Aluminum fork w/ front hub

Cold-E-Commuter

Cold-E-Commuter

100 W
Joined
Nov 27, 2009
Messages
201
Location
Fort Collins, Colorado
Hi all,
Just wanted to share info on my installation of a front hub motor with an aluminum suspension fork.
So here's the bike update info. Front hub motor is still an NC2806. I have been running this with a RST191 cheapo steel suspension fork and a v-brake for quite a while. The v-brake has been an issue for me for a while. When running 21s LiPo and reaching speeds exceeding 50 mph the margin for error was narrow. The fork recently developed a rust problem and became a solid fork so it was time to replace it. It has been replaced with a Rockshox XC32TK with 100mm travel, adjustable damper and rebound with a remote lockout. The drop outs are aluminum. Also replaced was the v-brake. I now have an Avid BB7 disc unit installed on the front. (looking for a bracket to do the same out back) This weeks rides were conducted using a Ping 48V15A pack (really 51.2 volts nominal and 57 volts hot from charger) as a low power base. Top speeds have been less than 40 mph. I'll up the power as time goes on and confidence is complete. Not ready to push 3Kw thru it yet, but I'll hopefully be here to let you know how that goes. To satisfy my safety requirements I have installed dual torque arms and added what I call a steel pinch point washer to go with the c-washers.
View attachment 1
Notice what I call the pinch washers on the inside of the drop outs of both sides as stated. My intent is to keep the aluminum drop outs as stable as possible and not allow them to spread. I have also carefully placed the torque arms so that they are turned as far to the initiation point as possible to keep the axle from ever contacting the drop-out. Also, the rotor had to be spaced from the hub 1.7mm to allow the caliper to clear the inside of the motor. Washers were methodically machined (using a file) to do so. The torque arm support on the disc brake side was ground to fit the shape of the caliper.
DSC00449.jpg

The total time spent on this was between 16 and 18 hours. Happy to share more photos and info for thise interested.

D
 
full-throttle-Point is that they are not steel! Had to grind the drop out from 9mm to 10mm. Not magnetic and seemed aluminum when sparks didn't ignite them. And you are more than welcome to come over and run an 88.8 volt 15Ah LiPo pack on a fresh build if you like. I personally prefer all of my bones as they are.
 
So a GPS verified speed of 54.2 mph might be a bit much? (on the old unit) I see you can appreciate my caution when ramping up the power.
 
lester, where is your sense of adventure? Push the envelope or it pushes you! That said, safety is not a joke. That is why I am asking technical input for the install. Steel washers inside, c-washers and torque arms out seems to me a way to clamp down (no more than 35 ft/lbs) on the aluminum c shape of the drop-outs. Thus keeping the axle from spin-out or the front tabs from breaking off. (C shape of drop-outs cannot become oh s**t if held by steel, hopefully) Many threads here have stated that you can run aluminum safely (up to 3000 watts) as long as the install is perfect. Those are the reasons I have done so. Many hours of research before the hours of work. Time will tell, but responses from those who have would be beneficial before an oh s**t situation occurs.
 
Is running an Alu front fork with torque arms considered OK?

I'm running a low power front hub motor setup with an Alu front fork, and have had no problems so far.

Do you tend to get more problems with 1kw+?

I do have steel front forks that I can use if I need to.

Thanks
 
I've run 47 mph at more than 3000w on front hub. I wouldn't consider it on alloy forks. I was using an old school, thick tubing, steel fork. Plus I welded some bomb proof torque arm mounts to the forks. No hose clamps.

I would go 1500w on alloy, I run 1200 now. I'd call 72v 20 amps the safe maximum. The main issue is that the toruqe arms become decorations if they can slip under higher power. And of course, to start with you cannot use mis fit washers that crack the forks as soon as you tighen a nut.
 
Cold-E-Commuter said:
So a GPS verified speed of 54.2 mph might be a bit much? (on the old unit) I see you can appreciate my caution when ramping up the power.
Click to expand...

There is a thread here, dating back a year or two, where Justin did some real world testing, quantifying applied torque vs. drop-out/torque arm breakage.
You should search it out for a much needed reality check.
 
The main issue as you go higher power is making sure the torque arm can't rotate at the joint if it's a two piece.

I did this.
http://endless-sphere.com/forums/viewtopic.php?f=6&t=18644&hilit=death+race+bike&start=30
Others have just tack welded the torque arm in position, so the arm fits perfect, but can't let the clamp slide down the fork. If the bolt slips, the arm slides down and lets the bottom piece rotate.
 
there is a muffler shop just south of the CSU campus on the west side of college i used to go too. not sure if they are there anymore but he was someone i could work with instead of the corporate type with rules against being in the shop floor.

can't remember his name now. but someone like that may be available for you to use to weld selective spots on the torque arm.

since you have that one notched for the caliper, you should actually put the clamp on the axle's side of that divot you have ground out so it is attached to a stronger part of the torque arm bracket piece.

with the axle assembled into the fork in the place you want it to remain permanently, have the guy spot weld the torque arm to the axle where it is exposed in the open end of the dropouts. he should be able to put almost 6mm of bead between the threads and the torque arm right there inside the open end of the dropout.

then where the torque arm is attached to the bracket you have clamped on the fork tube, he can run a short bead along the edge to weld the two pieces together and prevent it from moving too.

so between the two spot welds on each side you should gain a lot more strength to hold the torque arm fixed and if the dropout does actually break then having the extra strength there will help prevent the wheel from leaving the fork and jamming inside the fork while at speed.

you should still be able to get the wheel off when you have a flat if the C washer is aligned with the dropouts as it appears so that the entire assembly would slide out in that direction.
 
Yep. fit the arms, tighen the bolt, then take it off and have it welded at any shop. Once it's a one piece arm you're much better. Then use something stronger than hose clamps to attach it to the forks. Thicker metal and a bolt though a hole you drill. Mount them so the torque arm pulls on the strap.

See this page for some info if you are not sure which side that is. http://www.ebikes.ca/torque_arms/
 
Thanks all. I have not run it over the 1500 watts the Ping can provide as of yet. And I have kept the speeds to less that 35mph. I plan on having the arms welded to the supports this weekend and changing from hose clams to solid clamps with rubber back washers. I worry about applying too much force via a clamp that might distort the shape of the tubes and making the change to a better suspension fork pointless. Is that a concern with the Rockshox tubes. I just dont want to crush them or distort the shape. The ride quality is so much better than it ever was with the RST191's. And the Avid BB7 disc performs so unbelievably better than rim v-brakes could dream. The disc brake was another major reason to upgrade because high speed and rim brakes...don't mix. This whole thing has been a work in process and all of the information learned over the last several years has been great. Thanks again. I'll post more pics as things progress.
 
Are you welding to the forks? Can't do that with an alloy shock fork. You can get the torque arms welded so the pieces can't rotate at the bolt.

Some have built replacement steel dropouts. The whole thing clamps to the fork with a large steel sleeve, so it's basicly a bolt on dropout for an alloy fork.

Once properly held in place with torque arms that can't slip, a good quality suspension fork should be able to tolerate 2000w. People worry about snapping the crown off or the head tube. I feel that a real DH fork is built strong enough. They do take a load from disk braking after all. Cheap zooms or something is another thing.

Maybe you will still crack the dropouts running really high wattage, but if you've done your torque arms right, the wheel is not going to leave the bike. So you should be able to stop without going over the bars and biting the curb.
 
Not welding to forks. Just welding the torque arm to the support to create a single piece as so many have suggested. I am also looking at changing out the hose clamps with solid pipe clamp so I can bolt the single piece torque arm unit to the fork rather than pinch it. Here is what I am looking at.
http://idealclamps.com/catalog/clamps/catalog.php?sid=en&ID=12
Second down on the list. I would use the bolt thru the support strut of the torque arm rather than piching it to the fork. Maybe even put a rubber washer behind it around the fork to keep it from slipping or damaging the fork.
 
Yeah, you are on the right track. Something about the way you worded it made me think different. Sounds good.
 
the flexing will cause the fork to work harden because they put a lot of silicone in the aluminum for casting and it will just snap one day.
If you have regen brakes that will do it.
I have a front motor on another bike but I don't use it ever because one day it will just snap off.
Just get a rear motor the same style and relace the rear rim. Then make your torque arms welded or glued on.
 
The first thing I learned before purchasing my first ebike kit was if you using a front hub make sure you're using a steel fork. That led me to buying a cruiserbike with a steel frame. Even if you do this and attach a torque arm, you still need to check the nuts on the bolts each time before you go out riding. They will loosen up a bit from time to time. I use an adjustable wrench to make sure they're tight.
 
Lot's of members here use frt. mounted motors on alloy forks.
This one has over 1000 miles on it with nary a problem.
Just some simple common sense rules need be followed.
1)Quality fork
2)careful fitment w/torque arm.
3)Reasonable power, 900 Watts w/ this one.
 

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full-throttle said:
I'm being sarcastic - 3kW/40mph on a front fork is not a good idea.
Click to expand...

anyone got a general figure of an usable (max) amount of front power, I was thinking low 1KW is really all that is practically usable on a front drive
 
Lessss said:
FTFY:
3)Reasonable power, LESS THAN 500 Watts for aluminum front forks, 2 torque arms at 500, one at 250 and under.
Click to expand...

Please....
Get your facts right.
These Marzocchi Dirt Jumper II fork lower legs are magnesium, not alum., as are most quality MTB forks are.
Justin did the testing, here;
http://endless-sphere.com/forums/viewtopic.php?f=2&t=14195&hilit=dropout+testing&start=150
 
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