Poll: Has your front hub motor spun out of your forks?

Discussion in 'Electric Bicycles' started by Blaze, Jan 18, 2007.

?

Has your front hub motor spun out of your forks?

  1. Yes - and my kit did NOT have a torque arm/safety retainer

    98.9%
  2. Yes - and my kit DID have a torque arm/safety retainer

    0 vote(s)
    0.0%
  3. No - and my kit did NOT have a torque arm/safety retainer

    0 vote(s)
    0.0%
  4. No - and my kit DID have a torque arm/safety retainer

    1.1%
  1. Blaze

    Blaze Guest

    It looks like a lot of kits are shipping without torque arms to keep the axle from spinning, or safety retainers to keep the front wheel attached if the nuts come loose. This can result in the front wheel falling off, if your motor has enough torque to spin the axle.

    Manufacturers are telling me that if the wheel comes off, it's because I installed it wrong. Common sense tells me that you just don't put that much torque on the center of an axle.

    I haven't seen too many rear hub motors, but this poll is for the front hub motors only, since that is the kit I am worried about. Also, please let us know what kind of motor you have (high/low speed, high/low torque, voltage, watts, manufacturer, etc...)
     

  2. Blaze

    Blaze Guest

    my kit

    Mine has spun out of the forks. Hopefully, I have it fixed. I will post the info on fixing it when I get it put back together and tested.

    My motor:
    48v
    600w
    About 17/18mph actual top speed (advertised top speed was 24mph)
    High torque- climbs medium hills without pedalling and very steep hills with little pedalling effort
    Manufacturer- China Gas (via Don Grube), purchased from Spookytooth Cycles
    It's a silver motor with red rings painted on it.

    [​IMG]
     
  3. Wheels

    Wheels Guest

    Blaze would someting like pictured make a good torque arm or is it too heavy?

    wheels[​IMG]
     
  4. gone_fishin

    gone_fishin Guest

    wait a doggone minute...a poll i can't vote in...what's up with that? :/
     
  5. Blaze

    Blaze Guest

    Wheels- that might not work too well. It's not how heavy it is, but how thick. You only have so much axle space to use up. I will post photos of my finished torque arm in a day or two. It's made out of a 10mm wrench from ace hardware. It's cheap, light, strong, and fairly thin. What you want is something that has flat surfaces to hold the flat spot on the axle. You want to think about how a coaster brake arm works when you build a motor torque arm.

    Augi- Sorry you can't vote on this one. :) That's what I like about having one gas bike and one electric. It's like being bilingual.
     
  6. Wheels

    Wheels Guest

    So you have chosen forged steel for the arm, would not plate steel be thinner? Like to see some photos when you get it hooked up. Your art of problem solving is interesting.

    wheels
     
  7. Blaze

    Blaze Guest

    Yeah, plate steel would be great, if you have something to cut it with (all I have is a dremel w/cutting wheel). You would want something about the same thickness as the coaster brake arm. The wrench idea is just fast and easy because the wrench is already a good shape for the job. If you had plate steel that was roughly the same shape, but as thin as the brake arm, that would be the best solution by far. Especially since the wrench has to be modified so it sort of locks onto the axle and doesn't slip out. The wrench has an open end that slides onto the axle from the side. The plate steel could be cut with a closed end that could never slip off. I'll get some more photos up this weekend for sure. And I'll draw a quick template for the plate steel torque arm, too.

    Meanwhile, this drawing was the concept for my current torque arm.
    [​IMG]

    The final build is pictured below. I basically went with the planned design, but it was too hard to grind a slope on the axle, so I ground the whole wrench surface flat and just left two raised tabs on the ends. This way, I only had to grind two small notches into the axle instead of the whole slope. Installation and testing is tomorrow.
    [​IMG]
     
  8. Wheels

    Wheels Guest

    Why not just use a brake lever?[​IMG]
     
  9. Blaze

    Blaze Guest

    The hole in the end has to be shaped to get a tight fit on the axle to keep it from spinning. That brake arm in the photo would be perfect if it had a hole the exact shape and size of the axle, instead of a big square hole. A brake arm like that was the very first thing I wanted to use, but the hole just wasn't the right shape or size.
     
  10. gone_fishin

    gone_fishin Guest

    so, the axle has a flat/square section? anyone have an actual pic for us?
     
  11. Blaze

    Blaze Guest

    Yeah, that's why I use a wrench as a torque arm. It fits the flat spots on the axle and holds it very well. With many motors, the fork dropouts are enough to hold the flat spots, but my motor has hill-climbing torque, and it opened up the dropouts, which were the only things holding the axle. After looking at these photos, my drawings should make a lot more sense (this axle is for a rear hub motor, so the axle is a lot longer, but the flat spot looks the same)...

    [​IMG]
    [​IMG]
     
  12. Blaze

    Blaze Guest

    ...and here is what my perfect torque arm would look like (here is your template, wheels). I'm not sure if the hole I drew was to scale, but that's the basic idea. If the axle hole is so big it gets close to the edges of the brake arm, then you would need to start from scratch with a wider piece of sheet steel.

    [​IMG]
     
  13. gone_fishin

    gone_fishin Guest

    thanks blaze, i already pretty much understand an important aspect of front e-hubs :)

    sure don't seem like much to hold onto under torque, nor does there seem to be enuff room to really do a solid job of it. couldn't you make a stronger torque-arm if you worked on the outside of the dropout instead? i assume that's a lot harder than average bicycle axle-steel? do the flats themselves ever get twisted or worn?
     
  14. srdavo

    srdavo Active Member

    Blaze,
    Was there any permanent damage to your fork dropouts when they spread?
    Dave
     
  15. gone_fishin

    gone_fishin Guest

    i was just looking at my fork...what if you "layered" 2 more dropouts on the outside, then bolted all 3 together using the upper hole? would that be strong enough?
     
  16. Blaze

    Blaze Guest

    It won't matter if the dropout is on the inside or outside of the forks (but the inside is easier to work with because the fork tube can stick out a lot). The strength will be determined by the strength of the steel and the shape of the design. The dropouts don't work well because the steel is not hard enough and it is a horseshoe-shaped opening that the axle goes into. With enough force, the dropout openings will be spread apart because there is nothing holding the open end together. With the design I drew on Wheels' brake arm, there is a lot more structural integrity from having an actual hole instead of a horseshoe shaped opening. You can't really bend the hole wider. In order for the axle to spin in that setup, you would actually have to tear the steal. Both the dropouts and the brake arms are made of pretty much the same type of steel. It just goes to show how design can add as much strength as materials.

    The hub axles are no harder than regular bicycle wheel axles. They don't have to be. It's 2 or 3 times thicker, and I'm pretty sure they are both made of carbon steel, anyway. That's about as hard as it gets without getting into exotic alloys.

    Being made of carbon steel, the only damage I have done to them is a slight flattening of the ends when I hammered the hell out of them while re-seating the bearings. It made the nut go on a little tight at first, but no major changes. The odds of ever damaging the flats on the axle are slim at best.
     
  17. Blaze

    Blaze Guest

    Not really. They are just a little wider now. It doesn't really matter anymore, because I am not using the dropouts to keep the axle from spinning. All of that force is transferred to a torque arm now, so the only thing the dropouts have to do is hold the wheel on like a regular bicycle wheel. That doesn't take much strength. As long as the torque arm keeps the axle from spinning, the dropouts really don't carry much load at all. The only load they carry is the forward force from acceleration, and a backward force from braking, if you have front caliper brakes.
     
  18. Blaze

    Blaze Guest

    Bolting them together probably won't work. It might work if you heavily welded the layered dropouts together. Emphasis is on might. I wouldn't try it because it will cost you a fork to try it, and there is not a high enough likelyhood of success.

    The reason I don't think bolting them together will work is because of simple leverage. With the bolt so close to the axle, you aren't getting enough leverage to decrease the amount of force on the bolt. With nearly full axle torque on the bolt, it will probably shear.

    The reason torque arms work so well is because of their length. Think about removing a bolt that is stuck on. With a short wrench, you can't put enough force on it. Slide a pipe over the wrench, so it's like having a 2 foot long wrench. The bolt that was previously impossible to turn can now be moved with hardly any force at all. This is what torque arms so. The further they move the torque forces away from the center of the torque, the less effort it takes to hold the axle. By moving it far enough away, the entire axle can be held by just one small, thin clamp. If you try to hold the axle at or near the center of torque, there is so much power it will destroy heavy gauge steel. Pretty cool, really.

    [​IMG]
     
  19. Wheels

    Wheels Guest

    You are really clear on this Blaze, is vibration damping an issue? [​IMG]
     
  20. Blaze

    Blaze Guest

    No, vibration is not an issue at all on the electric bikes. That's one thing I absolutely love about them. It makes them so comfortable to ride.

    The clamp you have would be perfect, though. The rubber covering will keep your forks from getting scratched. That is the exact same style of clamp I would use.

    You would want the clamp to be mounted with the bolt tab pointing towards the rear. The clamp has the most strength holding something trying to pull away from it. If you look at a rear brake, which I use as an example a lot here, you will see the same setup. The brake arm is pushed down when you stop, so the clamp's bolt tab is poitning down. On the electric hub, the torque arm is pushed back when you accelerate.
     
Loading...