An Electric Bicycle

[S. Heslop]

I'm trying to build an electric bike. It's hard to find information about directly that on the internet since most people like to call installing an overpriced kit as 'diy/ homemade'.

One thing giving me alot of trouble is sourcing a suitable motor. On ebay looking for scooter motors and DC motors I can't find any over 350w, and searching on google just gives me a load of shady Chinese websites.

Are there any good websites/ catalogues for buying spare and surplus motors in the UK? Or could I maybe try looking for something else. I think I once heard a thing about using car alternators as motors for kiddie cars.

[vtsteam]

Older brushed generators would probably work.

I know it sounds weird but what about a brushless R/C motor and ESC?

Raynerd could probably help out there, since he built a CNC motorized mill spindle with one.

[vtsteam]

How about this one:

http://www.giantshark.co.uk/product/169401/xyh63-54-250kv-65a-outrunner

[vtsteam]

I don't know your price range Steve, but if you only want to get 500 watts out of it, the above would be nicely overbuilt, yet have the advantage of a low kV (meaning revolutions per volt) which will reduce your gearing down requirements.

If you limit it to 500 watts, you might be able to get by with an ESC of say 60 amps (rather than the more expensive recommended 100a ESC). You would need a slip clutch or some means of preventing over current/stalling, but probably would for a 100 amp ESC as well. Also, of course a throttle stop.

The lower the voltage the easier the gearing is going to be. 4 Lipos appears to be the minimum recommended for this motor, which is about 15 volts -- that would still yield about 600 watts @ 40 amps. Motor RPM would be about 15V  x 250 kV = 3750 RPM

If you went to 5 lipos, that's about 19 volts and you would run a max of about 25-30 amps to get you in the 500 watt range. Even a smaller ESC, but gearing ratio would need to be higher. Motor RPM would be about 19 V x 250 kV  = 4750 RPM

[S. Heslop]

Thanks for the reply.

Yeah that looks like a good motor. It's much smaller than the scooter motors I was looking at too, and about the same price (if not cheaper!). I guess the brushless controllers bring the price up though but it's still within what i'm happy to pay.

I guess the next problem is figuring out how to gear the motor down with the tools I have.

[vtsteam]

Steve also for a controller for the ESC (ie throttle), you can use what's called an R/C "servo tester" -- they are very cheap from some sources. They generate the pwm signal the ESC needs to set the motor RPM.

That motor listed by the way, has probably only limited availability. Looks like greatshark has sold out of that brand  for most of the other motors in the line. Though they say " by special order" for availability on the others, I doubt it.

I've used those same red motors branded as "EMP" and have had good luck with them.

[S. Heslop]

When it says outrunner does that mean the outer casing of the motor is the part that spins?

[mattinker]

The outer case is fixed to the spindle so that they both turn at the same time. From what I can gather they have more torque than the in-runner configuration.

Regards, Matthew

[vtsteam]

An outrunner has an outer ring that contains the magnets, and spins and is usually connected to the prop shaft. The coils and armature are stationary. Efficiencies can be up as high as the 90+% range. Higher than inrunners. Cooling is usually easier also.

One consideration would be to support the shaft outside of the motor (add a pillow block) in a geared, or chain drive for a bicycle configuration. An airplane loads the motor axially in thrust. Gearing will load it radially,

But it's not hard to add an external bearing. If needed also, the motor shaft can be replaced with a longer one fairly easily. Typically in a mill adaptation, an ER collet arbor is substituted for the original motor shaft. I think Reynard's forum thread on his CNC mill conversion goes into this.

Here are examples of servo testers that would provide the throttle potentiometer and control circuit for the  ESC. (ESC stands for Electronic Speed Controller):

http://www.ebay.co.uk/sch/i.html?_nkw=servo+tester

[S. Heslop]

Thanks again.

I'll order that motor and a controller tomorrow most likely. Still gotta think about it for a bit for £90.

All this motor stuff is really making me feel like a dunce though. Hopefully I don't cock it up!

[vtsteam]

Yes, thinking it over is good. It does mount up. And maybe someone else will have a lead on a less expensive way -- I'm going to look into that mention of an alternator conversion for a kiddie car. Sounds interesting.

[vtsteam]

Coming at it from the opposite direction, it looks like R/C modelers have been using ESC's to power auto alternators as motors. Here's a really extensive thread on the topic:

http://www.rcgroups.com/forums/showthread.php?t=905411

also, large ESC's can be had for considerably less than the place I linked to, if you are willing to purchase direct from China.

http://www.ebay.co.uk/itm/RC-Model-Airplane-Helicopter-60A-Brushless-Motor-Speed-Controller-ESC-SL025-/251528990050?pt=UK_ToysGames_RadioControlled_JN&hash=item3a904bcd62

[S. Heslop]

Alright, ordered the motor, speed controller, and servo tester. Thanks for the help.

Y'know I'm always amazed that you can order things for as little as £2 from China and still have free delivery.

[John Rudd]

Well I hope your order is fulfilled....

Giant shark use  to be Giantcod, run by Rob Carpenter until he sold up...
Gs is now owned by the same outfit that publishes ME MEW mags.... They've been transferring stock ready to hike up prices in line with other retailers....So our cheap products from China are drying up.....sadly....

[vtsteam]

Well I assumed a UK outfit would be more reliable than an overseas one, and more easily accountable if not. Apologies if that is a questionable seller. They list the part in stock and I don't see why they wouldn't ship it. But I don't know local sellers there like I do here.

If there are any problems, similar motors are available from Chinese sources, and I think HobbyKing UK, (though I'm no fan of HK and would likely recommend others if ordering direct from China).

I'm guessing Steve paid by PayPal, or credit card, so if it isn't shipped within a week he can speak to them locally, or cancel and purchase elsewhere.

[S. Heslop]

They shipped very quickly. The motor arrived this morning!

And it looks good. Even came with a mounting plate and an attachment/ nose cone for a RC propellor. Can't test it until the speed controller arrives from Hong Kong though. The servo tester also arrived and I bought a free wheel from halfrauds. It's exciting when things start to come together, but there's still a ways to go.

Thanks once again for the help.

[vtsteam]

Hey Steve great!! 

Steve -- just a suggestion -- don't over-rev it testing -- I'd put a load on it like a dummy propeller -- just a good straight grained piece of hardwood, balanced, roughly the size of a propeller to suit.

Don't stand in line with it, and be sure to bolt that motor down solidly before applying juice to it -- they can really torque around.

Be cautious!

Also, those bolt-on prop shafts are usually aluminum -- the loads on a plane motor are primarily axial, and not radial, so be cautious with that setup if trying out something other than a propeller.

You'll probably want to replace the steel motor shaft -- I think it's 10 mm -- with a longer steel shaft to take radial loads, and also support the longer shaft in an external bearing.

Well, exciting that you're on your way!!

[S. Heslop]

That's a good suggestion. Also supporting the shaft with another bearing wont be a problem now that the original gear plan isn't going to work.

I might have to bite the bullet and spend £30 or more on gears. I'm still really surprised by how expensive gears are! The two auctions for lathe change gears I was keeping an eye on ended up reaching nearly £50 so there goes that option too. Maybe i'll get implausibly lucky at the boot sale tomorrow, or at least pick up some cheap power tools to take apart (although I think the motor shaft having a gear milled into the end is pretty standard with them).

[vtsteam]

What about chain drive? Sprockets and chains are available from tractor/farming supply companies.

Have you worked out your wheel size and some idea of what kind of reduction ratio you want to try?

The larger the wheel size the greater the reduction needed.

Also, how many volts and what type of battery will you be trying?

It might be economical for testing and ballpark estimating to just find a used 12V car battery and make a wooden kart and see what that will do, then move on to whatever else you have in mind once you've established a baseline for components.


Also, aren't there motorized bicycles that use friction drive against the wheel rim? A clutch and reduction rolled into one, and a pretty big reduction ratio.

[S. Heslop]

Yeah i've tried a few. I think I might have it sorted though.

Placed an order for 2 sets of these.
http://www.amazon.co.uk/Repair-Spiral-Pinion-Makita-4100NH/dp/B00EZCQO7W/ref=lh_ni_t?ie=UTF8&psc=1&smid=A50DZI580G3JX

If it works out it'll be very cheap! Although the ratio is a bit low, the rear wheel will be turning at about 370rpm if the motor is going at 6000rpm. That'd be close to 30mph and might not give me alot of torque, but i've really got no frame of reference on how much is required and how much the motor supplies.

Here's the plan so far though.



There'll be a chain connecting the gearbox to the wheel's sprocket. It's a bit of a crazy plan, gripping a sprocket to the center hub (opposite to the existing sprockets) of the rear wheel via an aluminium block.

The things I'm concerned about is if the gearbox and motor will fit well in that small space between the frame and the wheel (I don't want to put it too far forwards in case it hits my legs as I pedal) and if there'll actually be enough of a gap to feed the chain through. I might need to make some kind of idler to push it down and out of the way maybe.

If it works out it should be a pretty good system though. The two main types of DIY electric bikes i've seen either turn the rear wheel via friction on the outside (which seems like it would have alot of problems), or turn the pedals (which would be tiring to keep up with, but I guess that's more of a power assist for steep hills). The free wheel I bought should ratchet if I pedal without the motor, so I won't be fighting against a gearbox and motor when purely peddling.

Boy i'm really using alot of weasel words. I'll honestly be surprised if this works out first try, but i'm having fun non the less!

[S. Heslop]

What about chain drive? Sprockets and chains are available from tractor/farming supply companies.

Have you worked out your wheel size and some idea of what kind of reduction ratio you want to try?

The larger the wheel size the greater the reduction needed.

Also, how many volts and what type of battery will you be trying?

It might be economical for testing and ballpark estimating to just find a used 12V car battery and make a wooden kart and see what that will do, then move on to whatever else you have in mind once you've established a baseline for components.


Also, aren't there motorized bicycles that use friction drive against the wheel rim? A clutch and reduction rolled into one, and a pretty big reduction ratio.

I'm aiming for 24 volts. I've got a whole bunch of old RC car NiCd packs I thought I could rewire to test it, and if it works out I'll go hog wild and build a gigantic lithium battery. I was thinking of using 12v sealed lead acid batteries, but i've been reading that they can't really supply enough current to keep up with brushless outrunners.

I live in an ex industrial area, all centered around the long gone Connsett iron works. But that means there's a whole load of disused railway cycle paths (complete with viaducts!) that go all over, and one goes right by house. It's a silly idea but I thought I could ride the bike up to my grandparents. I visit weekly and the bus fare costs £7 just to get there. My grandad usually drives me back home but he really doesn't feel comfortable leaving my grandma alone for too long in case she injures herself when he's not around. And I sure as heck can't afford my own car on a student loan.

But yeah i'd be surprised if I could produce anything rugged enough to survive long weekly trips, but at least it's all downhill back home if something breaks!


Y'know I never thought about running a motor on the wheel's rim. I'd only seen photos of people running them against the tyre. If I had a bike with disc breaks that might work well, but with the rim breaks on this bike I can't think of anywhere I could easily attach it.

[vtsteam]

Steve I just looked up figures for that motor and them ran them through Motocalc as a fictitious airplane to try to get some figures out of it.

As an estimate at 5700 rpm and 24 V  and a 7 cell lipo pack you should be hitting it just about at your target power --  485 watts output from the motor with an additional waste wattage of 66 watts, estimated motor efficiency 88%, current 23 amps.

Hypothetical, and based on assumptions and mfr's figures for idle current and resistance , but I'm pretty good at monkeying motocalc and I tend to get good results.

Will 500 watts motor output push you an your stuff at 30 mph?  Dunno that part. But I'm rooting for ya!

[S. Heslop]

Yeah i'd be surprised if 500w reached 30 mph but it should be enough to push me along under its own power at a lower speed. I kinda wish I ordered 3 sets of gears now! Although with a bigger gear box I won't be able to fit in the space i've got...

I guess I could always go for a bigger motor if needs be. I wonder how the tiny gears would hold up too. And i'm also wondering how speed controllers designed for RC planes would hold up. I guess you only learn by making mistakes~

[philf]

A very interesting project.

Unless I'm missing something obvious I don't think your Halfords freewheel is going to work on the left hand side of the bike (unless you try to ride it on battery power backwards)!

Going out on my bike now - 80 plus miles into Cheshire. I may be wishing I'd got electrical assistance for the big hill a mile from home.

Cheers.

Phil.

Edit: I've just been thinking about this on my ride and of course you can fit a single speed freewheel either way round but you will need a left hand threaded lock ring to stop the freewheel unscrewing. You can buy hubs which are designed for fixed on one side and free on the other which would do the job.

Just sat in a cafe waiting for my cheese and onion toastie.

Phil

Last Edit: It looks like not all single speed freewheels will fit the wrong way round. Phil.

[Joe in Oz]

I'm watching with great interest!
You will need to think about cooling for this motor. In an RC plane, it has the propeller wash cooling it - on your bike it has the draft from going forward when you do - up to about 30mph in your estimate. That's nothing like enough I believe. So you need to moount a little blower and shroud on the shaft as well.
Looking forward to  your results and reports - good or bad!
Cheers,
Joe