Is one torque arm enough?

[ZOMGVTEK]

Because the docbass torque arms i bought are so loose, they are basically $35 worth of scrap metal to me. I don't see how they'd work as clampers, especially when you're gluing something on, then stressing out the bond that glue ( ok, epoxy ) has made.

Did you measure the ID on them? IIRC Doc measured his 5405 at something like 9.8mm, which is a bit off from the more typical near 10mm width the torque plates were intended for.

[neptronix]

My digital caliper is outta battery.. but they are loose enough to rock around a bit on the MAC motor.. bit more snug on the golden motor, but still loose. That's all i know.

When i had the torque plates made, i made them a tad too narrow so that you could file them by hand to get 'em super super tight.

These are probably made to be tight for a crystalyte..

[psycholist]

Gotta be the poor quality epoxy.

OR ___________ . I'll leave it up to people to fill in the obvious answer on their own.

I don't believe in this glue stuff.. just does not calculate. bolt or weld it on..

Well, Being a certified welder, you can imagine what my biased opinion would be regarding this "glue". I had my doubts just like you guys. A company I worked for was testing this glue-bonding method with aluminum. I was truly shocked when I examined the results of the stress test. The aluminum tore at the parent metal adjacent to the bond, while the actual bonded section remained intact! This was ~12 years ago and I would assume the stuff available today is probably even better.

I do agree though, If you can bolt it or weld it, do it. ... dumb welder revealing his biases again.

[izeman]

i think epoxy is a really great thing. if used properly and if you got the right stuff.
there must be a reason why today many parts in cars are glued and not bolted or welded. glueing is superior to welding/bolting to some degrees and to some it's vice versa. it*s as simple as this.

[psycholist]

i think epoxy is a really great thing. if used properly and if you got the right stuff.
there must be a reason why today many parts in cars are glued and not bolted or welded. glueing is superior to welding/bolting to some degrees and to some it's vice versa. it*s as simple as this.

I totally agree with you. I believe the epoxy method could work in a torque arm application, providing the axle nuts are tight and the cutouts for the dropouts are snug. But I can also forsee problems when using regen or when there is excessive force applied to the torque plate in the same axial plane as the bond.

[auraslip]

drilling a hole with a not 100% good drill can make the plate very hot. and heat is the only way to remove epoxy. and once it got hot it's like dried jewing gum. can you pry the remaining epoxy off with a screw driver easily? if it falls of in small crumbles than you know it got too hot.

I think this was a large part of the problem. The plate got very hot. Hot enough to touch for a second, but still obviously hot enough to make the stuff fail. I didn't even think of heat being a problem even after reading completely through the long printed manual that came with the dp420.
Yes, the rest of the epoxy was easy to peel off.
I'm not going to lie, I didn't take machine shop in school, and it was totally my fault for letting drill run too fast. Up until yesterday I didn't know what feeds and speeds meant. Ironically, I was bitching about how hard docs torque arms were, but my frame is made of some type of air hardened tool steel and was actually harder to drill through than the TAs.

However, they are EXTREMELY sensitive to the materials being bonded, and prep involved. You can't glob some smoo on sanded paint and think its going to hold back 20HP. I was a bit worried when I initially noticed rather inexperienced people trying out DP420 for really critical stuff, looks like there was good reason.

Yup! Just the fact that the applicator gun is $75 should tell that this is stuff isn't for newbs. It might actually be cheaper to have someone weld these on. It would definitely be cheaper to buy the drill bits and taps to screw these in.

Because%20the%20docbass%20torque%20arms%20i%20bought%20are%20so%20loose,%20they%20are%20basically%20$35%20worth%20of%20scrap%20metal%20to%20me.

This may not be his fault. They may fit fine on some axles, but not on others. In any case, it should be up to the end user to file them down so they're tight enough for you to have to tap the axle into them with a mallet. He needs to leave a bit of extra space!


Here is what mine finished up to be. Clearances were tight, especially on the side you can't see.
I was worried that the top bolt would prevent it from clamping, but you actually don't need very much of a cut to make them clamp on the axle.

[John in CR]

Auraslip,

The drill bit was probably dead by the time you got to the bike piece. The expensive drill bits require low rpm and frequent cooling, even dipping in water a number of times for each hole extends the life tremendously. Get it hot with too much rpm and you can kill it in seconds. Typically a squeaking sound while drilling tells you the bad news.

I love epoxies and use them whenever I can, but there's just no way torque arms is an appropriate application. I did come up with one good thing to say about it. With good prep and using one on each side it's pretty unlikely that both are going to give at the same time.

The demonstration Doc did was like a 3M salesman's demo or those done to show how strong Superglue is, and I'm sure we've all seen superglue bonding failures. A more realistic test would be to bond a steel bar to aluminum, do a bunch of warming and cooling cycles, hang some weight on the bar, and then start banging on the joint with a big hammer hundreds of times to simulate each month of use. That's a lot closer to simulating what really goes on with a torque arm, especially with regen which is absolute torture with thousands of pounds of force at a 5mm radius alternating direction. Failure is all but certain.

Even simply considering the fact that a significant percentage of people will use a lesser epoxy and/or not adequately prep or cure. Almost no one appreciates the forces inside a dropout with a hubmotor until they've had a failure, and even then most don't appreciate the real risk. Spinning the axle and having to replace the motor harness is a real pain in the ass, but the real risk is if the spinning motion causes the the axle to climb right out of the dropout and suddenly the wheel is off the bike.

I got really lucky with my failure which was in the first 10ft of my first hubmotor ride. It was a front motor with a 72V20A controller. I fabbed 2 stainless steel torque arms with rectangular holes that fit the axle flats quite well. At the time I figured the 1/8th stainless on each side giving me .25" total was plenty strong. I was right that the stainless was strong enough, because it didn't deform at all. The axle torque just made it cut through the axle like butter, snapping the AL dropouts like butter. I only got lucky and avoided an asphalt face plant because it was only a couple of mph and the hose clamps securing the torque arms were able to hold the spinning axle in the slight indentation that remained at the top of the dropout.

I've used nothing less than 1/2" of steel with a tap in fit on each side since then, and regen deforms that fairly quickly. Clamping dropouts is the only solution, and I use it on every build. With Hubmonster I used 3/8" leaf spring steel to make these 20mm wide dropouts for each side. Even clamped firmly with 3/8" #8 bolts after less than 2 weeks with regen I heard the familiar clicking of rocking dropouts. It had all but disintegrated the lock washer, so now it's a hardened steel flat washer and red Loctite. If it happens again then I'll have to spring for the Norlocks.

Super V dropout for Hubmonster.JPG (18.56 KiB) Viewed 227 times

If I get looseness with this with 14mm dropouts on a 1" axle and an extra strong clamping bolt holding over a 3/4" width of axle on each side, imagine what a joke glued on 3/8" pacman torque arms that loosely fit less than 10mm flats are.

[auraslip]

The drill bit was probably dead by the time you got to the bike piece. The expensive drill bits require low rpm and frequent cooling, even dipping in water a number of times for each hole extends the life tremendously. Get it hot with too much rpm and you can kill it in seconds. Typically a squeaking sound while drilling tells you the bad news.

I know that now.... oh well.

I wonder if we haven't seen more failures of the epoxy because for most people, properly tightened nuts are strong enough?

[Ykick]

Bicycle power levels and no regen the pinch of properly torqued axle nuts does seem to be enough IMO. John's got the ideal design for high power setups though! That looks perfect while reasonably simple to execute!

I've burned enough drill bits to learn a simple rule - the harder the material, the slower RPM for the bit. Oil/water, glycol, ATF - use something to help cool the work.

[waynebergman]

My take on this is that if you have the epoxy between the flats of the torque arms and the original drop outs and this is your primary bond you may damage the epoxy by tightening the axle nuts. The compression put in place but tightening the nuts after the epoxy has set may be too great for the epoxy to take.

Doc's treatment if I remember right had a totally different method with a cut out of the original drop outs larger in diameter than the TA's so you are using the sheer strength of the epoxy with out crushing the epoxy with the force of the tightened axle nuts. Just my opinion here but I don't see anyone pointing this out yet.