Hub motor axle mounted in Downhill fork?
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Philistine
100 kW
- Joined
- Aug 15, 2010
- Messages
- 1,736
You can't use a hubmotor on a 20mm thru axle. The whole point of a thru-axle is that the axle slides through the wheel. A hub motor axle is fixed into the motor, and has axle flats.
No such word as cant, its just not straight forward, a small engineering problem thats all 
some slip over adaptors that fit onto the spindle flats and are clamped in the forks (if your forks have split clamps like the 888's do) or also engage into torque arms should do it.
some slip over adaptors that fit onto the spindle flats and are clamped in the forks (if your forks have split clamps like the 888's do) or also engage into torque arms should do it.Tench said:No such word as cant, its just not straight forward, a small engineering problem thats all
On top of this, it's also handy that a 20mm fork has 110mm spacing, so fitting a rear hub without freewheel could also be feasible in some cases. Some rear motors have wider stators than front = more torque.
dogman dan
1 PW
Can be done, but most just use a lesser fork than still has the regular dropouts. I don't mean a zoom, but maybe something good, but with traditional drops.
In either case, the motor must be mounted using torque arms of some kind that completly eliminate rotation, so that part of the problem is pretty similar. Mostly you'd just need some kind of bushing to fill the space between the axle and the 20 mm dropout.
The first thing that comes to my mind, is grind down some spacer washers like the ones used on rear hubs. I'm assuming they are too big stock. I haven't measured one.
In either case, the motor must be mounted using torque arms of some kind that completly eliminate rotation, so that part of the problem is pretty similar. Mostly you'd just need some kind of bushing to fill the space between the axle and the 20 mm dropout.
The first thing that comes to my mind, is grind down some spacer washers like the ones used on rear hubs. I'm assuming they are too big stock. I haven't measured one.
Better have someone grind a 20mm OD 2-piece axle vise that can be slid between the axle and dropout, also featuring a torque arm end clamped against the brake mount, if clamping power of the dropouts is considered too little. The good thing is, unlike standard QR dropouts, these can neither be spun, nor spread open by excessive clamping power of axle nuts. Look at motorcycle wheels - thru axles are standard for any heavy duty application.
Thanks for the replies. It sounds like I have two projects: adapter parts that will serve as a vice once they are placed inside the end holes in the fork. The other component would be the torque arm or arms.
Are two torque arms overkill? I am leaning towards one on either side.
The motor will likely be a 2806 Nine Continent front with disc mount with 25 amp controller, 48 volt 20 ah of LIMN at about 18 pounds.
I need 35 km range. I ride mostly wot. The elevation difference is about 400 feet, I start and end on opposite sides of a large valley. I weigh 170-195lbs. Going to convert a specialized enduro.
In the past, the weight of my xlyte 5304 rear hub with batteries in backpack or rear paniers has led to too much maintenance. Lots of busted spokes, two bent rims. On the positive side, I have become somewhat proficient at wheel building. At one point, I tried putting the batteries in front paniers. Steering was a little awkward, but I did get used to it. Problem was my front rack eventually broke, it couldn't handle the abuse of 20lbs of batteries. Rear racks I have tried have all held up better.
Next step is to sketch it up. I have a drill press and grinder. Might still get a machine shop to fab it though. Plan is to get rolling again in April. Since last spring, my route was unridable due to construction. Previously there was a bike path the last 5 km that should be replaced by the spring. Only way right now is on a multilane highway which is far beyond my comfort zone.
Are two torque arms overkill? I am leaning towards one on either side.
The motor will likely be a 2806 Nine Continent front with disc mount with 25 amp controller, 48 volt 20 ah of LIMN at about 18 pounds.
I need 35 km range. I ride mostly wot. The elevation difference is about 400 feet, I start and end on opposite sides of a large valley. I weigh 170-195lbs. Going to convert a specialized enduro.
In the past, the weight of my xlyte 5304 rear hub with batteries in backpack or rear paniers has led to too much maintenance. Lots of busted spokes, two bent rims. On the positive side, I have become somewhat proficient at wheel building. At one point, I tried putting the batteries in front paniers. Steering was a little awkward, but I did get used to it. Problem was my front rack eventually broke, it couldn't handle the abuse of 20lbs of batteries. Rear racks I have tried have all held up better.
Next step is to sketch it up. I have a drill press and grinder. Might still get a machine shop to fab it though. Plan is to get rolling again in April. Since last spring, my route was unridable due to construction. Previously there was a bike path the last 5 km that should be replaced by the spring. Only way right now is on a multilane highway which is far beyond my comfort zone.
dogman dan
1 PW
Re philistine, yes I see what you mean about one piece. The dropouts would have to be made like motorcyle ones, where a section of the axle hole is removable. If the bike ones have to slide in from the end, then there would be no way without cutting a notch at the least.
dogman said:
It can be done with upside down forks too, even without split axle clamp, but requires too much work to put it back together. AFAIK, none of the major DH forks use split dropouts nowadays. The most recent I recall were '03 Marzocchi Z1, Super T and Junior T, but the dropout design was poor.
dogman dan
1 PW
Ahh, I just assumed they would be like motorcycle stuff. I don't exactly keep up with forks that cost two months pay.
Philistine
100 kW
- Joined
- Aug 15, 2010
- Messages
- 1,736
I still don't understand how you guys are saying it can be done. If it is a true 20mm thru axle, the axle slides in from the side like a pin, and twists into its locking position in the fork. Unless you are going to mod your motor so that the axle can slide through the stator from the side (ie be removable easily), I simply can't understand how it would work. As Dogman says, unless you are proposing to cut the forks, which in my opinion defeats the purpose of having thru axle forks.
Are you going to be running two motors? if not I would just go with a rear motor and use the 20mm thru axle forks plain.
Are you going to be running two motors? if not I would just go with a rear motor and use the 20mm thru axle forks plain.
MadRhino
100 GW
You can make steel plate dropouts that are clamped on the Fork lowers and bolted on the through axle holes with a bushing. So yes, it can be done, but the fork will never work fine with the weight and torque of a motor.
My recommendation is to sell the fork and buy a helmet, if you want to have a motor in the front with any kind of interesting power.
My recommendation is to sell the fork and buy a helmet, if you want to have a motor in the front with any kind of interesting power.
Well I've been investigating a bit recently and found out there are few options to set up a reliable and bombproof front hub motor. But they exist! Let's see what I've found out so far, and hopefully get a couple more ideas together on top of that.
First we need a fork that's sturdy enough, preferably a double crown DH fork. To allow the axle into the dropouts, you either need an USD fork (Shiver, Dorado, DNM, Zoom) or a fork with removable brake arch, like the old school Marzocchi Monsters or Z1's that are not made anymore but can be found used at about USD 200-300.
The latter have a problem with axle design - unlike the USD forks that mostly employ a plain 20mm axle, these have a variable diameter axle with skinnier end section that's threaded rather than clamped in one of the dropouts, which makes fabbing an adaptor even harder for an average lathe user.
USD forks are great since they can be slid outta crowns and right onto the motor, using a 20mm OD adaptor. On top of that, a ZOOM fork can be had very cheap considering the amount of metal and rigidity. But for me they are a no go since they have no brake arch and thus can't use a mudguard close enough to the wheel. Their huge amount of travel makes it no better, though there are ways to reduce it.
Then there are moto forks, but they are at least twice as heavy and kinda defeat the idea of a bicycle altogether.
The last but not worst possibility is find a cheap fork with cracked cast lowers, like this one:
http://www.bikemagazin.sk/bazar/7-vidlice-tlmice/1851-888-rc.html
Then fab some kind of steel reinforcement brace to keep the brake arch together, and double as a mudguard holder.
An extremely viable option would be machining down the standard dropouts and use two oversize DH 1.5" steerer stems as new dropouts. The onepointfive standard has 38mm which could fit forks with 30-32mm stanchions and provide a huge 4-bolt clamp for the axle on both sides. But the fork would certainly become shorter, so a 26" fork would no longer be good for 26" wheels. A 29er fork could be just what we need then.
First we need a fork that's sturdy enough, preferably a double crown DH fork. To allow the axle into the dropouts, you either need an USD fork (Shiver, Dorado, DNM, Zoom) or a fork with removable brake arch, like the old school Marzocchi Monsters or Z1's that are not made anymore but can be found used at about USD 200-300.
The latter have a problem with axle design - unlike the USD forks that mostly employ a plain 20mm axle, these have a variable diameter axle with skinnier end section that's threaded rather than clamped in one of the dropouts, which makes fabbing an adaptor even harder for an average lathe user.
USD forks are great since they can be slid outta crowns and right onto the motor, using a 20mm OD adaptor. On top of that, a ZOOM fork can be had very cheap considering the amount of metal and rigidity. But for me they are a no go since they have no brake arch and thus can't use a mudguard close enough to the wheel. Their huge amount of travel makes it no better, though there are ways to reduce it.
Then there are moto forks, but they are at least twice as heavy and kinda defeat the idea of a bicycle altogether.
The last but not worst possibility is find a cheap fork with cracked cast lowers, like this one:
http://www.bikemagazin.sk/bazar/7-vidlice-tlmice/1851-888-rc.html
Then fab some kind of steel reinforcement brace to keep the brake arch together, and double as a mudguard holder.
An extremely viable option would be machining down the standard dropouts and use two oversize DH 1.5" steerer stems as new dropouts. The onepointfive standard has 38mm which could fit forks with 30-32mm stanchions and provide a huge 4-bolt clamp for the axle on both sides. But the fork would certainly become shorter, so a 26" fork would no longer be good for 26" wheels. A 29er fork could be just what we need then.
John in CR
100 TW
I have plans to do this kind of install, though I'll start with a cheap Zoom triple or double clamp (I don't know the difference, but the fork tubes slide out of the headset clamps) fork I have. It will get a little Fusin geared hub, so the freewheeling prevents the possibility of any controller or wire failure that could result in a plug braking faceplant. Plus the motor isn't heavy.
It's a 20mm thru axle connection to the fork. I'll start with some 7/8" or 1" bar stock, turn it down to 20mm to fit the fork, and tap threads in 2 pieces it to fit the axle like long round nuts. One on each side will screw all the way down to the shoulder on the axle. The right side will bear the motor torque, but spread over that length of threading will be fine, since I've done that before. Both sides will need an arm going from the 20mm axle sleeve to the fork, because the left side will stop the axle from unscrewing from the right side, though the unscrewing forces will be small due to no regen. The arms will get welded to the sleeves after getting everything aligned and centered like I want, and I will weld them slightly out of parallel so the force to put them into parallel is to screw them tightly to the axle shoulders to avoid slop later.
To keep it simple, I'll put the arms at the outside edge so they also act as a flange to prevent the axle from sliding laterally. Otherwise some kind of bolt on flange on the outside would be required.
Now that I've reminded myself how easy this is, I should go ahead and do one since I have a couple of bikes and a couple of forks. Too bad the existing axles on the forks aren't steel. That would make it simple as long as it wasn't very hard steel.
A bit of paint on these axle nut torque arms and it should be a nice clean install as long as I come up with a decent looking clamp for the end of the torque arms to the fork tube.
John
It's a 20mm thru axle connection to the fork. I'll start with some 7/8" or 1" bar stock, turn it down to 20mm to fit the fork, and tap threads in 2 pieces it to fit the axle like long round nuts. One on each side will screw all the way down to the shoulder on the axle. The right side will bear the motor torque, but spread over that length of threading will be fine, since I've done that before. Both sides will need an arm going from the 20mm axle sleeve to the fork, because the left side will stop the axle from unscrewing from the right side, though the unscrewing forces will be small due to no regen. The arms will get welded to the sleeves after getting everything aligned and centered like I want, and I will weld them slightly out of parallel so the force to put them into parallel is to screw them tightly to the axle shoulders to avoid slop later.
To keep it simple, I'll put the arms at the outside edge so they also act as a flange to prevent the axle from sliding laterally. Otherwise some kind of bolt on flange on the outside would be required.
Now that I've reminded myself how easy this is, I should go ahead and do one since I have a couple of bikes and a couple of forks. Too bad the existing axles on the forks aren't steel. That would make it simple as long as it wasn't very hard steel.
A bit of paint on these axle nut torque arms and it should be a nice clean install as long as I come up with a decent looking clamp for the end of the torque arms to the fork tube.
John
MadRhino
100 GW
Triple clamp, Double crown
John
You've got a lot of power already, and adding a motor in the front will not give you any noticeable advantage
It will handicap the function of the fork and wear the seals quickly, complicate the front wheel servicing, and add some weight where it is the most important to be light. At the speed that you ride, the weight of the motor will make the front wheel bounce and leave the ground on bumps because the fork won't be able to dampen the rebound properly. That is a good receipt for a front wash in the first bumpy turn. Gosh, I spend well over 2K on each of my bikes to have a light front end and a properly working suspension.
John
You've got a lot of power already, and adding a motor in the front will not give you any noticeable advantage
It will handicap the function of the fork and wear the seals quickly, complicate the front wheel servicing, and add some weight where it is the most important to be light. At the speed that you ride, the weight of the motor will make the front wheel bounce and leave the ground on bumps because the fork won't be able to dampen the rebound properly. That is a good receipt for a front wash in the first bumpy turn. Gosh, I spend well over 2K on each of my bikes to have a light front end and a properly working suspension.
OK, gave up on the triple forks for a while.
Here's the plan.
1x this:
http://www.kupkolo.cz/29er-rock-shox-xc-32-t-disc-100mm-lo-korunka_z91697/
2x this:
http://www.bikestore.cc/product_info.php/products_id/107580
Dremel out the dropouts, slide the stems into the motor and onto the lowers. No torque arms anymore.
Judging from hi-res pix, the lowers have 37.5 to 38.1mm diameter, exactly as much as the 1.5" stem.
This leaves me with two 1" ID clamps, one on each side, to accomodate the axle.
I may eventually cut half of each clamp's face plate to gain dropout width so it accomodates a rear hub. In that case, I'd have to run torque arms just in case.
Here's the plan.
1x this:
http://www.kupkolo.cz/29er-rock-shox-xc-32-t-disc-100mm-lo-korunka_z91697/
2x this:
http://www.bikestore.cc/product_info.php/products_id/107580
Dremel out the dropouts, slide the stems into the motor and onto the lowers. No torque arms anymore.
Judging from hi-res pix, the lowers have 37.5 to 38.1mm diameter, exactly as much as the 1.5" stem.
This leaves me with two 1" ID clamps, one on each side, to accomodate the axle.
I may eventually cut half of each clamp's face plate to gain dropout width so it accomodates a rear hub. In that case, I'd have to run torque arms just in case.
John in CR
100 TW
MadRhino said:
LOL ! It's not for my SuperV running 30kw. This would be a low power rig, FWD to start and maybe my out of shell Fusin motor as a mid-drive for 2wd later. Slow and easy on the trails with some pedal assist for exercise, and little if any air time.
So triple clamp and double crown are the same thing, and the 3rd clamp is to the steer tube? It's locked in like a steel trap now, so I hope it's right.
While I've got you here, am I correct in believing that the triple/double is stronger? I feel much safer with 2 tubes extending through 2 clamps and connecting to both ends of the steer tube, than the leveraged force of stopping transferred by the end of 2 fork tubes and the bottom of the steer tube in that smallish metal piece no matter how strong that metal is. I guess my question is does one fail catastrophically more than the other, and where is it forks typically break?
John
MadRhino
100 GW
Yep, a DH fork is stronger, on a DH frame of course.
On a weaker frame, it could "ovalize" or crack the welding of the head tube.
That is the first possible failure, a fork could also break at the lowers or bend at the stanchions.
Breaking at the lowers is nearly the only catastrophic failure, for the other failure eventualities are progressive almost all of the time.
Then, I don't really know about how cheap forks misused in DH where they don't belong could fail. I'm not crazy enough to ride a crap fork, the trail hazard is enough for my daily need of adrenalin. :wink:
On a weaker frame, it could "ovalize" or crack the welding of the head tube.
That is the first possible failure, a fork could also break at the lowers or bend at the stanchions.
Breaking at the lowers is nearly the only catastrophic failure, for the other failure eventualities are progressive almost all of the time.
Then, I don't really know about how cheap forks misused in DH where they don't belong could fail. I'm not crazy enough to ride a crap fork, the trail hazard is enough for my daily need of adrenalin. :wink:
