My 60mph ebike build

[MoonBassMan]

What fender is this or do you know of other fenders like this?

The specific one in that picture looks like its a mudhugger I've seen it them used on a few builds. People seem to like them. I plan to used mudhuggers.

 

[Newagebike]

Yep that's it, thank you!

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[kingjamez]

My QS205 50H 3.5T (~13KV) in a 17" Moto Wheel on 20S in an EEB frame goes faster than I care to without enabling field weakening. I was worried about the maximum speed and kicked myself for quite a while on only going with a 17" wheel instead of a 19", but now that I've got it running, I personally am not interested in going any faster.
I should have actual MPH numbers shortly, I'm still getting it all finished up, but my test runs have been "exciting".

-Jim

I did a speed run on a flat road today. With no field weakening I got up to a GPS measured 50mph on a 20S 20AH battery with a state of charge of 3.8v/cell. I may have been amp limited as my controller turns down the amps at particular battery voltage levels, but even if I wasn't, I'm 100% satisfied with that result.

-Jim

 

[Newagebike]

So I have doing a lot of caluations on the kv/tire of the QS 205 H50. Cool simple math help you figure out possible speeds.

My question is does higher kv tax the motor/battery/controller and if so what can be done to remedy a higher kv to achieve stability in that setup?

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[MadRhino]

Use a higher KV, lace it in a smaller wheel. Kingjamez did just that, fitting 17" instead of 19". Then a higher KV is still pulling more power. 50 Mph is slow for his motor in a 17" wheel. It could be because power is limited, weight is high, battery is low, or all of the above.

 

[kingjamez]

Use a higher KV, lace it in a smaller wheel. Kingjamez did just that, fitting 17" instead of 19". Then a higher KV is still pulling more power. 50 Mph is slow for his motor in a 17" wheel. It could be because power is limited, weight is high, battery is low, or all of the above.

I'm not sure I'm slow for my motor. I have a QS205V3 3.5T, running at ~76volts unloaded, in a 17" wheel with 71.25" circumference tire. Let's assume no voltage drop (which isn't true). 76V*13.3KV= 1011 RPM. 1011RPM*71.25"Circumference = 72,019.5" / 12" = 6001 FT/Minute. = 1.14 Miles per minute. = 68.2 MPH. Times a correction factor of 80% for unloaded vs. loaded motors and your looking at 55mph. So I may be amp limited, but not by much. Add in pack voltage sag, and I'd say I'm pretty much on.

Edit: I removed all amp limitations today. At 76 resting volts I got up to 54 MPH with no field weakening. Plenty fast for me.

Edit2: MadRhino was right. With no changes, on my commute in this morning I got up to a GPS verified 59.8 MPH with no field weakening enabled. I was at a higher SOC today than previously which I believe explains it. This was at 80V resting.

-Jim

 

[kingjamez]

So I have doing a lot of caluations on the kv/tire of the QS 205 H50. Cool simple math help you figure out possible speeds.

My question is does higher kv tax the motor/battery/controller and if so what can be done to remedy a higher kv to achieve stability in that setup?

Sent from my SM-N900T using Tapatalk

KV, Battery Voltage, wheel diameter and Power are all related. I don't have much experience with slowly wound hub motors, but I do have experience in RC outrunner motors of high and low KV winds.

You can roughly think of KV as a way to match your battery voltage to your wheel diameter. Or you can use wheel diameter to match your KV to your battery voltage.

In general motors of higher KV (more RPM/V) are wound with thicker phase wires (less turns) and thus have more power output capacity. It's not quite that simple, but as a general rule it works pretty well. Modern motors use many strands of phase wires, but the principle still mostly holds.

So if you have a motor with 5KV and another with 10KV and you want to go the same speed in the same wheel, you'd need twice the voltage on the 5KV motor as you would on the 10KV motor. Nothing comes for free though, the 1/2 voltage, 10KV system will need twice the amps to maintain the same power level. In reality the 1/2 voltage 10KV system will need a little less than twice the amps since it's a little more efficient than the 5KV system for the same power OUTPUT level.

-Jim

 

[MadRhino]

Yep, 60 Mph is much better for your motor/wheel combo. As close as you can come from the unloaded speed when riding your bike, is as close as you are from achieving the optimal performance/efficiency of your system. You can still improve with lower air drag, lower weight, lower rolling resistance, higher power...

 

[kingjamez]

Here is the fender I used. I just attached it to the rear shock.

https://www.amazon.com/SKS-Germany-X-Tra-Release-Bicycle-Fender/dp/B00NQKOBLK/ref=sr_1_29?ie=UTF8&qid=1494860313&sr=8-29&keywords=bike+rear+fender

I covered it in vinyl to match the rest of the bike.

-Jim