How do you fix alum drop outs that have been spun?

[zombiess]

My bike isn't even running yet (was supposed to tomorrow) but they guy I had doing the mechanical work for me took a die grinder to the drop out and made it way to big. It only needed a tiny bit of clearancing, but I'm not comfortable grinding on stuff like this so I had someone else do it. I spent $700 for this bike just a few weeks ago an have ridden it less than 20miles so far and now I think I have to find someone to weld T6 aluminum and re fab the drop out from scratch. Of course this means they need a ground point so I'll also have to have it repainted after they grind off the paint for the welding.

I'm kind of at a loss right now and ready to just scrap the whole thing before it costs me more money. Is there any other way to repair this or am I just screwed now?

This project has become a complete disaster.

 

[Alan B]

Bummer.

Welding aluminum softens the temper and it requires heat treatment of the entire piece to return the strength. Then complete refinishing is required.

Perhaps a good torque arm/plate could save the day.

 

[spinningmagnets]

Perhaps add two torque arms for now. That should hold everything in place quite strongly, and even cover up any ugliness for now. If the thought of the loose drop-outs still bug you, you can research other options and then implement them when convenient?

Is this the rear drop-outs, or front? which bike model?

edit: someone beat me to it! (I type slow) here a thread that will explain with pics, and also has links to some of the common options:

http://endless-sphere.com/forums/viewtopic.php?f=1&t=11570

 

[zombiess]

Rear drop outs. I know welding will kill the temper, but how big of a deal is that on the drop out where there is a lot of material? It just needs some fill on the back side and then ground back to shape.

Bike is a Diamondback Comp Recoil.

If i used wrenches for torque arms I'd have to open up the drop out bigger in order to mount the axle sideways (flat side top and bottom) or am I missing something? Seems like it would work and I wouldn't have to worry about it in the future. I'm an electronics guy not a mechanical guy.

 

[MadRhino]

It can be fixed without soldering, if it's big enough. A dropout can also be cut wide enough to fit an insert. Or else, a torque arm can be made to cover and bolt on the dropout. If the bike is a full suspension, the swingarm might be available... You'll find a solution and get it running, we all do. :wink:

A grinder can do the rough work, but precision is achieved with a file, especially with alu.

 

[zombiess]

Ok, just grabbed a 10mm Craftsman wrench out of the toolbox and tested it. It's going to work great with just a little bit more grinding. Should solve the problem, but the bike will never go back to being "normal" again. I think I'll be OK with that once it's up and running on the motor.

I'm glad I posted on here, you guys gave me some great ideas. The wrenches is some out of the box thinking.

 

[MadRhino]

...the bike will never go back to being "normal" again.

It's not likely that you'll want it back to its original state, but if you do, I just asked a friend and the swingarm is available for all this series.

 

[zombiess]

...the bike will never go back to being "normal" again.

It's not likely that you'll want it back to its original state, but if you do, I just asked a friend and the swingarm is available for all this series.

After riding a mild 8 miles today, I'm not much of a peddler so I'll probably be just fine with some sort of torque arm. I'm just trying to keep this bike from looking like it was put together by a hick, especially since I just spent all this money on it.

I'll be talking to my friends with fab skills tomorrow, really want to get this thing going. Electronics and wiring are 10x easier than mechanical things for me. All my friends who fab lack electronics/wiring skills so it tends to work out pretty good in the end.

 

[MadRhino]

I'm just trying to keep this bike from looking like it was put together by a hick, especially since I just spent all this money on it.

Don't worry, people will not look at your dropouts.

Can you see mine? They are ugly, though.

 

[zombiess]

I'm just trying to keep this bike from looking like it was put together by a hick, especially since I just spent all this money on it.

Don't worry, people will not look at your dropouts.

Can you see mine? They are ugly, though.

Nope, your bike looks good. What's that white stuff on the ground :lol: It was a nice 70F/21C today here in Vegas. I'm amazed at how many people on here ride their bikes in the snow/rain. I'm too big of a wuss for that.

I'm so excited to get this bike running, especially after watching all the videos of people riding the higher voltage bikes. After I have it running I also plan on doing some development dealing with the batteries. Got a few ideas on how to simplify LiPo charging and how to build a fairly low cost programmable BMS system.

 

[spinningmagnets]

The wrench was only the first post in that thread, but still good in a pinch! ebikes.ca, ampedbikes.com, and ebikekit.com all sell good torque arms that look good.

 

[neptronix]

A torque plate will solve this problem. It is like adding a steel dropout to the rear of the bike.

Please post shots of your rear dropout. Maybe you have a rear dropout design that will allow for this, maybe you won't.

 

[amberwolf]

EDIT: ignore the below; I missed the part about it being a rear dropout. But the torque plate would work the same way.


Depending on the dropout design, you could also simply add a short steel tube over the end of each fork leg with dropouts welded to the ends of the tubes. I don't recall who did that here on ES, but it looked like it would work quite well, and if the tubes are painted to match the bike, nothing need be changed on the bike itself. You don't even have to weld the tubes to the bike. Perhaps epoxy would be a good idea.

 

[zombiess]

The wrench was only the first post in that thread, but still good in a pinch! ebikes.ca, ampedbikes.com, and ebikekit.com all sell good torque arms that look good.

I already had my roommate look at it tonight and he came up with a good idea since he fabricates. Got another friend who is a frabricator coming by tomorrow to take a look at it. I have access to plenty of stainless steel scraps at work for free since we have a stainless steel sheet metal fab shop there.

It's just patience now (i'm not so good at that part).

Big thanks to everyone on this forum, hopefully I can contribute some help in the future once I get more involved with ebikes.

 

[TheKraftyRhino]

I have used HTS-200 http://aluminumrepair.com to repair drop outs in the past. Have also used it to make frame and head tube repairs even used it to rethread a crank that striped a peddle. There cheapest box is around $60 but I have had my box for 2 years and still have over half or it left. if you repair a drop out you can even build it up some more to make it thicker. The dropouts on my Fathers bike I built him a year ago I installed a torque arm and then bonded it to the frame.Built up the frame with the Dropouts to about 3/4 " and even flared the remaining part of the torque arm so it looks like its part of the frame. Going to take some file work and some practice. It only took me 4 rods to get it down on a spare frame.

 

[dogman dan]

The best Idea is a good well fabricated torque plate. there is too much variation in design of rear dropouts for a universal device to be made, like the front torque arms. The best designs for torque plates often use some kind of V shape that attaches to both stays, or a triangle that fits between both stays and attaches to both. Because of alignment issues, you may need to bend the steel, or perhaps weld arms to the plate part.

Lots of good examples, but all buried in the pics sections in build threads.

As for just tightening up the dropouts, I like the idea of widening them a bit more, allowing a steel shim to be used. We all end up grinding or filing dropouts, often deeper rather than much wider. Slow and carefull with a hand file is the best.

 

[Alan B]

Justin of ebikes.ca did a lot of testing (documented in a thread here on ES) and found that 1/8" was a bit thin for the torque arm/plate. He recommended 5mm or 3/16" material. Theirs are the curved units in the photo on the first page of this thread.

A small plate that picks up all the mounting holes in the dropout would seem to be a good way to go. 5mm or 3/16 steel would be ideal.

In lieu of that I've bought two of the ebikes.ca curved units as shown on the first page of this thread. On my setup there was not room for the nut on the bolt where the torque arm and strut meet, so I made my own struts. Instead of a slot I made the holes in the right place and threaded the one end. The holes are spaced just right and the right size so there is no free play. Simple to do, just drill two holes in a 1/8 by 1/2" piece of material at the right spacing, tap one and ream the other until it just fits.

The stress on the torque arm in the "D" hole is the greatest. The torque strut stress is lower. I calculated under 10K psi there. So I used 6061-T6 aluminum for the struts. The arm Justin makes is stainless.

 

[John in CR]

I've yet to see anyone really appreciate the forces involved until they've spun an axle, so don't rely on what your fabricator buddy thinks. The entire motive force of the bike is transferred to the bike at the dropout and the grip of the axle nuts. Thing of how hard your bike can pull during acceleration. That force is transferred by the wheel to the ground. On a 26" wheel the pull you feel is at a radius of 330mm. At the dropout the force is taking place at a radius of only about 5.5mm.

Another way of looking at it is taking a 10mm wrench, putting a cheater pipe on it to extend the handle to 13", and pulling on it as hard as your bike pulls. Now try it with wrench made out of aluminum. Heat treated or not, that aluminum wrench is going to quickly fail. Your dropout is that wrench, and aluminum is too soft, and if hardened through heat treatment it's too brittle. They just aren't designed for that twisting force. They're designed to take forces pushing the axle upward, and in that direction the aluminum is always at least an inch thick, so it works great for the designed use.

Having that axle wedged tightly or clamped between 2 nice thick pieces of steel is the only way to go. Some stopgap methods work at moderate power, but high power no. The too thin store bought torque arms have proven to fail, so forget that route. You have a buddy to do it so have him make 2 out of steel, and I'd go at least 1/4", that fit your dropout area and attach to the alloy of the bike at a far greater radius where the forces are many times lower.

 

[Alan B]

Just to add some numbers,

The calcs I did a few days ago were for the 9C 9x7 at 65A where it develops 70nm of torque (based on Justin's measurements). (Currents above this level will increase torque but at lower efficiency). This is about 50 pounds of thrust at 13", so 650 pounds at 1" which is where the end of the steel torque arm ends. And about 20 times as much at 5.5mm.

For those that put more current into their motors or use stronger motors the torque will be even higher.

The motor shaft is usually soft steel so using hard steel on the torque arm doesn't help, it needs to have enough thickness to support an adequate area of the motor shaft flats.

 

[John in CR]

Just to add some numbers,

The calcs I did a few days ago were for the 9C 9x7 at 65A where it develops 70nm of torque (based on Justin's measurements). (Currents above this level will increase torque but at lower efficiency). This is about 50 pounds of thrust at 13", so 650 pounds at 1" which is where the end of the steel torque arm ends. And about 20 times as much at 5.5mm.

For those that put more current into their motors or use stronger motors the torque will be even higher.

The motor shaft is usually soft steel so using hard steel on the torque arm doesn't help, it needs to have enough thickness to support an adequate area of the motor shaft flats.

Alan kinda lost me, but 50lbs sounds right, so that's 3000 foot pounds of torque at the axle flats. It's really a tremendous amount of twisting force, enough so that it's surprising we don't mess up more axles even with torque arms. I tried double torque arms with 1/8 stainless. It was a front hub running only 2kw peak, and it snapped the alloy dropouts and the torque arms cut the axle like butter. That was the first 10ft of my first hub motor ride. Lucky the torque arms were attached well enough to keep the wheel on the bike. Otherwise my ebike career could have been the shortest in history. Overkill is my motto now.

 

[zombiess]

Ordered up 2 torque arms from amped bikes. Also ordered some HT-2000. Going to have my friend use the HT2000 to fill in the gap for more support. He's also been wanting to try this stuff to see if it really works. He'll shape the new torque arms to match the contour of my bike so it will look decent as well. Since he welds and fabricates for a living I'm sure he'll do a great job. He completely understood the forces involved when I told him how much torque this thing is going to make.

Hopefully next weekend I'll get to make my first ride.

 

[Hillhater]

.....so that's 3000 foot pounds of torque at the axle flats. .

3000 ft lbs ....OK , im in, where can i buy that motor, ? ...I have the cash ready now.

PS..John, check your units. :wink:

 

[John in CR]

.....so that's 3000 foot pounds of torque at the axle flats. .

3000 ft lbs ....OK , im in, where can i buy that motor, ? ...I have the cash ready now.

PS..John, check your units. :wink:

Check your radius. 50lbs with that 13" (300mm) lever is 3000lbs at 5.5mm. My bike has more pull than that, though at a 10" radius. The number is good, and everyone underestimates it till they're looking at an axle with a portion no longer having a flat, broken bike dropouts, and a wiring harness to replace. A lot of times the controller is blown in the process as well. That why the store bought stuff is a joke, and for low power bikes only. Think of how thick a wrench you would want for cranking down a nut with a 10mm wrench with 50lbs of pull using a 13" cheater pipe. That thickness on each side is a good starting point. Imagine using a store bought torque arm as a 10mm wrench...They're all a joke and marginal for a legal ebike in Australia at 200W.

The motor is trying to climb right out of the dropouts, and a wheel coming off is an unacceptable catastrophic failure, so my attitude is that the torquearm/dropout isn't overkill until the axle would have to break first. It's a quite simple result to achieve.

 

[LI-ghtcycle]

My bike isn't even running yet (was supposed to tomorrow) but they guy I had doing the mechanical work for me took a die grinder to the drop out and made it way to big. It only needed a tiny bit of clearancing, but I'm not comfortable grinding on stuff like this so I had someone else do it. I spent $700 for this bike just a few weeks ago an have ridden it less than 20miles so far and now I think I have to find someone to weld T6 aluminum and re fab the drop out from scratch. Of course this means they need a ground point so I'll also have to have it repainted after they grind off the paint for the welding.

I'm kind of at a loss right now and ready to just scrap the whole thing before it costs me more money. Is there any other way to repair this or am I just screwed now?

This project has become a complete disaster.

Sorry if this is redundant, but if it was done by a shop, I would have them buy you a new frame! That is unbelievable that anyone with mechanical knowledge would just grind things out with out matching things to the axle going in. If it was done by a friend not knowing better, chalk it up to a lesson learned, but man I would be demanding a replacement otherwise! There is no excuse for anyone doing that and calling themselves a "mechanic".

 

[Rassy]

I hate to be negative, and don't mean to give the OP a hard time, but after following this thread for a few days, no one has mentioned the real problem. Namely, why would anyone buy a new aluminum bike as a platform for a DIY E-bike? If you studied the forum at all you would soon learn that you should stay away from aluminum dropouts for hub motors.

Thanks to the OP for posting his problems as he may help prevent others from making the same mistake.

I would like to wish zombiess the best in coming up with a good solution.