Mototec/Say Yeah 1000W Knock Out Scooter Upgrade

[mattskiva]

Hello,

I am a new owner of a Mototec Knock Out scooter, as seen here:
https://www.urbanscooters.com/products/mototec-knockout-48v-1000w-electric-scooter

Since I bough it a month or so ago, I have upgraded from the SLA 48v setup to a LiFe04 60v setup (soon to be 72v), upgraded the motor to a 2000w version from the same manufacturer, and installed a 2000w controller. I am getting faster speeds (about 28mph) with the 2000w motor, but of course not fast enough yet, so I am going to 72v.

This is the motor I installed in lieu of the stock one:
https://www.uumotor.com/ws/p/18x9-5-8225-55-8-60v-1000w1500w-brushless-dc-fat-tire-motor/

So, now, my challenge. I decided that maybe two motors (2wd) would be better than one. It probably won't help me on flat ground except maybe for acceleration, but it should improve my uphill performance. So, I ordered two of the 2000w motor, and planned to install one in place of the front wheel.

The problem is, the integrated axle in the hub motor is too long for the fork in the front (I am new to this so pardon the terminology). Photos attached. It appears to be too long by almost exactly the length of the rectangular portion on the end of the axle. Would it be safe/advisable to just cut this off with an angle grinder? The brake fits into the caliper properly on the left side, but leaves a good bit jutting out on the right. Alternatively, is there any other way to mount this?

Thanks for any advice - even if it's "don't do that"

 

[amberwolf]

Generally you don't want to remove those flats, because they are usually there specifically so you can secure the axle against torque reaction.

Unless the front thru-axle (presumably) clamps on that fork precisely fit the round part of the axle on the motor, and clamp down VERY securely, it isn't going to keep the axle from spinning out against the torque the motor creates. If that happens, it rips up and twists the motor cable, which then has to be repaired or replaced (and sometimes shorts out and destroys the controller). A regular wheel axle doesn't have this problem because it doesn't have any torque against the dropouts.

In that event, you're probably going to have to make custom clamping dropout plates for the front fork, for *both fork legs*, that secure the flats on both ends of the axle so they can't move. These will have to be secured to the fork legs so the plates can't move at all, as well, relative to the fork legs.


Look up the "torque arm picture thread" for a whole bunch of ideas.

 

[mattskiva]

Thank you for the suggestions - very helpful.

I get why the flats would be there, after reading up about torque arms, but there is no such configuration on the rear wheel of the bike currently -- the flats are simply bolted in through the metal frame with an m12 bolt that was, admittedly, EXTREMELY hard to get off (750psi torque wrench at full power difficult). So, I am not sure why I am not getting movement on it currently - or maybe I am and I just don't know it?

So, back to the front. If the better idea is to keep those in place, maybe some sort of arm that attaches to the existing forks and bumps out/widens them to attach to the flats? This would mean the wheel would sit a little lower than the forks, and I'd have to move the caliper presumably as well.

I don't think I can adjust the width of the forks - they are bolted in to what looks like a cast iron, or rough steel upper cross-bar that connects to the frame, and there is no adjustability that I can see.

So, I can definitely address the need for a torque arm, but still not sure how best to get the wheel to fit in the forks. Are you suggesting I do, in fact, cut the flats off, and then use a torque arm to address the torque problem?

I could cut down the width of the attachment point on each fork by probably about half and make it fit, but I would hate for that to reduce the strength to the point where it is no longer strong enough. The forks, including the mountain points, appear to be made entirely of some sort of composite/polymer material.

 

[amberwolf]

I get why the flats would be there, after reading up about torque arms, but there is no such configuration on the rear wheel of the bike currently -- the flats are simply bolted in through the metal frame with an m12 bolt that was, admittedly, EXTREMELY hard to get off (750psi torque wrench at full power difficult). So, I am not sure why I am not getting movement on it currently - or maybe I am and I just don't know it?

If the flats of the axle are engaging flats in the frame, then the frame is the torque plate. The bolts have to be very tight to ensure this doesn't loosen up with repeated torque application (especially if it has regen braking), if there are no clamps on the torque plate / dropouts.

Are you suggesting I do, in fact, cut the flats off, and then use a torque arm to address the torque problem?

No, you let it extend past the outside of the forks, and put the torque plates on the outside of teh forks to attach to the flats and the forks.

If the holes in the forks (not visible in your pics) are not round and large enough for the axle to pass thru them, then you'd have to find some alternate solution. Filing the thru-hole axle adapters to perfectly fit the axle might work, and if you mess up you could buy new adapters if they are a standard kind.

If the holes in the axle mounts in the forks are already square and fit the square ends perfectly, but the axle on the motor is simply too long, you could first see if the seller has a version that is slightly shorter that would fit. If they don't, you could see if you can get, or make, a new axle mount for the side that sticks out, that is longer and also sticks out by that amount, that will accept the axle the way it is.

I could cut down the width of the attachment point on each fork by probably about half and make it fit, but I would hate for that to reduce the strength to the point where it is no longer strong enough.

No, you don't want to do that. If something breaks up there and the fork hits the road it'll launch you forward at the speed you had been going...but face-first, no longer riding anything.

 

[mattskiva]

If the flats of the axle are engaging flats in the frame, then the frame is the torque plate. The bolts have to be very tight to ensure this doesn't loosen up with repeated torque application (especially if it has regen braking), if there are no clamps on the torque plate / dropouts.

They are not engaging flats in the frame, they are simply touching and bolted on through normal bolt holes. The bolts as mentioned were excessively tight, probably glued in with something; maybe that's how they kept it from having torque issues.

If the holes in the forks (not visible in your pics) are not round and large enough for the axle to pass thru them, then you'd have to find some alternate solution. Filing the thru-hole axle adapters to perfectly fit the axle might work, and if you mess up you could buy new adapters if they are a standard kind.

Yeah, the holes are round and much smaller, sized for the long bolt that acted as an axle for the non drive wheel that was there before.

I could bore the holes out, probably, or simply drill new, larger ones. The holes are built in to the polymer material of the forks, there are no adapters.

Not looking like a very easy answer, unfortunately. Honestly, the easiest answer is probably to cut off the flats and hope that I can make it work using a torque plate/arm. if I cut it to fit the existing holes on the inside and bolted both sides to the fork, and put torque arms on the outside of the fork connected to the bolt, that might work?

 

[amberwolf]

They are not engaging flats in the frame, they are simply touching and bolted on through normal bolt holes. The bolts as mentioned were excessively tight, probably glued in with something; maybe that's how they kept it from having torque issues.

Can you post good clear pics of what these look like? It would be useful for understanding what they have done, and thus what you might be able to do in front, if the axles are the same on both.

I could bore the holes out, probably, or simply drill new, larger ones. The holes are built in to the polymer material of the forks, there are no adapters.

There appears to be something around those holes, besides just the cast material of the forks. Can you post good clear pictures of both sides of each fork leg in that area, closeups with good focus and lighting?


Honestly, the easiest answer is probably to cut off the flats and hope that I can make it work using a torque plate/arm. if I cut it to fit the existing holes on the inside and bolted both sides to the fork, and put torque arms on the outside of the fork connected to the bolt, that might work?
If by "cut it" you mean cut the fork holes to fit the axle, then yes.

If instead you mean cut the axle, then no, unless you can put enough pressure on the axle with the bolt and the forks without deforming the fork material (allowing slippage or breaking the fork), to prevent any rotation no matter how small, of the axle. (any rotation that starts will start a process of wear that allows more movement that wears more that allows more movement and eventually spins out the axle....)

If you cut off the flats then you have nothing to connect the torque arm *to*. It only works if it has something to clamp around that cannot rotate within the arm's flats, splines or other surface.

If you have a large enough diameter round surface, and a tight enough clamping force, you can use a tube-type clamp, but with something finger-sized, it's difficult to get enough clamping force on the available surface area.


If this was the rear end, it wouldn't be as critical, as even if the wheel fell off completely it would jsut slide out in a crash. But on the front, if something goes that badly, the crash is a completely different type and usually much worse for the rider. I try to hedge against whatever worst case there might be....

 

[amberwolf]

If I were doing this the "easy" way, based on what little you've posted about the forks/etc so far, I'd file the holes in the fork adapters (or whatever they are) to fit the square ends, as precisely as possible, for the tightest fit possible, with rounded corners to prevent crack propagation under stress, and try that.

If I found during frequent regular inspections that there were problems (any kind of change) then I'd make tubes that slide over the fork legs that have their own built-in torque plates to bolt the motor to. THen bolt them on the motor axle, and tehn slide them onto the fork legs, and clamp them to the legs, so it could all come off to change the tire when necessary.