I know their meanings, but i just can't get my head around them.

[funkylyn]

This characteristic has nothing to do with the type of drive (crank vs hub). It depends on the control system. Chinese crank-drives including Tonaros (sorry Lynda) have the same control system as their hub motors, so they're the same.
.

Aah...but Dave,you dont know what Ive done to mine in one of my techie moments when I stripped down the thingy, added a whatchamacallit and split the whatsit ........

Lynda

 

[mountainsport]

Here is my version (for non engineers like myself - I know this is oversimplified at best : )

Acceleration is the word that describes increasing your speed over time.

Example, get on your bike and go. In the first second you are travelling at 3mph , in the second 6mph, the third 9mph and so on. Congrats - you are accelerating !! That's all there is to it.

Torque is a word used to describe the strength of the twisty motion your motor makes when it is switched on.

Example - think of a kids handheld windmill. The type they sell on seafronts around then uk. When power is applied (wind rather than electric) they turn around. Stick your finger in the way - it stops. Very low torque indeed

Now think of your wheel. Power gets it moving , stick your finger in the spokes and you will no longer have a finger ! Much higher torque - high enough to overcome the drag of your finger

Quite right too as the torque an ebike needs to produce must be enough to overcome the combined weight of you and your bike (not just a finger !) and added to that it is expected to push you up hills. Some bikes are better than others at this - Lower torque means not so good hill climbing, higher means better

Higher torque also means better acceleration - more twisty strength means it is less dragged down or stopped by weight and hills

This is the best explanation so far, but you had to spoil it when you finally had said that, "Higher torque also means better acceleration" which I do understand. basically, they can not work without each other?

MS. You can give up if you wish to KirstinS ...........

 

[Deleted member 4366]

And about the power now d8veh? Just kidding. Therefore in other words acceleration starts off first then torque ends up second, so does acceleration determine the cut off point for the torque or does the torque determine when for the acceleration to take over? (Sorry still trying).

MS.

Unfortunately it's not as simple as that.

Acceleration depends on torque, so the more torque you have, the faster you gather speed, but as your speed increases, the torque goes down until the torque you have is giving a force equal to those slowing you down. Those forces get bigger as you go faster or up hills, then you've reached max speed. So the torque is going down and the resistance is going up as you increase speed.

A crank motor is more complicated because this effect happens differently in each gear. If you started in first gear, you'd get good acelleration, but the motor would max out (motor speed high- torque zero) at low speed. You can change to a higher gear to reduce motor speed and get higher torque again from the motor, but the gearing reduces the torque to the back wheel, so you accelerate again, but less than you did in first gear. By the time you get to top gear, your speed is high so resistance forces are high, and although you have high motor torque, the gears reduce the torque in the back wheel so that the force is less than those pushing you back, then you have negative acceleration, so you slow down. How fast you ultimately go depends on power, which again is simple, but ends up being complicated with ebikes. There's so many changing factors that it's difficult to pin things down. Cars and motorbikes are easier because torque is more or less constant regardless of motor speed.

The best is to have a look at the simulator at Ebikes.ca (google it), which can work it all out for you, except there's no crank motors in there. It can tell you how fast your weight can go up a hill. Unfortunately also there's not many small motors like we use, but you can normally find something close enough.

 

[trex]

This question is for d8veh.
8-Fun BPM is approximately twice as powerful as their SWX used on most hub bikes sold today.
If 8-Fun fit their BPM to their crank drive kit (disregarding the price), would you buy it? and also, would it leave the the hub biting dust in a race?

 

[mountainsport]

Oh my dear MS, Im getting a headache now...why not just do as I do and enjoy the ride without having to know all the reasons why it goes like it does....its far less stressful I find

..... sorry, Im being a bit facetious, but Ive just inadvertently had a mouthful of vaping juice whilst changing a tank with my teeth, ( dont ask lol ) and its not my favourite tipple

I do, however, admire your enquiring technical mind.........

Lynda

Love can also be technical in a non-technical persons mind.

MS

 

[Deleted member 4366]

Interesting question.

Would I buy it? No, because it would over-stress the gearing and it would have a tendency to wheelie in first gear. The SWX gives sufficient power as a crank drive. I personally like to travel between 12 and 20mph, so I wouldn't need the additional power of the BPM as a crank drive.

Would it win in a race? Yes because if you have a low speed BPM as a hub motor, it would max out at 20 mph with power dropping off rapidly from 15 mph, but the same motor could produce max power at any speed as a crank drive with the right gearing. You could get a high speed version as a hub-motor, but it would be inefficient at low speed and not able to produce maximum power.

The crank-drive version would be faster, but use a lot more battery in most circumstances. I have the GNG, which has about the same power as a BPM with the same current. It's fun, but difficult to ride slowly. The 500w code 10, 11 or 12 is difficult to beat for all-round user-friendliness. It's simple, has enough torque to get up steep hills, can cruise at 20mph, puts no stress on the gears/chain, and is hardly noticeable when riding without power. Only the 270 rpm 500w CST is better. That motor at 36v with a 30 amp controller is ebike nirvana. If I could find something better, I'd get it. All ebikes should have that motor and then we'd all be happy.

 

[trex]

That's a very well reasoned reply. Perhaps more suppliers will do just what you suggest and replace the SWX with BPM and bring the price of BPM bikes down.