2WD (Two-Wheel Drive) FAQ

[hjns]

Well, that is contradicted by the other God among E-bike Gods: Methods. See this thread about his experiences.

[Alan B]

Higher power levels create more noise. It doesn't take much noise into the hall signals or into the throttle to cause problems. Methods was pushing the envelope with a pair of 10KW controllers. So it is not surprising there would be more problems.

If you need good balance on two motors (and a 2WD bike doesn't really need great balance, but a trike does) you should consider matching motor currents. One throttle drives two feedback loops that are both controlling either battery current or phase current. Battery current is easier. You might want to add anti-spin logic to that which would not be hard to do, as applying equal power to the motors in slippery conditions can cause a hard spin on one if it loses traction, but the other will still get good power since the feedback loops are separate. For anti spin logic look at a hall signal from both motors and don't allow one to get too much faster than the other. Override the throttle on the faster one and reduce its power so it is only a little faster, until it regains traction and slows and then ramp power back up on that wheel.

With these large currents flowing the controllers will at times have different and varying ground potentials. Since the throttle signal is referenced to this ground it is important to compensate for this otherwise the throttle signals will be unequal and varying.

[Kingfish]

The simplest solution is to craft a PCB with two CPUs with accompanying driver channels: We just have to agree on the features and set about making one. However I like Justin’s thought on using the CA to manage both throttles; it seems promising and I’ve yet to try that.

BTW – I just want to say that 2WD and AWD systems are advanced topics for experienced users. I would strongly suggest noobs go build a single-wheel drive system first before venturing into this realm, because most of us here already know well the aspects of common components. In other words – if you’ve never built an ebike before, then this is the wrong thread to read and post your questions.

Thank you, KF

[sangesf]

I have to disagree slightly (or more importantly with an addendum)...

Dual wheel (awd) on a regular bicycle can be done by noobs easily...
Just use two throttles and controllers..
Done.

[llile]

The simplest solution is to craft a PCB with two CPUs with accompanying driver channels: We just have to agree on the features and set about making one. However I like Justin’s thought on using the CA to manage both throttles; it seems promising and I’ve yet to try that.

BTW – I just want to say that 2WD and AWD systems are advanced topics for experienced users. I would strongly suggest noobs go build a single-wheel drive system first before venturing into this realm, because most of us here already know well the aspects of common components. In other words – if you’ve never built an ebike before, then this is the wrong thread to read and post your questions.

Thank you, KF

Good point. I'd have to echo the warning. I've got a $150 soldering iron and a a multichannel oscilliscope on my hobby bench, (my fourth scope, earlier ones were inadequate), and have a box fulla several generations of microcontrollers and programming hardware, plus a shop with several types of welders that can fabricate damn near anything I can dream up. Most people are trying to bolt a motor on a mountain bike, I'm dreaming up new chassis configurations out of raw 4130 tubing and trying to push bicycle technology into something more like a small ultralight car. You gotta start somewhere, and I'm not trying to diss anyone personally, but I've been at this game of fabricating stuff for quite a long time, so I am looking for more and more extreme challenges like a drug addict looking for a bigger high. We were building our first recumbent bike frames, powered bikes, and three wheel vehicle chassis in the early 1980's. Some of those early experiments even worked, although many failed miserably and humorously. What's worse, this ain't no brag, because there are plenty of folks on this board who have fabricated stuff that I couldn't even attempt. Stay away from multimotor stuff until you've built something straightforward K.I.S.S. simple and made it work.

Ain't nuthin' more fun than building stuff that makes people go "Holy Crap!!?!! What the hell was that?" and that actually works.

[Lebowski]

The simplest solution is to craft a PCB with two CPUs with accompanying driver channels: We just have to agree on the features and set about making one. However I like Justin’s thought on using the CA to manage both throttles; it seems promising and I’ve yet to try that.

BTW – I just want to say that 2WD and AWD systems are advanced topics for experienced users. I would strongly suggest noobs go build a single-wheel drive system first before venturing into this realm, because most of us here already know well the aspects of common components. In other words – if you’ve never built an ebike before, then this is the wrong thread to read and post your questions.

Thank you, KF

Are you guys familiar with my 30F controller build (viewtopic.php?f=30&t=34231) ?

I'm building a full sinewave sensored/sensorless modified Field Oriented Control controller IC with everything configurable
to the user over RS232 (or USB with a USB<->RS232 cable )

The options I built in for throttle control are ideal for multi-motor setup.

In my setup multiple controller IC's can be linked together via a CAN bus. One controller IC can be configured as throttle master, the
rest as throttle slaves. The throttle master has 1 or 2 analog throttle inputs (can be hall or potentiometer based). 1 can be used as
throttle, the 2nd can be used as regen (or a 2nd throttle). The analog throttle voltages are both converted to a 16 bit signal in
the 0 to 1 range. These two 16 bit words are transmitted over CAN by the master to the slaves.

Now each controller, independent of whether its a master or slave, uses the throttle inputs to regulate the motor phase currents (torque).
This is done according to

Code: Select all

x1 = throttle_1 [0..1]
x2 = throttle_2 [0..1]

y1 = a1 * x1 + b1 * x1^2 + c1 * x1^3       (a1, b1 and c1 are in [-8 .. 8] range)
y2 = a2 * x2 + b2 * x2^2 + c2 * x2^3       (a2, b2 and c2 are in [-8 .. 8] range)

motor_phase_current = max_motor_phase_current * (y1 + y2)

Coefficients a, b and c can be used to configure all kinds of linear / exponentional type throttle curves.
Negative values can be used to obtain negative motor_phase_current which is basically regen.

The beauty in a multi-controller setup is that all controllers share the same throttle_1&2 values
but that each has its own a,b,c and max_motor_phase_current. So the maximum torque and throttle
respons can differ between the motors. You can have a 350W Mac in the front and a 500W Mac in the
rear, both operating on the same twist throttle and thumb regen 'throttle'. Then during motoring the
coefficients can be such that the powers to the motors match their ratings. For regen you can enable
(by using a2,b2,c2) regen strongly in the rear motor and weakly (or not with a2,b2,c2 all 0) in the front.

On the physical side, the CAN interface can be build to work with a shared ground supply or, if
you use opto couplers, you can have completely independent batteries for your motors...

[Kingfish]

Are you guys familiar with my 30F controller ...

Lebowski, kind Sir –

In a word: Absolutely! I have been an avid lurker on both your awesome thread and with Ricky_nz’s. I am just a little bit out of my league to comment in a meaningful way other than to applaud your progress. But flag me as a subscribed lurker! I personally wanted to wait until either of you gentlemen was a bit farther along with your developments and in conjunction with my prototype before requesting direction/advice/solicitations.

Retreating somewhat, the idea of this thread is to identify the common off-the-shelf components that can be utilized to create 2WD (and AWD), and their related issues. Yet at the same time I pine to create new hardware specifically designed for 2WD/AWD, including motors, controllers, and throttling systems with ancillary features. If we proceed down the development path in our conversations then this thread no longer becomes a FAQ, but instead a spelunking Build-Thread.

We could always start a collaborative thread to separate the two goals. I would like nothing better to have a state-of-the-art controller and AF motor (x2) and go blow the doors off the Chinese competition! (I wouldn’t expect it to be cheap to build… just accomplished in the right way with extensible features.)

Open to ideas.
~KF

[llile]

Are you guys familiar with my 30F controller build (http://www.endless-sphere.com/forums/vi ... 30&t=34231) ?

I'm building a full sinewave sensored/sensorless modified Field Oriented Control controller IC with everything configurable
to the user over RS232 (or USB with a USB<->RS232 cable )

The options I built in for throttle control are ideal for multi-motor setup..

Nice! If my simpler cruder methods of balancing the two motors fail, I'll be getting out the soldering iron and following along. How fun!

[Ian]

Many thanks for an interesting thread everyone. I would appreciate any feedback for my particular circumstances, as sometime this year I should be able to sink some more money into the bike, up to $1,000, and I don't want to waste the money as once its gone, that's it for a while! I currently run a rear 9c2810 on 45v to 67v. evg bike, 26" wheels. I tend to use 45v to 48v for long, slower rides, and go to 63v just for fun, rides under 40 miles. Amp limit I peg at 26amp whatever the voltage so 1600 watts tops. It's a rugged, reliable motor at these levels and handles the hilly areas in my area pretty well. My setup is pings for 48v 20ah and I use lipo packs to add to the voltage.

Anyways, my problem is not speed or range but a 1.25 mile, steep gravel driveway to my home, that starts at 2,300 ft and ends at 2,750ft. For about 3/4 mile the grades are real steep, a few sharp turns and ruts, making the going a bit tricky. it will be paved one day, but maybe not for a couple years...

So far, the solution I have put into practice was to get the 2810, and then once I had experience of its performance, I got a small dedicated 67v nano pack just for getting up the drive. The 9c on 67v does the 1.25mile without stalling but it is definitely at its limit heat wise - especially as the motor can be quite warm already at the bottom of the drive, so I'm not starting with a cold motor. Also, I am sometimes a bit tired after a long ride and would like to somehow evolve the setup so I can get back up with less effort. So I got the following ideas each with their pros and cons methinks. (If I had the money, I'd try all of them just for the fun of it, but that's not gonna happen!) I don't want to over-think all this but just kind of move to the most sensible-feeling option if you catch my drift...all batteries are in good shape, motor is good so far, so would like to keep what I got whenever possible. So, what's the best next step?

1. buy a 9c2812 and buy more batteries so as to go from 60v minimum for long rides, to 75v for getting up the hill. HMm...gets a bit heavy adding another 12v to the rig, I am already maxed out. replace some of the ping with lipo would work. And would the 2812 really make much of a difference. not sure.
2a. Keep setup the same but add on a small geared hub to the front - the mxcus from cell-man perhaps - using separate controller and 2nd throttle. Just use this to help with getting up the drive. Seems like a small, no drag hub, should give me 500 watt on the front wheel for that 1 mile and not have a heat or gear problem. BUT... got to lug the darn thing around tho the rest of the time...
2b. As 2a option, but switch the 2812 for a 2808 on the rear, for faster cruising and overall lower voltage, maybe a tad more efficient for most of the ride, and just figure to use the mxxus front hub more often on the hills, keeping it within its 350 watt rating.
3. go to permanent 2WD setup with one throttle/2 controller using 2 x cellman 500w macs with voltage around 40v. I could refigure my packs and add a couple more 4s bricks to get a permanent 39v 40ah. 22mph top speed, and run a peak 750 watts on each motor for the drive . How much noise would 2 simultaneous motors make tho...what kind of efficiency would I get at 20mph cruising, around 1ah per 2 miles?
4. Replace the 2810 with one of the new crystalyte low speed (HT) motors, keep my voltages as-is for 20mph to 25mph top speeds. But I can't find any real world reviews on the HT. It seems like a nice motor, a few pounds heavier than the 9c and a bit more cogging from what I can gather. So maybe just a tougher motor generally?

well that's it for the options - I think!!!!!

[Alan B]

Or get a Cromotor. Wait, this is a 2wd thread. Never mind.

[amberwolf]

Cromotor front and rear...Hmmm.

[Ian]

Or get a Cromotor. Wait, this is a 2wd thread. Never mind.

Hi Alan - read thru the cro thread and too big n'heavy for me I think- although I will keep an eye on people's experiences of it for lower speeds and modest power levels like mine.

Anyways apologies if my post was not totally on-thread but it is an attempt on my part to resolve the right design 2WD in my particular circumstances. Which I think is defintely worthy for 2WD. I am satisfied that using 1 battery of correct capacity, 2 identical controllers and 1 throttle is straightforwards and tried and tested. The evg frame fortunately is robust with strong front forks so again a good candidate. I need something similar in efficiency as my current 9c, at speeds 22mph and under. I get around 2 miles per ah in normal use, which is WOT on the hills, fairly easy cruising, then all the downhills.

At this time, I don't think there are even that many choices. 2 x 9C is to heavy. 2 x magicpie too heavy. 2 x smaller DD hubs might work but too much drag? Are there any mid-size DD hubs however, worth consideration for a 'middle of the road' 2wd setup?

So what I see as the only real choice is 2 of the 500w geared from cellman or 2 smaller geared hubs such as bafang. I don't know if a smaller geared hub even when doubled up will be strong enough or temp resistant over the long haul, so I would like to read anyones experience or crunch some numbers as it is definitely a stealthy look and good weight. 2 x cellmann 500w seems on paper to be the best choice. It means that weight remains about the same as my current 9C and also means I can configure my battery packs to go down to 40v and attain a capacity of 40ah, use a slow torque winding to get around a 22mph top speed, and tackle steep hills at a 'sweet spot' for each motor, around 12 to 14mph at say 800w draw on each for no longer than 1/2 to 3/4 of a mile at a time.

The benefits seem to be that I would gain greatly (in comparison with the 9c) from thermal efficiencies when going majorly uphill, freewheeling with pedal assist on the flat helps a bit more, and never overstressing the system at any point. Even at my highest theoretical draw of 20amp per motor, I am still only 1C on the battery pack, and when cruising on the flat from 18mph to 20mph, I would still expect to use only 350w combined or 175w on each hub - total 9amps on the battery or under 1/4c. Therefore, I should get a theoretical range of 70 -80 miles minimum on level road, is that correct?

Well I will keep learning and looking through all the posts and see what others have already experienced!

[Alan B]

I was planning to try a 9C rear and a geared front hub. But have not done so.

The Cromotor is lighter than two 9C's, is it not? Avoids a second controller, another set of torque arms, a second CA, throttle issues, extra cables, problems with suspension and alloy forks, steering issues, front slippage, etc.

[motomech]

Or get a Cromotor. Wait, this is a 2wd thread. Never mind.

Hi Alan - read thru the cro thread and too big n'heavy for me I think- although I will keep an eye on people's experiences of it for lower speeds and modest power levels like mine.

Anyways apologies if my post was not totally on-thread but it is an attempt on my part to resolve the right design 2WD in my particular circumstances. Which I think is defintely worthy for 2WD. I am satisfied that using 1 battery of correct capacity, 2 identical controllers and 1 throttle is straightforwards and tried and tested. The evg frame fortunately is robust with strong front forks so again a good candidate. I need something similar in efficiency as my current 9c, at speeds 22mph and under. I get around 2 miles per ah in normal use, which is WOT on the hills, fairly easy cruising, then all the downhills.

At this time, I don't think there are even that many choices. 2 x 9C is to heavy. 2 x magicpie too heavy. 2 x smaller DD hubs might work but too much drag? Are there any mid-size DD hubs however, worth consideration for a 'middle of the road' 2wd setup?

So what I see as the only real choice is 2 of the 500w geared from cellman or 2 smaller geared hubs such as bafang. I don't know if a smaller geared hub even when doubled up will be strong enough or temp resistant over the long haul, so I would like to read anyones experience or crunch some numbers as it is definitely a stealthy look and good weight. 2 x cellmann 500w seems on paper to be the best choice. It means that weight remains about the same as my current 9C and also means I can configure my battery packs to go down to 40v and attain a capacity of 40ah, use a slow torque winding to get around a 22mph top speed, and tackle steep hills at a 'sweet spot' for each motor, around 12 to 14mph at say 800w draw on each for no longer than 1/2 to 3/4 of a mile at a time.

The benefits seem to be that I would gain greatly (in comparison with the 9c) from thermal efficiencies when going majorly uphill, freewheeling with pedal assist on the flat helps a bit more, and never overstressing the system at any point. Even at my highest theoretical draw of 20amp per motor, I am still only 1C on the battery pack, and when cruising on the flat from 18mph to 20mph, I would still expect to use only 350w combined or 175w on each hub - total 9amps on the battery or under 1/4c. Therefore, I should get a theoretical range of 70 -80 miles minimum on level road, is that correct?

Well I will keep learning and looking through all the posts and see what others have already experienced!

I think you may be over-complicating what's needed a bit. If you are more or less happy with the current set-up[except for the Hill], why not go all lipo[you could sell your Ping here, it's fairly new, right?], volt-up[and perhaps amp-down] to get the speed you want from your current rear motor and add a BPM 350W on the frt.. Stick with the kit controller and use a frt dedicated throttle since it will only be used as an Aux.
Sure there will be a loss of efficiency in rear-drive mode. But as Dogman has pointed out many times, folks worry too much about motor efficiency. It's small potatos when you can just throw another brick on the fire[figuratively speaking].
Don't mess with the minis if your fork is up to the BPM, you would have to branch off your pack as the pack voltage would be too high for a mini.

Money saved could be put into chargers.

[wojtek]

If i refer to auto industry, the whole point of AWD is when you lose traction in some wheels, the other will take over.
The only useful usage that would increase fun considerably would be to have AWG off road trike, used in extreme offroad conditions and on snow [putting aside the complexity of 3 WD]
I can't really see enough benefit of putting 2 motors on a standart bicycle. Put aside all the technical and mathematical calculations that some of geniuses has done here [full respect]

[motomech]

been plenty of 2WD builds here, all positive.
Read though and see.

[Kingfish]

If i refer to auto industry, the whole point of AWD is when you lose traction in some wheels, the other will take over.
The only useful usage that would increase fun considerably would be to have AWG off road trike, used in extreme offroad conditions and on snow [putting aside the complexity of 3 WD]
I can't really see enough benefit of putting 2 motors on a standart bicycle. Put aside all the technical and mathematical calculations that some of geniuses has done here [full respect]

Philosophically I would offer up that the reasons for crafting 2WD/AWD is more about fulfilling a functional need. Certainly there are bragging rights associated, but unless there is disposable income and copious time, that in itself is not enough reason.

For myself, the hills in and around Seattle Metro are steep. If we go back 15,000 years, the geography was covered by a mile of ice or more from contributing alpine and coastal glaciers. Smaller hills and mountains were ground flat first into rubble, rounded cobbles, gravel, then sand, and compressed under the tremendous mass of ice, depressing the crust beneath it. When the ice melted, the ground rose, and water carved out massive channels underneath as it made a path out to sea. What is left is a region generally like a plateau with steeply scarped sides that even today is still slowly bounding upward, rising. Some bedrock can be found in certain parts, but most of the hilly ground here is termed “consolidated gravels” and it’s nearly as hard as concrete.

Roads wind around, twisting to get to the summit: In the winter, they are slick from frost, rainy surfaces that have frozen during the night (or shade), or occasional from snow-turned-to-ice. AWD/4WD is pretty much required if you live and/or work on hills as are studded tires between November 15th to March 15. Even if it’s dry weather, riding up and over hill and dale from Redmond to Bellevue is a chore. Ever hear of the Seven Hills of Seattle?

As such, I have need for 2WD for my commute, and it’s pretty handy on cross-country. However, if I lived in a dryer flatter place, perhaps creating a 2WD would lean more towards bragging rights. Your needs and goals will be different than mine.

Best, KF

[Alan B]

2wd has a couple of valid features. One is double the thrust and heat dissipation of a single hubmotor. Another is a marginal increase in traction at low acceleration from the front wheel. With the advent of bicycle hubmotors with twice the power (such as the Cromotor) some of the advantages of 2wd are reduced.

[rojitor]

Ever since i turned my bike on a 2wd i noticed more stable rides, the weight at the front wheel makes a good balance, on top of that i can keep top speed climbing,sometimes i even pass gas motorcycles going uphill and i always know i can make it to home if i have a problem.Maybe with a cromotor or 54xx at the rear it is not so cool, time will tell.

[Kingfish]

Ever since i turned my bike on a 2wd i noticed more stable rides, the weight at the front wheel makes a good balance, on top of that i can keep top speed climbing,sometimes i even pass gas motorcycles going uphill and i always know i can make it to home if i have a problem.Maybe with a cromotor or 54xx at the rear it is not so cool, time will tell.

Yes, forgot - redundancy, which I used when the RWD went TU a couple of weeks before the FWD (rust).

Alan B, why not do a 2WD Cromotor?

Wouldn't that be fun, KF

[Alan B]

The Cromotor is so wide there is little room for freewheel cogs and would not fit in most front forks. But 2 of them would be quite interesting.

[rojitor]

2wd cromotors at 120v 200 amps .... Mmmm nah... That's not interesting, that's BRUTAL!

[wojtek]

The Cromotor is so wide there is little room for freewheel cogs and would not fit in most front forks. But 2 of them would be quite interesting.

You can get 135mm front forks. But i wouldn't put cromotor on them

[Alan B]

Probably the best reason to put a Cromotor in the front forks would be for regen braking.

[Ian]

asked for quote from cellman for 2wd setup based on fishamsterdam feedback, who has 500w rear and 350w front and likes it. hoping for 1000w torque on the rear and same on the front but front doesn't appear to be available, so it may have to be one of his 350w with the matched rpm winding I figure?. Still if you can actually run 800W continuous rear and 300W continuous front, keep at a respectable (and efficient) 13mph to 15mph with a spot of pedaling, and it all works thermally in the summer for 12 mile from 900ft to 2800ft, then I am in. Also asked lyen about a custom dual motor controller - be cool to just have one unit, programmable for both motors and not ridiculously massive like that crystalye dual controller, don't see why not he's an electronic wiz. will post how it goes and what options are recommended by the pros.