Idea for front forks torque arms.

[ynot]

Faced with trying to design torque arms for for my newly installed Jumper front hub motor, and faced with the fact that there is not enough spindle length to fit anything inside the wheel nuts,
I came up with this simple idea, and would like to know if it will work or not and with reasons why not.

Simply weld an 18mm socket to a bar about 12" long by 3/8" by 1" bar in such a way that the bar fits tightly against the forks, this probably means grinding the back off the socket so that it is the right width to fit snug on the nut and aligns along the forks.
The torque arm would look like a box end 18mm wrench. clamped to the forks it would strengthen the forks which of course addresses one of the major objections to front wheel hub motors.

The immediate reaction I get is people think its purpose is to stop the spindle nuts loosening, while it does do that the main purpose is to stop the spindle nut from moving fore and aft or up and down.
IMO the pro's are
works with and adds to the stability of the torqued spindle nut, and it's ability to stop the spindle from rocking.
Does not take up space on a spindle that is too short.
Strengthen the fork legs,
Eliminates the need to carry a wrench for the spindle nuts :-}

Repeat that the main purpose is not to stop the nuts backing off, that can be done with thread locker, or nylock nuts, altho on my bike I ground down the nut so that the mylon engaged with the thread with this torque arm that ceases to be important.

 

[Voltron]

It's not the worst idea ever. Mine that were along those lines went a lot of miles before I got better ones, but did eventually let the axle spin once as the wrench tips slowly spread, , and had to do wire repair. Full socket around there would probably stop that.

But I would def secure the bar to the fork leg with hose clamps or something, instead of only butted up against them, just for worst case of the fork tips breaking still.
A rear motor will mostly just spin in place, but fronts can really get separated from the bike.

 

[ynot]

I thought about using a 10mm open ended on the spindle flats, but the wrench I tried was a sloppy fit. If there was space for it it would make an enhanced C washer to clear the wiring, I see that yours is inside the nut and on my bike there just is not enough thread length.
For my freighter trike build, machined clamping dropouts but on the bicycle it is not practical.

 

[Voltron]

Yes, had enough length, but socket on the outside should work fine.

Ended up doing milled ones also after the wrenches. Mine was a 12mm axle in a 14mm dropout, hence the extra flange...

 

[dogman dan]

At least your idea would tend to keep the wheel in the fork. But if its going to spin, its still going to break an aluminum fork.

Wrong fork for that motor, or wrong motor for that fork, no solution to that. Change one or the other, so a thin torque arm can fit. Or you can weld an improvement onto a steel fork.

 

[ynot]

@dogman Dan

Surely the torque put on the spindle nut should be sufficient to stop the spin, and we're holding the nut so that it cannot move.
If I am wrong would much sooner find out now, so will defend my idea, but would rather be shown wrong than trust a sketchy idea.

 

[Voltron]

It actually seems better than the alternative, I've had torque arms inside the nuts have just enough slop that the axle wiggles just enough to keep trying to loosen the nuts, and one can get complacent about checking them until it spins. (Guess how I know that? )

But you definitely should be planning around worst case, full shearing of the fork tips, will the motor still stay hooked to the ends of the fork legs kinda thing.....

Little stuff like the dropout faces not being exactly parallel, so that the nuts deform them as they're tightened, tiny slop in the fit that didn't seem bad at first, etc, can really change things.

But if its medium power, no regen, not doing off-road jumps,
no big landings with the throttle still full on shock loading the torque on landing etc, it'll prob be ok.
Esp if you attach the bars to the sliders nice and solid.
And do both sides probably.
U bolts maybe, or multiple hose clamps, esp if you make notches in the bars to capture them maybe...

 

[Voltron]

P.s.

Saw you were a trike guy ... That was my full suspension with a differential in the rear axle party trike that my cat is sleeping under in that one picture lol.

 

[ynot]

P.s.

Saw you were a trike guy ... That was my full suspension with a differential in the rear axle party trike that my cat is sleeping under in that one picture lol.

Yep am building a freighter trike and the displays for it are in, will go and pick them up tomorrow, hopefully all we will have to do then is splice in the throttle to both controllers, and mount the displays and give her a whirl, will have to go easy because the trike only has a coaster brake until I machine the mounts for the disk brake calipers.

Bought her Ladyship a new 500 watt fat tire trike for xmas which she is getting more comfortable with each time she goes out, she is not ready to use her trike to go to the post office yet but that is coming.

Back to the topic, it is my impression that the drop outs on the forks breaking off is because the spindle rotates and forces the 'ear' of the dropout to be forced off, as the spindle flats rotate and cause the extra 2mm of spindle to press on the 'ear' (lug?). Is that an accurate assessment of what happened to the fork in the picture?

 

[Voltron]

Yes.
But it can def be contributed to by weird clamping forces from the nuts and axles faces, or slop in the fit.

 

[motomech]

Not sure how installing TA'a on a frt. mount suddenly got so complicated, 100's, if not 1000's of frt. mounts have been done. If the fork drop-out width is 100 mm's, there IS space to to put on the TA inside the axle nut.
You should be looking at one , or better, two from the TA selection @ Ebikes CA. You got four styles to choose from and I've used all. One or two of the styles will work. I've used the V4 to go over a caliper when nothing other than fabrication would work. Look at the angle relationship between the axle slot and how the arm will lay. V3 is a really delux piece, but probably one of the other two will work. Grin's TA's are the best and don't waste your time on anything else, especially the Ebay junk. This stuff is not cheap but a frt. mount is no place to skimp, especially when the donor bike has an alloy fork.
Use the proper ebike hardware, I believe the axle nuts have a slight interference fit on the threads and if the forks have "lawyer's lips", there is no substitute for the correct washers/spacers. Use the c-type or inside square inside hole ones and If you only have the "tab" type, grind the tabs off before using. They should lay flush inside the circle formed by the lawyers lips so everything is flat when the nuts are torqued down..
Use lot's of med. strenght Loctite on the treads and don't clean it the next time you have the wheel off, and over time a nice grunge builds up for nut security.
How much torque? Enough they don't come loose, but not so much as to strip the threads. It doesn't have to be "jump on the wrench" tight. And even if exposed treads that are available are only enough to get the nut on half way, that's enough. Ck tightness after the first couple of rides.
One or two? One is probably enough, especially if the power is kept low, but I always use two if two can be fitted. Gd. insurance.
note; I see Grin has the tab'type spacers, but they don't list the nuts. I suspect if you request a pr. they could come up w/ them.
https://ebikes.ca/product-info/grin-products/torque-arms.html

 

[dogman dan]

Hard to say what his real problem is. I wonder why the axle is not long enough to put a good TA on one side at least. Two TA's are best for alloy suspension forks.

And nobody said a shitty, loose TA works, it doesn't. You want a tight TA, or its just decoration. If loose, it rocks back in forth in the loose slot, unscrewing the nut.

But nut pressure can be enough to keep the axle from rotating, till it gets loose, when it wrecks the forks, or the axle flats, or both. Nut pressure alone can easily crack an alloy fork, if the install requires a c washer and that is omitted. I would venture to say that not using a C washer to fill the lawyer lip cup on the end of steel or alloy forks is the reason for the majority of broken forks and loose wheels that cut up the wiring on hub motors.

Holding that nut should help it not loosen, unless it loosens for the reasons I just talked about. A mis fit washer deforming, or the washer and nut deforming the fork will loosen the nut faster than any other fault.

 

[ynot]

Thanks for all the input.
Am thinking that if each spindle nut is tightened to a higher value than the max MN of the motor, and held fast in position, you have a safety factor of 100%.
Granted some nuts are machined to rather sloppy standards, but NM's is NM's and the spindles should be hardened enough to handle the strain of tightening. Some socket wrench's also are sloppy fits.
For me the motor/fork suitability involves my available finances so is what it is, but believe me that after a rather long life of building and operating machines, there just aint no room on the spindle, for a conventional torque arm unless I give up some thread length penetration into the nut, which is already shorter than required in structural steel assembly.
Wish I had the resources to test large series of forks, to do an engineering evaluation, buuuut.

 

[Chalo]

Am thinking that if each spindle nut is tightened to a higher value than the max MN of the motor, and held fast in position, you have a safety factor of 100%.

Nope. First of all, tool torque doesn't equal fastener torque, and fastener torque doesn't equal thread torque. Friction complicates these things. Holding friction changes when you load up the bike and ride over things, too.

Second, no material is infinitely stiff, and localized deformation can cause mechanical fits to squirm loose a little at a time at less than their break-free torque. Think of it as all being made of rubber, and maybe you can visualize what I'm talking about.

Axle nut tension is your first line of defense. You don't want to have only one.

 

[docw009]

By the way, what are you guys using for torque on a 10x12mm axle? The Jump motor allows me to use a torque wrnech on both sides, since the cable doesn't go thru the axle. I think I'm using 22-24 ft-lbs, which turns out to be a little more than I've been doing by feel with my hub motors/

 

[calab]

Go to home depot and buy some flat bar 1/4" and grab your angle grinder = have fun

 

[ynot]

Go to home depot and buy some flat bar 1/4" and grab your angle grinder = have fun

For the trike am building did something like that except I used my milling machine. The clamping forks I made are not as elegant as some I have seen but they seem to work.
Just wish I could do the same for my bike front wheel mount............. oh well.

 

[calab]

Every frame is different, I have lucked out and 1/4 x 1.5"x6" seems to work well, even if I lost the other 2 seasons ago in the winter but one holds out well for a frontie @ 1.8kw max.

 

[99t4]

...and the spindles should be hardened enough to handle the strain of tightening.

If by spindle you mean the motor axle, many have found that common hubmotor axles are not particularly well hardened, or even made of especially strong alloy.

The achilles heel of modernly available hubmotors? The axle (too small diameter) and its meager "flats" technology to resist spinout (too little real estate involved to contain the torque forces).

Long ago Heinzmann hub motors had integrated torque arms. Now hubmotors are a commodity item and seemingly resistant to change.

 

[dogman dan]

Crank it till it strips then, like so many of us have. Some axles strip at way less torque than that.

Still curious what you have, that the axle is too short to fit a torque arm on it. The solution is to ride it till the wheel falls off, then buy your new teeth. :lol:

Or, get a different motor, or different fork, that can have at least one torque arm that fits tight used.

 

[ynot]

Crank it till it strips then, like so many of us have. Some axles strip at way less torque than that.

Still curious what you have, that the axle is too short to fit a torque arm on it. The solution is to ride it till the wheel falls off, then buy your new teeth. :lol:

Or, get a different motor, or different fork, that can have at least one torque arm that fits tight used.

Suspect that the trike will be my daily driver, if so will pull the front hub wheel and put the old wheel on and sell it.
At my age, already bought the teeth, but the brain will be at the sharp end of the wreck.

 

[dogman dan]

Delta trike? Don't ride it faster than 15 mph then. That will eliminate crashes that hurt, and the motor spin will just ruin the motor and kill the controller.

Once you do ruin that motors wires, killing the controller, the motor you need is sold by E-bikekit. Axle will be long enough for any standard 100 mm fork.

 

[ynot]

Delta trike? Don't ride it faster than 15 mph then. That will eliminate crashes that hurt, and the motor spin will just ruin the motor and kill the controller.

Once you do ruin that motors wires, killing the controller, the motor you need is sold by E-bikekit. Axle will be long enough for any standard 100 mm fork.

Dogman am not understanding you.
The torque arms I propose are for my BIKE, an old iron clunker that in bike years is about my age, it has an original 250 watt brushed rear hub motor, have installed a jump wheel on the front forks, which works really well as this is a hilly area.

For the reverse trike, I had to make drop outs because the original front wheels spindles were around 5/8"Dia., so I made 2 clamping drop outs for each wheel.
15 mph is about as fast as I would ever go, but why is having a pair of jump bike motors on the front wheels of the trike hard on the motors.
So far have ridden the trike about a mile just around the block, not going to take it far, or fast, until after I make the brake caliper mounts for the motor wheels, the trike only has a rather weak coaster brake, until I do.

 

[dogman dan]

Sorry for the confusion, some days I get really stupid. Read too fast, next thing I know I'm thinking gorrillas, vs guerrillas, or whatever.

Check the bike with a wrench before every ride would work as good as putting a wrench on the nut permanently. It's not the trike vs the bike that matters with the motor, but some day that nut gets loose, then the axle spins and cuts the wires.

 

[qwerkus]

See attached files. I designed those and had them lasered at a local shop for little money. The small one (m12) is for rear dropouts and *could* be a bit tighter. The front ones (m14) fit regular suspension forks near perfectly. I have it on both sides of a dd hub in a spinner 300 on my cargo bike and despite loads of 200kg+ and regen, there is 0 wiggling.