Motorized Bottom Bracket

Does anyone know of a quality kit that utilizes a motorized bottom bracket instead of a hub motor? I would love to find DIY kit that could be comparable to the prohibitively expensive Optibike. Thanks!

ervet said:

Does anyone know of a quality kit that utilizes a motorized bottom bracket instead of a hub motor? I would love to find DIY kit that could be comparable to the prohibitively expensive Optibike. Thanks!

Click to expand...

We all want this... one of these days some smart innovator will figure out a way to sell a kit that would do something like you are asking.

This gets discussed more fully over in the thread:

Board index » Electric Bicycles » E-Bike Non-hub Motor Drives

http://endless-sphere.com/forums/viewforum.php?f=28

The most common is a kit from Cyclone.
http://www.cyclone-usa.com/

Hi,

This is perfect except for the 200 watt motor and probably the price:
[youtube]jmPUze3WBTw[/youtube]

http://www.gruberassist.com/english/product/product-description/

GRUBER Assist is a ultra-light drive for mountain bikes, trekking cycles and tour cycles, suitable for later installation. The skilfully conceived Gruber motor is invisibly built into the bicycle (seat tube with an inner diameter of 31.6mm required) and scores especially highly on account of its light weight (900 g).

A touch of the Turbo button at the bar end – and the burning sensation in your thighs disappears – the healthy perspiration, however, remains. The auxiliary drive, with its 200 watt of additional power, promises a performance increase of up to 100% - for up to 1.5 hours. When the drive is switched off, you continue cycling as normal. GRUBER Assist guarantees pleasurable cycling without a red face!

Product attributes

• The electric motor is very light
• The propelling assistance is invisible
• Cycling becomes fitness cycling and is thereby healthier
• Thanks to its retrofit kit, it is almost irrelevant what brand of bike you have
• The pedal assistance brings speed on flat and power going uphill

Click to expand...

It would be great if they would sell the kit, configured so a larger motor could be fastened to the seat tube, connected with a 90 degree gear and at an affordable price.

EDIT - photos here:
http://electricmountainbikes.blogspot.com/2008/11/gruber-assist.html

Hey Mitch,

That kit looks great! Any idea on when it might become available? Any feel for how efficient this would be compared to a 200W hub motor?

Thanks for the information.
Mike

hope u realize that it won't be anywhere comparable to an Opti which is 400W to 800W depending on the model.

The auxiliary drive, with a length of almost 22 cm and 200 watts of power, is permanently connected torque-proof with the drive shaft of the foot pedal through a bevel gear unit; gear changing is still possible. At an optimal pedal frequency of approx. 60 pedal revolutions per minute, the bicycle drive provides the rear wheel with up to 100 watts.

Click to expand...

i've seen bigger motors in floppy drives or printers, but I like it, its really different.
Figure some way of also stuffin the batt into the frame tubing/bar/forks & you've gots the ulitmate in stealth.
As long as expectations are realistic & the price was good it would be fun to try one on.

Hi Mike,

ervet said:

Hey Mitch,

That kit looks great! Any idea on when it might become available? Any feel for how efficient this would be compared to a 200W hub motor?

Thanks for the information.
Mike

Click to expand...

I posted it more as an illustration of what is possible, not necessarily as a recommended solution.

I'm pretty sure its available now (might be only in Europe).

Its very expensive. I read someplace that the entire kit with a Lithium pack is 2k (I don't remember the currency, probably Euro's).

I don't think the cranks freewheel. If I'm correct that would rule it out for me. If you find out for sure let me know.

I think 200W going through the gears would give you better performance than a 400W hub motor. I base that partly on Gary's posts. Here is one description. You can search his posts for somewhat more complete explanations if you want:
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=8035

Anyway, with a 55A controller limit, this setup peaks out at about 2600W, but because of the gearing benefit of going through the 3-speed hub, this combo actually outperforms the 24s4p 72V 5303-based setup with a 4110-modded controller set to about 65A.

This surprising performance "boost" by taking advantage of the bike's gearing has started me on this quest now, to convert all my bikes to similar weight-saving configurations.

Click to expand...

Hub 72v x 65a = 4680W
vs geared 2600W and better performance

Interesting concept. One thing that probably could be done is to replace the 200W motor with an RC-type inrunner with a long stator that is fairly small in diameter. The problem is that this sort of motor is going to want to run at pretty high rpm in order to get a decent amount of torque, so it would probably also need a multistage planetary gear box.

-- Gary

Gruber Assist is availble and buyable...
a Bikestore here in Vienna sells them..

2008 they were sold out, for 2009 they plan to increase the production by factor 2

its a setup for sport-bikers...
its VERY VERY light, so you don´t realy feel any negativ side-effects of the drivetrain

for the 100Watt -> don´t think that is that few...

i have a Bafang hub-motor
i have tested it with bikecontroller (currentlimit at 14A) and 36-48V which results in over 400Watt output
on a steep hill you get less than 100Watt to the wheel -> also when the motor can spin out in flat terrain you see 400-450Watt to the wheel with the same controller

look on the two graphics...
you can see: the higher the loads get (the amps go up), because of hill,
the more the controller has to limit the voltage, so the amps do not go over the controller set limit

positiv: the efficience stays relativley high, also when going up a hill...
the absolut lost Power (Watts) is not higher then when going fast, also the motor efficience is down

nevativ: on a hill you get a lot less power than it is possible when motor can spin fast

the gruber assist, optibike, Flyers, or bike-elektro-antrieb.ch can use the bikes gearing..
so also when going slow, the motor can still sturn fast, the controller still has not to limit the voltage...

for that: a hub-motor able to go 40km/h and putting out 400Watt will only put out maybe 100Watt when going up a hill with less than 10km/h
on the other side the bottom bracket motor can use the gearing (maybe 4:1), so can still put out the same power at 10km/h as he can do at 40km/h
and then a 200Watt Motor on a hill is stronger, than a 400Watt Hub (that puts only 100Watt out on the hill)

on the other side:
the maximum possible efficience of the gruber assist is not that high...
a 1:111 planetary gearing, then the 90° gearing --> that costs efficience
so it can never reach as high efficience as a hubmotor
on the other side: when a hub-motor drops way down under 50% the bracket motor can still be at his high efficience-spot

the little gruber-assist motor gives always the 100Watt to the wheel, because of the gearing
its made for going up hills, helping on climbing..
on slow speeds no 2000Watts are needed, 100W are already a good assistance !

for me a downside: gearnoise (and price)

for the freewheel: it has a freewheel (between planetary gearbox and 90° gear -> so the 90° gears are always turning, but than there is the freewheel
so when motor is off, you can drive the bike like a normal bike..

as said: this concept is for the real bikers, for athletes
not for daily-commuters who want to go fast without pedaling much to work...

another, stronger alternative:
http://www.bike-elektro-antrieb.ch

mit Strombegrenzung -> with current limit
ohne Strombegrenzung -> without current limit

P_aufgenommen -> power (watts) consumed
P_abgegeben -> power output
P_Verlust -> power lost (= heat)
Wirkungsgrad -> efficience
Drehzahl -> rpm
Leistung -> Power

The Germans / Austrians always build great stuff.

This comes very close to perfection... high efficiency... and you just bolt it onto the bike with few modifications. Simple and smart.

What we need in America is a 750 watt version.

(1000 watt input and 750 watt output)

ahh.. you americans

with 750Watt its like a Opti-bike... nice, but not realy a bike anymore..

the philosophie of drives like Gruber Assist:
YOU drive up the hill (150-200Watt, for short period a little more) and get a little help from a motor so it is easier...
thats still cycling..

the other way is:
add a motor that puts out 750Watt ...
wohuu... thats more than i can put on the pedals, thats then not a help, thats other way round.. you have a motorcycle, and - if you want - you can help the motor a little with your tiny 150-200watts

at least for me: wrong way...
if i could, i would exchange my bafang to a half as big and half as heavy and half as powerful motor
in the moment i run with 14A controller, maybe i can get the CA, so i can limit the current to more usefull 7-8A

well, two different philosophies..
gruber assist would be in my eyes the perfect system (powerwise, optical, weight, weightdistribution), when it was
a) a little cheaper
b) a little less noisy


besides: is this young Robert Downy Junior dressed up as our Wolfal ?
(Wolfgang A. Mozart) ?

Yes, an American pretending to be an Austrian....

Kraeuterbutter said:

the other way is:
add a motor that puts out 750Watt ...
wohuu... thats more than i can put on the pedals, thats then not a help, thats other way round.. you have a motorcycle, and - if you want - you can help the motor a little with your tiny 150-200watts

Click to expand...

People with ebikes like to go crazy with power. Read some of the big hub motor threads or the newer RC motor threads. There are people pumping out 2500 watts of power and above.

750 watts is as much as a professional athelete using full strength for about a minute... so it's still within peak human experience.

In the Tour De France they often average about 400 watts over long distances.

So I don't think 750 watts is excessive.

Plus... don't you just come to expect that Americans are loud, overpowering and obnoxious? :lol:

In the next week or so I'll be testing the use of a small geared hub motor as a bottom bracket drive. To me it has a best of both worlds possibility since it should be light weight, quiet, and with variable gears via a cassette, have the ability to run the motor in its efficient range even while climbing hills.

John

@Safe:
well, iam not realy interessted in 2000Watt..
it would be cheaper to buy a moped then

iam more impressed by concepts like this:
http://www.recumbents.com/wisil/tetz/e-assistmetric/

Hi Kraeuterbutter,

Kraeuterbutter said:

Gruber Assist is available and buyable...
a Bikestore here in Vienna sells them..

2008 they were sold out, for 2009 they plan to increase the production by factor 2

on the other side:
the maximum possible efficience of the gruber assist is not that high...
a 1:111 planetary gearing, then the 90° gearing --> that costs efficience

Click to expand...

Thats starting to get into the ballpark of sufficient reduction for a low kv RC Motor, particularly through the gears.

Kraeuterbutter said:

for the freewheel: it has a freewheel (between planetary gearbox and 90° gear -> so the 90° gears are always turning, but than there is the freewheel so when motor is off, you can drive the bike like a normal bike..

Click to expand...

Does the Motor Drive the Pedals or is there a freewheel to prevent that?

Thanks!

Mitch

hey...

Thats starting to get into the ballpark of sufficient reduction for a low kv RC Motor, particularly through the gears.

Click to expand...

can you right this with outher words or explain ? (my English is too bad to understand what you mean with that)

the crank spins with up to 90rpm
--> 1:111 Gearreduction means -> the motor spins with 9990rpm at that time

when i now look at RC-motors with less than 31mm diameter
--> that are for example the Lehner 15 series...
http://www.lehner-motoren.de/ms15.php

1. 29,3mm Motordurchmesser
2. 36/41/46/51/56mm Motorlänge (für 1515/1520/1525/1530/1535)
3. 1,5mm Flanschlänge
4. 10mm Flanschdurchmesser
5. 12mm Wellenlänge
6. 3,17 bzw. 4mm Wellendurchmesser
7. 16 und 19mm Lochkreis
8. M2,5 Gewinde

i have read somewere, that the gruber assist uses a 30V 4,5Ah battery
the slowest 15er-series Lehner motor, the 1535-40 has a kv of 613rpm/V
so this motor woul spin 18000rpm
also its the slowest motor in this series -> 18.000rpm is still too fast for the 1:111 gearing
maybe the 90° gearing is not included in this 1:111 ?
at least: puting in a slower turning motor to reduce the 1:111 gearing -> i don´t think you will find any rc-motor which can do that at 30Volt
(if that is what you meant, as said, i have not understood your meaning)

for the freewheel:
now i understand:
no, there is only a freewheel in one direction:
so when motor is off, you don´t feel it
but when motor is on, the pedals are turning..

this is by far not that critical as you maybe may think...
1.) "only" 100Watt..
so risk of injuries is MUCH MUCH less, than with a 1000Watt-us-style-setup

2.) athletes generally drive with "klippies" (the shoes are fixed to the pedals), so no slip off from the pedals

3.) there are 4 situations the motor stops automatically:
* use the brakes
* stop the pedals by force -> the mtoor notices that and will not feight against you
* frequenz of pedaling under 30rpm
* empty battery

as said: the gruber assist is a assistance motor, only used when pedaling.. so the missing freewheel in the pedals is not bad,
it also helps to make a smoother,more round pedaling, so trainings effect

This ought to be in the RC motor area.

Hi Kraeuterbutter,

Kraeuterbutter said:

for the freewheel:
now i understand:
no, there is only a freewheel in one direction:
so when motor is off, you don´t feel it
but when motor is on, the pedals are turning..

this is by far not that critical as you maybe may think...
1.) "only" 100Watt..
so risk of injuries is MUCH MUCH less, than with a 1000Watt-us-style-setup

2.) athletes generally drive with "klippies" (the shoes are fixed to the pedals), so no slip off from the pedals

3.) there are 4 situations the motor stops automatically:
* use the brakes
* stop the pedals by force -> the mtoor notices that and will not fight against you
* frequenz of pedaling under 30rpm
* empty battery

as said: the gruber assist is a assistance motor, only used when pedaling.. so the missing freewheel in the pedals is not bad,
it also helps to make a smoother,more round pedaling, so trainings effect

Click to expand...

Thanks for the clarification! I didn't think a system that turned the crank could allow the pedals to freewheel but I wanted to check.

Mitch said:

Thats starting to get into the ballpark of sufficient reduction for a low kv RC Motor, particularly through the gears.

Click to expand...

Kraeuterbutter said:

hey...
can you right this with other words or explain ? (my English is too bad to understand what you mean with that)

the crank spins with up to 90rpm
--> 1:111 Gearreduction means -> the motor spins with 9990rpm at that time

Click to expand...

First I thought that the figure you posted was 11:1, not 111:1. Is it really one hundred and eleven to one?

What I meant by starting to get in the ballbark of working with a low kv motor is with a motor of 120kv to 150kv and an additional (roughly) 3:1 to 5:1 reduction (for total of 33:1 to 55:1) the reduction would be sufficient. I realize that motors that have a small enough diameter to fit in a seat tube have higher kv's than 120 to 150. But if the system was affordable and the pedals freewheeled adapting a larger motor would be an interesting idea (to me).

I need a more powerful system so I can keep up with the flow of traffic in hilly terrain. For example a friend rides over a local hill on a bike path that is separated from a 8 lane highway by a metal fence. Its like biking through a waste land. The alternative route is a beautiful tree lined winding road. It isn't safe riding up that windy road on a bicycle because he is constantly being caught and passed by inattentive drives. At 20-25mph (30-40kph) cars couldn't keep up with the bike so he could ride safely on that road. At least for that one situation the option of a bike path exists. For many of the local roads bike path's are not an option.aaa


Thanks!

Mitch

oh, there are also bikes with the pedals freewheeling while the motor is running still through them...

the swiss version id doing this

as you said: slow turning and small in diameter/small in size --> thats not possible
also with your powerdemands

Kraeuterbutter, there is a section devoted specifically to the type of systems that you are working on. Try looking around in this area:

http://endless-sphere.com/forums/viewforum.php?f=28

...RC motors are the hottest thing in ebikes right now and we would love to have you post more in that area.