birdy bike

[marco001]

I have a MK2 classic Birdy, which I want to convert.
After a bad experience with Grin Ebike ca, I would like your advice.
I want to put a frontal motor but it has a fork, of somewhat special design, for those who know the Birdy sure they understand what I am talking about.
My main problem for now is to determine, which engine can fit there. I attach photos to see what I mean
Thanks in advance

 

[2old]

Depending on the width of the dropouts, a front hub system should be possible, but maybe not the best bike for one since you need to accommodate the suspension. For me, a separate bike would be preferable if this is an option.

 

[marka-ee]

Most hub motors would have a problem with that bracket that intrudes into the space between the dropouts. By the way, I really like that suspension design. I'll bet it's really smooth on even the smallest bumps.

 

[marco001]

Yes, it is very difficult to find an engine of that measure, I know that the Crystalyte Saw 20 have been used and an AKM, but I can't find any of the two and the AKM I do not know the exact model even.
By the way, if it is a very soft conduction, although the original springs have a lot of return, I have compressed air shock absorbers that are drier in the return.

 

[E-HP]

If you find a small geared hub for 75mm dropouts, but with an extra long axle, you may be able to add enough washers/spacers to make it fit. I don’t think many/any 100mm O.L.D. motors that will fit.

Something like this, but with longer axle flats.

AKM85SX(F1)_Aikema Electric Drive System (Suzhou) Co., Ltd_Motors_Batteries

AKM85SX(F1)-Aikema Electric Drive System (Suzhou) Co., Ltd_Motors_Batteries-Rated Power: 250W<br> Max Torque: 30N.m<br> Weight: 1.6kg

www.aikema-e.com

 

[marco001]

probably you are right and maybe the few option for this bike are a solution like that , i just like to know someone to confirm me that is the way .
I start the project with grin ebike Canada but after a misunderstood and their not kind costumer service now i have a battery of 52 v and Im try to learn the way to use it with a small motor like those akm85 and not burn it

 

[E-HP]

Do you have rudimentary metal working skills? Would a slight change in geometry (perhaps a welcome change for more high speed stability) be acceptable?
Just brainstorming here. Buy two of these to extend forward and narrow the dropout to fit the 75mm hub motor linked earlier.

3/8

CARBON HOT ROLLED FLAT ASTM A36

fastmetals.com

Drill two holes in each, that match the dropout and the hole right above it. Cut/file new dropouts to fit the hub. Bolt the extension on with appropriate fasteners. The 3/8” x 2 gets you within a washer of 75mm.

You could use 3/8” angle iron instead of the flat bar and narrow one side to 20mm (a decent amount of hacksawing), which would add more strength and the ability to add another bolt for an attachment point with the existing fork arm (rear of the existing dropout). You’ll need to see how much leeway you have in order to still have your brake pads line up, which you can try first to see if the idea is even viable. The good thing is, that with 3/8” steel, you can skip the torque arms all together.

This will move your wheel forward and slow the steering a little. I’m sure Chalo will have some thoughts on this.

 

[marco001]

Do you have rudimentary metal working skills? Would a slight change in geometry (perhaps a welcome change for more high speed stability) be acceptable?
Just brainstorming here. Buy two of these to extend forward and narrow the dropout to fit the 75mm hub motor linked earlier.

3/8

CARBON HOT ROLLED FLAT ASTM A36

fastmetals.com

Drill two holes in each, that match the dropout and the hole right above it. Cut/file new dropouts to fit the hub. Bolt the extension on with appropriate fasteners. The 3/8” x 2 gets you within a washer of 75mm.

You could use 3/8” angle iron instead of the flat bar and narrow one side to 20mm (a decent amount of hacksawing), which would add more strength and the ability to add another bolt for an attachment point with the existing fork arm (rear of the existing dropout). You’ll need to see how much leeway you have in order to still have your brake pads line up, which you can try first to see if the idea is even viable. The good thing is, that with 3/8” steel, you can skip the torque arms all together.

This will move your wheel forward and slow the steering a little. I’m sure Chalo will have some thoughts on this.

I need a drawing I am not sure to understand the idea. But yes, I have some mechanical skills

 

[E-HP]

I need a drawing I am not sure to understand the idea. But yes, I have some mechanical skills

No CAD, so here’s a sketch. Sorry, not too good at sketching either, but the cross hatched part is the mod. (Not to scale)
The arrow points to the extra attachment point with the existing fork arm, besides the bolts that will attach it via the existing axle slot and hole above it.

The new dropout has to be forward enough to allow the hub motor axle nut to turn. It can be slightly deeper to make the brake pads align, which I think will be the challenge.

 

[Epithemeus]

Does the rear have the same problem? Maybe there's a reason you've ruled out rear that I don't know but it seems to me it would probably be a lot easier based on pictures I googled of the rear dropouts.

 

[E-HP]

Does the rear have the same problem? Maybe there's a reason you've ruled out rear that I don't know but it seems to me it would probably be a lot easier based on pictures I googled of the rear dropouts.

Sorry, it sounded like you wanted a front hub.
Rear should be easier, but note that while the o.l.d. for most hub motors is 135mm, they require a washer inside the dropout, on both sides, so you need more like 140mm. Most frames can stretch without causing problems, to fit the hub in. I’m not familiar enough with how the swingarm is constructed to guess whether it can flex, but you could test that by taking off the wheel and tugging on the swingarm.
You’ll need torque arms.

 

[marco001]

I wanted an IGH Alfine with Belt Drive, that's why my first option is the Front Hub.
The rear hub is my second option. APPROPOSIT Do you know something good for rear? Maybe you could recommend something, I thought about something from 500W, if I don't have my IGH at least I want to have something good.
On your sketch it is super ingenious but there is a problem, if the axis moves, I will have brake problems.

 

[E-HP]

On your sketch it is super ingenious but there is a problem, if the axis moves, I will have brake problems.

It’s difficult to see if it would work without having the bike to see. But I made the new dropout slot deeper to bring the wheel up slightly, which might compensate enough to have brake pad alignment. If you take off the front whee and hold it in positions in front of the existing fork, you can tell quickly whether it would be feasible or a non starter.
If you go with a more powerful rear hub, then I would figure out what kind of battery you’d be able to fit first (I would start there regardless of which motor, since it’s the most important and costly part of any build).

 

[marco001]

actually i start this project with the people of grin ebike , but finally i returned his product. and now i have a 30ah 52volt 24700 from america electric so i don't think i will have problem for potency or range autonomy

 

[marco001]

I don't understand why is to difficult found for example this motor hub Component , i write them (bafang) but nobody have it
Is no like it is discontinue right

 

[marco001]

It’s difficult to see if it would work without having the bike to see. But I made the new dropout slot deeper to bring the wheel up slightly, which might compensate enough to have brake pad alignment. If you take off the front whee and hold it in positions in front of the existing fork, you can tell quickly whether it would be feasible or a non starter.
If you go with a more powerful rear hub, then I would figure out what kind of battery you’d be able to fit first (I would start there regardless of which motor, since it’s the most important and costly part of any build).

i try and is actually possible lol

 

[marco001]

You can believe that I am crazy, but, I was thought for something more radical. I have a Bike Helix and I was thought to modify the bicycle and design new parts. The rear fork and the front fork to carry 24 -inch wheels such as the Helix and maybe create space for a BB engine. Even I had made diagrams taken from the rear fork.
Now with the 3D titanium and carbon printer systems it makes me even more feasible than before. I had thought about doing a blueprint and making the pieces in chromolly or titanium. Now I could do it in 3D plastic to try it and then in carbon or titanium or both ...

 

[DaLanMan]

I have had parts sintered on a 3d printer, I was very happy with the results. My current fab gear doesn't go that far, but I could probably get the places deets for ya.

 

[marco001]

Component perfect size , nobody sell it , f**** lol

 

[marco001]

so could yo recommend me some rear motor ,I have 30ah 52v battery and I want to go 40 miles every week

 

[marco001]

I have had parts sintered on a 3d printer, I was very happy with the results. My current fab gear doesn't go that far, but I could probably get the places deets for ya.

i need that info please

 

[lnanek]

i have a battery of 52 v and Im try to learn the way to use it with a small motor like those akm85 and not burn it

FWIW, I've never seen a hub motor that can't run 52V. They are incredibly rare. Only a couple out there that have controllers built into the hub and things like that.

Most hub motors are just a bunch of wires wrapped around blocks of metal many times to make electromagnets. Higher voltage is more useful there since you can run fewer amps for the same amount of power. I used to plug home made electromagnets made from nails and wire into 120V house voltage without issue.

Many hub motors have hall sensors, but these never see the battery, nor phase voltage anyway. The controller you use will have a voltage converter circuit that supplies 5V to the motor via separate wire for these. So the only part that can get fried from high voltage is protected regardless.

It's true running a higher voltage than spec'ed for the motor will increase the top speed and decrease the torque. Due to every motor having a Kv factor which lets you know the rpm you'll get from a certain voltage. So theoretically if you had some tough, very long hill climbing planned, you might be more likely to overheat. Good motors have a temperature sensor, though, and good controllers, like any of Grin's, have thermal throttling logic such that the controller will give the motor less juice if it is overheating.

Tl;dr : the voltage spec on a hub motor is largely meaningless. The controller is what can be fried. But even Grin's weakest controller, the BaseRunner, handles 52V fine since 60V is a common max for the electrical components in a controller (MOSFETs and the like).

 

[DaLanMan]

Fathom I have worked with a few companies, I am gearing up to just doing it locally though. For the amount that I do (usually 1 off events) It makes sense to build my own.

I have also heard good things about a company in the UK, No clue where you are from though.

 

[Papa]

From your frame side view, I'd estimate 25-30mm positive trail. Means you likely shouldn't reposition the front axle forward more than 20mm or so. On such a short wheelbase bike, I'd discourage repositioning the axle anyway.

Replacing the fork is what I'd suggest.

 

[Chalo]

From your frame side view, I'd estimate 25-30mm positive trail. Means you likely shouldn't reposition the front axle forward more than 20mm or so.

Not even that. Natural trail is proportional to wheel diameter, so tiny wheels need short fork offset.

On such a short wheelbase bike, I'd discourage repositioning the axle anyway.

Replacing the fork is what I'd suggest.

I think the existing fork could work at long as a narrow hub motor with normal 100mm axle width is used. (And as long as the dropout eyelets are used to anchor torque arms.) Maybe something like the Q70, but with clamping dropouts fastened inboard of the bike's fork tips. That would allow a 13mm thick axle clamp.

I don't think going faster than pedal speeds on a donut wheeled bike is a good idea, though.