dual motor control?

[mikepday]

Hi all, brand new here, looking for help regarding info on a build.
my son is attempting for his A-level DT project to build an e-bike motor based mobility "Chair"/"Kart" for his recently partially disabled/reduced mobility Uncle, so he can get back out in the forests with his kids on their bikes.

We have a basic steel frame design and are looking to purchase the conversion kits to add power and motion. Currently the design is a 4 wheel machine with 2 wheel drive utilising 2 front wheel motors at the rear (it will not have any form of pedal/crank/chain drive and be solely electric driven) probably just 2x250W motors as speed is not a massive consideration.
Obviously we can just buy 2 full conversion kits and effectively operate them completely independently using 2 throttles and 2 speed controllers and 2 batteries although this is rather 'inelegant', if a slightly simpler solution electrically. (electronics would be my nemesis if I'm honest!)

Does anyone on here know if we could control 2 motors using a single speed controller and throttle? and importantly where we could find one? this would save space, weight and hopefully enable a sync'd/matched motor output. I've previously built a twin motor skateboard using a single dual output speed controller from a large electric model speedboat, utilising a single throttle input, and it works just great, but the speed controller only takes 150Amps peak and would probably be fried by draw of the 2 bike Motors.

could I for instance use a single 500W speed controller and double the outputs off the board to each motor wheel?

sorry if this seems a stupid question? but I'm open to all options and ideas.

cheers Mike.

 

[vfr400]

There are two options available to you. firstly, there are controllers for dual motors. Don't forget that you'll need a high discharge rate battery to supply double the current, which would be 34 amps in the example below:

T-06SS 36V/48V KT Dual Motor Driving Brushless Sine Wave Controller [T-06SS Dual Driving controller] - $61.75 : Zen Cart!, The Art of E-commerce

Zen Cart! T-06SS 36V/48V KT Dual Motor Driving Brushless Sine Wave Controller [T-06SS Dual Driving controller] - ★★★★★ T-06SS 36V/48V KT Dual Motor Driving Brushless Sine Wave Controller 1--Rate Voltage:36V/48V 2--Rated Current:8A 3--Maximum Current:17±1A 4--Low Voltage Protection:DC30/40±0.5V...

www.topbikekit.com

The second option is to use two separate controllers with a shared throttle or pedal sensor or both. To share the throttle/PASs, you take the ground and 5v from only one controller and split the signal wires to both controllers. You must not take separate 5v wires from each controller. If you use two separate batteries, one for each controller, you need to join the grounds.

There are some special wheelchair kits with matching left and right motors that look after everything, but you have to search for them because I have no links. Here's a couple of kits from Golden motor:

BLDC motor,electric outboard, GMX motorcycle,Golden GMX,BLDC motor controller,EZ Outboard Motor,EZkontrol,EZ-kontrol,foldable electric wheelchair,portable electric wheelchair

www.goldenmotor.com

One problem you need to think about is that the typical 250w hub-motors normally have a one-way clutch, so one on each side can only go in different directions unless you match their orientations. You could use the big heavy 500w direct drive motors if you need both sprockets inboard, but they're wound for much higher speeds than you want.

 

[mikepday]

There are two options available to you. firstly, there are controllers for dual motors. Don't forget that you'll need a high discharge rate battery to supply double the current, which would be 34 amps in the example below:

T-06SS 36V/48V KT Dual Motor Driving Brushless Sine Wave Controller [T-06SS Dual Driving controller] - $61.75 : Zen Cart!, The Art of E-commerce

Zen Cart! T-06SS 36V/48V KT Dual Motor Driving Brushless Sine Wave Controller [T-06SS Dual Driving controller] - ★★★★★ T-06SS 36V/48V KT Dual Motor Driving Brushless Sine Wave Controller 1--Rate Voltage:36V/48V 2--Rated Current:8A 3--Maximum Current:17±1A 4--Low Voltage Protection:DC30/40±0.5V...

www.topbikekit.com

The second option is to use two separate controllers with a shared throttle or pedal sensor or both. To share the throttle/PASs, you take the ground and 5v from only one controller and split the signal wires to both controllers. You must not take separate 5v wires from each controller. If you use two separate batteries, one for each controller, you need to join the grounds.

There are some special wheelchair kits with matching left and right motors that look after everything, but you have to search for them because I have no links. Here's a couple of kits from Golden motor:

BLDC motor,electric outboard, GMX motorcycle,Golden GMX,BLDC motor controller,EZ Outboard Motor,EZkontrol,EZ-kontrol,foldable electric wheelchair,portable electric wheelchair

www.goldenmotor.com

One problem you need to think about is that the typical 250w hub-motors normally have a one-way clutch, so one on each side can only go in different directions. That means you would need the big heavy 500w direct drive motors but they're wound for much higher speeds than you want.

This is great info thanks very much.
i'd be using e-bike wheels in custom made separate 2 wheel frames joined by a single seat frame (think along the lines of a seat with a bike frame each side as shown below which was 2 separate complete e-bikes) id just be getting rid of all the extraneous pedal bike stuff and keeping it fully electric driven only.

Also I don't think the motor reversal issue is a problem, they'd both be mounted as though they were travelling forwards.
The Kart is also intended to travel quite a bit faster than walking pace too to keep up with his rapidly growing young boys on bikes so hopefully 2x250W motors will provide the necessary pace.
I like the single controller, single throttle solution with a single high discharge battery.

thanks again.

 

[mikepday]

I suppose I could wire 2 X 17 ah batteries in parallel to get the Desired 34 ah on a single controller input. It strikes me it’ll be easier to get 2 “17’s” Than one ”34”. Means I can dual charge batteries quicker too I’d have thought.

 

[vfr400]

You're getting capacity and discharge rate mixed up. You can get 40 amps out of a single 10Ah battery if it has the right cells and BMS in it. the cheaper batteries that you get on Ebay are normally 20 amps. The ones they claim are 1000w batteries are often 25 amps and 48v. 40 amp batteries take a bit of hunting out.

 

[mikepday]

You're getting capacity and discharge rate mixed up. You can get 40 amps out of a single 10Ah battery if it has the right cells and BMS in it. the cheaper batteries that you get on Ebay are normally 20 amps. The ones they claim are 1000w batteries are often 25 amps and 48v. 40 amp batteries take a bit of hunting out.

Sorry, yes now you've pointed it out it seems so obvious. ooops!

So its the peak discharge current that needs to match the combined max current draw of the controller to each motor (in my case)
so using the T-06SS dual motor controller you linked to above which has a rated current of 8A and a max current draw of 17+/-1A as an example, with a single battery pack.
Is that max current draw to each motor ie 17+17 A therefore requiring a 34A peak discharge output battery? or is that max current total ie 8.5Ax2=17A peak.

what I'm getting at I suppose is...... am I looking for a battery that provides 16A continuous discharge and 34 peak/max discharge? or 8A continuous and 17A peak/max to suit that specific controller.
(obviously it should be a matching voltage to the motor controller and motors and ideally have the largest AH rating I can afford to maximise range).

PS thanks ever so much for your help so far.

 

[vfr400]

I've not had one of those controllers, but I can see that it's double length, so would have double the output circuits, which would be 17 amps each and 34 amp total. there won't be many circumstances where you need or will get that much current, so any battery with a BMS that can give at least 40 amps should be OK, but the higher the continuous current available, the better.