Build two wheel drive without cycle analyst

[Cyclomania]

Up to date, good quality hub motors have efficiencies in the 80-something percent range. Geared ones usually rate in the low 80s. The controller costs another few percent, up to 10 but not usually that high at full load. Add a little loss in your plugs and cables, and you're looking at 75% overall efficiency in a near-ideal case.

Chances are very good you won't even be getting 900W to the wheel. But since you can't easily measure that value, and you can easily measure input power, it's a decent rule of thumb to say 75% overall efficiency for a good quality system and maybe 65% for a cheap-cheap but recently made one.

What do you think about running two of these controllers and one 36 volt battery? Both motors are 250w each. Guess I am already overvolting them quite a bit. So a 48 volt battery might toast the motors don't you think?

 

[Chalo]

What do you think about running two of these controllers and one 36 volt battery? Both motors are 250w each. Guess I am already overvolting them quite a bit. So a 48 volt battery might toast the motors don't you think?

Volts give you RPM. Amps dictate both torque and heat. So changing the voltage by itself has little bearing on how much you heat up the motors.

Also, a motor's rating (especially for a hub motor) is only slightly related to its power capabilities. I run "350W" Bafang hub motors on 48V x 22A (over 1000W), and they barely get warm. Most motors rated less than 1000W are rated to comply with restrictions and limitations, rather than to let you know what they can do.

 

[Cyclomania]

Volts give you RPM. Amps dictate both torque and heat. So changing the voltage by itself has little bearing on how much you heat up the motors.

Also, a motor's rating (especially for a hub motor) is only slightly related to its power capabilities. I run "350W" Bafang hub motors on 48V x 22A (over 1000W), and they barely get warm. Most motors rated less than 1000W are rated to comply with restrictions and limitations, rather than to let you know what they can do.

Maybe try with the 48volt battery then?

I thought heat came with wattage or something. But that is basically only done by the amps then? Good to know.

I was also thinking about the picture that Mica has in his video, where his black cable splits in two from the battery bracket. And his red cable splits in two as well. So the black cable splits in two and it goes as one for each controller, and then his red cable does as well.

Would a connector like in this picture/link do the same job you think? Then going from the battery bracket/mount:

https://www.aliexpress.com/item/1005002966849022.html?spm=a2g0o.order_list.order_list_main.106.21ef1802dafghy

(Third or fourth version)

Or would I be better of soldering this two part split on the cables on my own?

 

[DaLanMan]

Hold it, I am still stuck on "why would you put 2 motors on"
I am doing it because I have ridden every stupid idiotic and ridiculous motorcyle money could buy, I bought a 1600 cc Katana, Loved, it, scared the pee out of me, but loved it.. Then I got a Monster9 because I was done with Japanese stupid, I wanted Euro stupid.

I had a Race bike, Sold it when my daughter was born, never got time to actually race it, but honestly, 200 miles an hour is not as scary as 45 at 7pm on the 405...

I am building a dual drive bike entirely by the happenstance of running across the parts for cheap and finding out someone had a build with exactly the same parts... So yep... It is in the last phases of assembly.

 

[Cyclomania]

Hold it, I am still stuck on "why would you put 2 motors on"
I am doing it because I have ridden every stupid idiotic and ridiculous motorcyle money could buy, I bought a 1600 cc Katana, Loved, it, scared the pee out of me, but loved it.. Then I got a Monster9 because I was done with Japanese stupid, I wanted Euro stupid.

I had a Race bike, Sold it when my daughter was born, never got time to actually race it, but honestly, 200 miles an hour is not as scary as 45 at 7pm on the 405...

I am building a dual drive bike entirely by the happenstance of running across the parts for cheap and finding out someone had a build with exactly the same parts... So yep... It is in the last phases of assembly.

Ah interesting. Have a picture?

How did you solve the cable going from the battery into the controllers? Soldered on an extra black and an extra red on both ends going out of the battery bracket? Or did you use a split cable like the one I have linked above?

Also folks, how do you solve the display so everything runs on only one? Is that possible to do by just taking out the wwire on one side like with the throttle, where the signal wire connects into both controllers. But the red and black to only one controller.

Possible to do something similar with a display? Or do you normally skip dislpay completely on these builds?

 

[DaLanMan]

Ah interesting. Have a picture?

Nope, I habitually get caught up in doing things and forget to break out the camera, besides, it came to a rather screeching halt when I realised that I still had not ordered rubber.. .bare rims seem painful (there are some pics in my build thread)

How did you solve the cable going from the battery into the controllers? Soldered on an extra black and an extra red on both ends going out of the battery bracket? Or did you use a split cable like the one I have linked above?

I have a splitter, like I said, no clue what is gonna happen when I fire it up... I do have spares of the things I expect to let the smoke out of.

Also folks, how do you solve the display so everything runs on only one? Is that possible to do by just taking out the wwire on one side like with the throttle, where the signal wire connects into both controllers. But the red and black to only one controller.

I have a display, it is wired in, it appears to see a wheel.. not even sure which one...

Possible to do something similar with a display? Or do you normally skip dislpay completely on these builds?

Normal? brother there is nothing normal about me...

Oh, uhmm.. no clue, first time doing this, When it comes to deep knowledge consider me a saucer.

I started dinking with bikes when I inadvertently bought 5 instead of the 1 I had set out to purchase... it is actually a lot easier to do than you think....

 

[Cyclomania]

I have a display, it is wired in, it appears to see a wheel.. not even sure which one...

Yeah I have built a few before but this is my first try on the dual motors. Regarding the display I wonder if someone else could give us some input on that.

I mean, the throttle can be splitted so it has two signal wires. Connecting the green one to both controllers like in the video I posted. But I dont know if something similar should be done with the display(?). Or is it enough to connect the display to one controller as long as the other wheel is connected to the throttle and the battery(but not the display).

 

[DaLanMan]

The display issue is not nearly as worrying as what is gonna happen when I get wheels on this and try it out.. My primitive monkey brain wants them both to fire off slightly out of sink ending in a comedic Hannah Barbarah dust cloud...

The skeptic in me thinks it is doomed, but this is not a lark. I actually read up on it and am kinda/sorta following a build concept of someone smarter than I.

 

[Cyclomania]

Would it be a problem if the front wheel- motor is 250watts and the rear is 350watts? I now am the proud owner of a frontwheel of 250watts. But my rear wheel is 350watts.

If the two controllers are the exact same controllers pulling the same amps how would this affect my bike? I guess they should ideally be the same watted motors. Front and rear.

But could this work and would my bike be affected in a bad way in some way?

 

[Cyclomania]

Would it be a problem if the front wheel-motor is 250watts but the rear is 350watts? I am now the proud owner of a front-wheel of 250 watts. But my rear wheel is 350 watts.

If the two controllers are the exact same controllers. And they are pulling the same exact amount of amps(I am thinking max current 17), from my single battery, how would that effect my bike's performance? I guess they should ideally be the same watted motors. Front and rear.

But could this work and would my bike be affected in a disadvantageous way of some kind?

 

[Chalo]

Would it be a problem if the front wheel-motor is 250watts but the rear is 350watts? I am now the proud owner of a front-wheel of 250 watts. But my rear wheel is 350 watts.

If the two controllers are the exact same controllers. And they are pulling the same exact amount of amps(I am thinking max current 17), from my single battery, how would that effect my bike's performance? I guess they should ideally be the same watted motors. Front and rear.

But could this work and would my bike be affected in a disadvantageous way of some kind?

It doesn't matter at all what the power division between your motors is. It only matters what RPM they're trying to run at.

If they turn at different speeds, they'll only work together until the slower motor reaches its no-load speed, then the faster motor will work alone or even begin to drag against resistance in the other motor.

I recently built myself a two motor bike with a "350W" front hub running 44V x 22A, and a "500W" rear hub running 44V x 30A. Because they both turn at the same speed, they pull together through their entire speed range.

 

[Cyclomania]

It doesn't matter at all what the power division between your motors is. It only matters what RPM they're trying to run at.

If they turn at different speeds, they'll only work together until the slower motor reaches its no-load speed, then the faster motor will work alone or even begin to drag against resistance in the other motor.

I recently built myself a two motor bike with a "350W" front hub running 44V x 22A, and a "500W" rear hub running 44V x 30A. Because they both turn at the same speed, they pull together through their entire speed range.

Cool. Very cool

Can I measure this somehow? To see what rpm they are I mean? The motors I have I got as standalone wheels form a bikeshop that sold them so I am not sure how to calculate rpms for them. Would be nice to know if they could work together. But I guess that is a slim chance right(?) since they are two different brands.

 

[Cyclomania]

I recently built myself a two motor bike with a "350W" front hub running 44V x 22A, and a "500W" rear hub running 44V x 30A.

44volts? Is that 36 volt battery then? Or do you have some other standard in the States?

Do you think i could go above 17 amps for my motors of 350 watts back and 250 watts front? Or would that be a stretch? Not quite sure how to calculate if I am making a fast bike, or if I am only doing motor-barbecue.

 

[Chalo]

44volts? Is that 36 volt battery then? Or do you have some other standard in the States?

I'm using automotive modules with 12 lithium ion cells in series, rather than the more common 10 cells ("36V") or 13 cells ("48V").

Do you think i could go above 17 amps for my motors of 350 watts back and 250 watts front?

I think you certainly can with the 350W rated one, to 22A at least. If it uses the common small diameter 9 pin waterproof plug, I would not use more than 25A. Nominally 250W motors are so all over the place in terms of their actual power capabilities, I can't guess whether yours will tolerate more than 17A. If it's about the same size and weight as your higher rated motor, then probably it can take 22A as well.

I checked my motors' RPM by attaching a zip tie to the wheels so they would click the frame/fork, and running the motors unloaded in the bike stand one at a time while comparing against beats per minute videos on YouTube. Once I found a BPM tempo that matched the first motor, I compared it to the second motor.

If you do something like that, remember to run the motors at their maximum setting and full throttle, or else the controller will artificially clamp their speed.

 

[Cyclomania]

I checked my motors' RPM by attaching a zip tie to the wheels so they would click the frame/fork, and running the motors unloaded in the bike stand one at a time while comparing against beats per minute videos on YouTube. Once I found a BPM tempo that matched the first motor, I compared it to the second motor.

If you do something like that, remember to run the motors at their maximum setting and full throttle, or else the controller will artificially clamp their speed.

Aha. So if I notice one is slower than the other I should raise the amps on that one? Or how do you make them even out? Or did you just find one that had the same rpm?

 

[Chalo]

Aha. So if I notice one is slower than the other I should raise the amps on that one? Or how do you make them even out? Or did you just find one that had the same rpm?

I had a bunch of different hubs available to choose from, so I made an educated guess and it worked out. But another way you could do it is to use a configurable controller and display like KT for the faster motor, and use the parameter programming to limit it to the same top speed as the slower one.

 

[Cyclomania]

I had a bunch of different hubs available to choose from, so I made an educated guess and it worked out. But another way you could do it is to use a configurable controller and display like KT for the faster motor, and use the parameter programming to limit it to the same top speed as the slower one.

Aha but then I would not be able to squeeze out as much power out of the stronger one?
Yeah I think understand and I will try it out.

Hmm perhaps better to use a "250 watt motor" in both the front and back then? A bit of a waste to use this 350watt motor on this bike then ? Since I will not be able to squeeze its true power out of it anyway I mean.

Better to use that one for another bike and go with 250 back and front so I can get them both pretty close to their true power capacity?

 

[Chalo]

Aha but then I would not be able to squeeze out as much power out of the stronger one?
Yeah I think understand and I will try it out.

Hmm perhaps better to use a "250 watt motor" in both the front and back then? A bit of a waste to use this 350watt motor on this bike then ? Since I will not be able to squeeze its true power out of it anyway I mean.

Better to use that one for another bike and go with 250 back and front so I can get them both pretty close to their true power capacity?

Wattage rating has zero to do with RPM per volt, which is the figure of interest. Also, reducing maximum RPM electronically will probably not reduce the motor's peak power at all. Output power naturally diminishes as the motor's speed rises towards max RPM. So trimming off the upper end of that speed range most likely only affects it at speeds where the motor is putting out less than its peak power.

 

[Cyclomania]

Wattage rating has zero to do with RPM per volt, which is the figure of interest. Also, reducing maximum RPM electronically will probably not reduce the motor's peak power at all. Output power naturally diminishes as the motor's speed rises towards max RPM. So trimming off the upper end of that speed range most likely only affects it at speeds where the motor is putting out less than its peak power.

Hmm so 350watt back and 250watt front might be ok then? Just thinking about whether it is a waste or not. I have to do that test I guess to find out how fast their rpm is.

But if I limit the top speed of the faster motor with a KT controller and display, would that not be a waste of power?
If the motor in front is slower I mean.

 

[Cyclomania]

I had a bunch of different hubs available to choose from, so I made an educated guess and it worked out. But another way you could do it is to use a configurable controller and display like KT for the faster motor, and use the parameter programming to limit it to the same top speed as the slower one.

So KT controllers and displays have that feature? Sounds like an interesting idea.

 

[Cyclomania]

Are you still going to use the bbs02 on the rear ?

No I actually wrote in the wrong thread. I thought I had up the thread about double motors. But I am going to do the bbs02 as well. But then I want to change the controller to have max ah 30a. And have that one externally.

 

[Scootdan]

this is the 2 wheel drive bike I built to experiment with a lot of the ideas on this thread. I tried dual throttles, various ways but quickly ditched that idea. Two controllers with one throttle worked best and is simple and easy. I absolutely love 2wd bikes because I find them way faster and more fun. I tried front drive and rear drive and find rear drive the most boring. But add even a small front motor and magic, instant fun. This ugly bike with a lot of the weight in all the wrong places was an absolute blast to ride with acceleration that was awesome for only a 500w front and 1500w rear hub motors and 52v battery. In my humble opinion the 2wd bike history is still being made. Hope to see you have great success with your build sir.

 

[Scootdan]

I also found the brakes to be insufficient when you add the weight of a larger battery and even one motor, much less two. Here I experimented with adding monster motorcycle brakes which was wild! It worked beyond awesome but was hella heavy and many times overkill for size. I would use a smaller motorcycle one next time. I also experimented with two displays and separate keyed shut offs for each motor. I found with both motors running off one battery one display/speedo and one keyed shut off worked best. My big scooter is 2wd but has one battery and display for each motor. Each motor can be run independently for awd, fwd, or rwd, but of course I always prefer awd. I also have separate three speed motor switches, which I highly recommend. I find it really useful to dial in the power to each wheel, as it really affects performance and handling. I have also learned the rear motor works harder and will eat more energy than the front motor. No big deal for one battery, but it is nice to adjust power to get more equal battery use when using two batteries. AWD rocks!

 

[PrimeGoat]

Sorry, I don’t want want to derail your thread into a pros vs cons of dual motor debate, but every time I I see someone proposing doing it I wonder what the compelling reason is.

It’s an unusual use case in which the redundancy, traction, or weight balance benefits counter the negatives (cost, complexity, weight, risk, ugly wiring, troublesome tube/tire repairs).

If you already had a more than capable battery running a rear wheel setup that was a little underpowered, and a motorised front whee fell into your lap for free, I could completely understand.

But as a starting point for a design … I have to wonder what the decision tree looked like for someone to arrive at such an outlying branch.

Like I said, the only practical things that could/should steer you in that direction are redundancy, traction, or weight balance.

And even then, weight balance is better solved by a mid motor, so that one’s tenuous, and most traction concerns can be addressed via geometry and tire selection. That leaves redundancy as the only real compelling practical reason. But it’s not compelling, because there’s already intrinsic redundancy in the form of legs and cranks.

I’m only stating the practical perspective, not denying the validity of other criteria. A bike with a motor is cool. Two motors is definitely more cool, and at least twice as impressive.

I have a dual motor ebike and never want to go back. Sharp turns are much more stable, climbing up onto the curb is a joy, and just the overall feel is much more balanced and enjoyable. It also seems to handle better in the rain.

 

[Hwy89]

My current bike packing rig is a Surly Big Dummy with aBBS02 mid drive and a Q128 slow wind geared hub up front. It’s a heavy awkward beast but the nicest ride ever. This is my third iteration of dual motors on this bike and the best so far. I run the mid drive all the time in pedal assist mode and use the throttle on the front motor when starting and from time to time for a boost on hills. The combo saves a lot of wear and tear on the rear drive train by keeping stress off the chain. I also find that I do a lot less gear shifting when I can use the throttle to help with acceleration.
I do a lot of back country riding and often in deep sand. That’s where the 2WD really shines as heavy as it is it just floats over sand with the front wheel pulling.