GRIN Front All Axle in Aluminum Fork?

[notdeadyet]

Not sure where to post this Question

I have an Aluminum Front Fork Greenspeed Anura Delta Trike. (20 inch front Fork)
Now for what has turned into decades the rule was you don't stick a Hub Motor in an Aluminum or Aluminum/Mag Alloy Front Fork unless you want to feel what a Face Plant feels like.

But this has always applied to Hub Motors with an Iron Axle but since the GRIN All-Axle is missing an Iron Axle am curious if I have nothing to worry about?

The All Axle Motor was too Wide for my Terra-Trike Rambler All-Terrain Tadpole's Rapid Axle and WizWheels who now sell Terra-Trikes don't sell a longer Rapid Axle and the Machinist I was using doesn't think a longer Axle was a good idea so that project is dead. So to avoid having a Paper Weight I figure I'll see if it works on the Greenspeed Anura Aluminum Fork instead.

 

[richj8990]

Maybe that was before torque arms. I've put a 500W rated front hub drive in two different aluminum fork dropouts, used TWO torque arms, have gone up above 1000W at times, absolutely zero problems. Please show me the link to any problems with front hub drives with two torque arms on the fork. I'd like to see what supposedly happened. When people mix power with ignorance and/or recklessness, bad things can happen; that mantra doesn't just apply to front hub drives...

Have you thought about a boosted 110mm wide fork to put the all-axle in. I'm sure you can get an entry-level boosted air fork for around $400 USD. That should be enough room. I don't know if they sell 20/24/26 boosted forks, but even 27.5 will work, it will just raise the front end up a few inches. Remember, two torque arms. If you are going to put one on, just put two on. You don't even have to take them off when you take out the wheel, you just loosen them from the axle and nuts. It's really not a big deal, takes a few minutes, maybe 5-6 at the most.

 

[amberwolf]

The probem is not really what the axle is made of. The problem is with the torque applied by the axle to dropouts not intended to resist that torque (which means, any bicycle dropout, front or rear). (specifically it's the extremely tiny intersecting area of the axle flats and the dropouts having to take all the torque of the entire system)

If you use a correctly-designed torque arm or plate sufficient to handle the expected torque forces, that is properly mounted to the frame or fork, and perfectly fits the axle so there can be *no* movement in any direction of the axle in any way, then you can use a motor in any frame or fork that you can put this solution onto.

The GAA by necessity has a torque arm solution that doesn't involve this problem.


The two most serious problems you may find if any of the above is implemented properly is that if you have suspension forks with simple bushings they may bind anytime the motor is providing traction or braking power; better forks with better sliding mechanisms may not do this (or not as badly). Also, if you have single-crown forks the traction or braking forces (or rather, the combination of them one after the other, repeatedly) may cause assorted problems depending on their design and quality. (dual crown / double/triple-tree forks are supported above and below the headtube so the forces then act only on the frame at the headtube/frame join).

The issue I had on CrazyBike2 was that eventually the headset bearing / race would loosen up and I'd have to retighten the stack, or replace the lower race cup. And on the cheapest suspension fork I had on it (that was actually useful suspension) the crown flexed back and forth enough to feel during acceleration and braking.

I still have the first problem on the SB Cruiser trike, but there's no motor on the front, it's just disc brakes and it's because that single brake handles all the deceleration of hte trike that is much heavier than the bike and carries much bigger cargo loads. The forces involved actually began to deform the crown of a cheap steel fork; I've since built a dual-crown to prevent that problem.

 

[notdeadyet]

Maybe that was before torque arms. I've put a 500W rated front hub drive in two different aluminum fork dropouts, used TWO torque arms, have gone up above 1000W at times, absolutely zero problems. Please show me the link to any problems with front hub drives with two torque arms on the fork. I'd like to see what supposedly happened. When people mix power with ignorance and/or recklessness, bad things can happen; that mantra doesn't just apply to front hub drives...

Have you thought about a boosted 110mm wide fork to put the all-axle in. I'm sure you can get an entry-level boosted air fork for around $400 USD. That should be enough room. I don't know if they sell 20/24/26 boosted forks, but even 27.5 will work, it will just raise the front end up a few inches. Remember, two torque arms. If you are going to put one on, just put two on. You don't even have to take them off when you take out the wheel, you just loosen them from the axle and nuts. It's really not a big deal, takes a few minutes, maybe 5-6 at the most.

I created the first Torque arms in 1999 for what at that point in history was a massively powerful Brushed Hub Motor at 250W that had the weight of a boat anchor. The Greenspeed Anura is a Bent Delta Trike with a Tie Rod to the front Aluminum Fork. I've already looked for a Steel Fork and none exist where the Anura Tie Rod connects and I'd like to avoid having a mount welded on. As per your suggestion of a Boosted Fork it has to be the stock Greenspeed Fork. What I was looking at was the FAST 9C Hub Motor if the GRIN All Axle won't work and YES twin Torque Arms might work except I've encountered Aluminum Forks that have the fork blades twist and break at the crown via high torque.

 

[notdeadyet]

Ya'll might find this interesting. First Torque Arms for Front Brushless Hub Motors were Open ended Wrenches on Left and Right Fork Blades held on by double sided Tape and Hose Clamps. This was only 23 years ago when we had Controllers with an unbelievable power level of 10 AMPS......We've come a long way in 2 decades.