Torque arm for Front Hub Motor Review

[knightmb]

I bought this one:
http://www.poweridestore.com/Hub-Motor-Torque-Arm

Pros:

1. Cheap compared to having a local shop fab one for me
2. Straight forward steel, very strong.
3. Has a side attachment plate (removed in my pictures) to run power cable should you put it on the same side as where the power cords come out from the motor
4. Designed for this kind of thing, fit without any issues on even my large shock forks

Cons:

1. Screw to bind it to fork not big enough for mine. Had to make a trip to hardware store for a longer screw and bolt.
2. Locking washers would be nice, again, cheap hardware store trip for this one.
3. Heavy

Conclusion:
I was very impressed with this. It is very strong and easy to install. In my experience, the front fork always fails on the side in my pictures due to rotational forces on that side wanting to "spin out" of the fork where as on the other side it's trying to "spin in" to the fork. If you are going to use anything above 36 volts on a non-steel front fork, I recommend getting one of these. It's very strong and with my test at 72 volts, didn't even move a little in my test of just pealing out from a dead stop over and over with all of my 175 lbs of weight on it (plus battery packs, etc). I think this helps those that want a front hub motor out greatly in preventing a fork failure at least up to 72 volts on a 406 motor. Not sure what would happen if you had a more torque monster in the front. A very easy and cheap way to power up the front hub for some torque and speed.

 

[xyster]

Great there's finally a sturdy pre-fab'd solution. Any problems you think fitting these on the rear?

My dropouts are probably not as strong as Lowell's, so I may need two for my rear X5 as I push the wattage up to 5kw.

 

[knightmb]

Great there's finally a sturdy pre-fab'd solution. Any problems you think fitting these on the rear?

My dropouts are probably not as strong as Lowell's, so I may need two for my rear X5 as I push the wattage up to 5kw.

A good question, when I look at the back of my bike and look at the torque arm, it looks like it would be sitting straight up if I had a hub motor in it. Since the back is angled much more than the front, I think these might not work as well as they do on the front. I attached a rotated picture of the torque arm. It would depend on which way your back is angled. If it's straight up, it probably won't work unless you had an extension arm come out from the frame to hook to it instead of the steel sleeve that is uses for the front fork. Maybe a simple steel rod that is angled towards the torque arm and then held together by a bolt and screw.

 

[tsellers]

Going to try the above with a brushless, geared, hub motor, will probably use 2 of them. Is it a Crystalyte product?

Here's one for the rear our eBike guy sold me for $15.00 that I used with a 409.

[/img]

 

[knightmb]

Going to try the above with a brushless, geared, hub motor, will probably use 2 of them. Is it a Crystalyte product?

No, not a crystalyte product. It's something I think the business is having the local shop fab for him, but I'm not certain. He's real friendly, e-mail or give him a call I'm sure he'll be glad to answer.

 

[tsellers]

Thanks for that. The reason I asked is on his product page there is a link for the product's home page and if you click on it, it takes you to the Crystalyte site. If it was a more generic product I may also be able to find it in Canada and avoid cross border shipping. I'll have to see if it will require much in the way of modification to make it work with the geared hub motor I'm looking at.

 

[knightmb]

Thanks for that. The reason I asked is on his product page there is a link for the product's home page and if you click on it, it takes you to the Crystalyte site. If it was a more generic product I may also be able to find it in Canada and avoid cross border shipping. I'll have to see if it will require much in the way of modification to make it work with the geared hub motor I'm looking at.

I see now, good point. I didn't find it anywhere on the crystalyte page either. I've always wondered why their website is so plain, LOL :lol:

Is there any reason why they can't ship it postal? I thought that was pretty cheap to Canada and since the price is under $100, I can't image any duties or tax on it since we have the NAFTA thing going on for North America Continent.

 

[DeeL2003]

Going to try the above with a brushless, geared, hub motor, will probably use 2 of them. Is it a Crystalyte product?

Here's one for the rear our eBike guy sold me for $15.00 that I used with a 409.

[/img]

Does that just work for your frame or is it a universal torque arm. I need one bad for my TF frame

 

[tsellers]

It's universal, at least Universal in that it works on the Crystalyte hubs. I think he gets them from a supplier in the US, if you can't find them send me a note and I'll give you the contact info. I had to dripp a hole for the top screw as I had the braze-on that I could use. You need to adapt it to fit your own requirements.

 

[Doctorbass]

Nice custom torque arm you have!

2 days ago i just wated ti check if the bolt on the axel of the hum motor was correctly tighted.... I was affraye to see that one bolt was a bit unscrewed!!... i just can't immagine what is would happen if i hav'ent checked it!!! :lol:

So i decided to put serious torque arm in it.. each side of the axel!

I will try to put some metric tool key. One on each bolt (a 22mm) and one on each acel flat side (10mm) and then attach these on the bike frame... i ever seen something like that and that seem to be ok.

My simple conclusion: a 5305 +offroad trail +66V +50A = DANGEROUD without torque arm!!

Doc

 

[DeeL2003]

Just installed the same torque arm that Tsellers has on his frame. The top screw is mounted on the brake caliper mount. I hope this will hold up. I didn't have space on the other side. Man, it was such a pain to drill through the steel plate. I used my crappy camera phone for this pic, hope it's clear enough.

 

[knightmb]

Just installed the same torque arm that Tsellers has on his frame. The top screw is mounted on the brake caliper mount. I hope this will hold up. I didn't have space on the other side. Man, it was such a pain to drill through the steel plate. I used my crappy camera phone for this pic, hope it's clear enough.

Picture looks great. The nice thing about disc brakes on the frame, it gives you a place to secure the hub motor to. Makes sense, if it's good enough to stop the bike, why can't it make it go forward to?

 

[tsellers]

From the note I just sent my supplier. Note this is the same torque arm I earlier posted on a different bike. The controller on that bike burnt out so I switched over to a front hub system on a full suspension bike. Following is the result. (BTW, you cannot use the stamped steel torque arm pictured at the start of this post for the 4XX series crystalyte hub motors, that's why this one was used).

Hi Gary,

I just went to test the bike with 72V pack attached. I got about 20 meters and either the hub spun inside the torque arm and then snapped the drop-out off, or the drop out snapped off first because the torque arm was able to pivot forward (because the installation design allowed it to "hinge"), and then the hub spun inside of it. You'll see in the attached pictures that what used to be a slot in the torque arm has become an oval hole. In any event, it would appear the torque arms are not made from hard enough steel. I just caught it in time before I ripped the wires out of the hub, obviously after three days of work setting all of it up this is a major bummer, but I suppose I should consider myself lucky at least the hub motor is OK.

I think we're back to the drawing board on these torque arms, probably they'll need to be made from stainless or a harder grade of steel.

Regards, John


Post Installation damage overview (right side):

Note torque arm used to be slotted, now oval:

The result:
Left Side-Wire harness wrapped to almost 360 degrees around hub but still OK:

The resulting broken Dropout on the right side:

 

[Miles]

I just caught it in time before I ripped the wires out of the hub, obviously after three days of work setting all of it up this is a major bummer, but I suppose I should consider myself lucky at least the hub motor is OK.

Thank goodness you're ok....

 

[fechter]

Ouch! that looks nasty!

Destroyed fork and torque arm, possibly motor too.

This torque arm idea definitely needs improvement. If the axle manages to spin, the flats will push apart the dropouts. If the axle can be positively fixed so it can't rotate, I don't think the dropouts would ever fail, even aluminum ones.

It does look like it may have prevented you from totally eating it when it failed.

 

[Miles]

The flats on the axle are not very wide. Best to make the new arm out of gauge plate and harden and temper it. It really needs to be an interference fit, with the slot no longer than the flats.

 

[tsellers]

Thanks guys,

The hub motor is OK, and so am I, fortunately I was barely moving when I felt something go and stopped immediately, which saved both man and machine, or at least part of the machine. The wire harness got wrapped almost to 360 degrees around the hub but there was enough slack to allow it to do so.

I'm thinking that the Cannondale Headshok bikes are probably the best candidates for conversion, however I'm stuck with my ROcky Mountain Frantik for now.

THe problem would be, if you made torque arms out of stainless steel, you'd have one hell of a time drilling them in order to adapt them for your specific fork design. A steel piece with a stainless insert would be nice, but prohibitively expensive to produce in small batches.

 

[Miles]

I think it's really up to the makers of hub motors to provide something better to fix a torque arm to....

 

[knightmb]

I think it's really up to the makers of hub motors to provide something better to fix a torque arm to....

I agree completely. Unless you really lock washer the crap out of it, the defaults provided are not close to enough for anything over 36 volts (maybe 24 for some hub motors with a lot more toque)

In my pictures at the beginning, I'm using over sized lock bolts for more grip area, double flat washers on the outside of the fork arm and the torque arm you'll notice is on the inside near the motor instead of the outside for more leverage control. The motor is also a 406, so it's not a low end torque monster to further help negate an axial spin from a stop.

About the best thing you can do is drill a hole through the center of the axial and use a pin system to lock it into place. I just don't have a good drill press than get get through the metal "cleanly" to do this. Otherwise, that might be a good way to help secure these motors better on the e-bikes.

 

[tsellers]

The pin system sounds like it may have potential. I also recall a boat I had with an small inboard 3.5HP engine, the shaft had a slot milled into it with a keyway that matched with a compatible collar that also had a slot that slid over the key. That way the coupling could not freewheel on the shaft. But you'd still have to find some way to attach the collar to the dropouts. It's starting to look like an expensive visit to the machine shop is going to be required...

 

[Mark_A_W]

From the note I just sent my supplier. Note this is the same torque arm I earlier posted on a different bike. The controller on that bike burnt out so I switched over to a front hub system on a full suspension bike. Following is the result. (BTW, you cannot use the stamped steel torque arm pictured at the start of this post for the 4XX series crystalyte hub motors, that's why this one was used).

Hi Gary,

I just went to test the bike with 72V pack attached. I got about 20 meters and either the hub spun inside the torque arm and then snapped the drop-out off, or the drop out snapped off first because the torque arm was able to pivot forward (because the installation design allowed it to "hinge"), and then the hub spun inside of it. You'll see in the attached pictures that what used to be a slot in the torque arm has become an oval hole. In any event, it would appear the torque arms are not made from hard enough steel. I just caught it in time before I ripped the wires out of the hub, obviously after three days of work setting all of it up this is a major bummer, but I suppose I should consider myself lucky at least the hub motor is OK.

I think we're back to the drawing board on these torque arms, probably they'll need to be made from stainless or a harder grade of steel.

Regards, John

I'm sorry, but that torque arm was totally useless...you got lucky.

Mine is like this :

I just need to add some M12 Fine nuts to the outside to clamp the arms - but finding them hard to source, need to go to a dedicated bolt store.

If the dropouts fail, the arms are capable of bearing the load on their own.

 

[tsellers]

Now that's a cool setup:

It's hard to tell from the picture, is that a sleeve sort of setup that runs the full length of the tube?

I see you managed to also retain your disc brakes, were your forks already wide enough or did you have to spread them?

Which model bike is this on?

Regards, John

 

[Mark_A_W]

It's all here

http://endless-sphere.com/forums/viewtopic.php?t=1533

 

[DeeL2003]

tsellers: Thanks for the heads up! Now I'm worried. Wow, 72v on a front suspension fork! That's ballsy! At least you're okay. I wonder how fast you were gonna go. I almost went that route(high voltage front alumin fork) but guys like YPedal, Justin, and the rest from the old V forum screamed, "Hell NO!" Let me know what solutions you're working on with the machine shop and I'd like to pitch in for a new torque arm.

Mark AW: Nice setup and it sure makes our torque arm seem very brittle compared to yours. But not everyone can(or will) do the machining and welding that you had done to your fork, so we're looking for a more simple solution to securely "bolt-on" to a front and rear(for me) fork.

I tried buying a torque arm from Doug (EVTech) that he sells with his BMC motor kits, but he keeps telling me to call "next week." Ever since the fire took out most of his inventory, he's been busy trying to rebuild. I'll give him another call soon. Alot of the BMC/Puma owners here use the torque arm with no reported breakage yet. Most, if not all of them, are high voltage rear motors. I don't know if Doug sells front version though. Tsellers, at least you can use it on your rear setup. Hmmm, maybe Gary can come up with something.

 

[tsellers]

Well, I was fully aware of the caveats on front mounting a hub motor on front suspension, but I see no reason why if the installation is done properly, it cannot be achieved. In fact, I would not even try doing it on steel front forks without torque arms as well. My installation was obviously not done properly. I should have drilled my required holes and done any required grinding first, and then I should have had the torque arm tempered, something which our welder at work may be able to do for me. More info on tempering is here:
http://asuwlink.uwyo.edu/~metal/heat.html

Even the great system posted above by Mark would be prone to the same failure as mine if his slot stripped out and became oval, perhaps taking out his wiring at the same time.

Granted the next concern then becomes bending the fork tubes as a result of the torque forces. I've considered the huge forces the downhiller's and dirt jumpers place on their forks and they normally report blowing out the seals rather than bending the heavier dirt jump forks like the marzocchi bombers. Then there is the ground-tire interface, you'll probably be spinning out before you could bend the fork tubes, and it's probable you need the fattest tire possible for this set up such as a 26-2.7. Anyway, need to get the problem solved at the dropouts first before moving to the next possible problem.