2WD Crystalyte based Ebike Drive Bias Discussion

[BiGH]

I'm having a debate with Albie at the moment, about whether any of these systems would work (they're all 2wd systems)

clearly a 407 front and 407 rear motor with matching controllers ran off the same throttle would be fine (both running the same voltage).

ok now what if we were to have two controller of different max amperage...

rear: 407 with 72v 50a controller
front: 407 with 72v 35a controller

would this stop back emf issues, and allow the rear to provide more of the power used in acceleration?

ok now what about this if you used a front 406 and rear 407.
rear: 407 with 72v 35a controller
front: 406 with 72v 35a controller

this means the front has less low down torque, so the rear provides more power while moving slowly, the front takes precident at higher speeds because it would want a higher speed. but as the torque is lower at high speed, less stress would be placed on front dropouts..


ok time to throw this open - what does everyone think? is my reasoning wrong here?

 

[Rassy]

as one of our most esteemed members says:

"One test is worth a thousand opinions"

I don't think you will know the answers to your questions until you do some controlled tests with various options.

However, having used both two and three matched motors at the same time I know they enhance each other as they share the load, and I am sure the forces on the dropouts decreases significantly.

But to answer your question, IMHO, any mis-matched arrangement will be more detrimental than any matched arrangement. If one is after power and not extreme top speed, two matched high torque setups would surely accelerate/climb hills the best. On the other hand, for high speed, once you exceed the top speed for the high torque motor, it just becomes extra weight, along with its batteries, probably decreasing your final acceleration, your top speed, and your range. I will concede that the initial acceleration would probably be better than with two matched high speed set-ups.

In summary, I think any two motor e-bike would be impressive, but the performance issues between matched Vs unmatched motors would be very interesting.

 

[BiGH]

as one of our most esteemed members says:

"One test is worth a thousand opinions"

problem is the cost!

But to answer your question, IMHO, any mis-matched arrangement will be more detrimental than any matched arrangement. If one is after power and not extreme top speed, two matched high torque setups would surely accelerate/climb hills the best. On the other hand, for high speed, once you exceed the top speed for the high torque motor, it just becomes extra weight, along with its batteries, probably decreasing your final acceleration, your top speed, and your range. I will concede that the initial acceleration would probably be better than with two matched high speed set-ups.

In summary, I think any two motor e-bike would be impressive, but the performance issues between matched Vs unmatched motors would be very interesting.

i tend to agree, but i'm thinking... what about the difference between say the max loaded speed vs max no load speed. - ie
if the 408 has a max speed of 55kph with no load of 65kph, and the 407 has a max load speed of 60 no load 75kph then unless you're travelling over 65kph then the 408 will still be contributing to the power... however it clearly won't be contributing very much because...


hmmmm..... interesting....

i'd love for someone to try this.. maybe someone who has a whole bunch of crystalyte motors laying around *hint Hint*

i wonder what it would be like with two pumas,of different rotational speeds too... i'm guessing the freewheel could also come into play though wiht that and matched motors would be a necessity.

 

[fechter]

I think it would sort of depend on what you were trying to accomplish.

If you used two identical motors but at different current limits, I think that would work great. You could get maximum acceleration without wheelspin.

If you used motors with different no load speeds, I think you would lose some efficiency. At low speeds, both motors would be working, but the faster one would be bogging more, losing some efficiency. At high speeds, the slower one would eventually stop contributing and just become excess drag and weight. The faster one would need to do all the work at higher speeds, and more work than if it were alone. Things could get ugly if the faster one goes fast enough that the slower one starts regenerating. It would be like riding with the brakes on. If the slower one had a freewheel like a Puma motor, then it would just be extra weight.

The greater the speed difference of the two motors, the worse it would get.

Two smaller motors might have some other advantages over one big one.

 

[Ypedal]

i'd love for someone to try this.. maybe someone who has a whole bunch of crystalyte motors laying around *hint Hint*

I resemble that remark !

If my big battery would sustain the drain.. we would know this by now.

But this is something i am going to try soon .

I predict that 2 similar motors would be the best all-round-all-wheel-drive solution..

That said, unless you need the 2 motors to do the job.. one motor pushed hard usually gets the job done ! both at lower cost.. and weight.

 

[agent86]

Widely mismatched motors run 1 at a time for different conditions might make sense - lightweight geared motors would be better than direct drive for that approach. Here's someone who's done that:
http://www.wisechat.com/carl/2stage-rocket.htm

 

[BiGH]

I resemble that remark !

That said, unless you need the 2 motors to do the job.. one motor pushed hard usually gets the job done ! both at lower cost.. and weight.

funny about that - it was directed at you Y

yes two motors would be good - in allowing you to run more power through the wheels - say 50a rear 35a front - @ 96v - 4800w + 3360w = 8160w! (well into motorbike territory there though)

I think it was xyster that said dual 408s would have more thrust than a single 5304 and the weight wouldn't be *too* different. 8kg x 2 = 16kg vs 12kg. and quite frankly i'd prefer dual motors as it would help to balance the bike a little.

The real ultimate as discussed in a previous thread would be dual pumas - due to their light weight construction aren't well suited to high power applications - dual pumas at 20a or 35a would run more reliably and still be lighter than a 408! the only downside is the pumas cost a mint

Dual X5s would only really be useful on a motorcycle frame - due to the extreme weight - but it'd have fairly good acceleration. This is also something i want to do in time (but have to find a suitable motorcycle frame)

thanks for the link agent86 - thats very cool.

 

[albie]

I've been thinking about this type of setup since Haydon and I discussed it...

first of all costs aside...

first of all, you would need a custom frame to mount everything to make this run successfully.

secondly... battery packs... I would probably have a battery pack for each of the motors (ie 1x 72v power pack possibly for each hub).

A controller for each hub.

then someway to controller both controllers with 1 throttle!

With all this equipment... of course there would be extra weight etc.. but a very unique setup.

Although the downside of having this type of setup is that when you hit the gray area of the cruising speed of both mismatched hub motors, they would still be working roughly the same efficiency of having matched hub motors.

but this is all theoretical though.

 

[fechter]

running two controllers off a single throttle is no problem.

You could also power both controllers off the same battery if desired.

 

[Mark_A_W]

Haydon! Your bike goes plenty hard already!

You don't need to upgrade it's motor. The next step is a motorcycle.

(You need to move the batteries forward for better balance...AND ADD SOME TORQUE ARMS...oops..sorry).

 

[Stevil_Knevil]

I can attest to the fact that two X5 hub motors of the same wind count, laced into the same diameter wheel/tire combo, works VERY well with two 35A controllers when their throttle inputs are connected to a single throttle by a ' Y ' coupler. Also, the controllers can be fed by a single pack IF the chemistry and pack construction are designed to bear the continuous load of the motive kit.

Of course, all of this could be scaled down to work with 400-series motors. Which leads me to wonder, how well would a dual 404 in 20" wheels @ 72V-35A perform? How about the geared Puma/eZee variations?


-Stevil

 

[Ypedal]

404 at 72v = not a good idea... too fast to be useful.

 

[Stevil_Knevil]

too fast to be useful.

55+ MPH?! Absolutely.. for a pedal-assist ' ebike ' :wink:


-Stevil

 

[Drunkskunk]

Just a thought, but I wouldn't run seperate batteries. or if I used 2 packs, I'd run them in parrallel. The distance traveled by the front wheel of a bike is usualy 5% greater or more, in a straight line. if you are going around a lot of curves, the number goes higher. As you ride, the front wheel crosses back and forth through your Center of Gravity to keep you balanced, while the back wheel usualy tracks behind without leaving the COG.

it might not cost the battery more than 3-5% more power on the front wheel, but eventualy, that will kill the battery faster, and shorten your range. if you link the batteries together in parrellel, you'll eliminate the problem all together.

 

[Volt]

Last summer i installed two x4 each complete with there own battery and controller ( 2*48v) . The result was a heavy and unimpressive lug of an ebike . A single x5 in a 20'' would be a better option.

 

[BiGH]

volt, were you running both at 48v?

I agree, I don't think that running controller under the maximum, is worthwhile. running two 408s at 72v 35a insted of a 5304 running 72v 50a. ( yes the 50a controller is lower than the two 35a controllers in total amperage but would allow you to run a higher total power than one motor alone.)

if you want to run higher power than a single motor can reliably handle, then twin motors would be worthwhile, otherwise as volt said it would be a waste of weight.

 

[Volt]

Yep both hubs were run at 48v . 72v on a x5 is a really good recipe for death , why would you want to go that fast on a bike ? even an expensive dh bike would wear out fast at those speeds . What did that dead guy use to say "danger danger " using my best aussie accent ... My x5 (503)in a 20 rim at 48v delivers more torque and speed then ill ever really need . If you have the need for speed why not just convert a motorcycle ?