Mid Drive and Hub drive combination?

[OldAusDigger]

Hi guys, I don't own an e bike - yet.
I've read about the pros and cons of both mid and hub drives, but what would happen if you used both on the same bike?
Say you had a Bosch powered mid drive and you were to add something else that is "high end" to the equation like an Bionix or GoSwiss hub drive kit that uses torque sensors?
Surely the extra torque that is put through the chain from the mid drive would be picked up by the hub drives torque sensor to exponentially add to the overall power delivery.
I imagine such a set up would make an awesome climbing machine.
I know there would be a definite weight penalty, but maybe spreading the drive across two motors at say 50% each might be more efficient than both running at 100%.
Any thoughts?

Digger

 

[boss]

Interesting experiment, but IMO infeasible with a rear hub motor; probably work well with front hub system but coordinating torque sensors could be tricky. Also, AFAIK BionX has shut down. Easily accomplished with mid-drive and front- rpm sensor combination IMO.

 

[OldAusDigger]

Thanks for your input fos'l.
Yes I agree that if the two separate torque sensors wont work together then there's no point. I'm not very knowledgeable about any of this really, but the way I pictured it in my head was the hub drives sensor working by measuring stress on the chain and the mid drives torque sensor somehow working independent of the chain, which could be incorrect - I don't know enough about it really.
I was imagining riding around for the majority of the time with both systems on a low assistance setting with the extra torque or stress on the chain that the mid drive might give at say 100% assistance effectively doubling your pedal power which in turn is picked up and magnified again by the rear hub drive at whatever assistance level you've chosen. When you encounter a steep hill then maybe you could ramp up the assistance levels to max on both motors to really fly up the hill!
So, if you could produce 500 watts by yourself and your mid drive could convert the power output at the crank to 1000 watts at a 100% assistance setting, then this 1000 watts (1kw) is again magnified by whatever assistance level your hub drive is set at.
Does it work like this or are the limitations set by the motors and regardless of what input is coming through the chain from the crank the rear hub drive can only deliver so much regardless of what percentage increase you are requesting from it?


Digger

 

[boss]

1) Doubt most individuals add more than 250w, but you could be exceptional.
2) BionX had the most powerful PAS rear system. The more powerful motors are throttle-only AFAICT.
3) The BBSHD is the most powerful mid-drive with PAS that I know of although others (Cyclone 3000 or larger) may be possible.
4) Combining 2 & 3 not feasible IMO even though BionX is torque-sensor through the hub and BBSHD is RPM.
5) BBSHD and front motor with RPM should be easy.
6) Probably you know this, but you're talking about a moped; I haven't explored higher powered systems; they'll need license and insurance in CA.

 

[eBikesmith]

This is kind of interesting, and has definitely been done before. Most examples I've seen are with front hub motors though, making the bike AWD.

This is also something I contemplate on doing, but I'm curious as to what your reasoning behind it is. Like what obstacle are you trying to overcome, or what advantage do you feel it presents, by having both types of drives?

The reason I ask, is because there are both mid-drive and hub-drive motors that are more than powerful enough to do almost anything. Therefore, when you're talking about having a mid-drive, and hub motor in one setup, there are only a few reasons I can think of.

 

[JRT_in_WMass]

Keep it simple.

 

[boss]

Primary reason for some is to provide back up if one fails. Also wonder if 2WD would be beneficial for sand or snow. I tested a BH (Easy Motion) bike with front and rear motors; great acceleration, but not exceptional in any other way but weight (heavy).

 

[eBikesmith]

Gotchya. Well, if you really want to have two motors, this is what I would consider.

Your biggest obstacle is going to be wiring the controller for PAS or Cadence sensing or throttle. If you're doing a custom build like this, I would probably recommend going with a Cycle Analyst type controller. Make sure you get the right one, because they are different.
If you decide to go with 2 identical hub motors, I don't see why you cant just splice and wire them in parallel as one. You should have no issues.
If you decide to go with two different motors (any combo of hub or mid-drive), this will get a little bit trickier. Technically (I've seen this done), you could just have two completely separate systems on board, with one wired up as torque or cadence sensing, and the other as throttle only. Otherwise, I think there are a lot variables in play that could effect how the motors would react if they are completely different to one another and wired up to the same controller. Theoretically though, I think its definitely possible to wire two different motors to the same controllers utilizing the torque/cadence input and throttle. On the other hand, if it's the motor controller that gets fried (happened to me before on a really hot CA summer day), that would put you back in square one when it comes to having a backup.

I hope this helps. Oh, and having 2WD will definitely help with traction in sand, snow, etc. Check out the Easy Motion Evo Snow.

 

[JVG1967]

Glad I ran across this thread because I'm getting ready to start such a project using an Enduro E Bike frame. I attached a pic of a bike but I'm purchasing only the frame. For motors I'm planning on using a BBSHD mid drive and a Bafang 750 watt geared hub motor in the rear with a seven speed gear set up. Each motor will have its own 52V battery for power. I'm planning on keeping this as simple as possible so only the rear hub motor will use PAS and a twist throttle. The BBSHD will be a thumb throttle only and used kinda like nitrous on a car for when I want an extra blast of power. I'm sure there are things that I'm overlooking and will have to be worked out during the build process.

Before anyone complains, this is a street bike and being built out to the nines for testing the frame as I may start selling the bikes in a 750 watt configuration if the quality is good.

 

[eBikesmith]

JVG1967,

I'm definitely interested to see how the build goes, and more specifically how you end up wiring everything up. I do have a question though; why use the mid-drive as a throttle backup and the hub with the PAS?

 

[JVG1967]

Really just trying to keep things simple. I may look at hooking both motors up to PAS but in the beginning I'm going to have only the rear hub on PAS and throttle. The thumb and twist throttle will be mounted on the right side next to each other so I can use both motors together using the throttles for max power.