My bike is slow...

R

rg12

100 kW
Joined
Jul 26, 2014
Messages
1,591
Hey Dudes,

I have a big generic hub motor on my downhill bike.
I measured 4200w on full charge.
21s 10Ah LiPo (25C)
Controller (it's my second one with the same results) is a generic AliExpress Chinese one that works great, delivers 47A (measured).

Top speed: 68kmh (oh and 26" rim)
Measured on straight road, no wind, fresh charge.
Measured with a speedometer and a GPS, same results exactly.
Bike weighs 34kg, I weigh 70kg

I've seen much heavier people ride weaker setups go at this speed.
 
42mph is crazy fast, I barely get that with 20s.

it could depend on the KV of your motor, the diameter of your tire and also some controllers can be programmed to run more than 100% throttle.
 
skeetab5780 said:
42mph is crazy fast, I barely get that with 20s.

it could depend on the KV of your motor, the diameter of your tire and also some controllers can be programmed to run more than 100% throttle.
Click to expand...

I get people here running some unknown setups going 80kmh to even 100kmh...I really don't think it's crazy fast for a light weight high powered setup.

What is KV? is that the winding thing (thin for speed vs thick for torque)?
2.5" Maxxis, that wouldn't change much, I'm talking about people much faster than me.
I've got 120% on my controller, it's the third click in my 3 mode switch but that makes the wheel go to that 120% speed (crazy fast) only when there is no load and the wheel is in the air.
 
rg12 said:
skeetab5780 said:
42mph is crazy fast, I barely get that with 20s.

it could depend on the KV of your motor, the diameter of your tire and also some controllers can be programmed to run more than 100% throttle.
Click to expand...

I get people here running some unknown setups going 80kmh to even 100kmh...I really don't think it's crazy fast for a light weight high powered setup.

What is KV? is that the winding thing (thin for speed vs thick for torque)?
2.5" Maxxis, that wouldn't change much, I'm talking about people much faster than me.
I've got 120% on my controller, it's the third click in my 3 mode switch but that makes the wheel go to that 120% speed (crazy fast) only when there is no load and the wheel is in the air.
Click to expand...

The kv (konstants velocity??, or something like that) of the motor is how many rpm it will do per volt applied and this is linked to the copper windings inside the motor. Less turns with thicker wire equals faster motor, thinner wire with more turns equal slower motor. I beieve that all things being equal they will make the same torque.
Your motor is probably topping out at this speed as it is reaching the maximum rpm for the voltage.
Either add another lipo brick or two series (which may make no difference)or buy a motor that has a kv or rpm rating.
42mph sounds ok for your average chinese motor.
 
brumbrum said:
rg12 said:
skeetab5780 said:
42mph is crazy fast, I barely get that with 20s.

it could depend on the KV of your motor, the diameter of your tire and also some controllers can be programmed to run more than 100% throttle.
Click to expand...

I get people here running some unknown setups going 80kmh to even 100kmh...I really don't think it's crazy fast for a light weight high powered setup.

What is KV? is that the winding thing (thin for speed vs thick for torque)?
2.5" Maxxis, that wouldn't change much, I'm talking about people much faster than me.
I've got 120% on my controller, it's the third click in my 3 mode switch but that makes the wheel go to that 120% speed (crazy fast) only when there is no load and the wheel is in the air.
Click to expand...

The kv (konstants velocity??, or something like that) of the motor is how many rpm it will do per volt applied and this is linked to the copper windings inside the motor. Less turns with thicker wire equals faster motor, thinner wire with more turns equal slower motor. I beieve that all things being equal they will make the same torque.
Your motor is probably topping out at this speed as it is reaching the maximum rpm for the voltage.
Either add another lipo brick or two series (which may make no difference)or buy a motor that has a kv or rpm rating.
42mph sounds ok for your average chinese motor.
Click to expand...

Oh, I thought it was the other way around, thick for slow, thin for fast (seems logical as thick sounds like power and thin more like speed...oh well...)
So it doesn't give more torque for thinner winding?
One question that is a bit less related...Is it true that for example producing a 1000w with 50v and 20A will be faster than 1000w produced with 20v 50A?
It sounds logical after reading your "konstant voltage" explanation, that the speed is per volts.
Also, Is it true that it is always better to have more volts than amps to lower heating even though the end result will be the same wattage?

btw, I rarely crues in top speed, it's just that everyone was bugging me about it and I was wandering what was going on, so I'm gonna stick with my "lame" 68kmh

P.S love your nick name brumbrum ;)
 
Watts is watts but how you make it and how you use it to do work is i suppose where windings come into play.

Thicker winding will handle more amps than thinner winding before turning it into waste heat, but thicker less wound stator will need more amps to do work.
 
More amps may give your motor more thrust/acceleration. But more amps will also cause more waste heat.
 
You're already well into "illegal on any public road" speeds, unless you've somehow registered your bike as a motorcycle. That's not slow.

At best, you're probably getting 4hp peak to the wheel, probably less than that at top speed. The numbers make sense to me. Plug what you've got into Grin's simulator and see what it comes up with.
 
Chalo said:
You're already well into "illegal on any public road" speeds, unless you've somehow registered your bike as a motorcycle. That's not slow.

At best, your probably getting 4hp peak to the wheel, probably less than that at top speed. The numbers make sense to me. Plug what you've got into Grin's simulator and see what it comes up with.
Click to expand...

Well you can be illegal with 26kmh, so if your going to brake the law...

Grins what?
 
rg12 said:
Chalo said:
rg12 said:
Grins what?
Click to expand...

http://www.ebikes.ca/tools/simulator.html
Click to expand...

Cool simulator thanks, too bad that "unknown generic Chinese pile of steel" brand isn't there...
Click to expand...

It doesn't have to be. Just pick any of the DD hub motors and start playing around. Although you won't be able to simulate your exact motor, you will be able to see how much power is required to go certain speed, the effect of increased voltage, current, tire size, slope, weight, etc. It's well worth the time and effort.
 
Most no-name motors are clones of something else that probably is in the simulator.
 
Oh cool, I'll mess around with it then...
Mine is probably a copy of a copy of a copy of something original...
Most hubs look alike to me (yeah I'm a hub motor racist)...there's crystalyte, cromotor and the rest look all the same to me...
 
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