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High Voltage(?) build based on MBS Comp 95 [EU]

DIY Builds
#1

Doing my first build and was aiming for a eMTB with a lot of torque to play around with on mountainbike trails and break som bones in a skate park.
Trying to source as much as I can within Europe.
Would appreciate your help and suggestions since I have zero experience outside other peoples posts and youtube clips…

Base: A complete MBS Comp 95… Matrix 2 trucks, bindings etc…

ESC: Spintend UBOX

Battery: LiPo 16S. 5Ah or more…

Motor mounts: IDEAS v7.8 he does not have a webpage but he does have a facebook.
https://www.facebook.com/ideatb

Motors: Low kV ???

Questions:

What motors would you suggest? Have you maybe used a motor together with a “high voltage” VESC?

Does the F5 bindings work well with smaller feet? I´m a size 39-40. If not, any suggestions?

What charging solution do you use for charging multiple LiPo at the same time?

Any comments / thoughts based on experience is greatly appreciated.

Have an awesome day :slight_smile:
/Peter

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#2

I would say yes as you can adjust both sides of the binding frame and not only one like on other bindings.

I personally do not like to charge lipos parallel.
If you run 1p only anyway you can just get a 16s charger and a 16s bms and charge them in series. Don’t forget to charge the pack up to 3.7-3.9V for storage. Everything above or below will reduce your lipo cycle life.

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#3

I dont see any reason you need more then 12s for your application

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#4

best lipos
or maybe tattu if you want

16s for slower riding on trails isnt necessary

#5

The reason >12S appeals to me is that I can use very low kV motors for a lot of torque.
While the higher voltage allows me to keep some of the top speed for shorter durations (risk over heat or over spinn the motors).

For me it´s all theoretical at the moment since no one I know rides eMTB so I can´t try it. Maybe I should start with 2x6s battery and try. If I´m not pleased with the topspeed I can easily add another one.

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#6

Been using Turnigy for years, the Nanotech version. Love them, been abusing them without an issues what so ever. :ok_hand: :+1: :+1: :+1:

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#7

Like @Andy87 said, a BMS with a normal charger works best. If you want more range than 1p lipos can offer, you can run packs in parallel. You have to make sure to be careful wiring both the main harness and the balancing harness so that the parallel packs will balance themselves on a cell to cell level, not just as a pack.

#8

You can still do that with low kv motor. The higher voltage would only give you higher topspeed and I can’t see why or how you could ride that fast on mountainbike trails and skate parks.

2 Likes
#9

The main limit our motors experience is thermal throttling. And how much a motor heats up is proportional to the torque applied, not the current. So your low kv motor should perform about the same as a high kv motor when it comes to torque; the high kv motor will just require more current. (In fact, the low kv motor will heat up a bit more due to increased core losses) (Another fact: both low kv and high kv motors will eat up the same amount of power for a given torque load and speed; low current high voltage or high current low voltage)

Anyway, If you have an ESC that can’t output a lot of current – sure, go low kv! But if you have an ESC that can easily supply more current than the motor can handle – go high kv if you need that top speed.

TL;DR: don’t configure your build over a fixed motor kv value if you don’t have to. For more torque, get a higher gearing reduction, or a larger motor. Then pick the lowest available kv motor that still gets you your desired top speed. If the available motors are too slow at that gearing / your 12s ESC is at its limits, then go high voltage.

#10

Im curious about that. Do you have any sources or calculations to explain this? I always thought the higher current leads to more losses.

A motor with half the kv would only need half the current for the same torque. Why does it heat up twice as much from the same current compared to the double kv motor? Internal resistance?

#11

Heres a good article on the subject:

http://vedder.se/2014/10/chosing-the-right-bldc-motor-and-battery-setup-for-an-electric-skateboard/

TLDR;
KV of the motor primairly concerns the Battery and ESC choice rather then choosing a motor to fit a specified performance goal.

Lower KV motors will produce more torque per Amp while high KV motors will produce higher RPM per Volt. But aslong as the motors have the same amount of copper and are in mechanical constrains identical, they have will be able to produce the same amount of power just at different RPM/Voltage/Amps.

“Suppose an 8 turn(example 50KV) motor has one ohm winding resistance. The winding resistance is proportional to the wire area times wire length. Making the same motor with 4 turns(example 100KV) would allow twice as thick wire. Since that wire also is half as long, the resistance is four times lower: 0.25ohm. Further, since current times turns is proportional to torque, we need twice as high current with 4 turns to produce the same torque as with 8 turns. The copper losses are the voltage across the windings times the current: UxI. The voltage across them is RxI, so the losses are RxIxI. This square relation means that doubling the current will produce four times as much losses, however, since we got four times lower resistance the losses are the same for the 4t motor with double the current as for the 8t motor with half the current. Also note that the 4t motor will spin twice as fast as the 8t motor at the same voltage, so it will have double the kv. Putting this together, the 4t motor is equivalent to the 8t motor, but at half the voltage and double the current.”

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#12

Just hit a major road bump… The vendor I ordered the Comp95 just go back to me and said that their stock was off so they have none available… :unamused:
Anyone have a lead on a Comp95 without breaks available within EU…?
MBS Europe and America(!?) is out. Coronation DE only has the one with brakes in… Shit.