Don't Use Aluminum Forks with front hub motors!

[MadRhino]

Building anything powerful with a front hub motor is dangerous, and alu forks are only adding another danger to the list. Build with a rear motor, or build legal power if you really want to go front. We are not on 4 wheels, there is absolutely no advantage to front traction, other than saving the cost of a freewheel.

[shock]

My reasoning tells me not to use front motors at all...

[Green Machine]

Front motors have some advantages especially if you are like me and do not like derailleurs. Imo iGH shifters are the way to go on an ebike when weight isnt much of a factor...and front wheel drive often times improves the balance of the bike.

As dogman said...as long as you are careful and take precautions, there is no reason hub motors cant be used up front.

[dingoEsride]

Ive been using alloy forks with front hub for thousands of K's, but as with anything take precautions just like walking eg. don't walk into a post or a brick wall cause it may hurt, a good quality fork, torque arms are a must and for high power use the power gradual, they do seem to have nice balance and handling, and of course don't power too much into corners or wheel may slip, but the same can be said for rear drive, also avoid regen braking cause this will create continual opposite forces

[dogman]

Something to think about, whether the motor is front or rear. Say you pop a small jump, the motor starts spinning faster in the air. Then when you land, that's going to be a serious spike of torque.

Front or rear motor, you can tear stuff up even at lowish power levels if you are relying only on the pressure of the nut to controll torque.
For sure, you have to do it right to run high power on a front hub. When I did it, (3000+W) it was steel forks, and several bolts attaching the two torque arms. No weak hose clamps for that much power.

[casainho]

Something to think about, whether the motor is front or rear. Say you pop a small jump, the motor starts spinning faster in the air. Then when you land, that's going to be a serious spike of torque.

That was exactly what I did on the only first 30 seconds I had the bicycle with me - I lift a bit the front wheel because it was funny to get it skidding, and when the wheel got to the ground/road, the wheel/motor went ahead and left me and the rest of bicycle to behind -- well, in reality I did jumped over the handlebars.

I got a opinion here that makes me decide to going front wheel motor since I will always be pedaling:

Assuming the battery is located at the rear of the bike, you get a better weight distribution (as opposed to a typical front wheel drive).
Also, practically you get a two wheel drive (rear wheel pedaling and front wheel motor assistance). A two wheel drive is better for use on slippery surface because you get better handling (Just like a four wheel drive automobile). Another thing is that the front wheel motor assistance won't cause any unintended wheelies on sudden acceleration.

What do you guys thing of this?

I will be driving only on tarmac road and only at sun days but maybe on some corners I may get some sand and/or watter.

[MadRhino]

Your leg power is nothing compared to the power that can be fed to a hub motor, calling it 2 WD because you pedal is dreaming if you feed it anything more than 500W. The fact is that a motor can make your front wheel slide in a curve on anything but a perfect surface, if it has more than legal power. The only thing needed is some sand, water hole, or just a distraction that make you shift your weight incorrectly. Front motors are for low power, anybody building high power on the front and riding above 30 Mph is 5 times more likely to miss a turn. Controlling a rear slip is difficult already, a front slip will result in a loss of control most of the time, even with the best riders who have the nerves to avoid over reacting.

[dogman]

I still use a front hub on my best commuting bike. It just makes it better all around because with the motor up front, I can carry more cargo in the panniers in back before it gets too squirrely. I carry a 15 pound battery on top of the rack, and often carry more battery or cargo in the panniers. In my case, it's a Y frame bike, so carrying any battery in the triangle is out.

So it's definitely a compromise. It's good within a certain envelope, and bad out side the limits. It works good for me for riding on dry pavement, or wet that is not too steep. It's no good for dirt riding, trail riding. You just gotta have a rear hub for that. Dual hub can be nice in dirt, but really I prefer to have a light front so I can pull a small wheelie over larger obstacles. I run 1200w max, 48v. So I burn a little bit of front tire rubber, but nothing that alarms me. You should get quickly used to a small wheel spin the first foot or so as you start. Do be cautious about going from 0 throttle to full on a corner with wet or sand. But if you are already spun up, you can power through a corner fine.

Occasionally front hub in dirt can be fun. On the right surface, and with a good tire, you actually can do front hub drifting just like a rear wheel drift. It's just harder to do, and if you blow it it hurts more to crash. But it Is fun. You can ride dirt roads with a front hub, but you will do some wheel spinning. So if you have a dirt shortcut, it's not forbidden. If you are building a bike for dirt though, it must be rear hub, or at least dual hub.

[motomech]

One of my fav. builds was Chinaphil's "Quest for Super Stealth".

viewtopic.php?f=3&t=24866&hilit=chinaphil

Built specifically to negociate steep, winding, mountain paths in his part of China, and do it in a silent fashion, he mounted dual MXUS mini-motors.

See it in action,

http://www.youtube.com/watch?v=WDm7lIHih8U

Not one to be given to exaggeration, he wrote,

QUOTE= " I always carry batteries (4 off 6s 5,000mAh 25C) in a backpack, easy to hear the LV buzzers.

Just climbed some 15% inclines and the speed is higher than the 500W Cyclone bike with all of its gearing - guess 15km/h versus less than 10 km/h - the inclines are narrow so there is no time to look at speed readouts.

At this stage I am content with the visual stealth, audible stealth, hill climbing ability and top speed."- END OF QUOTE

For technical, tight "trials" type riding, I'm thinking dual mini's would be hard to beat. Obviously, with this type of riding, the idea would be to keep both wheels on the ground. If a guy is "smoking" the trails, railing berms, jumping etc., yeah, a DD rear would be the way to go.

Splitting relatively low power between wheels creates a traction advantage, not to mention the small amount of added unsprung weight, less stress to the chain stay, better overall bike balance, etc.

2WD drive definately has it's place, I.M.O.

For low-powered assist riding, my FWD has been great, no control problems at all.

[MadRhino]

...
2WD drive definately has it's place, I.M.O.

For low-powered assist riding, my FWD has been great, no control problems at all.

For that, I agree. Yet, steep climbing doesn't benefit at all of a front motor, for it has no significant traction on 15% incline and up. The only advantage of a 2 WD is to share the heat, so it could climb longer before bust, and that is only if the climb is not too steep to let the front motor help at all. For climbing steep, nothing can beat high power on the rear wheel, and sharing the power with a front motor only steal some off where it is needed, along with adding weight in a discipline where it is so important to be light.

[casainho]

So it's definitely a compromise. It's good within a certain envelope, and bad out side the limits. It works good for me for riding on dry pavement, or wet that is not too steep. It's no good for dirt riding, trail riding. You just gotta have a rear hub for that. Dual hub can be nice in dirt, but really I prefer to have a light front so I can pull a small wheelie over larger obstacles. I run 1200w max, 48v. So I burn a little bit of front tire rubber, but nothing that alarms me. You should get quickly used to a small wheel spin the first foot or so as you start. Do be cautious about going from 0 throttle to full on a corner with wet or sand. But if you are already spun up, you can power through a corner fine.

Ok, it's decided. I will go with the Bafang BPM 500W front motor on aluminum forks but using 2 arm torques.

My travel is 50km (25km + 25km to return) on flat dry pavement/tarmac roads (I live near the ocean). 2 years ago I did this with 180W front motor, 1 year after with 250W front motor and now I want to go with the Bafang 500W.

My controller gives 22A at 48V, which is 1056W at start. Since I came from a 250W motor and I just need more 50 or 100W, I will do 2 things:
- limit the maximum throttle with a circuit to 0.7, 500W*.7 = 350W
- ramp up the acceleration of throttle with the opamp circuit(or Arduino) to have 3 seconds of ramp from 0 to maximum power

Limiting the power to 350W to be safe, also because I don't have gears to go over 44km/h (maximum speed with the 250W motor were 38km/h) and I want to always pedal, also I will ride 50km with a charge but I plan to increase for the 70km/h.
I wish I could limit the power and ramp up on the controller, so when lifting to the air the wheel like on a bump, the wheel would take time to accelerate and so more safe.

I hope to survive to any possible accident due to front motor and have the chance to change for rear motor

My actual electric bicycle is this one (V2.1 in Portuguese):


It is a Cute-85 motor for 16'' but installed on a 26'' wheel, 250W, 24V. Battery 24V 25Ah.

[amigafan2003]

This carbon fork with alloy dropouts and a front motor will make many of you cringe then



Just passed 1000 miles on it.

[casainho]

This carbon fork with alloy dropouts and a front motor will make many of you cringe then

Just passed 1000 miles on it.

You are pushing your luck by not using arm torque. You don't know if you are near the limit.

[dogman]

It would make me cringe if it had any power. Properly installed, nut torque alone is proven to provide enough resistance for lower torque levels. And I do see a torque arm.

One thing to note, Sometimes the wider width at the cover common with gearmotors will not fit between the tubes of a suspension fork. You need the type of fork that has the dropouts mounted to the inside of the tube. Many forks have the dropouts centered on the fork tube, and typically the motor cover is too wide to fit. Usually a 9 continent dd motor will fit most forks. It's narrower at the cover, but sometimes still rubs on the bearing housing of a tight fork.

So measure it before you order.

[casainho]

It would make me cringe if it had any power. Properly installed, nut torque alone is proven to provide enough resistance for lower torque levels. And I do see a torque arm.

Sorry for my mistake amigafan2003, now I see you are using torque arm.

One thing to note, Sometimes the wider width at the cover common with gearmotors will not fit between the tubes of a suspension fork. You need the type of fork that has the dropouts mounted to the inside of the tube. Many forks have the dropouts centered on the fork tube, and typically the motor cover is too wide to fit. Usually a 9 continent dd motor will fit most forks. It's narrower at the cover, but sometimes still rubs on the bearing housing of a tight fork.

So measure it before you order.

dogman, thank you for sharing. Are you suggestion me to measure before order? If so, I already ordered 2 pairs of BMSBattery arm torque and a KU93 controller (current is KU123, the one that broke the alu dropouts).
I don't know if BMSBattery arm torque are good and if they will work, but before ordering I were ready to make myself them so I will verify and think the BMSBattery ones and if needed weld them or the steel sheet I will use.

[dogman]

I was talking about measuring the motor itself. Moot point if you have it already and it fits. Depending on the fork design, some motors are too wide for the forks. The dropout is still standard 100mm, but the measure between the two tubes might be only 80 mm. So the motor won't fit between the two tubes.

[amberwolf]

Sometimes the wider width at the cover common with gearmotors will not fit between the tubes of a suspension fork.

Yes, the first Fusin I got from you fit fine on DayGlo Avenger's cheap RST Omni fork. But the cover fasteners on it were domed phillips screws, and those on a second Fusin from you were taller squared-profile allen-head bolts, which would only fit if I took the lockwashers out, on one side. Why they fit on the other side I dunno, but they cleared fine there.

So even the very "same" motor from the same company may not always fit! And it might not be obvious why it doesn't fit at first, either. The Fusin was obvious, as it clicked on each bolthead. What wasn't obvious at first was that the suspension would "stick" once it went down, and not rebound, so the next bump wasn't absorbed as well or at all, with the spacer in there. Eventually it wore inside the fork enough to work normally again, probably less than a hundred miles.

[amigafan2003]

This carbon fork with alloy dropouts and a front motor will make many of you cringe then

Just passed 1000 miles on it.

You are pushing your luck by not using arm torque. You don't know if you are near the limit.

I am using a torque arm - look closer

EDIT: I see you've noticed

It would make me cringe if it had any power. Properly installed, nut torque alone is proven to provide enough resistance for lower torque levels. And I do see a torque arm.

Yeah, it's only pulling 750w max.