Cargo bike electric conversion

[matt]

Hello everyone.

I have recently acquired a new cargo bike that I wish to make electric. Here is a photo of it:



I have a few questions though.
Should I use one rear electric motor or two front electric motors?
If I use two in the front will I lose range compared to one in the back? I am looking for lots of range here. I have two 48v 20ah packs that will go in a wood bench/chair thing in the front basket.
Thanks!

[truly_bent]

Given that one 48V 20AH is good for one MP to travel about 100 km (with pedal assistance), then two motors and two battery lumps ought to give you about the same distance - carrying twice the load.

Gary has experience with multiple MP's on one bike, but they were mounted front to back, not side to side. I'd be a little concerned about balancing the speed between the two. I'm assuming you'll be running separate controllers for each motor. If unbalanced, your rig might have a tendency to pull to one side. Maybe not a big problem.

You might consider having one controller handle both motors. Would have to be pretty beefy controller though; 60+ amps beefy. That would take care of the straight line problem, although cornering could be an interesting experience.

Look into Dennis' Morgan replica for insight into all things tadpole. He went with the single driving wheel in the rear. That resolves any turning issues. Where he stashes all the grandkids in that rig is still a mystery to me though. 

Nice bike, btw.
Jeff

[matt]

Given that one 48V 20AH is good for one MP to travel about 100 km (with pedal assistance), then two motors and two battery lumps ought to give you about the same distance - carrying twice the load.

Gary has experience with multiple MP's on one bike, but they were mounted front to back, not side to side. I'd be a little concerned about balancing the speed between the two. I'm assuming you'll be running separate controllers for each motor. If unbalanced, your rig might have a tendency to pull to one side. Maybe not a big problem.

You might consider having one controller handle both motors. Would have to be pretty beefy controller though; 60+ amps beefy. That would take care of the straight line problem, although cornering could be an interesting experience.

Look into Dennis' Morgan replica for insight into all things tadpole. He went with the single driving wheel in the rear. That resolves any turning issues. Where he stashes all the grandkids in that rig is still a mystery to me though. 

Nice bike, btw.
Jeff

Thanks for the reply. I have decided to use a rear motor after discovering the front wheels are 24" and not 26" (I already have one 26" Magic Pie). What would be the difference between a 250 and 500 watt motor? I will be carrying over 200 pounds of cargo in the bike sometimes, will 250w even be enough for such loads?

[truly_bent]

The Magic Pie is rated 1440 watts at 48V. I don't understand your question about 250 watts being enough.

What motor are you talking about?

[matt]

Oh I had to order a new Magic Pie because my old one is for the front wheel. I have some no name 250w hub motor in my shed and I am wondering if it will be worth it to install it while I wait for the Magic Pie 3 rear wheel to be delivered. Sorry for the confusion.

[truly_bent]

I suppose the answer to that might be determined by who you bought the Pie from. If you bought from Gary (go Canada!) then you're not likely to have enough time to Monkey around with the small stuff. If you bought directly from GM China, then consult with the ship's manifest.

I honestly can't imagine riding a 250W bike anymore... I wonder if there's a 12 Step program for power withdrawal?

Jeff

[matt]

I did buy it from gary, and I decided not to even bother with the 250...
I finished building the battery box / seat in the front cab today. Cant wait for the motor to arrive so I can get this thing going. I will post pictures and maybe a video when I'm done for anyone that is interested to see

Thanks for the help

[e-lmer]

If unbalanced, your rig might have a tendency to pull to one side. Maybe not a big problem.

Actually that might be a cool feature if it could be tuned properly, you could apply a rheostat to the steering
mechanism that increases the throttle voltage to the outside wheel to get a kind of power steering.

[truly_bent]

Nice observation. I missed that possibility entirely.

By rheostat do you mean potentiometer? If so, the controllers would have to be hardwired together for a common reference. I think.

In order to avoid any voltage mismatch issues in shared signals both systems ideally should be running at the same potential. This effectively means running off the same battery pack, or connecting the two battery packs in parallel (in series if your looking for a rush).

If not running the two controllers at the same potential, i'd be inclined to opto-isolate any signals, which may be an expensive option - especially for analog.

Now, if the two controllers could be networked... Then we're talkin'
Jeff

[Morgen 3Eman]

I finished my painting today (I think) , so I've got time to spend making the universe a better place! 

Concerning front 2 wheel drive or rear single wheel drive, I have  a rather strong opinion that can be boiled down to "KISS" , Keep It Simple,Stupid.

So you can figure that I wouldn't even think about actually buying two of everything, and having to wire up two of everything, and having two of every thing to go wrong....

But, if you really wanted to use two motors, and build an electronic differential into the system, it wouldn't be too terrribly hard to do.  First off, you have to decide if you are using one battery or two.  If two are used,I would join the negative sides of the batteries together to make a common reference voltage for the control signal from the throttle. The DC power to the throttle needs to come from only one controller.   I would not even think about using regen.  The throttle output signal and the throttle inputs to the controllers needs to be modified so when the steering moves it proportions the throttle signal differently to each controller.  Since I don't actually know what the controller input circuit schematic looks like,  I would a 100K Ohm resistor from the throttle signal input pin to ground.  I would guess at about a 5-10K ohm linear pot would be pretty close to the right value, but would do the math  to determine what the smallest turning radius demanded for the differential  value.   Anyway, the pot needs to be driven by the steering somehow, with the wiper in the middle when straight ahead; you figure that out.   The throttle output signal should be routed to the wiper of the pot.  The ends of the pot  would be hooked up so that when the wheel is turned left, the resistance to the left controller input pin is increased.  That way the signal developed across the 100K resistor on the left side would see a signal decrease, while the right would see an increase. 

Now ask yourself: "Why do I want to go to all that trouble?" and "What are the chances this old fool is wrong about everything?"

Feel free to use or ignore anything and everything I have stated above.



TTFN,
Dennis

PS Anybody figure out the odd battery discharge yet?

     

[truly_bent]

I would join the negative sides of the batteries together to make a common reference voltage for the control signal from the throttle

Thought of that Dennis, but if only the negatives are tied, the positive values will be at different potentials. Depending on usage, the battery voltages could be out by several volts. By running the batteries in parallel, I'm leaving any variance in potential to the BMS side.

Anyway, the pot needs to be driven by the steering somehow, with the wiper in the middle when straight ahead; you figure that out.

As per the type of work I do, I would be heading immediately for Embedded Control Alley. Regardless of how the steering position becomes data, the difficult nut is going to be the differentiating function itself. (A 360 ppr encoder, tied to an Arduino would would make someone an interesting starter project. Yes, I'm a fan of the Arduino ).

I'd rather be screwing things up in software than hardware.
Jeff

[Morgen 3Eman]

Hi Jeff,

What I should have said was that if only one side of the batteries are tied together, it has to be the negative side,  since that is where the throttle signal is referenced. 

And it would be smarter to just connect the 100k resistors to the ends of the pot, (referred to ground, ) and just run the signal wires from the pot/resistor junction into the unmodified circuit board connection.

I totally agree with you about the Arduino.  What a great little product.  And incredibly cost effective!    But some analog things are actually easier to implement in hardware.

And there is still no way I would put two motors on a three wheeler.

TTFN,
Dennis

[truly_bent]

D;
Think of all the fun you'd have tinkering with it.
J

[Morgen 3Eman]

Well, yeah, that is kind of appealing...

TTFN,
Dennis