Recommended Gearing for 350kv

theice45

10 µW
Joined
Apr 24, 2016
Messages
6
Hey guys,
I'm new around here, so please let me know if I'm violating any sort of rules.

I have a Turnigy Aerodrive SK3 - 4250-350kv motor around, and was thinking about building a board (have access to a 3d printer, so I could make a motor mount and such easily)

I was wondering if you guys could help me figure out a nice gearing for it (on 76mm wheels)
I'm aiming for a minimum of 15mph in terms of speed, but with the 350kv, I'm worried about torque.

I was looking at a 1:2.864 ratio due to nice sizing on the pulleys for the wheels.

Any thoughts would be greatly appreciated.
 
Your motor is a bit smaller than normal. It may be a bit of a tall order to ask for 15mph from that motor. Generally (for a single motor), you want at least a 50mm diameter motor.

Figuring out gearing is just a matter of doing the math.

Multiply Kv times voltage to get motor rpm.
Divide by reduction to get wheel rpm.
Multiply by circumference of wheel (in inches) to get inches/min.
Convert to miles/hour. (multiply by 60/12/5280) (60 min/hour, 12 in/ft, 5280 ft/mile)
This is your unloaded speed. A rough estimate of top speed would be to multiply by 0.8.


For you, assuming a 5S 18.5V battery, a 2.864 reduction on 76mm wheels would net you 20mph unloaded so about 16mph loaded if your motor doesn't burn up getting there. 16mph probably requires about 800W (just a guess, my longboard doesn't go that fast), which is gonna be pushing your little motor to its thermal limit.
 
Hi
Don't want to burst your bubble but only try that if you really have no use for the motor at all.
Might work on a flat, with a kick push start, but even then I think it will probably run very hot. Glancing sideways at a hill will pop it almost immediately I would wager.
 
thepronghorn said:
Your motor is a bit smaller than normal. It may be a bit of a tall order to ask for 15mph from that motor. Generally (for a single motor), you want at least a 50mm diameter motor.

Figuring out gearing is just a matter of doing the math.

Multiply Kv times voltage to get motor rpm.
Divide by reduction to get wheel rpm.
Multiply by circumference of wheel (in inches) to get inches/min.
Convert to miles/hour. (multiply by 60/12/5280) (60 min/hour, 12 in/ft, 5280 ft/mile)
This is your unloaded speed. A rough estimate of top speed would be to multiply by 0.8.


For you, assuming a 5S 18.5V battery, a 2.864 reduction on 76mm wheels would net you 20mph unloaded so about 16mph loaded if your motor doesn't burn up getting there. 16mph probably requires about 800W (just a guess, my longboard doesn't go that fast), which is gonna be pushing your little motor to its thermal limit.

WeeChumlee said:
Hi
Don't want to burst your bubble but only try that if you really have no use for the motor at all.
Might work on a flat, with a kick push start, but even then I think it will probably run very hot. Glancing sideways at a hill will pop it almost immediately I would wager.

Don't worry, I appreciate the feedback.
So for a more sane setup, based around what I've been reading, I'm now thinking of a 6S setup on either an Alien 6355 Outrunner 230KV, or 5065 270KV at the same gearing as mentioned above (1:2.864)

I've calculated that those should get me to around 13-15mph respectively, am I correct that this is a more sane setup?
 
If you are going single motor then definitely go for a 63mm.
The 6355, 230KV would, at 6S, easily get you to where you want to be.
What gears exactly you wanting to use? (Tooth numbers)
 
WeeChumlee said:
If you are going single motor then definitely go for a 63mm.
The 6355, 230KV would, at 6S, easily get you to where you want to be.
What gears exactly you wanting to use? (Tooth numbers)

14:40,

Would it be detrimental to buy the 270kv? I don't mind going faster, but I'm still trying to learn how much torque corresponds to kV.
 
The 50mm motor is great for a dual but for a single motor build they just do not provide enough torque.
Definitely go 63mm for a single. Not just KV but sheer size is the main contributor here.
 
WeeChumlee said:
The 50mm motor is great for a dual but for a single motor build they just do not provide enough torque.
Definitely go 63mm for a single. Not just KV but sheer size is the main contributor here.

Alright, great!
Any chance you have some recommendations for motors of that size?
The alien power system one I referenced seems to have great reviews, yet the shipping cost is killing me..
Worse case, I'll get it from them, just wondering.
 
I am in the UK so I got all my motors from Alien but in the US you have http://diyelectricskateboard.com and Hobby king.
Hobby king SK3 motors have a good rep but are hard to get hold of.
 
WeeChumlee said:
I am in the UK so I got all my motors from Alien but in the US you have http://diyelectricskateboard.com and Hobby king.
Hobby king SK3 motors have a good rep but are hard to get hold of.

http://diyelectricskateboard.com/product/electric-skateboard-motor-6355-230kv-2650w/

so this motor should work nicely?
I'm concerned about it being sensored (in sensor-less setup, they mention it needing a kick on startup, is this true?)
 
theice45 said:
WeeChumlee said:
I am in the UK so I got all my motors from Alien but in the US you have http://diyelectricskateboard.com and Hobby king.
Hobby king SK3 motors have a good rep but are hard to get hold of.

http://diyelectricskateboard.com/product/electric-skateboard-motor-6355-230kv-2650w/

so this motor should work nicely?
I'm concerned about it being sensored (in sensor-less setup, they mention it needing a kick on startup, is this true?)

Unless you want to ride your E-board like a hoverboard, a little kick before starting is no biggie. The motor will be fine even when used "unsensored."
 
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