Is 1200w too much power for a front hub...

#1
I have a steel cruiser bike with a 48v 1200w front hub motor, over volted with a 52v li-ion battery. It's fitted with torque washers and a steel torque arm.

I just finished the build 2 days ago, its fast fun and looks pretty cool too. But I think I can already see the torque washers digging into the steel drop out... I could hear some kind of creaking noise while accelerating but could not diagnose it. When I took it to my local bike shop they didn't point out the washers and couldn't hear the creaking (I was shocked). Is my wheel gonna jump out? Is 1200w too much power?? I just put a lot of money and effort into this bike and would truly hate seeing it go to waste.

Why would anyone sell 1200w front hubs if they're just plain dangerous for bikes? The motor is by Ebikeling btw.

Any help is appreciated.
 

JRA

Well-Known Member
#2
I have over 2k on a 1200w (48v/25A) 9c front hub motor mounted on a carbon fiber fork. I have kept an eye on it all this time and no signs of movement nor dropout fatigue with the torque arm set as in the picture into a fender mount.

IMG_20180609_165254923.jpg



An old internal geared hub trick is to grease the axle threads and tighten the piss out of it (35 ft. lbs.).

So to answer your question if properly set up a 1200w, which is peak and not always in use, is fine. For the road it is my preferred setup. It's not just about the going though and being able to stop from speed is a good feature. Hope your cruiser has good brakes.
 
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rich c

Well-Known Member
#3
I don’t know how you would keep from spinning out every time you were on anything but pavement with that much power. Why would the sell it? Because someone will buy it!
 

JRA

Well-Known Member
#4
I'm pulling over a thousand watts doing this climb and the only spinning going on is my legs.


It's not for everybody but it does work. I would probably be riding my mid drive there now however but at the time it didn't exist. For mixed bag adventures I still prefer the hub bike.
 
#5
Well, most of the people who have gone over Niagara Falls in a wooden barrel have actually lived, with only a few dead, but it is still an incredibly stupid idea.

Also. 1200 watts is NOT repeat NOT "peak Power", it is peak SUSTAINED power, peaks will reach well over 2000 watts on such a motor, and on carbon fiber? No Way.

With Regen braking, which hits your nuts in the opposite direction, you are literally asking to re-arrange your face.

Good luck to you both, and could you offer your life insurance policy as an investment opportunity for the rest of us?

Most folks would put max power on a front fork somewhere in the 500 to 1000 watt range, and Never, Ever. on a carbon fork.
 

JRA

Well-Known Member
#6
"Also. 1200 watts is NOT repeat NOT "peak Power", it is peak SUSTAINED power, peaks will reach well over 2000 watts on such a motor, and on carbon fiber? No Way."

You might want to study up on your Ohm's Law Mr. Nelson. To reach over 2000w I would have to be feeding over 40A at the controller and as I said mine is limited to 25A. I use a CA3 which is arguably the most sensitive instrument you can mount on a bicycle to measure current and have never even seen 1200w on it. Hard off the line starts and steep climbs it is in the under 1100w range. I average about 15wh/mi with the bike which means I don't go there that often. But it is nice to have it there in reserve.

"With Regen braking, which hits your nuts in the opposite direction, you are literally asking to re-arrange your face."

Forgot to mention that I also use regen. It is set through the aforementioned CA3 and even at it's highest setting really only works as a drag brake, but for that it works very well.

I am not advocating for everyone to start using a 1200w front hub motor, I was just trying to answer the OP's question based on my experience which has been positive to date and I feel will keep me happy for the style of riding I do on the bikes I have setup with it for many miles to come.
 
#7
I'm on an all steel bike that will only be seeing pavement. Still has me sketched out though. I might try to put a moto fork on there (if I can figure it out). I don't need to go 35+ mph everyday but it'd be nice to know I can. Am I the only one that feels this way :p
 

rich c

Well-Known Member
#8
I'm on an all steel bike that will only be seeing pavement. Still has me sketched out though. I might try to put a moto fork on there (if I can figure it out). I don't need to go 35+ mph everyday but it'd be nice to know I can. Am I the only one that feels this way :p
I never feel like I need to go 35+mph on a bike unless going down a huge hill.
 
#9
I guess I should apologize to JRA for not using my crystal ball and understanding that what was given as a battery spec was actually a hard limit set thru unspecified hardware which allowed his equipment to perform strictly within those limits in a way that other similar motor kits absolutely do not do. Ohm's law does not apply.

Regen braking applies torque forces to the dropouts in the opposite direction to motor torque. Softer is better, but rocking back and forth is still rocking back and forth. Not good for long-term structural reliability.

Consideration should be given to exactly what happens when the front wheel departs from the bicycle, as opposed to the rear wheel. It is very much more hazardous. The human leaves the machine head first. This also is not good for long-term structural reliability.
 

JRA

Well-Known Member
#10
"1200w (48v/25A)"

Don't know how I could have been more specific in my first post. It's just simple math presented in a way that is universal to describe v/A=w anywhere I have seen.

Ohm's law applies to all electrical devices: https://learn.sparkfun.com/tutorials/voltage-current-resistance-and-ohms-law

Every e bike has a controller and the A limit x the v is the most that it can put out. The kit motors such as found online from Asia are also limited by the A limit of the controller and the v of the supply. These values of course can be modified or bought as such but outside of the ES crowd I don't see much evidence of it going on.

i did research, considered my options and took steps to maximize my safety long ago. Thanks for your concern.
 
#11
I've used 1000 W in front fork of a 1970's steel cruiser (huffy savannah). I have the 18 lb battery mounted on the front fork using angle aluminum. No problem except the motor/controller won't run more than 13 miles. I don't ride over 20 mph powered but do carry 60 lb supplies up 15% grades in a rear basket. The Reason I wanted a front motor, the weight distribution is 20/80 lb without supplies, motor, battery, or me on the bike.
I do have 3" long torque arms mounted to the angle aluminum. I made these myself, cutting the oval hole with flats with a die grinder. The controller had a 26.5 A limit, and the battery is a nominal 48v LiFePo4 with a 61.4 v charger shipped with it. Battery wires are 12 ga.
The motor I bought is geared so torque is one way. Second nut holding aluminum angle to hub shaft is already stripping the axle threads @ 40 ftlb torque, so overtightening is not a good idea on $300 hubmotors.
 
#12
I don’t know how you would keep from spinning out every time you were on anything but pavement with that much power. Why would the sell it? Because someone will buy it!
Isn't spinning out more a factor of too much torque at too low of a load rather than max power?

I.e. so long as the torque was ramped up smoothly, I don't see it being an issue with the power level. You might still have issues with traction on slick surfaces but that's true of any front hub I'd think.

I mention it because I looked into pairing a front hub with a phaserunner initially when I built my DIY bike, and it seemed like a good match - the phaserunner's throttle input directly maps to motor torque unlike most controllers, and you can adjust the ramp-up.
 

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