1 controller operate 2 wheels?

[idiot magnet]

I'm looking at building 2 wheel drive bike (I already bought a rear wheel hub 250w Pro-Rider E-Voyager) I'm thinking to keep the system minimal:- 1 large battery, 1 controller (ie 500w) and a pair of matching hub wheels (ie 2x250w)

Any possible problems? Thanks for looking.

 

[Deleted member 4366]

Not possible. You need two controllers and a battery capable of providing at least 30 amps. Back to the drawing board, I'm afraid.

 

[idiot magnet]

So, out of curiosity, what's the difference between a single 500w wheel and 2x250w wheels?

 

[Alan Quay]

I think you need to tell us what you are looking to achieve.

2 wheel is going to add more weight and complication, and may not produce the result you are expecting.

 

[Deleted member 4366]

So, out of curiosity, what's the difference between a single 500w wheel and 2x250w wheels?

2WD gives better traction for riding on slippery surfaces. Other than that, there's little advantage, except that it can reduce your sprung to unsprung weight ratio to make suspension work better.

 

[idiot magnet]

I like the idea of balancing the weight, better off-road traction and possibly better acceleration/torque. I'm just wondering why (electrical terms) would there be a difference in using a pair of 250w's against a single 500w?

 

[trex]

like many concepts, the 2WD seems like a good idea until you try to build one or ride one.
Motorized wheels are less stable than normal wheels when starting off, weight at the wheels make the bike less maneuvrable than normal wheels when cornering etc. Unless you have one of those specially made controllers for 2WD, you need to have two controllers, one for each wheel, and to design your own electronics to share battery, throttle, brake and pedal sensors.
2WD is not a good idea.

http://endless-sphere.com/forums/viewtopic.php?f=2&t=33429

 

[Deleted member 4366]

There's very little difference in power and torque between 2WD and a larger single motor provided that the total current is the same, e.g. 2 x 15A vs 1 x 30A. Therefore, there's little point in making a more complicated two motor installation.

Speed depends on the motor windings, so adding an extra motor won't make you go any faster. If you want more speed, you have to choose motor/s with a higher winding speed.

 

[idiot magnet]

so as long as the 2 (250w) wheels pull less current than the controller (500+w) then I should be able to wire the 2 wheels in parallel?
There isn't any feedback wires off the wheels going to the controller is there?

 

[trex]

it depends on the motors. Most modern e-bikes have brushless DC motors (BLDC), each has three phase wires, the current going through these phase wires must be locked to the rotor's position, otherwise the rotor won't move. There is no way you can keep the two motors synchronized, therefore you can't wire them in parallel.

 

[selrahc1992]

it depends on the motors. Most modern e-bikes have brushless DC motors (BLDC), each has three phase wires, the current going through these phase wires must be locked to the rotor's position, otherwise the rotor won't move. There is no way you can keep the two motors synchronized, therefore you can't wire them in parallel.

That never occurred to me (was wondering why it wouldntbwork), but are they really in parralel? I imagine the two motors don't know about each other and are only aware so to speak of the controller as if it is all there is? Apologies if this is very noob

 

[trex]

that's what i.magnet planned to do. Even with two brushed motors, you would want to split the power 40% to the front and 60% to the rear.
With BLDCs, if they have Halls, you can only connect one set to one controller, if they don't have Halls, then you can't parallel them anyway, because the controller relies on the back EMF to work out the rotor's position in relation to the stator.

 

[Alan Quay]

That never occurred to me (was wondering why it wouldntbwork), but are they really in parralel? I imagine the two motors don't know about each other and are only aware so to speak of the controller as if it is all there is? Apologies if this is very noob

A brushless DC motor will only spin if the correct sequence of coils are energised, and at the correct frequency and direction of current. In fact, the bit between the controller and the motor is really AC. The controller contains a microprocessor that senses and delivers the correct sequence.

If you could guarantee that the motors would always be in the same position then one controller would work. But you can't do that on a bike.

 

[idiot magnet]

OK, so that's explained that problem (I've wired 3 phase 415v motors before) I assumed the rotation would be sequenced regardless of wheel position and the wheel would eventually catch up to the motor's spin speed (as does AC motors).
So next alternative is 1 large battery, 2 controllers, 2 wheels & 1 throttle...

on the throttle (the one's I've seen) there's usually 3 wires:-

ground, v supply & pot value return

If I use a pair of same controllers, I should (in theory) be able to common the ground and just link over the pot return and be able to use 1 throttle (?)

 

[Alan Quay]

OK, so that's explained that problem (I've wired 3 phase 415v motors before) I assumed the rotation would be sequenced regardless of wheel position and the wheel would eventually catch up to the motor's spin speed (as does AC motors).
So next alternative is 1 large battery, 2 controllers, 2 wheels & 1 throttle...

on the throttle (the one's I've seen) there's usually 3 wires:-

ground, v supply & pot value return

If I use a pair of same controllers, I should (in theory) be able to common the ground and just link over the pot return and be able to use 1 throttle (?)

Yes, that should work (never tried it myself though). They are normally hall effect sensors, not pots.

Also, on some controllers I've noticed a start-up check. If the throttle is not present when powered on, it will be ignored until power cycled.

 

[Deleted member 4366]

The controllers share the same ground from the battery, so you should only connect the signal wire from the thtottle on the second controller. If the 5v is a bit weak, you can get glitching of the throttle signal when you split it between two controllers. If you get glitching, you need to buffer it through a transistor. If you search for "throttle buffer" you should be able to find a schematic.

 

[Christopher John Holmes]

Sorry to butt in i run a 2wd (2 controllers) 2 throttles the front is on Left hand side and a thumb type i do use 2 batterys
i have 36v 250w front motor used for pullaways & main 48v 1000w rear for all donkey work

works well but it is a bit back heavy on the rear rack 48v+ lipo for back & 36v loin for front but iam 17 stones and it pulls well?

not sure about 2 controllers off 1 battery

 

[martin@onbike]

Not seen one of these yet...wonder where they've hidden the second controller?
http://www.bhbikes.com/en/bicycles/ebikes/evo-snow-29--ev775.html

 

[Croxden]

Not seen one of these yet...wonder where they've hidden the second controller?
http://www.bhbikes.com/en/bicycles/ebikes/evo-snow-29--ev775.html

Stainless steel spokes, are these liable to give problems?

 

[martin@onbike]

Nah, most spokes are made from Stainless Steel.

http://www.sapim.be/spokes

(and Sheldon says....)
"Spokes
The material of choice for spokes is stainless steel. Stainless is strong and will not rust. Cheap wheels are built with chrome-plated ("UCP") or zinc-plated ("galvanized") carbon-steel spokes which are not as strong, and are prone to rust.
The leading brands of spokes available in the U.S. market are DT and Wheelsmith.

Titanium is also used for spokes, but, in my opinion it is a waste of money. Titanium spokes should only be used with brass nipples, and the combination is not significantly lighter than stainless spokes with aluminum nipples.
Carbon fiber spokes have been available, but turned out to be brittle and dangerous. If you bend one, it breaks like uncooked spaghetti! Carbon fiber, aluminum alloy and polycarbonate plastic spokes all have to be thicker than steel spokes, and the added air resistance slows you down more than the weight saving speeds you up -- unless you only ride uphill."

I'd like to think that the old broken spoke issue on the BH rear motors has been resolved now, after several instances of them breaking and having to be replaced/repaired. It looks like they're finally getting their act together in terms of producing a bike that is ready to be ridden without too much fettling out of the box. Better diagnostics, faster service so far this year.....I do hope it continues as they are capable of producing nice bikes as proven with the Panasonic powered bikes that still stand the test of time.