Some Questions from a potential GM owner

[bike4ever]

Hello All,

I have read almost ever post in the forum.  I am looking to get a ebike kit and have spent hundreds of hours reading online about all kinds of different options, types, qualities, etc....  GM seems to be the way for me to go.  I do have a few questions before I make my first purchase.  I have to add that Gary, the GM distributer here in Canada has been great.  Some background info on what I want, well its pretty basic.  Two kits one for myself and my wife.  I want as much power and range as I can afford for each bike.  I am leaning towards the 1000W motor or the MP with 48V batteries.  I think it will be the 1000W motor, just seems like I can play with that a little more than the MP.  But here is a big question, though I know the general answer I want as much detail as possible...

How much resistance does the 1000W motor cause when the system is running unpowered?

I have read that all BLDC motors will offer some resistance.  For example ebike.ca explains that the Crystalyte 5x series offers a LOT of resistance to pedaling without power.  I will be using my bike a lot for both ebiking and good old fashion human powered riding, for fitness.  I love to ride for long rides, sometimes 60-80km and do so with gear and fear the idea that the motor will add a of resistance. 
It would be great if someone out there could do me a huge favor!  I know this is a lot but if you have a MP or 1000W motor could you post a youtube video of the wheel spinning freely till it stops on its own?  this will provide me with exactly the info I am looking for.  If I could see the wheel roll to a stop on its own it would clearly show if there is a lot of resistance.  I know there is some and I also know that the 250 has a free wheel for eliminating rolling resistance.  this is the final thing I need to get specs on befor I take the plunge and get my two new kits.  Thanks in advance for you hlep folks and I am sure I will be posting here a lot.

Ride On

[Hardcore]

well if it really helps you I will try and make a vid of my mp rolling resistance

[bike4ever]

Thanks hardcore!

Until the vid can you comment on the resistance?

Can anyone comment on resistance to rolling or pedaling unpowered?

[GM Canada]

Thanks hardcore!

Until the vid can you comment on the resistance?

Can anyone comment on resistance to rolling or pedaling unpowered?

Hello,

My experience with the rolling resistance is you would not want to peddle very far without the power of the motor helping you. Most people assume that if there battery dies they can just peddle home. Allthough I`m sure this is possible, it would certainly be a challenge. You could always go with the mini motors that freewheel. Maybe a front and rear setup, then you can peddle freely whenever you want, but since you are looking for power and speed, I`m not sure this is the way you would want to go.


Gary

[Bikemad]

Just out of curiosity, I just gave my rear wheel a quick flick with my hand, and the most I can get is around seven revolutions before it stops.

It's not just the drag, as the additional weight of the motor and batteries greatly increase the weight of the bike, making it a heavy bike to pedal normally.

Alan
 

[bike4ever]

Thanks guys,

This means I am going to need two different bikes for sure.  I don't mind extra weight, often I carry quite an extra load, however if the wheel only turned 7 times that seems like it is quite the resistance.  Of course I don't know how hard you flicked your wheel but 7 turns seems pretty low.  I would love to see a vid just the same, I wish I could test one before I bought it.  Anyhoo thanks folks for your replies, I am going to need to think more about this.  All input is appriciated and welcome.  More comments regarding this would be great from others who have a MP or 1000W.  Again I don't mind weight only rolling resistance.\

Cheers!

[Hardcore]

THe vid isn't going to come, youtube doesn't support my format.
Sorry.
But yeah it only turned 5 times unplugged and 6 with the battery plugged in. maybe my power isn't constant.
Yeah, if you can afford 2 bikes and want Nm and power. Go for a big motor and 48v

[e-lmer]

I have found that the rolling resistance is not a big issue,
the real killer is the extra weight you have to drag up
every little hill.

Even a 'flat' road will have some grade, and I will bet dollars
to doughnuts that when the power if gone, the hill will
be up instead of down.

My bike masses in at 20kg.  (lets ignore the fat rider for now.)

When I mis-calculate the charge, I usually pedal to the nearest
pub and enjoy a cold one while the bike charges.
(It's worth it to carry an extension cord too.)

[Leslie]

I rode my bike home 10km's with 28kgs of lead strapped to my frame. 

The weight was the killer.

I was thinking of a dual mini motor on a racing bike.  Would a mini motor improve the weight and free wheel resistance situation?

[bike4ever]

Thanks for the input!

I don't mind weight as much as drag.  I am an avid cyclist.  I usually ride 20+km a day.  The motor to me is for extra speed on my rides.

I do ride with a lot of gear.  I have not weighed it but with my rack and bags I am surely adding about 8-10kgs of weight.  I do this to kinda train for touring.

The motor is to go for fast crazy rides and still workout.  I keep my HR above 150 for my rides and still want to do this when I use my motor.  I will install a 52-53 crank and simply put on the cruse control for that extra bit of energy.

I put out about 200Watts myself or so.... a very rough calculation based on my home trainer.

The weight is not the issue, I simply don't want drag becuase from time to time I will strip off the battery and rack and ride for 100km.  Don't want drag on those runs... and don't want to have to change a tire either.


I am looking at the Ezee motor... its sweet but expensive!

[Bikemad]

Resistance to pedalling becomes very noticeable when the voltage being generated tries to exceed the battery voltage.

Using a 24V battery you would hit the increased resistance at a much lower speed than with a 48V battery. If you are used to cycling reasonably fast then I would think this may be extremely undesirable.

As the wheel speed increases the voltage rises steadily until it reaches the battery voltage level, if you try and go faster the motor starts to charge the battery (even without regen being operated) and the amps start to rise, and you have to supply the power which is actually doing this.

I also discovered another problem with this generating effect:
If you disconnect the battery and pedal fast enough (with brake lever pulled in so that the regen is on) the voltage being output does not go above ~60V which is fine, however, if you do not apply the brakes, the voltage continues to rise well above this level.
By winding the pedals as fast as I could by hand, I made the wheel spin pretty fast. I looked at the voltmeter and observed a reading of ~77V , so I immediately grabbed the brake because I was worried about damaging the controller with such a high voltage going through it.
Unfortunately I don't have a speedometer on the bike to measure the wheel speed, but I would think this could be a real problem going fast down a steep hill, and even more of a problem if you have smaller wheels.

If I can get hold of a speedometer, I will try and repeat the test so I can record some voltage and speed readings and find out the safe maximum speed, but for the sake of the components in the controller, I will try not to exceed 63V again.

Alan
 

[e-lmer]

I think he is talking about open circuit rolling resistance,
not in line resistance.

The weight is not the issue, I simply don't want drag
becuase from time to time I will strip off the battery and rack
and ride for 100km.  Don't want drag on those runs... and don't
want to have to change a tire either.

The 'classic' 36V motor turns pretty freely when you do not have
the speed controller connected.

I am not sure how this would work with the magic
pie since you cannot unplug the motor from the
controller.

If someone remembers how to do an Atwood machine from
high school physics and has a wheel off the bike perhaps
they could post the results, otherwise I will do it when I get
back from my road trip next week.

[Wheels]

There is a bit of discussion on this on ebikes.ca's webpage.
the bike shop line is it feels like the difference between a knobby tire and a slick.
you may want to look into a geared motor so that it freewheels and therefore has no resistance.  They seem to be  a bit more in cost but that might be offset by the fact you could just have one bike, plus geared hubs weigh less.


http://www.ebikes.ca/hubmotors.shtml

[MasterCATZ]

Interesting thread

I was hoping for a lot less restance myself

Dual Magpies might kill me then ... I was planing on doing up an old Mongoose NX 8.3 Dual Suspension Bike

I was also planing on doing 100km runs and use motors for the hills with 2x 48v packs ( possibly used as an 96v kit when magpie v2 comes out .. )

here is a question

how much power would be needed to let them free spin with out resistance maybe another standalone battery / capasitor system that can just keep them unlocked and regen recharged for when cycling ?

[Bikemad]

how much power would be needed to let them free spin with out resistance maybe another standalone battery / capasitor system that can just keep them unlocked and regen recharged for when cycling ?

The amount of power will depend upon your speed and wheel size.

To give you a rough idea, a 26" Pie would probably require somewhere between 25Watts at 22km/h and 45Watts at 33km/h (per motor).

This is where the cruise control is very useful, if you ride along a few km/h below your normal riding speed and press the cruise control button, when you go above this set speed, the motor will no longer assist, but when you fall below it, the motor will automatically start to provide the required power to try and maintain the set speed.
As long as you stay above the set speed, it will only consume the power mentioned above.
(Drop below it, and it's a different matter.)

Alan