Purely Hypothetical

[rodp]

Something crossed my mind today as I was stood by my bike talking (it's in the factory) . It has a rear hub motor, so one wheel drive, and me being a four wheel drive person all my life (and that's a long time) I wondered why no one had tried a two wheel drive. I know the two wheel drive motorcycles from days gone by were virtually unrideable, but times have moved on. Could two motors (front hub and rear hub) be synchronised for speed but keep full power. That is, if one broke traction would it be possible through electronics to stop it spinning away (traction control)
No intention of building one, just curious that's all.

 

[Woosh]

several 2WD projects were posted on the forum over the years but there is no real advantage, just more weight. About 2/3 of your weight is on the rear wheel. Adding a front wheel drive would only add about 50% extra traction and you lose on maneuverability. The rotating mass of the motor creates an inertia that resists you when making turns.
If you want 2WD, you should also have automatic traction control.
Just not worth the hassle.

 

[rodp]

Not intending to do it, just pondering if two motors could be synchronised for rpm without cutting down torque ?

 

[Gringo]

twin motor ebike - Google Search

 

[Woosh]

Not intending to do it, just pondering if two motors could be synchronised for rpm without cutting down torque ?

the two motors don't need to be synchronised.
They work independently but because they are attached to the same bike, their output is added together to propel the bike.
The special dual controller shares the same brake sensors, pedal sensor and throttle but each half receives its independent hall signals.

 

[RossG]

There's just one thing to remember if you attempt that....

 

[Sturmey]

I have a few mountain roads beside me with 300 meter climbs and over 12% grades in places. My single hub yose 350w rear was just stalling on the climbs (my legs were not strong enough to keep it going) so I stuck a spare old mxus xf07 on the front to try it out. It was great, so I left it for the time being till I fix up something better.
The motors are not synchronized, the setup is simple. The rear works with PAS only and is controlled by the pedals. The front is on simple throttle only and no lcd. I have two separate batteries which I would need anyhow because of distances. Both motors are totally independent of each other.
I also have another single hub bike as well as 250w tsdz2, but I prefer to use the twin hubs for the mountain roads as its a very strong and durable setup. But I have given it plenty of use with the yose lcd3 gone around the clock. (over 10,000 km). The extra motor adds about 3Kg to bike.
Although I have three bikes, they are all 36v and I have a setup where I can transfer the batteries from one bike to another, so I dont have batteries lying idle. It doesn't cost much to run extra bikes if batteries can be transferred.
PS I dont have a car at the moment so the bikes get a lot of use.

 

[vfr400]

I've built several 2WD electric bikes. Obviously, you get double the power with two motors at the expense of range. Their main advantage is traction on slippery surfaces, like wet grass, mud and snow. For every other situation, a single rear motor that's powerful enough for what you need would be a simpler solution.

You need a good battery for two motors.

 

[Woosh]

single motor is predictable. How do you split the power of double motors without traction control? I rode my fat bikes on snow a few times, it's scary enough with the 48V Bafang MaxDrive motor on snow.

https://wooshbikes.co.uk/2017/fatsix/warrior.jpg

didn't you have an accident with your 2WD at the Park Street run in Bristol?

 

[Sturmey]

The link below is the model of both motors climbing a 10% grade. (1 in 10). Both motor run to the max and so power splits well. A lower pas (4) is selected for lesser grades. Now I am not really a fan of 2wd as such and have no problems from a traction point of view. Actually, a lot of the time, the front motor is freewheeling and this setup performs well in terms of range. But the 2wd gives me over 30 + 30 = 60 newtons/meters at wheels to get me over the mountains. The little tsdz2 also does this with the 34 tooth rear but more slowly.
I would be interested if someone could point me to a really powerful hill climbing rear hub that could perform as good as the twin hubs or as good as the mid drive. I would need at least 60 newton meters at wheel to be as good as the 2wd or better still 75nm to match the middrive.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

www.ebikes.ca

 

[RossG]

single motor is predictable. How do you split the power of double motors without traction control? I rode my fat bikes on snow a few times, it's scary enough with the 48V Bafang MaxDrive motor on snow.

https://wooshbikes.co.uk/2017/fatsix/warrior.jpg

didn't you have an accident with your 2WD at the Park Street run in Bristol?

Technology to the rescue.

EXCLUSIVE: Cycle lift proposed for Park Street

Encouraging more people to cycle in a post-Covid world

www.bristol247.com

 

[Gavin]

The link below is the model of both motors climbing a 10% grade. (1 in 10). Both motor run to the max and so power splits well. A lower pas (4) is selected for lesser grades. Now I am not really a fan of 2wd as such and have no problems from a traction point of view. Actually, a lot of the time, the front motor is freewheeling and this setup performs well in terms of range. But the 2wd gives me over 30 + 30 = 60 newtons/meters at wheels to get me over the mountains. The little tsdz2 also does this with the 34 tooth rear but more slowly.
I would be interested if someone could point me to a really powerful hill climbing rear hub that could perform as good as the twin hubs or as good as the mid drive. I would need at least 60 newton meters at wheel to be as good as the 2wd or better still 75nm to match the middrive.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

www.ebikes.ca

I like what you've done there @Sturmey but surely you've started with the wrong base.

If you put the hub motor on the front of the TSDZ bike you'd have the best of all worlds- 2wd when you want it and selectable gears for better hill-climbing...

 

[Sturmey]

I like what you've done there @Sturmey but surely you've started with the wrong base.

If you put the hub motor on the front of the TSDZ bike you'd have the best of all worlds- 2wd when you want it and selectable gears for better hill-climbing...

Actually, if you think about it, nearly all front hub pedal assist bikes are two wheel drive. (legs drive rear, motor drives front). Anyhow, I would not fit a front hub to tsdz2 as its fast enough for me as its is and has enough torque, and anyhow, its possible to get even more torque by changing chainwheel gearing etc. Its also a reasonable light and well balanced setup as it is.

 

[Woosh]

I would be interested if someone could point me to a really powerful hill climbing rear hub that could perform as good as the twin hubs or as good as the mid drive. I would need at least 60 newton meters at wheel to be as good as the 2wd or better still 75nm to match the middrive.

mid drive torque is given at the chainring - 75NM is roughly 75NM*28/44=65NM when compared to a rear hub. I do like your 2WD combination.

 

[rodp]

Just wondered if it was possible to synchronise front and rear motors so if you lift the front wheel it wouldn't spin up? Synchronise the speed but keep full torque?

 

[Woosh]

not with the kits on sale at the moment. You will need traction control for that.
How are you going to detect that the front wheel is lifted?

 

[Gavin]

mid drive torque is given at the chainring - 75NM is roughly 75NM*28/44=65NM when compared to a rear hub. I do like your 2WD combination.

Woosh, educate me....

What's the 28/44 bit all about? Is that a known formula for conversion?

Also, is that 75 X (28÷44)?

 

[Woosh]

What's the 28/44 bit all about?

28T is my favourite rear sprocket when climbing a steep gradient, 44T chainring is usually fitted to CD kits.

 

[vfr400]

single motor is predictable. How do you split the power of double motors without traction control? I rode my fat bikes on snow a few times, it's scary enough with the 48V Bafang MaxDrive motor on snow.

https://wooshbikes.co.uk/2017/fatsix/warrior.jpg

didn't you have an accident with your 2WD at the Park Street run in Bristol?

That was on my 5 1/2 KW triple motor drag bike on a road that had been completely chalked over, then it drizzled. Not quite the same thing.

For slippery conditions, two low power motors work better than one high power. I made a double throttle by gluing in a second hall sensor. Because of the distance from the magnets, the one signal always gave a slightly lower power, which I used for the front motor. another good way to do it is PAS to the back wheel and throttle to the front. That way you can control any tendency to slip on the front.

 

[Woosh]

That was on my 5 1/2 KW triple motor drag bike

you should rebuild it with 20 x 4 wheels!