Torque arm for Schwinn S-series bikes

[lazarus2405]

That's the point. I have no fab skills or tools, so I'm designing one with help from the folks here so fit specifically on my S. Then, I'll take the schematic somewhere to be made. Since the S-series is so popular here, I'll upload the schematic here for anyone else to use, should they choose. That way, you could just print it out and take it to a shop.

So, latest version:



It's full size, to be fit onto one page.

 

[disadvantage]

Lazarus, you need to specify the thread pitch in your drawing, so the machine shop knows what to do.

The word "threaded" doesn't say enough. Do you want 1/4-20 or 1/4-28 threaded holes?

20 tpi (threads per inch) is coarse, and 28 is fine threaded. I recommend 28 to make the clamping force stronger.

In my torque arm drawing, I wrote "M5x0.8" by each threaded hole. M5 specifies the diameter, and 0.8 is the distance in mm between each thread.

 

[lazarus2405]

Thanks for the help. I didn't know what pitch would be suitable, so i figured I'd just ask them.

So, edit made:



Anything else?

 

[docnjoj]

Actually, the Poweridestore torque arm fits quite nicely on my rear suspension of my modified TRicruiser. The key is to have horizontal dropouts.
David

 

[marty]

Do not like clamp style torque arms because there are 2 things we need to worry about:
1. Motor axle turning
2. Axle coming loose from bike frame.

Will try to explain.... If you first clamp torque are to axle? Axle nut will not tighten properly. If you first tighten axle nut? Clamp style torque arm will not tighten properly.

Think a better design torque arm is like wrench picture on first page of this topic. getadirtbike is selling these custom made for $50 a pair. Go here to see http://endless-sphere.com/forums/viewtopic.php?f=3&t=3057 Or steel plate cut on a CNC Laser Cutting machine. Either way - The double D shaped hole needs to fit tight over axle. Same as a wrench on a bolt.

Look at http://www.emachineshop.com Trace the flat drop out shape on your frame. Are there disk brake mount holes to attach to? Draw with the free program download from emachineshop.com I know nothing about emachineshop.com There are also local CNC Laser Cutting places. Look in the phone book. If you don't trust your drawing skills? Take bike frame and motor to local CNC shop and let then design and build. CNC = computer numerical control

Its important for fabrication shop to have CNC Laser Cutting machine. Do not pay a welder $75 a hour to file a hole for you. If you enjoy spending hours with files? Make your own double D shape hole.

 

[PerplexArt]

I'm in the process of building a torque arm for my Specialized Rockhopper.
I have a CNC shop where I can make couple extra torque arm for you guys if I know your bike's dimensions.

 

[disadvantage]

Will try to explain.... If you first clamp torque are to axle? Axle nut will not tighten properly. If you first tighten axle nut? Clamp style torque arm will not tighten properly.

No, both the axle nuts and the clamping screws force the frame, axle, and torque arm together. You can help this action by tightening the nuts and screws a few turns each until all are tight.

I actually built a clamping torque arm, and rode safely all last season with it. See my build thread for details.

The problem with a cut-hole torque arm is: the hole has to have some slack or you can't assemble the arm on to the axle. But with that slack, there is some room for the axle to twist back and forth, round the carefully-shaped hole, and eventually twist the axle clear around.

The clamp allows ample slack for assembly, yet eliminates it with tightening.

 

[lazarus2405]

Jonathan,

This is what hub motors do to front dropouts:

With a mid-size motor and torque arms in the front, it's pretty safe. But Something torquey like a Puma or x5...Well, you get the idea.

 

[PerplexArt]

Holly Cow! lazarus2405, that's 8mm thick aluminum that your motor just ripped through. And I though with that thickness it should handle it. Yikes!
I found that the dropout of S25/S40/S60 are all the same. What's troubling is the distance of the axle to the frame tubing. I can modify my posted design to handle accelerated torque but not braking. To do it right it will have to be specifically design for the Schwinn instead a generic design that originally planed of.

I finished the conceptual design of the torque arm for typical mtnbk hardtail & recreational hybrids. This will not work with full suspension mtnbk.
The main torque arm is 6"x2"x1" 304SS milled down so the main force transfer thickness is 1/4"x2"
I plan of using aluminum pad instead of steel where it actually make the contact between the torque arm and the frame aluminum tubing.

For a 72V/50A/26"/100% throttle there's about 80 lbf*ft. By using this torque arm it would spread the torque of ~ 33 lbf*ft across the 2" aluminum pad.
This design should handle both the accelerating torque and braking torque.

What's really critical with this design is the reliance on the 15* angle of the bottom tubing and the milled slot M14 axle. If this angle is off then all that's preventing the rotation is the 3/8-24 screw.
I might have to change the bottom pad attachment design so there two bolt connection (vs 1 currently). The far bolt for compression while the nearer one to the axle will be used for guiding.

I looked up Clyte x5 dimension their axle is M14 with a 10mm chord-chord mill slot. I was not able to get the exact dimension of the BMC motor.
You guys with BMC motor out there, can you let me know their axle thread size. Is it full form M10 or milled slot M14 or other.
I'm pretty sure the 10mm dropout (front or rear) is standard so if their axle bolt is any larger than 10mm it have to be milled down.


YouTube Assembly Video
http://www.youtube.com/watch?v=m3pdd3D5F5I

 

[Link]

Holly Cow! lazarus2405, that's 8mm thick aluminum that your motor just ripped through. And I though with that thickness it should handle it. Yikes!

No, that was the front fork. He ripped through 6mm of steel .

 

[PerplexArt]

ah my bad for not reading carefully.

 

[lazarus2405]

Agh, pronoun confusion. The above fellow, whose pic I posted of his dead front drop was 6mm steel. It snapped off, with no surrounding material to which to transfer the force. Regardless I ripped through 8mm 6000-series aluminum.

Yep, the angle is what makes it so difficult to make a one-size-fits-all torque arm. A real pain.

To do it right it will have to be specifically design for the Schwinn instead a generic design that originally planed of.

Well now, that's the point. A number of us here run the Schwinn S-series, so a torque arm specifically designed for it would be a boon to the community. Especially if it was good for braking torque, even if it was through the use of clamps or ties.

For a 72V/50A/26"/100% throttle there's about 80 lbf*ft.

What motor, and where are you getting the numbers? They don't look far off, though. Using the hub motor simulator at ebikes.ca, I figure the max torque I need to be able to withstand is ~150ft*lbs. That's with all units in anglo-american, a 5303 motor, 112v, and 100a, and a 24" wheel for a 12" lever arm, making the lbs thrust equal to ft*lbs torque.

A couple weeks ago, I ran numbers on braking torque, and put the numbers in the second or third post. I think the maximum conceivable braking torque was ~150 ft*lbs, corresponding to a deceleration of 14mph/second. Throw you off your handlebars, that will.

As far as I know, the BMC hub motors' axles are of the exact same dimensions as the clyte ones, perhaps the only standard in the industry. Disadvantage can verify that.

 

[CGameProgrammer]

The problem with torque arms is that everybody's rear dropouts are at different angles, with different frame tubing around them, etc... it's almost mandatory that everyone design their own arm for their particular bike, except of course when several people have the same bike (like the Schwinn S).

I'm in the middle of building my torque arms but I had to take into account the exact angle of the dropout, the location of it relative to the bottom tube of the swingarm (which was completely different on the left side vs the right), the angle of the bend of that tube (again, different on the left vs the right), and taking into account obstacles like the tubes near the dropout which stick out, or the derailleur mount which is very near the right-side dropout.

PerplexArt, the problem with a solid arm is it doesn't clamp onto the axle and it doesn't clamp onto the swingarm. I think hose clamps are a good idea for the swing-arm because you tighten them to fit, and the part around the dropout should ideally be two pieces secured with bolts like others have mentioned. I've attached an MSPaint of one such method; the red lines are bolts of some sort. A properly tight one-piece arm would be almost impossible to slide over the axle, which is why people have suggested this.

 

[PerplexArt]

Here's the one for the Schwinn S-XX.

The parts that actually engage the axle is stainless steel while everything else is aircraft aluminum.
If we don't have to deal with regen torque the solution is much simpler.

It's a challenging solution to deal with multiple off axis bends and attempting to align everything properly in their plane.
I did leave the trailer hitch 12mm hole like lazarus2405 requested/

My angle measurements were quite different from the few drawing I've seen. Don't know which is right but we will find out soon next week when I have sometime to make the prototype.

Now a quick sanity check. Do you really need the torque arm? The front dropouts of the S-XX bikes are 6.5mm while the rear is a nice beefy 10mm. Normally through the back you don't endure the same road "punishment" as the front.

Another things, did you guys ever weight your bike? My friend told me that the stock bike not that light.
Front wheel set - 5 lbs
Rear wheel set - 6.5 lbs
Frame & all - 21 lbs

This thing is a whooping 41 lbs.

 

[lazarus2405]

That, sir, is beautiful. Beautiful.

I would place your measurements in greater esteem than my crude ones. Also, when I worked out the axle flat angle, it was to a tolerance of perhaps a dozen degrees, since my drops are (now) round.

Do we really need the torque arm? Well, I have a dead controller and motor in need of repair as evidence that, at least, I do. With torque both ways, on a part designed to only handle compression, the sharp axle threads can eat into the aluminium, until it shears it round.

My damage: