Wrench as torque arm, box end on nut or open end on axle?

[Dan K]

I've been reading up about how people use wrenches as torque arms for front hub motors. Seems there are 2 schools of thought on how to do this.

School 1: Box wrench on axle nut
reasons: Box end won't come off nut, is fairly secure once tightly hose-clamped to fork.

School 2: Open end on axle flat
reasons: Stops axle itself from spinning, where box end can allow axle to spin inside nut. Also fairly secure once tightly clamped to fork, but arguably not as secure as box end is on axle nut.

Anyone care to make an argument for either way?

Also, are you guys using lock washers with these, or typical bike axle washers? Again, care to make an argument for one or the other?

Thanks,

Dan

 

[Drunkskunk]

Don't put it on the nut, the axle can still turn inside the nut. maybe not much, but enough to crack the dropout and break its self loose.

I used the open end of 10mm wrenches on the axle its self, although I used a file to make the rounded inside of the wrench fit better to the axle, and welded washers to it so it would sit flatter against the bike. They have been bulletproof.

 

[Dan K]

Good deal. I don't have a welder, but I do have access to some serious epoxies, as well as JB Weld. Where do you have the wrench on the axle? Outside the axle nut? And I assume it's hose clamped to the fork? Any pics of the setup? One on each side?

 

[Drunkskunk]

Hose clamps are a bad idea. You've heard a chain is only as strong as it's weakest link? A hose clamp is only as strong as it's thinnest spot. look at the edge were one of the many holes in the band is cut. you only have around 2mm of very thin and soft stainless steel. I break off hose clamps working on cars instead of unfastening them. its easy to snap them off with a screwdriver. I thicker strap of metal could be used


JB weld would be fine for the washers as long as it was just being a gap filler and the washer was touching the wrench near the middle. you can't put much torque on an axle nut since the threads strip easily, so the JB weld would be fine. I used to rock climb, and some of the rogue sites we climbed used JB weld to secure the grip rocks to concrete walls.

I welded the wrenches to the bottom of a rack I made, but you could just as easily have done this with bolts.

 

[Dan K]

Sweet. Thanks for the reply. That rack/torque arm thing is sweet. I'm really starting to run out of reasons not to buy a welder...

 

[dnmun]

why waste a wrench when you can just buy a torque arm which would work? why waste 2? and the axle's still gonna spin out.

 

[Dan K]

why waste a wrench when you can just buy a torque arm which would work? why waste 2? and the axle's still gonna spin out.

Because I have wrenches by the dozens, and am not sure what torque arm will work. I'm not even sure which bike this is going to go onto yet. If I could swing into my local bike shop and pick up a universal torque arm, I would. I should have the kit soon, it left GA today. Staying on the east coast to MA, I'll have it next week. I don't think I could get a torque arm by then, even if I could I wouldn't be sure it would be the right one of fit properly (I've read quite a few reports of them not fitting a certain application) and it would cost more than a wrench anyway.

How do you figure the axle is still going to spin out, if I go Drunkskunk's route and use a wrench right on the flats of the axle?

 

[Gordon]

I have a torque arm on the left side that fits the axle flats.
I have a boxed end wrench on the right side nut. If the axle wants to spin it would add tightening to the nut.

 

[Gordon]

Any pics of the setup? One on each side?

http://www.endless-sphere.com/forums/viewtopic.php?t=8979

First picture is my torque arm.
2nd is the wrench.

 

[Dan K]

Gordon,

Thanks. Seems like a good idea. I'd use a wrench for each side, but one on the axle and one on the nut seems like a good move.

Question though. Looking at the bike from the drive side, the wheel would spin clockwise, correct? Seems if the hub/axle wanted to spin inside the nut, it would want to loosed the nut on the right (drive) side? Seems at first glance that your setup is backwards, and you'd want the left (non drive) side axle nut and the right (drive) side axle grabbed. Am I missing something?

 

[Zoot Katz]

Gordon,

Thanks. Seems like a good idea. I'd use a wrench for each side, but one on the axle and one on the nut seems like a good move.

Question though. Looking at the bike from the drive side, the wheel would spin clockwise, correct? Seems if the hub/axle wanted to spin inside the nut, it would want to loosed the nut on the right (drive) side? Seems at first glance that your setup is backwards, and you'd want the left (non drive) side axle nut and the right (drive) side axle grabbed. Am I missing something?

Regenerative braking?
For that, I'd want the axle locked in both directions.

 

[Dan K]

Gordon,

Thanks. Seems like a good idea. I'd use a wrench for each side, but one on the axle and one on the nut seems like a good move.

Question though. Looking at the bike from the drive side, the wheel would spin clockwise, correct? Seems if the hub/axle wanted to spin inside the nut, it would want to loosed the nut on the right (drive) side? Seems at first glance that your setup is backwards, and you'd want the left (non drive) side axle nut and the right (drive) side axle grabbed. Am I missing something?

Regenerative braking?
For that, I'd want the axle locked in both directions.

Good call. I completely forgot that the kit I have coming is supposed to do regenerative braking. Based on the description provided, I'm not sure how hard or for how long, but it's still a worth concern. Both sides on the axle it is. Thanks for catching that. Still doesn’t answer my question regarding Gordon’s setup, since I don’t believe the ezee allows for regenerative braking. It is a good reason to secure mine by the axle on both sides though.

As an aside, interesting seeing you over here. I assume you are the one and only Zoot Katz from r.b.t., where I have not seen you in probably a year?

 

[Zoot Katz]

Regenerative braking?
For that, I'd want the axle locked in both directions.

Good call. I completely forgot that the kit I have coming is supposed to do regenerative braking. Based on the description provided, I'm not sure how hard or for how long, but it's still a worth concern. Both sides on the axle it is. Thanks for catching that. Still doesn’t answer my question regarding Gordon’s setup, since I don’t believe the ezee allows for regenerative braking. It is a good reason to secure mine by the axle on both sides though.

As an aside, interesting seeing you over here. I assume you are the one and only Zoot Katz from r.b.t., where I have not seen you in probably a year?

Right. E-Zee is a geared motor, easier to pedal but no regen. Justin <ebikes.ca> runs his E-Zee front with only one torque arm. His X-Canada Xlyte bike probably has only one too, and it has regen. (He charged at the top or Rogers Pass, oops!)
I'd think that as long as it securely holds the axle flats, the only consideration is how the forces affect the fork legs.
What about left and right hand threaded axles? Whether to think about them from a Swiss, Italian, French or British POV is a coin flip.

r.b.m is where I mostly post. Many of those are x-posted threads. I've not been as active on Usenet since ~'06-'08 when I started cramming here.
This is truly the dark side. Great bunch of folks and though the idea of moderation/censorship troubles me, I've seen some of its benefits. People here are civil and it rubs off on ya.

 

[MidniteTweeker]

http://www.texaselectricbikes.com/catalog/torque-electric-motors-p-228.html sells a laser cut stainless torque arm. Tougher than heck. I had to file it slightly to fit. I mean slightly...like a few 1/1000ths of an inch. Took forever. It goes under the nut.

When you install a torque arm (at least for single direction non-regen use) you should try to bias it during installation so that there's already tension in the arm countering the rotation of the axle. This will help ensure that any initial clearance between arm and axle that might have allowed a small amount of rotation is already taken up.

The thing about a torque arm is to visualize the geometry of the fit between the axle flats and the slot in the arm. It may help to sketch it out. The only thing that resists rotation are two very small points (or lines, if you want to be picky) of contact where the "corners" of the axle contact the flats of the torque arm. If any movement occurs, the contact pressure (pounds per square inch) at those points is huge because the radius is small, the torque is large, and the contact area is extremely small. Lots of pounds on a very small area. Keeping the fit tight helps by maintaining a geometrical advantage as much as possible. Even then, the contact pressure or force can be high enough to deform a soft material (corner rounding.) Once that begins, the geometrical advantage is lost, more rounding occurs, and eventually something spins.

If you can get a good tight fit with an open end wrench, great. But by definition a wrench already has clearance built into it. You might want to consider using an undersize wrench and tuning the fit with a disk sander to get it perfect.

MT

 

[Gordon]

Gordon,

Thanks. Seems like a good idea. I'd use a wrench for each side, but one on the axle and one on the nut seems like a good move.

Question though. Looking at the bike from the drive side, the wheel would spin clockwise, correct? Seems if the hub/axle wanted to spin inside the nut, it would want to loosed the nut on the right (drive) side? Seems at first glance that your setup is backwards, and you'd want the left (non drive) side axle nut and the right (drive) side axle grabbed. Am I missing something?

Yes, the wheel spins clockwise but the motor torque is in the opposite direction. Think about which way the axle would spin if the wheel was held stationary.

 

[Gordon]

Right. E-Zee is a geared motor, easier to pedal but no regen. Justin <ebikes.ca> runs his E-Zee front with only one torque arm. His X-Canada Xlyte bike probably has only one too, and it has regen.[/quote] The Ezee kit from ebikes.ca comes with a thin torque bar and a heavy tabbed torque washer. I am sure they would be sufficient on a steel frame bike. With my aluminum dropouts I decided to go a bit heavier.

 

[Dan K]

Regenerative braking?
For that, I'd want the axle locked in both directions.

Good call. I completely forgot that the kit I have coming is supposed to do regenerative braking. Based on the description provided, I'm not sure how hard or for how long, but it's still a worth concern. Both sides on the axle it is. Thanks for catching that. Still doesn’t answer my question regarding Gordon’s setup, since I don’t believe the ezee allows for regenerative braking. It is a good reason to secure mine by the axle on both sides though.

As an aside, interesting seeing you over here. I assume you are the one and only Zoot Katz from r.b.t., where I have not seen you in probably a year?

Right. E-Zee is a geared motor, easier to pedal but no regen. Justin <ebikes.ca> runs his E-Zee front with only one torque arm. His X-Canada Xlyte bike probably has only one too, and it has regen. (He charged at the top or Rogers Pass, oops!)
I'd think that as long as it securely holds the axle flats, the only consideration is how the forces affect the fork legs.
What about left and right hand threaded axles? Whether to think about them from a Swiss, Italian, French or British POV is a coin flip.

r.b.m is where I mostly post. Many of those are x-posted threads. I've not been as active on Usenet since ~'06-'08 when I started cramming here.
This is truly the dark side. Great bunch of folks and though the idea of moderation/censorship troubles me, I've seen some of its benefits. People here are civil and it rubs off on ya.

Good to see you again. i post mainly on rbt and rmd... find the signal/noise a bit much on RBM. Good call on the reverse threaded axles as well. For my application, with regen, I think both to the axles and securely mounted to the fork legs will be the ideal move. How to secure to the fork legs seems like the big question now, and will likely depend on which bike I go with. I'll figure it as it comes.

 

[Dan K]

http://www.texaselectricbikes.com/catalog/torque-electric-motors-p-228.html sells a laser cut stainless torque arm. Tougher than heck. I had to file it slightly to fit. I mean slightly...like a few 1/1000ths of an inch. Took forever. It goes under the nut.

When you install a torque arm (at least for single direction non-regen use) you should try to bias it during installation so that there's already tension in the arm countering the rotation of the axle. This will help ensure that any initial clearance between arm and axle that might have allowed a small amount of rotation is already taken up.

The thing about a torque arm is to visualize the geometry of the fit between the axle flats and the slot in the arm. It may help to sketch it out. The only thing that resists rotation are two very small points (or lines, if you want to be picky) of contact where the "corners" of the axle contact the flats of the torque arm. If any movement occurs, the contact pressure (pounds per square inch) at those points is huge because the radius is small, the torque is large, and the contact area is extremely small. Lots of pounds on a very small area. Keeping the fit tight helps by maintaining a geometrical advantage as much as possible. Even then, the contact pressure or force can be high enough to deform a soft material (corner rounding.) Once that begins, the geometrical advantage is lost, more rounding occurs, and eventually something spins.

If you can get a good tight fit with an open end wrench, great. But by definition a wrench already has clearance built into it. You might want to consider using an undersize wrench and tuning the fit with a disk sander to get it perfect.

MT

Thanks for the lesson. I was leaning toward filing a slightly smaller wrench already, you just cinched it for me. I'll use the closest undersized fit, which will probably be a domestic wrench on the metric axle flat.

 

[Dan K]

Gordon,

Thanks. Seems like a good idea. I'd use a wrench for each side, but one on the axle and one on the nut seems like a good move.

Question though. Looking at the bike from the drive side, the wheel would spin clockwise, correct? Seems if the hub/axle wanted to spin inside the nut, it would want to loosed the nut on the right (drive) side? Seems at first glance that your setup is backwards, and you'd want the left (non drive) side axle nut and the right (drive) side axle grabbed. Am I missing something?

Yes, the wheel spins clockwise but the motor torque is in the opposite direction. Think about which way the axle would spin if the wheel was held stationary.

Makes sense now, thanks for explaining that. I figured I was missing something. Appreciate the heads up before my install. Depending how the regen works and how much force it applies, I'll probably have to go neutral in my application. Well, as close to neutral as I can.