Starting my first ebike. Need some advice.

[patrick reavis]

Hello, My name is Patrick I am new here but have been looking at this fourm for almost a year, very cool stuff. I finally have some extra cash to start my project.I have a specialized hardrock MTB that I plan to do a self engaging friction drive on using a scorpion 5525 170kv (2300 watts continuous) geared 2:1 driving a 3in diameter long board wheel as my spindle, I will use a 44 volt battery. My main Question is, can i exspect to get the full 170kv out of the motor under a moderate load (500-1000 watts)? Assuming I do, at WOT it would go 33 mph. I want to run the motor at an efficient rpm at my intended cruse speed (25-30) mph. I also plan to set the motor up with delta-wye switching. Digging into the windings of a $200 motor scares me a little, but the idea of a 2 speed electronic transmission sounds so cool. I figure Wye configuration would be great for climbing hills with a top speed of around 18mph. I have started the process of gathering parts for the drive unit. $450 so far and thats without the ESC and battery! I figure another $800 for every thing else. I would only engage the motor once I have pedaled up to 10 mph or so, never from a dead stars. Under those circumstances do you think it wound be worth the extra work to add hall sensors? I Will start posting pics soon. If any one has some advice i would love to hear it.

Thanks for your help

 

[AussieJester]

Search for Keplers friction drive uses the actual can of the outrunner
pressed against the tire works brilliantly, best friction drive setup i have seen
and they usually hold little interest with me.

Best of luck

KiM

 

[patrick reavis]

Kepler's design is what originally got me interested in the idea of a friction drive. I love the simplicity of his design, but I want to have the ability to adjust my gear ratio. I also feel like Kepler's design might be hard on the bearings in the motor. Does anyone know if a properly setup friction drive is efficient. Does any one with a friction drive have a reading of how many watts the system pulls with the tire off the ground?

 

[patrick reavis]

Finally got some parts for my drive unit.

 

[patrick reavis]

seperating the wires in the scorpion was very simple.

 

[MitchJi]

Hi Patrick,

I will use a 44 volt battery. My main Question is, can i exspect to get the full 170kv out of the motor under a moderate load (500-1000 watts)?

No. kv is the no load speed. Figure about 90%.

I also plan to set the motor up with delta-wye switching. Digging into the windings of a $200 motor scares me a little, but the idea of a 2 speed electronic transmission sounds so cool. I figure Wye configuration would be great for climbing hills with a top speed of around 18mph.

It won't actually be a 2 speed electronic transmission. More info here:
http://endless-sphere.com/forums/viewtopic.php?f=10&t=11469&p=177105#p175208

Also bear in mind that Delta/Wye and Series/Parallel aren't the equivalent of a gear box. You can only trade speed for torque with a mechanical gearbox.

http://endless-sphere.com/forums/viewtopic.php?f=10&t=11469&p=177105#p175770
http://endless-sphere.com/forums/viewtopic.php?f=10&t=11469&start=15#p177119

I would only engage the motor once I have pedaled up to 10 mph or so, never from a dead stars. Under those circumstances do you think it wound be worth the extra work to add hall sensors?

Probably not. Check here and decide for yourself:
http://endless-sphere.com/forums/viewtopic.php?f=28&t=18792

 

[dontsendbubbamail]

Patrick,

Where did you get those bearing holders?

Bubba

Finally got some parts for my drive unit.

 

[EVTodd]

Looks like an interesting project. I always like to see what people come up with using friction drive.

I'll leave your electronic questions up to the pros on here, I don't even have a watts up meter on my bike yet .

I'm a little confused about the reason for using a 3 inch roller and gearing it down. I'm always concerned when I see people using large drive rollers. With a larger roller it takes a lot more motor torque to get the bike moving which increases the chances of the roller slipping on the tire. The roller on my bike is only 1.25" and it pulls really really well even from a dead stop. In my opinion I've always thought it was best to start with a smaller roller and match the motor's kv to the top speed you want.

 

[patrick reavis]

Where did you get those bearing holders?

They are not really made to be bearing carriers, but the work perfectly.
http://www.vxb.com/page/bearings/PROD/Kit7228 8mm.
they sell these in 8, 12, 16, 20, 25, and 30mm sizes, they a very high quality, that website also sells bearings in every size you could imagine.

I'm a little confused about the reason for using a 3 inch roller and gearing it down. I'm always concerned when I see people using large drive rollers. With a larger roller it takes a lot more motor torque to get the bike moving which increases the chances of the roller slipping on the tire. The roller on my bike is only 1.25" and it pulls really really well even from a dead stop. In my opinion I've always thought it was best to start with a smaller roller and match the motor's kv to the top speed you want.

Regurdless of the diameter of the roller, the surface of the roller will be traveling the same speed for any given speed of the bike. My idea is that with equal roller perssure on the tire a larger roller should have a slightly larger contact patch than a smaller roller. I think a larger roller would be more efficient too. what is your roller made of?

 

[EVTodd]

Regurdless of the diameter of the roller, the surface of the roller will be traveling the same speed for any given speed of the bike. My idea is that with equal roller perssure on the tire a larger roller should have a slightly larger contact patch than a smaller roller. I think a larger roller would be more efficient too. what is your roller made of?

You might be thinking about tire diameter. The roller size makes a huge difference in torque and top speed. A bigger roller is essentially like using a larger gear and it makes the motor work harder. Now at higher speeds, I would agree, it would be more efficient. You have to find a balance and I honestly think 3" is going to be too big. I know you're going to have a lot of torque but unless you plaster it on the tire it's just going to slip (even with a variable pressure system).

I'm using a knurled, hardened steel roller. Have a look at my build (link below) if you haven't already. Go to around page 7 to see the drive in it's current form.

 

[Kepler]

I just wonder though Todd if it would be proned to slip more. Thinking about it, to take off at a given speed needs the same amount of torque whether its a large diameter roller or small diameter roller. Given the large diameter roller has a larger contact area, wont this provide better grip?

I agree a smaller roller like yours is like using a lower gear to take off but in gearbox terms, a lower gear means more torque.

 

[patrick reavis]

You might be thinking about tire diameter. The roller size makes a huge difference in torque and top speed. A bigger roller is essentially like using a larger gear and it makes the motor work harder. Now at higher speeds, I would agree, it would be more efficient. You have to find a balance and I honestly think 3" is going to be too big. I know you're going to have a lot of torque but unless you plaster it on the tire it's just going to slip (even with a variable pressure system).

what I was trying to say is that if your bike is going 30mph, then the surface of the roller is also traveling at 30mph reguardless if it is 1in in diameter or 3in in diameter. obviously, the larger the diameter of the roller the more you must gear it down. With your roller being direct drive a small roller is needed. My roller is geared down so i can run a larger roller. With the larger roller i will have a larger contact patch which means better grip and less wear on the tire.

 

[Kepler]

seperating the wires in the scorpion was very simple.

How much work ss involved with separtating the phases? Dit you need to untwist the wire right back to the windings?

 

[EVTodd]

You might be thinking about tire diameter. The roller size makes a huge difference in torque and top speed. A bigger roller is essentially like using a larger gear and it makes the motor work harder. Now at higher speeds, I would agree, it would be more efficient. You have to find a balance and I honestly think 3" is going to be too big. I know you're going to have a lot of torque but unless you plaster it on the tire it's just going to slip (even with a variable pressure system).

what I was trying to say is that if your bike is going 30mph, then the surface of the roller is also traveling at 30mph reguardless if it is 1in in diameter or 3in in diameter. obviously, the larger the diameter of the roller the more you must gear it down. With your roller being direct drive a small roller is needed. My roller is geared down so i can run a larger roller. With the larger roller i will have a larger contact patch which means better grip and less wear on the tire.

Yes... But since you are gearing it down you will have even more torque at the roller. I would almost be willing to bet you will have tons of slip with that big of a roller especially using a reduction before it.

The slight difference in contact patch is really a moot point if you use a variable pressure system. Why not use a smaller roller and negate the need for a reduction? I know people have talked about doing this in the past but why not keep it simple if you can get the same results?

And please don't take this as me trying to argue. I'm really just trying to help since I've gone the wrong way down the friction drive path before. I guess I'm just so flippin' happy with my drive that I want to spread the word about how simple it can be. lol

 

[EVTodd]

I just wonder though Todd if it would be proned to slip more. Thinking about it, to take off at a given speed needs the same amount of torque whether its a large diameter roller or small diameter roller. Given the large diameter roller has a larger contact area, wont this provide better grip?

I agree a smaller roller like yours is like using a lower gear to take off but in gearbox terms, a lower gear means more torque.

I see your point, but my thinking is the reduction would give the roller more torque. Like I said in the other post, I think the added surface area is a moot point. I'm just thinking smooth roller with lots of torque = slip. Wouldn't the reduction give more torque throughout the range of your throttle? And think about riding a bike without a motor, how much of your power would it take to accelerate in your biggest gear from a dead stop. Could a roller transfer that kind of power to a tire without slipping? Again though, that's just my thinking. I've been wrong a couple of times before. lol

Heck, I remember people telling me my drive wouldn't work. I'm glad I didn't listen.

Back to your build... Are you going to use a clutch bearing inside the roller?

 

[patrick reavis]

no clutch in the roller. I am going to do something like keplers design and have the roller swing out of the way when not in use.
I understand what you are saying about the larger roller having more torque but think of it this way. with each revolution of a 1.5in roller your bike will travel 4.71 inches. With each revolution of a 3in roller the bike will go 9.42in, therefore requiring 1/2 the rpm but twice as much torque.

on the motor i just un twisted the wires down to the stator. very simple process on these larger scorpion motors

 

[etard]

I will be following your build Patrick, one more friction drive, and another Scorpion motor build. The last Scorpion used seemed to perform really well as I recall. How do you intend to implement the Delta/Wye switching? What controller will you be using? Good Luck with the build.