Torque arm for Front Hub Motor Review

[DeeL2003]

Well, I was fully aware of the caveats on front mounting a hub motor on front suspension, but I see no reason why if the installation is done properly, it cannot be achieved. In fact, I would not even try doing it on steel front forks without torque arms as well. My installation was obviously not done properly. I should have drilled my required holes and done any required grinding first, and then I should have had the torque arm tempered, something which our welder at work may be able to do for me. More info on tempering is here:
http://asuwlink.uwyo.edu/~metal/heat.html

Even the great system posted above by Mark would be prone to the same failure as mine if his slot stripped out and became oval, perhaps taking out his wiring at the same time.

Very true. BTW, was there any damage to your motor? How fast does a 4011 go @ 72v. Super torque monster.

 

[tsellers]

BTW, I never had a chance to see how fast the 4011 would go, as it failed within the first 20 meters of its life! The 409 on 72V went 40 km/hr, but didn’t have the torque required for our mountainous terrain, especially if you had to carry some extra gear.

However there is a great simulator on Justin's site where see the torque, output power, and efficiency curves plotted as a function of the vehicle speed at: http://www.ebikes.ca/simulator/

It seems to indicate that the 4011 will return a top speed of 23 km/hr at peak efficiency on 36V and 47 km/hr on 72V. However as I am after torque to get up the mountainside, it would appear I could expect 46 N-m of Torque on 72V and 25N-m at 36V if I read the chart correctly, (which I may not be doing, I was a bit confused by it).

 

[xyster]

The 409 on 72V went 40 km/hr, but didn’t have the torque required for our mountainous terrain, especially if you had to carry some extra gear. ...
It seems to indicate that the 4011 will return a top speed of 23 km/hr at peak efficiency on 36V and 47 km/hr on 72V. However as I am after torque to get up the mountainside, it would appear I could expect 46 N-m of Torque on 72V and 25N-m at 36V if I read the chart correctly, (which I may not be doing, I was a bit confused by it).

Is a rear 5-series too heavy or awkward for your application? According the sim, the 5304 generates 110 N-m at 72v35a with a top speed of 70kph in a 26" wheel.

 

[tsellers]

With 2 4011's I'm pretty much commited now. I previously ran the 409 in a rear configuration and subsequently went to front for the following reasons:

Pros:
1: can retain rear skewer to mount purpose built rear bike racks for full suspension bikes. Racks such as Old Man Mountain Sherpa rack is rated for 40lbs.
2: can retain existing 9sp rear cassette instead of having to use old 7sp freewheel cluster
3: can switch back to regular bike quickly, retaining the advantages of #2 above.
4: distributes weight more evenly
5: is cheaper
6: can use on fork mount Yakima vehicle roof rack, not too heavy to lift onto roof with front wheel removed. With hub still on bike probably exceeds weight rating of roof rack. 90% of my riding involves vehicle transport to starting point.
7: You end up with an "all wheel drive" system if you are pedaling uphill at the same time. May help with slipping out on front wheel.

Cons:
1: Need to replace your disc brake on the front where 70% of your braking power is with a V-Brake. Fortunately I already have a Deore XTR V Brake from my old bike.
2: Spins out easier, requiring larger front tire which increases rolling resistance.
3: hard to mount with front suspension systems.
4: greater potential to bend front forks.
Any contributions to the above list greatly appreciated.

I think I am going to go this route with getting torque arms made up:
1: I'll buy these axel retainers from my supplier Garry:

2: I'll get a tube sleeve setup welded on by our welder at work so it ends up being silmilar to what Mark in Australia did above.
3: I'll get the end tempered once it all fits and doesn't need any more modifications.

 

[tsellers]

Further to the above post, does anyone know what is the maximum tire size that V Brakes will generally work with? It just occurred to me that possibly a 26 X 2.5 tire would be to wide for my brakes to make contact with the rims. SO I took a pair of vernier calipers and measured out 1.25" from the center of my exisiting tire and it looks like the arm of the V Brake will clear the tire. I does appear that the only downside will be I will have to remove one of the brake pads or deflate the tire to remove the wheel even with the V Brake cable disconnected.

 

[Mark_A_W]

Even the great system posted above by Mark would be prone to the same failure as mine if his slot stripped out and became oval, perhaps taking out his wiring at the same time.

Granted the next concern then becomes bending the fork tubes as a result of the torque forces. I've considered the huge forces the downhiller's and dirt jumpers place on their forks and they normally report blowing out the seals rather than bending the heavier dirt jump forks like the marzocchi bombers. Then there is the ground-tire interface, you'll probably be spinning out before you could bend the fork tubes, and it's probable you need the fattest tire possible for this set up such as a 26-2.7. Anyway, need to get the problem solved at the dropouts first before moving to the next possible problem.

Well, yes, my axle could spin, but that would be annoying, not disasterous...I'd still keep my teeth.

And yes, they are Marzocchi Bombers

 

[BiGH]

Hi Mark,
beautiful torque arms there did you say u got these from brett? if so how much (and what) modification did u have to do?

really are great!.

I definitely need some for my bike. the avanti 2005 frame is just not designed for this kind of motor.

 

[Miles]

Well, I was fully aware of the caveats on front mounting a hub motor on front suspension, but I see no reason why if the installation is done properly, it cannot be achieved. In fact, I would not even try doing it on steel front forks without torque arms as well. My installation was obviously not done properly. I should have drilled my required holes and done any required grinding first, and then I should have had the torque arm tempered, something which our welder at work may be able to do for me. More info on tempering is here:
http://asuwlink.uwyo.edu/~metal/heat.html

John,

You'll need to make it out of hardenable steel. I should imagine the one you had was just made of mild steel. Here in UK you can get what's called "gauge plate" or "ground flat stock", for toolmaking. After machining, harden it (cherry red heat and quench in oil) and then temper it right back or it will be too brittle and might fracture.

As I said, it's important to get a snug fit on the axle flats, too.

Miles

 

[Mark_A_W]

Hi Mark,
beautiful torque arms there did you say u got these from brett? if so how much (and what) modification did u have to do?

really are great!.

I definitely need some for my bike. the avanti 2005 frame is just not designed for this kind of motor.

No push bike is designed for this type of motor


The arms came from Brett, they were just the 100mm long plain arms on his website (but they didn't fit the axle). I filed them out, then we flattened them (they were slighltly formed), and welded them to the tube half. They got quenched during the flattening process, which will harden them somewhat. Then the other tube half bolts on through holes in the welded on blocks.

After all the work that went into the basic arms, it would have been quicker to make some from scratch on the mill. It's also why they look a bit wonky.

But if you don't have a full workshop at work, make/adapt some arms from Brett. Like on his webpage. You will probably need help from someone with a welder.

Do BOTH sides. And in my opinion, the arms should be able to bear the load of the bike+rider if the axle spins in place AND the dropouts fail, which is the intent behind mine. Not so critical for a rear wheel, but for a front wheel like mine your life could depend on it!

 

[tsellers]

Here's an interesting dropout, the Magura Ronin has stainless inserts, but at $600.00 I guess a torque arm at $15.00 is a bit cheaper:

 

[Miles]

Here's an interesting dropout, the Magura Ronin has stainless inserts, but at $600.00 I guess a torque arm at $15.00 is a bit cheaper:

What's the advantage of having stainless steel inserts?

 

[BiGH]

stength - steel is stronger than aluminium for the same size, alu is lighter though.

alu is really "soft" if you're working on it steel, esp high tensile is very hard.- kind of like the difference between pine and a hard wood - if that makes it easier.

 

[knightmb]

Here's an interesting dropout, the Magura Ronin has stainless inserts, but at $600.00 I guess a torque arm at $15.00 is a bit cheaper:

What's the advantage of having stainless steel inserts?

And why $600?!?

 

[Mark_A_W]

Aluminium is also far more subject to fatigue failure, and when it fails it cracks rather than yields gracefully (it's more brittle than normal steel).

Hi Tensile Steel is not all perfect - it's strong, not tough. When it fails it will crack rather than yield too.

(Rubber is tough, glass is strong.)

 

[Miles]

stength - steel is stronger than aluminium for the same size, alu is lighter though.

alu is really "soft" if you're working on it steel, esp high tensile is very hard.- kind of like the difference between pine and a hard wood - if that makes it easier.

Thanks but, I've had plenty of experience working with aluminium alloys, copper alloys, mild steel, hi-tensile steel, pine, beech, ebony, lignum vitae.... :wink:

But how does a tiny stainless steel insert make a torque arm redundant?

 

[Mark_A_W]

But how does a tiny stainless steel insert make a torque arm redundant?

I wouldn't trust my life to that little insert...would you?

 

[Miles]

But how does a tiny stainless steel insert make a torque arm redundant?

I wouldn't trust my life to that little insert...would you?

No.

I'm sure it serves its real purpose, though - getting someone to part with $600...

 

[Mark_A_W]

$600 is nothing on forks.

My Marzocchi Bomber Junior Ts were once worth more than that

 

[BiGH]

stength - steel is stronger than aluminium for the same size, alu is lighter though.

alu is really "soft" if you're working on it steel, esp high tensile is very hard.- kind of like the difference between pine and a hard wood - if that makes it easier.

Thanks but, I've had plenty of experience working with aluminium alloys, copper alloys, mild steel, hi-tensile steel, pine, beech, ebony, lignum vitae.... :wink:

But how does a tiny stainless steel insert make a torque arm redundant?

hjehe awesome - well the inset would still be stronger, but i agree, so not worth it!

 

[The7]

Here's an interesting dropout, the Magura Ronin has stainless inserts, but at $600.00 I guess a torque arm at $15.00 is a bit cheaper:

The weakest part is the aluminum around the stainless insert.
Don't think it will be better than the one without it.

 

[D-Man]

$600 is nothing on forks.

My Marzocchi Bomber Junior Ts were once worth more than that

The front shocks for my car are only $25 for each one. I don't know of any shocks on a regular car that would cost that much. Bicycle front forks are one of the biggest rip-offs of mankind !!!!!!!!!!!!!

And golf clubs too. I Went into a golf store the other day and I saw some drivers that were $500 a piece. What a joke. :lol:

 

[Mark_A_W]

I didn't say I paid $600 - they are 7 years old, I paid next to nothing

 

[tsellers]

Perhaps this should be a new topic, but some forks must be better than others for the purpose of eBiking and fabricating a custom torque arm. For example, our welder wants me to make sure I bring him forks that are not tapered if we are going to fabricate a sleeve to cover them. Which type of fork construction would be least likely to bend due to the torque exerted by the hub motor, etc.? It would be interesting to come up with a list of the best forks for this.

 

[Mark_A_W]

This is why my Marzocchi Bomber Junior T 2000 model were good.

The lower legs are not tapered, so a simple tube cut lengthways (on bandsaw...fun..) fits around them nicely.

Mark

 

[recumbent]

The lower legs are not tapered, so a simple tube cut lengthways (on bandsaw...fun..) fits around them nicely.Mark

Now that's an idea, slip the tube over the fork end, squeeze the end flat, drill the hole to the minor dia (the flats) file the bore longer to fit, voila, invisible torque arm, no bolts needed. It's late, might not sound good the morning after.