Bent the Doc Bass torque arms

[themadhatter106]

Ok, Ok, to be fair I had to cut a chunk out of both of them so my rack mount would still be accessible. They lasted for a few months at 6 KW before they let the axle twist. I snapped at least 1 hall wire in the process too.

Disc side:



Chain Side:



I need to completely redo both sides in a way which is stronger. I probably could have cut a little less off (maybe 1/8") in making room for the rack mount but that isn't a whole lot stronger.

What I really need are bolts on both sides of the torque arm. However, the holes in the torque arm are in the wrong place and too big of a hole on the other side to bolt down. I might be able to fill the hole with a weld. I think I want to make torque plates for both sides. I have an extra set of torque arms but I don't think that recutting them a bit closer would help that much. I can use my hydraulic press to push the old torque arm back together and then weld it down to some plate. I also really don't like having those big nuts sticking out on the derailleur side since it makes it much more difficult to tighten it with a wrench. I'd hate to drill more holes in my dropouts though. Any ideas?

 

[John in CR]

Did you really think they could do their job after cutting off so much material in that area?

If you were able to cut material off of his torque plates then you obviously have the tools to simply cut your own custom torque arms. This time forget the glue and make proper clamping torque arms. Then less material is required at the root of the slots, because the clamping end prevents spreading too. That should make your rack easier to fit. I'd make the bolt for the rack part of the torque arm attachment to the frame. Keep in mind there's no need to go with such a hard steel that's nearly impossible to drill. Harder than the axle means the axle gets damaged first, and they're a hell of a lot harder to replace than torque arms. With clamping type torque arms even mild steel in a good thickness work just fine, and much easier to work.

 

[KalSteve]

I suggest you lower your exposure to mercury and undergo a chelation program. Once sanity returns I am sure you will see what you have done.

 

[spinningmagnets]

If you are willing to do this much custom work, mount the rack supports in a different way. The rack supports were never in any danger. If your battery is on a rear rack, and you are using 6kw...get a another bike (new or used) specifically for converting to electric. I recommend a triangle battery, and if you hadn't cut out some of the DocBass TAs, they would take 10kw for the rest of your life.

 

[themadhatter106]

I suggest you lower your exposure to mercury and undergo a chelation program. Once sanity returns I am sure you will see what you have done.

Thanks for your very informative post. Your knowledge seems quite vast!

If you are willing to do this much custom work, mount the rack supports in a different way. The rack supports were never in any danger. If your battery is on a rear rack, and you are using 6kw...get a another bike (new or used) specifically for converting to electric. I recommend a triangle battery, and if you hadn't cut out some of the DocBass TAs, they would take 10kw for the rest of your life.

I might be able to move the attachment point for my rack up a bit more. Then maybe I can use a new pair of torque arms and weld a tab onto them where the rack could mount.

The only reason I don't like clamping torque arms is that it seems to make it more inconvenient to change a tire. When I get a flat on the way to work I want to be able to change my tire as quickly as possible.

 

[John in CR]

If you are willing to do this much custom work, mount the rack supports in a different way. The rack supports were never in any danger. If your battery is on a rear rack, and you are using 6kw...get a another bike (new or used) specifically for converting to electric. I recommend a triangle battery, and if you hadn't cut out some of the DocBass TAs, they would take 10kw for the rest of your life.

Not 10kw of power if it's at just a few rpm. It's unlikely that any part of any of our bikes could handle even 1kw at 1rpm. When are you more experienced guys going to stop using power and torque interchangeably? Torque is what matters when it comes to torque arms, so the measurement is in Nm or ft-lbs, and at the tiny radius of a hubmotor axle applying force to a dropout the forces are tremendous. Let's say a motor is making 50ft*lbs of torque, fairly tame torque for a high power rig. That torque is leveraged at an average radius of say 1/4" for simplicity. 50ft*lbsx12"/.25"= 2400lbs of force where the axle contacts the dropout.

Power on the other hand is equal to torque x rpm, so at higher rpm a motor could be making lots of power at relatively low torque. I run my ebike at extreme power and to make take-offs comfortable and safe I set my controllers to reduce low speed torque, but that has exactly zero effect on my bike's power. I could easily double the maximum torque on launches without changing maximum power one iota.

Knowledge of our motors' torque is simple to estimate, so there's no reason to avoid talking in terms of torque. If you know the Kv, then you also know the torque constant, Kt, because they have a direct inverse relationship. Kt in Nm per amp of current = 9.549 / Kv in rpm/volt. To make it even easier, the common ebike winding having at Kv of about 9rpm/v gives those motors a torque constant of about 1 Nm/amp of motor current. FWIW one ft*lb = 1.36 Nm.

 

[John in CR]

The only reason I don't like clamping torque arms is that it seems to make it more inconvenient to change a tire. When I get a flat on the way to work I want to be able to change my tire as quickly as possible.

At 6kw of peak input it's no wonder you're having to worry about changing flats. I'd suggest using moped or moto tire and make flats a thing of the past. I've picked up a nail or screw in the tire a couple of times while I was out, and both times I was able to ride home on the flat before fixing them.

Even if you don't improve your tires, removing an allen head bolt from a tapped clamping dropout just takes a handful of seconds. Compare that to the hours of repairs you have now.

If you have a steel bike, then clamping dropouts is the way to go. Then you can even dump the axle nuts and pick up some flat changing time that way. Plus you don't have to lug around a tool big enough to remove them.

 

[nutnspecial]

Hi, I would agree in new arms and moving the rack mounts. Pretty :lol: to remove that much material instead, but everybody makes mistakes, and if this is the same build you did over 4 years ago (sig)? they held up until the 6kw. Surprised you even tried that on those tho.

 

[999zip999]

DocBass has a guarantee for life you didn't kill it ? Drop him a line.
I think it was a wild beaver.

 

[Doctorbass]

LOL..,

nothing to add here.... everything has been said already 8)

in this transformed state These are no more considered Dr Bass torque arms after all... so... they simply break! just Normal....

I sold close to 550set (1000+T-A) of these and none of these ever break... In fact some really tried to break these and they bent their axel and T-A remain intact

Please leave this post as is themadhatter106... This will show a great exemple of what to NOT do :wink:

Doc

 

[Samd]

I suggest you lower your exposure to mercury and undergo a chelation program. Once sanity returns I am sure you will see what you have done.

This wins today's internet.

 

[999zip999]

You have ground it down to the point is now a hinge you just need to put a door on the other side of it.

 

[jpgey]

Are we in The Ebiker Joke thread ?

 

[grindz145]

I mean, somebody had to do it

 

[MadRhino]

If you were able to cut material off of his torque plates then you obviously have the tools to simply cut your own custom torque arms.

They are f*'n hard to drill and cut, way overkill material. But no material is strong enough, after there is not enough left of it. Use 1/4 mild steel plate, cut a pair of custom tru-axle bolt-on drop outs including disc, tensioner, mud guard and rack mount holes... In less time that you did mod those.

 

[Chalo]

You see? This is why we can't have nice things.

And it's why sub-20 mph e-bikes are a good idea for many of us.

 

[longwise_suck]

just an idea but whey didnt you make a mounting on the torqe arm for the rack

 

[themadhatter106]

You see? This is why we can't have nice things.

And it's why sub-20 mph e-bikes are a good idea for many of us.

Someone needs to entertain you guys with foolish mistakes :lol: .

OK after a lot of work I completely redid my torque arms and also fixed my motor. I made a torque plate with everything I wanted, a rack mount, trailer hitch, and disc caliper mount. Custom caliper location in the same position as the front caliper because the torque arm and rack block the normal mounting location.



There is just one problem. When I use my brake the axle has a tendency to slip out of the dropout on the disc side. This happened on the first test but after I fixed it and really tightened the nuts down real good I couldn't get it to happen again. Still, I want to fix it so that even if my nuts loosen up the axle will not come out when I use my rear brake :lol: .

I am thinking of welding on 1/4" keystock on both sides of the torque arm opening to stop the axle from slipping out if the nuts get loose.



Is there a better way?

 

[themadhatter106]

I guess this is the way I will do it. I welded on the keystock like I planned to with some nice meaty welds.



I don't think the axle will slip out even if the nut loosens up. Its too early to tell but I think that if the nut does loosen up the axle might shift 0.5 mm or so and mess up the disc brake caliper alignment. This would be annoying because I would need to stop my bike, fix the axle and re tighten the nut. I guess I'll just need to periodically torque down on the axle nuts to make sure they are always tight.

I bought a 21mm wrench so I don't have to use an adjustable wrench any more. I hope this will allow me to torque down the nuts tighter without having the wrench slip and round the edges of the nut like what would occasionally happen with the adjustable.