 1500W and 2500W. Does that number indicate maximum power output?

Third, what does the shaft length of a motor mean? Some manufacturers offer the choice between 8mm and 10mm but I’m not sure what the difference is and if I should choose one over the other.

Fourth, I wanted to know if the built in heat sink in the VESC would be enough to keep the VESC cool assuming I 3D print an enclosure with no windows (I still need to do some research on the materials for that).

Fifth, is dual 6354 motors enough for hill climbing? I would like someone to check me on my physics Assuming a total load of 90kg with my board, my backpack, and myself, 100mm wheels and 25% hill grade, the torque to keep me at a constant velocity would be F * r = sin(arctan(.25))*m*g*(d/2), which is 10.7 N*m. Torque is the rotational analogue of acceleration, so the approximate 5 N*m of torque fudge factor would theoretically be able to push me up the hill from a dead stop. To go up a hill at 8 m/s, the power delivered by my motors need to be F * v = sin(arctan(.25))*m*g*|v|, giving me 1711W.
Assuming that this website below is right in calculating the maximum torque, I have enough torque to push me up the hill with some fudge factor left over. Furthermore, 1711W dissipated across two 1500 watt motors (totaling 3000w) should be enough to keep me going up the hill at a decent velocity. This means that my setup should be enough to push me up that hill. Is my physics and line of thinking right?
https://calc.3dservisas.eu/?Tc8xD8IgEAXg_8JsmsNCq65onDQkTexuO2AilqSj8b_LexDj9t1x94C3urugDur5WF5qk4trLtqmy17dkF3k0aUcJCIsjqj6xpYCQ7ocMFNnpqFupr_F5NE1FJa2ELNaS6LZkb-gKbiaNIVT1k7IG9YNHF1NigjXPI9-gQ0JWSmjbGN4Hle-uofPF86QI27D52fcthf1-QI=

Sixth, I wanted to know the influence current max current has on hill climbing ability. If I fudge around the numbers for the current running through each of the cells, the torque remains constant. That doesn’t make sense. Shouldn’t max torque be dependent on max current? At least, that’s what some random threads I looked at said. Did I get something wrong? If torque isn’t dependent on max current, that means I can reduce the weight and cost of my build by adopting a 6s2p battery configuration. Is there something I’m missing?

This post looks like it’s a lot longer than I originally intended, so sorry for the wall of text. In any case, I would appreciate any help I can get. Thank you and happy holidays!