2WD (Two-Wheel Drive) FAQ

[Floont]

I use a left hand throttle for my Front Wheel Drive motor, so the left throttle goes with the left brake, which both operate the front motor and brakes.

In my Rear Wheel drive build, I'm keeping the right hand throttle with the right brake, which both control the rear equipment.

For curiosity sake, for those who use dual throttle setups for their 2WD's, which side do you control the rear motor from and which side do you control the front motor from?

[sangesf]

I use 2WD and have for over 2 years...
From MY experience, I PERSONALLY, get MUCH better efficiency then using a single motor.
When using a single motor, single battery setup, I get about 35 miles out of a 36v 20AH battery...
Now, from what I'm seeing most people are saying that adding another motor/battery would be less efficient?!? (Using ONE small battery on TWO motors yes.. BUT!!)

Not even close... When using both motors and both batteries I get a MINIMUM of 80 miles...
Now mind you, that I (almost) NEVER run WOT... and 99% of the time I'm barely at half throttle...
Using much lower loads (re: amps) gives me MUCH more AH (Actually WH/Mile) out of my batts/motors..
Look at it this way.. Pull 20amps out of your 20ah battery constantly and then pull only 6amps from each of two 20AH batteries (which for me, equates to the same speed as pulling 20a out of one motor) and see what the distance is comparatively speaking..

For me it went from 70 miles (2 batteries (One at a time) / 1 motor) to EIGHTY miles using both batteries and both motors.. that's a 15% increase in "efficiency".. It's basic "battery physics" and REAL WORLD (FOR ME) facts...

For curiosity sake, for those who use dual throttle setups for their 2WD's, which side do you control the rear motor from and which side do you control the front motor from?

And to answer your original question..

Left Throttle = Front Motor
Left Brake = Front Brake / Rear Brake Light
Right Throttle = Rear Motor
Right Brake = Rear Brake / Motor Cutoff for Both Motors.

For those that think I'm "full of it".. Here's a pic I just took of my bike...
(I'll have a better pic of it tomorrow when it's daytime. )



P.S. This "new build" is in the process of being worked on, so it's not exactly 100% "pretty" yet..
(I'm waiting on my custom Tread Plate (Brite) Aluminum Battery Boxes...)

[hjns]

In a PM, ~methods nicely pointed out to me that he developed a dual hall sensor single throttle solution that drives two controllers. Link here: viewtopic.php?f=2&t=12356&p=220262&hilit=dual+throttle+methods#p220262

Anyone out there has experience with this solution?

[Floont]

...
Left Throttle = Front Motor
Left Brake = Front Brake / Rear Brake Light
Right Throttle = Rear Motor
Right Brake = Rear Brake / Motor Cutoff for Both Motors...

Thanks! That's the way I think it ought to be. The motor throttle goes with the brake for that wheel... very intuitive.

[sangesf]

...
Left Throttle = Front Motor
Left Brake = Front Brake / Rear Brake Light
Right Throttle = Rear Motor
Right Brake = Rear Brake / Motor Cutoff for Both Motors...

Thanks! That's the way I think it ought to be. The motor throttle goes with the brake for that wheel... very intuitive.

Every ebike I've ever bought had a motor in the rear and the throttle on the right...
Just easier to setup starting from that configuration anyways.. So when adding a second (front) motor, the new throttle has to go on the left anyways.. Hehe

[cassschr1]

2wd rocks, no doubt about it. Don't knock it till you tried it.I'm the guy Methods built the throttle for in that thread. My bikes are both tidal force's. One is a dual 9c 2807 60v 20a V konion and the other a 5305 28s5p a123. These are the only e-bikes I've rode. Cass

edit,,,,2wd is running off one battery

[sangesf]

2wd rocks, no doubt about it. Don't knock it till you tried it.I'm the guy Methods built the throttle for in that thread. My bikes are both tidal force's. One is a dual 9c 2807 60v 20a V konion and the other a 5305 28s5p a123. These are the only e-bikes I've rode. Cass

Are they both running off of one battery or two?

[Kingfish]

Are they both running off of one battery or two?

Good question Let’s put a bit of perspective on it:

• Yes, it is possible to run the motors on separate batteries.
• It is also reasonable to operate both controllers off of a single battery pack.
• You can also have multiple battery packs connected to a main battery bus which is how I managed my system for cross-country; it was the only way to solve my weight distribution problem.

Notes:

• When charging, I split the Main Bus from the Panniers and connected the Meanwell array in-between to complete the circuit. Not perfect, though it worked in a pinch. The original idea was to have the charging on the other side of the Speedict device, although I couldn’t get the unit to work, so it was bypassed.
• All the local connectors from the batteries were barrel, although the ends that connected to the Battery Bus were 75A APP, and I used the plastic lock-pin to prevent separation. Stuffing 8-AWG wire into one of these was a real bugger.
• If I had to do it again, I’d used up-rated barrel connectors instead of APP.
• The DC-DC Converter put out 60W total and never fully utilized. It would have been quite easy to pull the 12V line back to the controllers and have independent isolated supply unaffected by WOT.

~KF

[hjns]

Wow, KF!

Did I count correctly, and did you carry 13P 15S with you? Assuming 5Ah per lipo, that would be 3.6kWh....

[Floont]

...Every ebike I've ever bought had a motor in the rear and the throttle on the right...
Just easier to setup starting from that configuration anyways.. So when adding a second (front) motor, the new throttle has to go on the left anyways.. Hehe

My first ebike was front wheel drive. The kit came with the standard right hand throttle. Since it didn't make sense to me, I bought and installed a left hand throttle to go with the front wheel drive bike.

So, it's not a no-brainer. Design ergonomics need to be well thought out so we respond correctly under stress or in any emergency situation.

[Kingfish]

Wow, KF!

Did I count correctly, and did you carry 13P 15S with you? Assuming 5Ah per lipo, that would be 3.6kWh....

The total was 5S1P 5Ah LiPo x 3 = 63V => @ 26P = 130Ah = 8.2kWh. Range varied depending on conditions. I never did get a fix on what this was over flat level ground.

For commuting, it's just the Triangle @ 63V 30Ah which is enough to go 50 miles @ WOT, though probably could squeeze 80 miles if I took it lightly (but then... why?)
~KF

[Alan B]

Kingfish, why do you think the 5V regulator was the problem with the throttle dropping out?

[Kingfish]

Kingfish, why do you think the 5V regulator was the problem with the throttle dropping out?

The problem consistently occurred when demanding WOT after bottoming out on a descent or rising out of a curve towards an incline; at maximum load. The Front had power (driven by the “primary” controller which provided the 5V supply) however the slaved Rear would drop out. If I feathered the throttle then the issue would not display. I don’t think there was enough current to push the signal to the other controller in those conditions due to sag. Maybe the 5V supply in the “primary” needs a bigger cap. Maybe it’s the 12V supply to the 5V regulator that needs the bigger cap; I don’t really know for certain cos I’m not an EE and don’t have the chops to debug the circuit properly.

Beefing up the skinny wiring to the throttle though would reduce resistance, just as shortening the cable.
~KF

[Alan B]

The current required for the throttle is so small I suspect something else was going on.

Ground Differentials on 2WD Controllers

My concern is the voltage drop between the two controller grounds. How much resistance was there between the controller PC board and the junction where the current split.

Not sure you want to discuss this in your FAQ thread, though it is on topic.

Take an example, assume:
[list=]
* 50 amps battery current to the primary controller
* 20 milli ohms from controller pcb to current split point
* 50 x 20 = 1000 milli volts of drop would then occur from the split to the controller ground.
[/list]

This 1 volt of drop would RAISE the ground potential of the throttle and the main controller compared to the junction point. This would also raise the +5 and the throttle output by the same amount.

Now this would increase the apparent throttle voltage to the secondary controller (that is not yet drawing much current). Which would tend to cause it to accelerate and 'catch up'. So on the surface it seems somewhat opposite what happened, and self correcting.

However, what if the throttle input to the secondary controller exceeded the max allowed input and caused it to go into 'shutdown'. Most controllers will reject a too-high throttle input value as a 'fault'. At WOT there is very little room to 'overdrive', so it would not take much voltage differential to cause it.

Feathering the throttle would allow the secondary controller more time to catch up at a lower throttle voltage before it was driven into cutoff. As it draws current the voltage difference between the controllers will be reduced as both of them will have a similar drop from the junction to the controller ground.

It is very important that the controller grounds be referenced together and have very low impedance between them if a common non isolated throttle is to be used. Or use an isolation amplifier to re-reference the throttle signal to the local ground on the slave controller.

Could this have happened to KF's setup?

[hjns]

It is very important that the controller grounds be referenced together and have very low impedance between them if a common non isolated throttle is to be used. Or use an isolation amplifier to re-reference the throttle signal to the local ground on the slave controller.

Could this have happened to KF's setup?

Hi Alan,

I am working towards a 2WD setup now. I can always try the dual-Hall-single-throttle solution, but I am interested in hearing how you would re-reference the throttle signal to the local ground on the slave controller. How would you do it?
thanks!

[Alan B]

It is very important that the controller grounds be referenced together and have very low impedance between them if a common non isolated throttle is to be used. Or use an isolation amplifier to re-reference the throttle signal to the local ground on the slave controller.

Could this have happened to KF's setup?

Hi Alan,

I am working towards a 2WD setup now. I can always try the dual-Hall-single-throttle solution, but I am interested in hearing how you would re-reference the throttle signal to the local ground on the slave controller. How would you do it?
thanks!

One way is to use an Instrumentation Amplifier:

http://en.wikipedia.org/wiki/Instrumentation_amplifier

[Alan B]

Perhaps a better choice is a difference amplifier. Here is one example:

http://cds.linear.com/docs/Datasheet/1990fb.pdf

[hjns]

Perhaps a better choice is a difference amplifier. Here is one example:

http://cds.linear.com/docs/Datasheet/1990fb.pdf

Thanks, however... these amplifiers are way beyond my electric knowledge and skills....

And I am really trying to understand why these amplifiers would get rid of the voltage differences between the two grounds of two different controllers, unless one would connect the ground as V+. But if you do, which ground is than connected to the battery ground?

[Alan B]

They use magic.

Sorry.

In a way, they measure the voltage on the master side, send a message to the slave side, and generate a voltage on the slave side that has the same value but is relative to the slave controller's ground. So the ground difference is not eliminated, but the throttle signal is correct with respect to the slave ground.

The problem is the grounds on the two controllers will be shifting around depending on the battery current. This shift is not large if the controllers are well grounded but could still be many millivolts due to the significant currents involved. This gets added to, or possibly subtracted from the common throttle voltage as seen by the controller chips. Another way to think of it is to measure the differences in grounds in real time, and add or subtract this from the throttle signal to the slave controller.

Using two separate halls on one throttle is a great way to go if you can match the positions and get the same value from both outputs.

[Fishmasterdan]

1 wheel drive= Grin
2 wheel drive= Permanent smile and giggles.

Seriously;
I have burned out SEVERAL motors and ESC's over the last few years .
I have not been able to burn out my 2wd set up. Dual halls throttle, Cell man made the whole package and it just plain works.

My personal opinion;
2wd if you want a motorcycle. To heavy to be a fun bicycle.
1 wheel drive for assist. Keep the weight down.

[hjns]

I used method's method to create a twinsensor throttle. Posted my results here: viewtopic.php?p=501963#p501963

Next steps will be to create a twin-3-speed-switch, a common shunt for the CA to measure current, splitting the main power to both controllers, add a key switch, fuse, motorped EU approved lights, and approval from the Swiss cops that I can drive my 2WD on the roads....

[John in CR]

1 wheel drive= Grin
2 wheel drive= Permanent smile and giggles.

Seriously;
I have burned out SEVERAL motors and ESC's over the last few years .
I have not been able to burn out my 2wd set up. Dual halls throttle, Cell man made the whole package and it just plain works.

My personal opinion;
2wd if you want a motorcycle. To heavy to be a fun bicycle.
1 wheel drive for assist. Keep the weight down.

Best 2wd post yet. Assist, what's that?....Isn't that when my motor(s) gets bogged down and I assist it via the pedals?

[Kingfish]

Assist via pedals
Funny you mention that: I would say “yes”. Going through the analysis of my next 2WD incarnation I’ve considered having pedaling as an option rather than a requirement.

I would also agree that as a bicycle mod, 2WD creates an experience closer to moped and motocross that is certainly EV-grin worthy! You are right: Adding a second motor will increase the frame weight by another 14-20+ pounds, and that too is a good point of discussion.

Let’s talk about weight:
As a cyclist, we work very hard to shave off grams & ounces from our frames, all of which factor against us when beginning from a standing-stop, climbing hills, and endurance. Depending on use, a typical complete bike assembly weights between 26-40 pounds before rider & accouterments.

As an electric bike, we give up double that at the onset due to the mass of the motor, the controller, the batteries, the wiring, and the minimal accessories to go just 20 miles. I recall fretting that my first commuter battery pack was about 9 pounds and thinking THAT was heavy! And I could feel the difference in the way the bike handled when I strapped on the 13-pound extender: If I pedaled aggressively it was possible to go 50 Seattle-miles on a charge (using LiFePO4). For a noob coming from the bicycle world, this extra weight was difficult to accept, although the electric augmentation that came with it is so enticing, well – it’s only weight and within a few weeks our muscles will adapt, our chests will expand, our arms and hands become stronger, and our senses – become more alert.

Now we throw in another motor to complete the architecture: Twice the torque to the ground. The economies of efficiency begin to go by the wayside because a person that accepts this additional weight understands that they are improving the performance with a penalty, just as if I were to bore out the cylinders and drop in oversized pistons on an ICE. We add more batteries to compensate for the loss of distance, and this is not a 1:1 exchange: It’s closer to the inverse/cube-root function where the first and second doublings are profound, but then the weight of more battery additions are in fact their own flaw, and we’re back to counting grams & ounces.

If we’re talking about just bicycles modified for 2WD, then the weight limits of the frame and the safety of the experience comes about rather quickly, especially if the rider has a large body type: The effects of weight create self-limiting configurations that have their best utility in commuting and sport where the distances & duration are reasonably short.

These past few weeks I’ve been working at the other end of the weight problem: I need to go the distance at speed for hours. I can find/make a frame to handle the weight & speed. The problem is how to charge it at the end of the day. But this is a conversation for a slightly different 2WD application. Regardless – weight factors large, and the way to reduce that is to increase the efficiency of the system as a whole by examining the components. During that process of discovery, everything must be suspect to improvement.

Yikes, another novella! I’ll stop now to brew another pot.
<mmm> Fresh cup! KF

[sangesf]

I believe all your posts depend on the predication of having a single battery..

From MY experience.. If you're using 2WD AND the appropriate BATTERIES.. It is WAY more efficient than a double motor / single battery setup.
(The point being, that with 2 motors / one battery, you're pulling twice the C-rate as opposed to only one battery.. (especially if you're using only one throttle). In the case of a dual motor / dual battery setup, your using much less current to accomplish the same as a "single setup" and creates much more efficiency)

Again, this is MY experience and as always.. YMMV.

From one of my tests, I've found that if you pull only .2C from a battery as opposed to 2C from a battery, you can get (up to) an additional 11% (depending on size and type of battery) battery capacity. (This was using a 60Ah Thundersky battery setup)..

Questions/Comments/Queries, welcomed!

[miuan]

Nice KF, keep it comin'!
How much kWh do you need to charge and how quick? What cell IR?
If lipo, have you considered splitting the giant pack into more parallel groups that can be joint in series for charging? This way you could go the ghetto way of rectifying mains voltage and using a bulb as a current limiter.. never worked for me, but hey that's a serious hack for serious challenge.