2WD (Two-Wheel Drive) FAQ

[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.

[Alan B]

Now I'm really confused. The 9C has a 14x10 axle and the HT has a 12x10 axle. That appears to be an HT axle in the photo?

[hjns]

I have sent Amberwolf a PM to move the TA discussion to a new thread.

[amberwolf]

Done:
viewtopic.php?f=2&t=36696

[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.

Cellman replied re 2wd drive setup. He recommended 500w rear and 350w front, matched motors so for me a 10t wind running at 40v will get me over my 20mph target cruising speed. Shipping is $150 x 2 though. So figure around a grand to get set up. It seems like this is a very strong & reliable option and I like the idea of being able to get spares too just in case, although I'm not a high power user, for me its just for relaxation and watching the scenery

I also am considering the idea of cellman 1000w rear motor and mxus 350 min-motor on front, but with two seperate throttles. Would cut down on the overall noise and also perhaps be more efficient, once you get real world experience of the 1000w motor's thermal limits up hills, then it would be a simple matter to just dial in another 400 to 500 watts of pulling power from the front wheel. I would have thought a combined 1200 watts from 2 brushless geared motors spinning at high rpm to be faster and more efficient up any hill in comparision say to my 9c 2810 pulling 1200watts up same hill, which is still good but really likes to be running at 14mph or more and so you got to run at high voltage.

I see e-bike kit are also saying they are working on a warrantied dual drive (in their faq). Also hightekbikes do dual drive systems so am checking in to that.

I did ask Lyen about just one controller for both motors. I know he does one buts it's quite big. He will get back to me after his race and perhaps it is possible to downsize and even develop a controller that's programmable for both motors.

[motomech]

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.

Cellman replied re 2wd drive setup. He recommended 500w rear and 350w front, matched motors so for me a 10t wind running at 40v will get me over my 20mph target cruising speed. Shipping is $150 x 2 though. So figure around a grand to get set up. It seems like this is a very strong & reliable option and I like the idea of being able to get spares too just in case, although I'm not a high power user, for me its just for relaxation and watching the scenery

I also am considering the idea of cellman 1000w rear motor and mxus 350 min-motor on front, but with two seperate throttles. Would cut down on the overall noise and also perhaps be more efficient, once you get real world experience of the 1000w motor's thermal limits up hills, then it would be a simple matter to just dial in another 400 to 500 watts of pulling power from the front wheel. I would have thought a combined 1200 watts from 2 brushless geared motors spinning at high rpm to be faster and more efficient up any hill in comparision say to my 9c 2810 pulling 1200watts up same hill, which is still good but really likes to be running at 14mph or more and so you got to run at high voltage.

I see e-bike kit are also saying they are working on a warrantied dual drive (in their faq). Also hightekbikes do dual drive systems so am checking in to that.

I did ask Lyen about just one controller for both motors. I know he does one buts it's quite big. He will get back to me after his race and perhaps it is possible to downsize and even develop a controller that's programmable for both motors.

Quote from a previous post,

" I don't want to over-think all this..."

I think you still are.

Consolidate your requirements and review the basics.

A 14 % hill that is 3/4 of a mile long does not require 2WD. Of the things you have mentioned, really only one justifies it.

Also from a previous post,

"...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?"

I had suggested a sm. helper motor up front, but if you really want to replace the 9C, you only need to go to a single Mac rear.

If the BMC V2 Torque is used in place of a 10T Mac[they are very close, same no-load R.P.M.]on the Ebike C.A. simulator you see it can exceed your needs.
I also used,
52V Ping[a default batt.]
35 A controller
14% hill
220 lb. MTB
It spit out,
17 m.p.h. climb speed @ a strong 216 r.p.m.[no-load-255].
1660 watts-max.
Un-assisted top speed-25 m.p.h.[very useful for a 44/11 geared MTB]
Over-heat in 9 min.[non-factor, once you @ the top, you are home]

A very nice budget system.

If you feel that you must test the 2WD waters and want to persue the options below,

Quote- "I see e-bike kit are also saying they are working on a warrantied dual drive (in their faq). Also hightekbikes do dual drive systems so am checking in to that.

I did ask Lyen about just one controller for both motors. I know he does one buts it's quite big. He will get back to me after his race and perhaps it is possible to downsize and even develop a controller that's programmable for both motors."

You need to re-think your listed budget upwards by a factor of .5 to 2X.

[Hangdog98]

So I've been following this with keen interest and I started to do so because I wanted to experiment with dual Q100's on a road bike running a single battery. When I began this journey into 2WD I was hypothesising that two motors would provide double the available torque of one motor OR for my application, the same torque at half the Amps on a given hill, with half the heat, give or take. This is my reason for considering two motors though I'm still not sure if this is correct. Can anyone provide this answer

If you feel compelled to tell me that I only need one motor twice the size, please try and resist the urge, I get that. I want very small lightweight under-stressed geared hub motors for this build.

Regarding the throttle(s), I planned a mechanical solution instead of an electrical one by grafting the two throttle mechanisms together on the one twist grip, keeping their wiring intact and running them to their respective controllers. Has anyone tried that solution?

[motomech]

So I've been following this with keen interest and I started to do so because I wanted to experiment with dual Q100's on a road bike running a single battery. When I began this journey into 2WD I was hypothesising that two motors would provide double the available torque of one motor OR for my application, the same torque at half the Amps on a given hill, with half the heat, give or take. This is my reason for considering two motors though I'm still not sure if this is correct. Can anyone provide this answer

If you feel compelled to tell me that I only need one motor twice the size, please try and resist the urge, I get that. I want very small lightweight under-stressed geared hub motors for this build.

Regarding the throttle(s), I planned a mechanical solution instead of an electrical one by grafting the two throttle mechanisms together on the one twist grip, keeping their wiring intact and running them to their respective controllers. Has anyone tried that solution?

I only played Devil's Advocate with the previous poster to Point out that to climb one moderate hill, 2WD really isn't needed

I just ordered a q100 rear to match up with my MXUS frt. I had been holding off, trying to figure out which wind to go with. Not easy given BMS Battery's obtuse labeling system , but recently, both Grindz and Zukster have confirmed that the that the BMS Battery's 201 "slow-wind" is not really a slow-wind. More like a mid-speed, probably close to the MXUS's 255 rpm @ 36V[maybe BMS B. used a speed measured @ 24V

At any rate, there are good reasons to go with 2WD, IMO.
In my case there are three,
1]I already have a MXUS on the frt. and I like it a lot. And it doesn't stress the forks and I can be secure with one off-the-shelf torque arm..
2]I'm retiring this year and moving back to Tucson Az. and I want to do some "light' trail riding and I think 2WD would be fun for that/
3]I like to tinker and "fustz" w/wiring and things electrical..
The obvious question is, " Why not go with another MXUS, indeed, why not?". It could well be the best of the mini.s and the price is right. And there are reasons the go with an exact match[battery, controller and motor]as Miuan has pointed out. But I think the Q100 is close enough and it has some advantages when used as a rear mount, namely will fit a 9-speed freewheel and the wires exit on the left[non drive-line]side.
Researching here, I've come to the conclusion that 2WD systems come in two flavors, each with a different set of "do's and don't".
What we are talking about, dual mini's is one, the other being dual powerful motors and motors of mixed types[geared and DD's].
If we stick with the first, dual mini's, things become much easier I.M.O.

QUOTE "When I began this journey into 2WD I was hypothesising that two motors would provide double the available torque of one motor OR for my application, the same torque at half the Amps on a given hill, with half the heat, give or take. "

Yup, The biggy being the heating up part. As Dogman has pointed out on various occassions, heat saturation on hills is the Achilles Heal of the Mini Motor. On steep, long hills, the speed drops into the lee-side of the efficiency curve, more heat than motive force is generated, and the " vicious cycle" begins[vicious as in a Chihuahua can be vicious].

EDIT Opps, i hit submit by mistake. Oh well, it's Sat nite, the girls have passed out and I'm a bit drunk....
To be continued...

P.S. You might want to check out Garykards thread, Dual Cute Motors, I think it was titled.

[Kingfish]

Generally you will consume more power than one motor doing all the work, and less than two motors sharing the load. The best use of 2WD is starting off the line and hill-climbing. The least benefit is when cruising on level ground; often one motor just tags along and lets the other take the load – or they go into contention if the two wheels and controllers are set identical. To prevent contention on my ebike, I deliberately set each wheel to a different physical size, and overtly set the power-levels different as well which worked out pretty dang well.

If you are looking to gain efficiency – this is not the thread for you. The fact is that 2WD can and does provide about twice the torque to the ground over a single motor at the same power; two motors individually set to X-wattage will push roughly twice as fast as a single motor set to X-wattage. Another way to look at it: 2WD will get off the line and climb hills faster and cooler than a single-wheel at twice the power; two motors using a total of X-wattage will outperform (though at an economic price) a single motor at the same X-wattage. The downside to 2WD is that you have twice the weight and twice the freewheel drag, but then you get twice the regen braking.

There is no free lunch: 2WD will use more power than a single-wheel drive.
It’s also a heck of a lot of fun! KF

[motomech]

Generally you will consume more power than one motor doing all the work, and less than two motors sharing the load. The best use of 2WD is starting off the line and hill-climbing. The least benefit is when cruising on level ground; often one motor just tags along and lets the other take the load – or they go into contention if the two wheels and controllers are set identical. To prevent contention on my ebike, I deliberately set each wheel to a different physical size, and overtly set the power-levels different as well which worked out pretty dang well.

If you are looking to gain efficiency – this is not the thread for you. The fact is that 2WD can and does provide about twice the torque to the ground over a single motor at the same power; two motors individually set to X-wattage will push roughly twice as fast as a single motor set to X-wattage. Another way to look at it: 2WD will get off the line and climb hills faster and cooler than a single-wheel at twice the power; two motors using a total of X-wattage will outperform (though at an economic price) a single motor at the same X-wattage. The downside to 2WD is that you have twice the weight and twice the freewheel drag, but then you get twice the regen braking.

There is no free lunch: 2WD will use more power than a single-wheel drive.
It’s also a heck of a lot of fun! KF

I'm not particualy interested in overall power consumption, not going to be hyper-mile'ing and if I need more range, I'll add more Lipo. My reference to efficiency was in regards to being able to climb a formidable hill @ more than 5-8 mph and not self-destruct a single mini motor. Yes, there have been claims of increased efficiency running two SMALL motors[one rider claiming incredible gains], but until I can explore that myself I tend to dismiss them. It seems clear from real-world 2WD users[of which you are the King], that there will be a loss in efficiency.
But almost all of these discussions[including yours]are from the POV of using two POWERFULL motors.
Real world reports of two small motor set-ups are more rare, Garykard and Chinaphil come to mind. There is evidence that running two small motors all the time may not extract a major penality[as a side note, it would seem that both Chinaphil and Garykard have moved on to Mac rear drives. This should probably tell me something ].
Aside from the LARGE and SMALL motor 2WD catogories, there can be futher sub-divisions as described by John in CR,

"For the mountains and going slow I'd use identical lower speed wind motors that they call the torque model.....The reason I'd say identical motors is the high stress of steep climbs. You want to share that load equally. For street riding a difference in torque for the two motors could make sense, and that's the route I'm considering with less torque but higher speed capability of the front motor. My goal is different though, and I'm after maximum acceleration and speed while not so much on the front that the wheel spins. That route I get a large wheel on front, which I prefer at the speeds I ride, and the front motor will always be assisting the rear. I will have to dial in the current settings, so the front doesn't get stressed and overheat from carrying too much of the load.".

So what we have here is one approach where the two motors/controllers are the same[in this discussion, I am assuming one battery, as there would appear to be no benefit to using two]and the goal is to raise the performance levels within the parameters of the single motor envelope. The exception here, and this might be considered in the realm of increased efficiency, would be the ability of two small motors to help "pull" each other slightly higher into the zone between power/load and no-load speed. Reports of two small motors vs. one seem to bear this out. For a mini motor user, increasing top speed from say, 21-23 mph to 23-24 mph without raising the voltage is deffinately a big deal.

The second approach attempts to expand the parameters by over-lapping winds, types, controllers, etc.

Since I am seeking a light duty trail bike[more like trials actually] and have no desire to be able to exceed 23-24 mph[Tucson has a wonderful network of bike trails/lanes, but it also has an enforced bicycle speed limit of 20 mph], I am interested in the first approach. And it just seems more elegant to me.
Muian said'

"To run 2 motors, you need two controllers, one throttle and one battery. It's best to combine 2 identical controllers to make sure both will have the same understanding of throttle signal. The same applies to motors, but sometimes a motor you like is not available for front and rear, so then you have to match 2 motors that will have same or very similar no load speed, and play with the simulator to make sure the motors will pull together well."

He, as well as others[Neptronix in particular]go on to say[and I am paraphasing], for a street machine, up to speeds that a mid-sized gear motor can achieve on moderate voltage, one is better off just using a rear Mac/Puma/BMC or BPM. Very effective, less complicated and in the case of the BPM, less expensive. Heck, for the serious off-roader this probably would be a better approach, as it would keep the frt. end light, enabling the rider to loft over trail obstacles. I rode dirt bikes for over 40 years and I understand this well, but I am at the point in life where I would be more inclined to stop, get off, and carry the bike over something like a log.

So now we come full circle and get back to the questions of how to do a 2WD mini-motor rig.
As I mentioned in an earlier post, I think one of the advantages to using low-powered motors is the freedom from worry about applying frt. to rear power differential. Sure, I can get my frt. mounted MXUS to spin on dry pavement, but I have to try and do so. And a spinning frt. tire is easier to control than a rear.
For a purely street ride, I would be inclined to simply run both controllers off one throttle[no mechanical hash-ups are needed]with one switch to drop one motor out of the loop if so desired. Or better yet, one throttle into a Cycle Analyst as Justin has described and one of the two out switched. Which motor to run at say, 80% cruise? Not sure, since I will be using two slightly different motors some experimentation would be required[the fun begins].
For off-road, i think two throttles would provide max. giggles. I already use a trigger left-mounted so it is a "pusher', so it seems to me that adding a right-hand half twist would be the most intuitive set-up. They both require a "forward" motion.
Combining these two approaches would obviously require some creative switching networks, even more fun

[Alan B]

Two motors provide the torque of one at essentially the same total current, but in the dual motor case the per motor current is half.

Most people experienced in this indicate that a spinning front tire is harder to control than a spinning rear tire. The front tire is used for balance control, when it is out of traction balance is quickly lost. Whereas a spinning rear tire can be compensated for by steering the bike under the center of gravity maintaining system balance.

On the efficiency issue, for motors operated in their good efficiency region, two are just slightly less efficient than a single; but for the situation where a single motor is operated in a region of low efficiency or overheat dropping the power in half and adding a second motor can raise the efficiency and lower the heating in each motor and produce a net efficiency gain. This typically would be in the very low speed high torque region.

Two small motors will be really stealth if the rest of the gear and wiring can be hidden. Having two separate controllers also will provide a ride home capability in the case of a controller, hall or motor failure.

Combining two throttles into one needs to be done carefully to avoid the magnets interfering with each other. Some have used a single magnet but dual hall sensors to accomplish this.

[Kingfish]

Good stuff guys.

• +2 Both motors equal. The field tests agree
• +2 Both controllers equal. Likewise with above I agree completely, although with different power settings to avoid contention. The alternative is a <hint hint> multichannel (initially-dual) controller that understands and compensates when one wheel slips more than the other. Downgrading the front will prevent slippage; the amount though depends upon the terrain and environment and tires. If it were an easy option, I would like to change the ratio of sharing on-the-fly so long as contention was managed. See next item.
• +1 on the Unified Throttle; work needs to be done here to create a commercial offering. As a wishful feature, imagine a secondary ring that could be set on-the-fly that balances attenuates the signal of A||B from 1:1 to < 1. The idea came to me from an old A/V receiver that had two volume controls: Gross & Fine on concentric rings. The load-sharing ring would simply attenuate the selected (or perhaps non-favored) signal. This in my mind would provide quite a bit of control, and complement the 3-Way current control. Ah, here's a thought: The Throttle and 3-Way should be unified as well – right where the thumb can get to it.

Hmmm <rub chin>, now if only we had cruise control with persistent presets…
<slurp coffee> KF

[hjns]

Hi all,

Just reporting back about my experiences.


I have tried 2WD with front 9C 2810 and rear HT 3525 on 20S3P for a couple of weeks. Initially, I had the 9C axle rotating out of the front dropouts, destroying the dropouts of my Fox TALAS fork. Cause was identified as too much torque and not enough torque arm (only one). After fixating with 2 torque arms, no issues there anymore. I used the unified throttle with dual Hall sensors to 2 Lyen sensorred 12 FET controllers, fed by a single 20S3P pack. The throttle would give first a signal to the rear and at a speed of about 5km/h would also start driving the front motor. Total bike weight was about 30kg including two motors, 2 controllers, 10kg lipo pack.

In short; I did not like it.

Advantages
Hill climbing was super. Just great, and with 10% hills, I felt I could climb forever. None of the motors would even get warm. I could climb them with speeds over 45 km/h, and not even going WOT. Never tried WOT, because all hill-roads here are snaking around the hills, so 45 km/h is already quite fast.

Pulling the trailer with the kids was also super. And biking with a lot of wind was - due to the large weight - also super, with great tracking.

Disadvantages
However, for commuting and drafting through traffic, such a heavy bike is just not fun. It might as well be a scooter. The real advantage of an E-bike for me is it's capability to go where scooters and motors can not go or are not allowed to go. And these are precisely the parts of the road where a lighter bike makes a difference. Therefore, I removed the front 9C motor and the second controller, and continued biking with "just" the rear HT 3525. Initially on 20S, now also on 30S, reaching speeds >70km/h (42mph). On my 2WD, I would feel very insecure at those speeds. 50km/h was really the max. Now, with the lighter bike, 75km/h is a nice challenge, but does not feel unsafe.

Another disadvantage I noticed was the difference in front wheel and the effect on front suspension. With each bump, the front suspension had noticable difficulties dealing with it. No change in front suspension configuration (increase/decrease air pressure, rebound, more/less sag, etc) could get rid of that. Also, the added mass in the front wheel made it much more difficult to deal with more technical parts of an off-road bike trail. I do not have a lot of experience with that, but without the front motor I can much better deal with off-road trails.

Conclusion
So, I reverted back to RWD, and I will probably stick with this configuration. 2WD was a good experience and learning curve for me. Time to move on.

[wojtek]

many thanks for sharing your experience Henk, very interesting!

[hodgie]

@hjns: Yes, thanks, that was alot of explanation, but very valuable to me.

[Lebowski]

So Henk, you got a front wheel for sale now ?