Help me re-create this "pedal assist" road bike on the cheap

[grndslm]

[youtube]WsbOD09doRI[/youtube]

I've seen that geared motors can be either freewheeling or regenerative. I would prefer a freewheeling one if possible.
I would also think the gear reduction, as the guy in the video has, is necessary as well.

Not sure what he has really.... 24v, 250W. Anybody have any idea??

 

[grndslm]

The end of the video points to this URL --> http://bike-elektro-antrieb.ch/

So from the looks of the motor on that site, I'm now guessing it's actually 36V, 350W (250W to 400W range?).

And that site is obviously promoting the heck out of freewheel cranks, but are they actually necessary??

It appears just after 40 seconds into the video, that the guy actually freewheels without a freewheel crank. Trying to keep this as simple and inexpensive as possible.

Anybody got a list of inexpensive parts I'd need to make this happen??

- Motor =
- Controller =
- Throttle =
- Batteries =
- Charger / Adapters / Wiring =

 

[Drunkskunk]

That looks to a a Currie motor, and that looks to be an average of a 10% grade up those ramps. If so, the guy riding is pedaling like a mad man to assist the motor. a 250 watt motor would never be capable of that incline at that speed o n it's own.

I would say the closest thing that would give the actual performance that appears in the video would be a 48volt 450 watt kit like this one: http://www.gngebike.com/450w-brushless-mud-guard Trying to get the parts separate would probably cost more.

Then you'll need another $500-600 for a good battery that can handle the amp dump you would need to tackle a steep incline like that, and the charging system with shipping.



That's about as cheap as it gets and still be useful. You might shave $50-100 off the motor kit if you have access to a CNC mill and could manufacture your own parts, but the bulk of the cost is in motor, controller, freewheel crank system, and battery.

 

[grndslm]

That is a damn good price for the kit, for sure.

But, honestly, I want to try to build something without a freewheeling crank. I want it just like the guy in the video. If the motor is turning, I want my legs to move.... kinda like a fixie. Which is why HUGE output is not really needed. Hence, why this is a "pedal assist" bicycle.

I think the motor is slightly larger.... as I said, the site at the end of the video is promoting a 36V, 350W (250W to 400W range?) motor... so this is likely what he has, or close to it.

And again... in the video I posted, you can hear him coasting just after the 40 second mark... so I really don't understand the need to add weight in the jackshaft and freewheeling crank and such. Actually, now that I'm looking at the link you posted.... the video is a regular electric motor, but the pictures add a jackshaft driven by a belt, what may be a freewheel on the output end, and then another freewheel for the crank. That all seems a bit much to me. Why are the pictures different from what's shown in the video??

 

[MadRhino]

...If the motor is turning, I want my legs to move.... kinda like a fixie.

Believe me, you don't want that. That is a very stupid design, for it can hurt the rider and/or cause accidents.
It is not very brilliant already to ride a fixie on the street, a fixie with a motor is asking for troubles.

You can pedal just as well with a freewheel. There is no advantage to build it fixed, other than a thief trap, because anyone unaware trying to ride your bike will hurt himself. Such thieves traps are turning against the owner most of the time. I know because I had the stupid idea to set my controller to reverse when parked, and I ended up being the one to have a tibia badly scratched, kissing the front tyre, and having balls crushed on the stem.

 

[grndslm]

Notice that I said, "If the motor is turning, I want my legs to move.... kinda like a fixie."

I didn't say, "If the wheels are turning, I want my legs to move... like a fixie."

There's a huge difference here.

It's no surprise to me now that the guy freewheels at around the 40 & 50 second points now. The issue of a freewheeling motor is only necessary for me if I want to actually pedal the bike without the motor (i.e. - when the batteries die).

Soo... how hard is it to pedal a freeheeling geared motor???

 

[grndslm]

I guess the worst case scenario is that I add a master link to the small chain and quit acting like it's such a big deal, but it is a concern before I start piecin these parts together.

 

[Sunder]

Are you talking about where he stops pedaling at the bottom of the ramp? In that case, that's done by the freehub in his bike, just like any other non-powered bike. From the photos at the start, there is no chance in hell that's a freewheeling crank. As long as the motor is going, so are the pedals. He switched off the motor going down the ramp.

That said, I would be really cautious about using a mid drive bike without a freewheel crank, especially if you have any kind of pedal assist sensor, or don't have everything perfectly weather sealed. I had my PAS decide that I was pedaling pretty hard when I was stopped at the lights - that was with a front hub motor. Luckily I just laid the bike down. Removed the PAS after that. Imagine if it happened to you when you had your full weight on the ground, and the motor decided to push the pedal up against your leg.

Also, Considering the speed he hit the ramp going up, and the fact he was pedaling, there's no way we can make any kind of judgement call on how powerful the motor was. I reckon I could hit that ramp at that speed, and not lose noticeable speed by the top on my direct drive bike with the power off causing drag. There's just no way you would know if I (he) was phantom pedaling, or hammering it up the ramp.

 

[grndslm]

Are you talking about where he stops pedaling at the bottom of the ramp? In that case, that's done by the freehub in his bike, just like any other non-powered bike. From the photos at the start, there is no chance in hell that's a freewheeling crank. As long as the motor is going, so are the pedals. He switched off the motor going down the ramp.

Yup, it just clicked to me that the bike should freewheel when motor is off.... but how well it freewheels when pedaling with dead batteries is the real question that I'm sure somebody has the answer to.

That said, I would be really cautious about using a mid drive bike without a freewheel crank, especially if you have any kind of pedal assist sensor, or don't have everything perfectly weather sealed. I had my PAS decide that I was pedaling pretty hard when I was stopped at the lights - that was with a front hub motor. Luckily I just laid the bike down. Removed the PAS after that. Imagine if it happened to you when you had your full weight on the ground, and the motor decided to push the pedal up against your leg.

Well, this isn't any normal "pedal assist system"... it's merely controlled by the throttle.

Speaking of the throttle, are there thumb-lever potentiometers / throttles available?? I am not a huge fan of twist grip throttles.

Also, Considering the speed he hit the ramp going up, and the fact he was pedaling, there's no way we can make any kind of judgement call on how powerful the motor was. I reckon I could hit that ramp at that speed, and not lose noticeable speed by the top on my direct drive bike with the power off causing drag. There's just no way you would know if I (he) was phantom pedaling, or hammering it up the ramp.

Understood. Well, there aren't really ANY hills where I am... just one bridge. So this is more for assisting completely medium to long trips on flat ground. Which means, the smaller motor the better, really... just to keep batteries light and lasting long.

I'm assuming that an el cheapo 250W motor w/ built-in reduction would suit me fine. Only problem is that these always seem to be brushed motors. I've held off on my eBike projects because I always wanted a brushless motor. What's the lowest rated brushless motor w/ built-in reduction??

Now all I need is a thumb-lever throttle, a decent controller, and the best batteries money can buy.

 

[Sunder]

Yup, it just clicked to me that the bike should freewheel when motor is off.... but how well it freewheels when pedaling with dead batteries is the real question that I'm sure somebody has the answer to.

I don't have any experience with mid drive motors (Researched them, but decided against it. Preferred the simplicity and stealth of a hub motor) However, thinking it through, the freewheel would have to be on the motor, not the crank, correct? I actually suspect that they'd call it a clutch rather than a freewheel, so that only when power is supplied is the motor actually attached to the output spindle

Well, this isn't any normal "pedal assist system"... it's merely controlled by the throttle.

Speaking of the throttle, are there thumb-lever potentiometers / levers available?? I am not a huge fan of twist grip throttles.

You mean a thumb throttle like this?

(Vertical travel)

Or like this?

(Horizontal travel)

I'm assuming that an el cheapo 250W motor w/ built-in reduction would suit me fine. Only problem is that these always seem to be brushed motors. I've held off on my eBike projects because I always wanted a brushless motor. What's the lowest rated brushless motor w/ built-in reduction??

These babies are brushless:

Now all I need is a thumb-level throttle, a decent controller, and the best batteries money can buy.

What happened to "inexpensive"?

 

[MadRhino]

A freewheeling ebike let you pedal as easily as a normal bike when it is unpowered. The only difference is the extra weight of motor and batteries.

 

[grndslm]

I don't have any experience with mid drive motors (Researched them, but decided against it. Preferred the simplicity and stealth of a hub motor) However, thinking it through, the freewheel would have to be on the motor, not the crank, correct? I actually suspect that they'd call it a clutch rather than a freewheel, so that only when power is supplied is the motor actually attached to the output spindle

I'm not sure the operation of these freewheel geared motors, but apparently there are freewheeled hub motors, as well. I was under the impression that all motors were split between internal hub and external geared motors. But that is not the case... there are geared hub motors as well. Something I recently learned is that all motors are split between regenerating and freewheeling. But how exactly these "freewheel" mechanisms work I do not know.

You mean a thumb throttle like this?

(Vertical travel)

Or like this?

(Horizontal travel)

Yes!!

I prefer the horizontal travel, honestly. Where do I get one?

These babies are brushless:

That's close. I was preferring a reduction motor, but I guess if its output is closer to 400 RPM, then reduction wouldn't be necessary.

I guess I really need to figure out optimum gearing for specific RPMs first. Or would I be able to use a controller to limit output?? That could be a good solution if possible.

What happened to "inexpensive"?

Everybody knows you can't skimp on batteries, right?? :lol:

Just makes sense to design the bike around components that should last a while. And sink money into the batteries for multiple reasons, primarily to steer the market in the proper direction so that by the time I need replacement batteries, lithium polymer prices will be better and there will hopefully be a better type of battery to consider at that point. There's no better way to vote.

A freewheeling ebike let you pedal as easily as a normal bike when it is unpowered. The only difference is the extra weight of motor and batteries.

That would depend on your definition of "freewheeling", I'm afraid. Would a fixie with a "freewheeling" external geared motor [that's provided no juice from the throttle] actually pedal just as well as a fixie with the motor chain off?? If that's the case, then I'm surprised I don't see more of these setups around.

One reason I'm not attracted to the hub motors is that I have to pay for spokes to be cut & threaded, possibly pay for a new rim, then have to lace & true the wheel. If I somehow happen to bend a rim, then I have to do the whole damn thing all over again, instead of just being able to buy a $30 replacement wheel at the LBS.

Another reason is that adding the motor to the hub adds a greater deal of inertia to the wheels, which is the #1 place that I don't want more mass.

 

[DrkAngel]

24V 450watt motor - $85

24V 30A Controller - $37.50

24V Thumb Throttle - $10.50

RC Lipo would probably be lightest-best-cheapest for good surge use.

About $135 plus battery.

OK for a trial-test.
Simple and cheap to build, but ... !

For safety-convenience you really want a freewheeling crank and freewheeling motor.

I plan on building one with the listed components, prior to shelling out $$$ for a freewheeling crank.
Test bike is a full suspension, F/R disc brake, 26" mountain bike w/7spd freewheel.


But ... Rather than spend $$$ for a freewheel crank ... I'm afraid I would drop the cranks, swap the freewheel for a 7spd 11-34T DNP, push to 44.4V(832.5w), add foot pegs and keep a 7 speed eMotorbike.
3x the torque in low gear, peaking at 10-12mph, and winding out in top gear at 30mph.
Important to add a firm chain tensioner immediately behind front chainring, as a shifting buffer!!
Chain guards also important!
You do not want you pantleg-leg pulled into a geared electric motor!!!

 

[MadRhino]

...
One reason I'm not attracted to the hub motors is that I have to pay for spokes to be cut & threaded, possibly pay for a new rim, then have to lace & true the wheel. If I somehow happen to bend a rim, then I have to do the whole damn thing all over again, instead of just being able to buy a $30 replacement wheel at the LBS.

Another reason is that adding the motor to the hub adds a greater deal of inertia to the wheels, which is the #1 place that I don't want more mass.

DD hub motors are not for those who want pedal assist. I use them to ride 50 Mph, with 10+ Kw of power up the mountain trails where pedals count for nothing.

If you build a powerful mid drive setup, building and maintenance cost will be much higher than with a hub build.