Build idea, postresearch questions | Loaded Dervish Sama | 3500w 85A 140\170 Kv | 12s3p 21700-40T | ESC?

[Rasmatarmac]

So I have this beautiful Loaded Dervish that I never use anymore.

I used to run it with a two Alaskan huskies in front in the city i was younger and we had a breaking distance of like 50 meters sometimes. If you planned your ride it was possible to do it relatively safe, I did go through a few left shoes though. Anyway, now we are all too old, dead or scared to do it anymore and electrical skateboarding seems fun!

I am going to need to shave off every penny if i am gona afford this project right now so im gona use the trucks and even the 75mm wheels and drill holes through them with a drill press.

Its a bit low with the 75mm wheels and it’s really flexible so i think I am going to have to mount the motor behind and up but im not sure.

I have done a fair bit of research for a few days but i still have a couple of questions. Here is what I am thinking:

Battery: Make it my self with 21700-40T cells. 12s2p or 12s3p, I have access to a spot welder ( I realise i wont get alot of range )

Question - Do i understand correctly that if the 35 contstant discharge rating on these cells is really 35A, i still wont be able to fully utalise the motors max current with the 12s2p configuration?

Motor: 3500W 85A 140 KV from Flipsky

Question - Will it be to slow? I weigh almost 100kg nowadays so i want the torque. but maybe because of the 75mm wheels i will still have that and should opt for a higher KV motor? the “same” motor comes in either 170 or 190 KV as well.

ESC: Really not sure

The ones I am looking at all have a continuous current paramenter of 50Amps, this confused me alittle at first since most builds including mine have a motor that when accelerating and going uphill i understand can recieve much more than that? Then i searched and realised that i could set the limit higher than 50Amps.

The question that remains to me though is how long exacly can i send lets say 85 amps to my motor without burning the continuous 50amp rated ESC? After how many seconds of climbing should i start to worry? I also appreciate any tips on cheaper ESC options that would work with my build. I want to have FOC though so i get that i wont be able to go all that cheap.

For the motor mount, remote, anti spark switch and pulley system the hope is that i can scavange and build it my self mostly. any links to solid motor mount builds is appreciated. How well does the clamp on ones that you buy work btw?

Thank you for any input. Bash away.

[sander_m]

So I can’t answer all your questions, but i’ll try to give you some insight.

Battery: For your battery, indeed you can’t use the 85A of the motor specification at high speeds. On lower speeds however, you can (i’ll get back to this).

Motor: Speed is something that can be changed with you motor KV spec and your gear ratio. So you could buy your motor on 140KV and use a 14 to 28 Teeth gear, and change gears (increase motor gear or decrease wheel gear) when you want more speed (and lower torque). So I wouldn’t spend too much attention on the motor KV spec.

ESC: The ESC is a bit more difficult. You could buy a VESC which you can configure and fine-tune, or buy a off the shelve ESC from hobbyking or any other supplier. However for both the rule is: more amps means higher cost.

Now like i mentioned, your ESC will control how many amps go to the motor and this depends on your batteries and the speed at which you are running. Long story short at lower speeds you will use the complete 85A of motor current, at high speeds the 70A from your battery.

For more info on how the current is modulated, see this comment: Understanding current limits on VESC motor settings - #16 by PXSS

When climbing or putting a heavy load on the motor the only limiting factor is temperature. When the temperature gets too high, everything needs to cool. There is no solid number to “how long you can climb”. This depends on incline, outside temperature and other factors. The VESC has a temperature limit built in (for ESC itself and motor temperature if available).

Motor Mount: I had designed one from scratch, a clamp design. But this is… bad practice. You are better of with off the shelve trucks and off the shelve motor mounts. But to be honest it may be more fun to try and build something yourself first and fail (like i did).

[Rasmatarmac]

Thanks for the reply. I have realised i need to read more on electricity overall and especialy ESC, VESC and revise my plans abit What do you think about The makerx mini foc though?

And maybe you could mount it on coppercooling stuff from salvaged laptops for some more hill climbing margins?

Thanks again. Ill be back in a few days with some revised plans

[sander_m]

That looks like a better candidate if you want the 80A on the full throttle range. The VESC 4.12 has a theoretical current limit of 50A, but can’t reach that because of lack of cooling. You can’t cool the mosfets on the package, but you can on the PCB (which the VESC 4.12 has no room for).

The MINI-FOC has the heat dissipation shell which helps a lot with removing heat from the mosfets. Say you add a simple radial fan on the cooling shell and it can take the 80A for a relative long time.

[Louis]

@Rasmatarmac

makerx mini foc

The makerX mini is a decent choice, cheap and reliable, I’ve heard good things. For an extra $10 you get the ‘Plus’ version with a higher current rating (basically will get less hot doing the same thing), probably worth it. I highly recommend VESC compatible ESCs over others!

For a flat-land cruiser with one motor, you will have enough Amps to wear out your dogs with 12s2p. 45V * 50A = 2.2kW = A damn powerful personal Vehicle.

Going up to 12s3p will give you more range, so 10 miles+ should be possible with that many batteries. If you can fit the extra batteries (and afford them) it’s worth it, you cannot add batteries to a pack to add later, and range is king. So make the investment, everything else can be slowly upgraded as needed.

You don’t need to worry too much about the ‘electricity’, the ESC (Electronic speed controller) will get warmer the harder you push it. If you’re walking dogs (not racing up grassy hills), I doubt you need anything other than attaching the ESC to the deck. Just don’t totally wrap it in foam, and it will be unlikely to ever get too hot. If it does, attach it to more metal (with a bigger surface area).

I suggest you work out your gears next, as these are probably your biggest challenge (and you can select 140/190kV to suit). You could try the calculator to give you confidence in your selection calc.esk8.news

Then your Enclosure (so you can size up the best battery design to fit the deck), remember you will need to buy a BMS, buy lowest current you can find, this is only for charging and health monitoring, I can recommend Daly/DeliGreen ones, but there are others.

The motor can be almost horizontal, as you really haven’t got much space to avoid it hitting the board. Having it upwards will likely cause clearance issues when you turn, or end up rally long.

I would suggest you grind some flats on your truck to stop your motor mount from being able to spin.