2WD (Two-Wheel Drive) FAQ

[Kingfish]

the differences in volts and amps is to compensate for the lack of 2810 motor in the sim. The sim only has the 2805, but the performance of the 2806 at half voltage amd double amps is similar the 2810 at 126v 45amps.

So, thanks for your input! My intention was to indeed have 126v and 45amps going into both motors. With the 2810 in front, it would deliver approx 70% of the torque delivered by the rear ht3525.

Ah, got your thinking now! Thanks
~KF

[grindz145]

I love 2wd for two reasons: Power and Power. Obviously not going to be efficient.

I'm really looking forward to my 2wd build. 5304 +9C 9X7. Should be brutal...

Thanks for the FYI kingfish.

So did you just parallel all 3 throttle signals without issue?

[Rassy]

grindz145 said:

So did you just parallel all 3 throttle signals without issue?

This question probably was to KF, but I have paralleled all 3 throttle signals on both two and three controller systems, both brushed and brushless with no problems.

In all cases the multiple controllers were sucking off of a common battery pack.

There have been comments in the past by experts that understand controllers that this technique could lead to problems. I tried it years ago and used it a lot and never had any problems, so ignorance is bliss.

[Alan B]

I have not done this yet, but have been following a number of 2WD builds. Here is my suggestion/plan:

Connect the controller power grounds together very close to the controllers. You want those controllers at the same ground potential. Hopefully within inches of the controllers. The battery feed should be common, heavy, and split very near the controllers.

Connect the ONE throttle wire between the controllers. Determine which controller is the "main" controller (probably the rear drive), and connect the throttle to that controller and run the one throttle signal wire across to the secondary controller. I would twist it with the throttle ground wire on its way to the secondary controller to provide some shielding (or use shielded cable), but not connect the thin ground wire at the secondary controller.

I would not connect the other throttle wires together. Connecting throttle 5V or ground connections together is asking for a problem. It won't necessarily be a problem immediately, but if there is ever a connector glitch or a big voltage spike and the battery current gets diverted onto the throttle wires it will do a lot of damage to the control part of the controller. For safety put a small resistance in series with the throttle lines, say a few K ohms. This might prevent a problem in one controller from damaging the other controller. You want to send the throttle voltage over to the second controller, but if for some reason there was a large voltage difference you want to limit the damage current.

Note that if the two motor/controller combos don't have roughly the same throttle voltage to ground speed curves they won't share the load all that well. They don't have to be precisely matched, but if one is significantly different from the other the sharing will be lopsided.

[Kingfish]

On my system:

• Both controllers share GND through the Battery connection. The controllers are wired very close together; about 12 inches apart if measuring the wires.
• I have a “primary” controller that drives all the dashboard controls. Except for Throttle, all of these controls share the same single GND.
• Throttle gets +5V, GND and Signal (SP) from the primary controller. The Signal is then forked to the “Secondary” controller SP pad, and I do not share the any other throttle wire.
• This setup is workable with some flaws: I noticed that if I really get on it with WOT going up an incline that the battery voltage will sag for a moment which likely affects the output of the 5V regulator; the primary will have signal/throttle but the secondary will drop out – unless I feather the throttle.

A better solution is to provide a solid independent +5V supply and use that to drive both controllers, bypassing the local 5V regulator circuit. And if I went that far... might as well replace the +12V supply as well. But then we’re getting into 2-channel controller design discussions and less about 2WD

But if you want to talk about 2-channel controller designs, maybe we aught to spin those threads back up!

My ½ watt, KF

[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.