Bafang BPM 500W broke again the aluminium fork dropouts

[casainho]

1 - I almost killed myself when riding for the first 30 seconds, the aluminium fork dropouts broke.

2 - I bought arms torque, weld them and carefully installed on the bicycle. I also change the controller from the KU123 to KU93, which provides less power to motor and so less torque.

3 - I tested again with the arm torque:

Here is the bicycle with the arms torque:






The arm torque seems very strong however I decided to make some tests before ride the bicycle. I were afraid that dropouts broke again. Please see the following video to see the simple tests I did, by trying to simulate going at high speed and do a jump because of some bump (I were pushing the handlebars of the bicycle to the ground, to try block the wheel):
[youtube]yKymcX6aNSM[/youtube]

And one dropout broke with the tests:


The BMSBattery torque arms are very strong but they may had slipped a bit because the fixation to the fork may not be perfect. As dogman told and I agree:

(...) I would not be a bit suprised if my forks would fail that test too. That bump test is pretty harsh. It simulates the torque you'd have if you landed a jump with the brakes locked. Landing a jump, the wheel would not try to stop so hard normally, it would just keep rolling.

 

[mr.electric]

I think the hose clamp you are using is not holing. You will probably have to make a torque arm that holds to the fork better. Even if you make an excellent torque arm it will be difficult to trust the safety. The most conservative, safe approach would be to switch to a steel fork and use torque arms or switch to a rear motor and use torque arms.

 

[casainho]

I think the hose clamp you are using is not holing. You will probably have to make a torque arm that holds to the fork better. Even if you make an excellent torque arm it will be difficult to trust the safety.

2 new forks broken, I do not want to use any more motor on forks.

The most conservative, safe approach would be to switch to a steel fork and use torque arms or switch to a rear motor and use torque arms.

My mechanic don't have steel fork for my bicycle.

On my actual bicycle, I can put a rear motor (the same Bafang 500W, isn't it to much powerful??) but my mechanic tell me that rear dropouts are even more fragile and so they will also broke.

Very strange, I want a sport bicycle to be able to pedal and ride quickly, this my BTT bicycle seems perfect but due to use of the aluminium it can't handle the motor and I think I will need to go with a old, heavy and worst bicycle of steel... are there other options?

 

[pchen92]

You must never do what you have done !!!
When you try to slow down the motor by "bumping" the wheel, the kinetic energy of the wheel and the torque of the motor are going in the dropouts ! And since this motor has an amazing torque, you instantly broke your dropouts ! With an hub motor, it is extremly dangerous to keep the throttle on when the wheel is not on the ground. When you hit a bump, you have to stop accelerating ! I don't know if I am clear...
A dropout of fork is really weak compared to the frame's one. That's why we run rear hub motor. I have a BPM code 8 @ 48V 35A in my rear dropouts (without torque arms). Great torque and speed (50-55km/h on the flat).

 

[casainho]

You must never do what you have done !!!
When you try to slow down the motor by "bumping" the wheel, the kinetic energy of the wheel and the torque of the motor are going in the dropouts ! And since this motor has an amazing torque, you instantly broke your dropouts ! With an hub motor, it is extremly dangerous to keep the throttle on when the wheel is not on the ground. When you hit a bump, you have to stop accelerating ! I don't know if I am clear...

pchen92, thank you for your help.

With an hub motor, it is extremly dangerous to keep the throttle on when the wheel is not on the ground.

But that can happen when we hit on the road a bump or something like that, right?

Do you think the tests I did are over rated?

A dropout of fork is really weak compared to the frame's one. That's why we run rear hub motor. I have a BPM code 8 @ 48V 35A in my rear dropouts (without torque arms). Great torque and speed (50-55km/h on the flat).

1. So, you are using the almost same 500W motor, but rear and without torque arms?

2. Aluminum or steel frame/dropouts?

Can you please share some pictures, mainly from the dropouts? Thank you.

 

[neptronix]

rear motor.
rear motor.
rear motor.

Rear motor, bomb proof torque plates, and never ever worry about it again.
Front forks are not meant to take these loads and i find most torque arms to be decorative.
And once aluminum has cracked anyway, it is nearly impossible to repair it.
Sorry casainho, you need to give up on this front motor business ( with that fork anyway ).. or go to a steel front fork ( order it online, the surly forks are good deal ), then run some torque plates / arms on em.

But rear is always always better..

Find a bike frame you can make some torque plates for. Mine have stood up to 6000-7000w. You will never have a worry again with a setup like above.

 

[kfong]

I would only use steel forks for a front hub motor. Old RST omni are steel, but not much travel. If you live in the states, I can send you mine for cheap. 1-1/8 steer tube uncut.

 

[John in CR]

Casain,
Forget those torque arms, but on the bright side you still have 2 perfectly good forks for hubmotors. You have welding capacity, so you need to fab a steel sleeve or bracket that slides right on the fork that supports clamping dropouts. These are some that I have done to give you some ideas, so you can come up with something better and prettier. All I care about is functionality. Note that the one with the vertical drops was on my first hubmotored ebike that snapped the dropouts off just like you and was before I came up with the idea of clamping dropouts, which I now recommend on all dropouts or torque arms. For all of my most recent dropouts I use leaf spring steel for the faces that clamp, which is much stronger and harder than mild steel, and you can get a nice wide clamping surface (use at least 12mm wide) without the kind of weight of my early models.

 

[casainho]

rear motor.
rear motor.
rear motor.

Rear motor, bomb proof torque plates, and never ever worry about it again.
Front forks are not meant to take these loads and i find most torque arms to be decorative.
And once aluminum has cracked anyway, it is nearly impossible to repair it.
Sorry casainho, you need to give up on this front motor business ( with that fork anyway ).. or go to a steel front fork ( order it online, the surly forks are good deal ), then run some torque plates / arms on em.

Thank you for your feed-back.

Yes, now I want to go rear motor, for sure.

But rear is always always better..

http://neptronix.org/forumpics/torqueplate3.jpg[/img
[img]http://neptronix.org/forumpics/torqueplate4.jpg[/img

Find a bike frame you can make some torque plates for. Mine have stood up to 6000-7000w. You will never have a worry again with a setup like above.[/quote]
Now my question is: will my current bicycle rear dropouts be ok for a motor of 500W?? my mechanic tell me not.
[url=http://www.flickr.com/photos/43558168@N00/5594812343/sizes/l/in/photostream/][img]http://farm6.staticflickr.com/5187/5594812343_f1d23dacff.jpg[/url]

So, I am thinking in getting a rear motor but smaller and lighter: Q100 36V350W, 2.1kg and drive it at 48V in the hope to get ~45km/h.

 

[neptronix]

How about you remove the wheel and take a picture of each dropout?

If it is a nice and flat, you can pretty easily make some plates for it.

 

[casainho]

I would only use steel forks for a front hub motor. Old RST omni are steel, but not much travel. If you live in the states, I can send you mine for cheap. 1-1/8 steer tube uncut.

Thank you. I live in Portugal - Europe (that's why I buy from BMSBattery, shipping is relativity cheap.

Casain,
Forget those torque arms, but on the bright side you still have 2 perfectly good forks for hubmotors. You have welding capacity, so you need to fab a steel sleeve or bracket that slides right on the fork that supports clamping dropouts.

Thank you John. I had to pay for the welding, but yes, I have luck to have a good shop on my city (and know about it).

I am decided to go rear motor now but I am still worried with the rear dropouts and to much power of the motor, I am afraid to loose control of the bicycle due to much power/speed/acceleration. I wish there was some OpenSource controller I could configure for power ramps, etc.

 

[John in CR]

If they're good quality, how about selling me the 2 broken sets of forks for really cheap, since they're worthless as-is? Keep in mind that your BPM may not have a long enough axle for a rear, and even if it does there are fabrication issues to run it as a rear motor. If you're getting a new motor, sell me the BPM too. I've wanted to try one out free of it's outer shell.

John

 

[dogman dan]

John's Idea is definitely the final solution. I've got something like 4000 miles or more on aluminum forks with no problems. Two good torque arms, with C washers in the fork cups. 1200w measured with a CA. But I would not be a bit suprised if my forks would fail that test too. That bump test is pretty harsh. It simulates the torque you'd have if you landed a jump with the brakes locked. Landing a jump, the wheel would not try to stop so hard normally, it would just keep rolling.

 

[John in CR]

...Landing a jump, the wheel would not try to stop so hard normally, it would just keep rolling.

Or landing the jump it may have positive torque from not letting off the throttle and the motor spins itself right out of the dropout with those type of retail torque arms. The way I do it the forks would break before the dropout sleeve.

 

[motomech]

I'm pretty sure that Casinho used the BMS Battery torque arms, of which some of us were suspect.
When his mechanic gets it apart, I predict that the axle slots spread because of too soft metal.

For now, STAY AWAY FROM BMS BATTERY TORQUE ARMS!!!!!

 

[casainho]

I'm pretty sure that Casinho used the BMS Battery torque arms, of which some of us were suspect.
When his mechanic gets it apart, I predict that the axle slots spread because of too soft metal.

For now, STAY AWAY FROM BMS BATTERY TORQUE ARMS!!!!!

No, BMSBattery torque arms are very strong.

I think the problem were more like Dogman told:

I would not be a bit suprised if my forks would fail that test too. That bump test is pretty harsh. It simulates the torque you'd have if you landed a jump with the brakes locked. Landing a jump, the wheel would not try to stop so hard normally, it would just keep rolling.

 

[cwah]

Damn, the torque arms were not strong enough to handle the power... You should try doc torque arm

 

[casainho]

Damn, the torque arms were not strong enough to handle the power... You should try doc torque arm

You are wrong, that BMSBATTERY torque arms are really strong. Their installation were not perfect and the tests I did were to much harsh.

 

[cwah]

Do you mean the torque arm installation wasn't tight enough? Or maybe badly placed?

 

[casainho]

Do you mean the torque arm installation wasn't tight enough? Or maybe badly placed?

Yes, the torque arm may have slipped a bit. As dogman told and I agree:

(...) I would not be a bit suprised if my forks would fail that test too. That bump test is pretty harsh. It simulates the torque you'd have if you landed a jump with the brakes locked. Landing a jump, the wheel would not try to stop so hard normally, it would just keep rolling.

 

[cwah]

Yeah, but I would hope my torque arm would be able to handle the torque if I jump with my brakes locked.

 

[casainho]

Yeah, but I would hope my torque arm would be able to handle the torque if I jump with my brakes locked.

Why don't you make the test as I did? Please do, record a video and show us.

 

[dogman dan]

Why? If you do that you'll just slam face first into the pavement.

Besides, how many times have we repeated over and over that if you are going to do trail riding or stunting you need a rear hub. The only exception to this would be for a dual hub bike.

 

[dnmun]

no picture of the dropouts before without the motor in place.

no mention of the C washer for the lawyers lips.

i think maybe the aluminum had already been stressed and fractured when he tightened the nut.

 

[Racer_X]

I don't think BMSbattery includes C washer with their kits

but you can get them here.
http://www.ebikes.ca/store/store_motors.php