Two motors?

[peckerman]

Are we not overlooking the point? If you have two motors you can out run the plod, and never get caught......he he.

 

[john]

Maximum Continuous Power sounded very much like an engineering term to me, so I did some digging on motor specs and definitions and found the following.

Maximum Coil Temperature (Tmax)- The temperature at which coil failure is expected due to excessive thermal expansion in the wire or insulation failure (which happens at around 150-170C).

Maximum Power Dissipation - The continuous power losses of the motor when when the coil is at Tmax and the ambient temperature is at 25C (i.e. how much waste heat the motor can get rid of without breaking down.... So if you feed 250W into an 80% efficient motor then you have 50W of heat to get rid of.)

Continuous Current (IcTMax) - The coil current corresponding to the maximum power dissipation of the motor. (i.e as much current as the motor can use indefinitely in 25C ambient air without melting itself.)

Maximum Continuous Power - Amps * Volts for the required amount of power to make the motor operate just below breaking point.

This seems to all make sense to me. The motor has to be able to get rid of all the waste heat or it melts its internals (such as when people decide to up the voltages). The point at where it can no longer get rid of it's waste heat is the absolute most work it can be made to do. When you're at that point and you try to give it more work, it melts... When you give it less work, it cools down... and it is all measured at 25C in still air. - That is the maximum continuous power that can be sustained.

Now.. for peak power, you can really make up any number you want.. but somehow or other you have to be able to get rid of the heat. You've got a couple of kg of copper coils which can soak up heat when it's cold and this takes care of stop/stall states. However, when the motor is stalled, all of the energy is being fed into it is dissipated as heat and 250W heats up 2KG of copper coils pretty rapidly.

Does that make sense to anyone except me?

Yes, that is about right although I believe that the rating is for output rather than input power. It is about how much heat the motor can dissipate and so prevent overheating.

De-rating a petrol engine is fairly easy as it is rated at maximum power, but I am not sure how this could be done practically for a motor where the rating is for continuous power; other than perhaps adding some insulation . In fact others have done the opposite, drilling holes in their hub motor to increase heat loss and so increase the motor rating.

 

[Tiberius]

Fecn,

You are right. What the motor itself will have is a maximum continuous current rating.

That will translate into a range of maximum continuous power ratings depending on the application and the assumptions made.

If the manufacturer declares a power rating, then it will be on the basis of one set of assumptions about how it is to be used. The user of the motor could legitimately say that he was operating it under different conditions and then declare a power rating that was higher or lower than the motor manufacturer.

In fact, the proper engineering approach would be that the motor manufacturer refuses to declare a power rating, but does declare enough information for the motor user (ie bike manufacturer) to calculate a power rating for that particular application.

Nick

 

[flecc]

In fact, the proper engineering approach would be that the motor manufacturer refuses to declare a power rating, but does declare enough information for the motor user (ie bike manufacturer) to calculate a power rating for that particular application.

Nick

One alternative though is the Panasonic one, where motor, all electronics and battery are a fully integrated single unit in which case they can fix the rating.
.

 

[Cyclezee]

Ignoring the legal side of this proposed project, if someone does get round to building a two motor e-bike, won't it be so heavy that most of the extra power would show only a minor increase in performance.
There would be the extra weight of a motor, controller, cables, throttle, etc., and probably an extra battery. This could be quite a handful to ride and corner with, then stopping it would also need careful consideration.

Would it not be much easier and cheaper to build a completely illegal bike in the first place with a single high power motor, then remove any stickers or labels from the motor so nobody has a clue what you are riding

J hn

 

[flecc]

Would it not be much easier and cheaper to build a completely illegal bike in the first place with a single high power motor, then remove any stickers or labels from the motor so nobody has a clue what you are riding

J hn

I agree John, though there is an attraction in a two Tongxin Nano motor bike, relatively light, free rolling and silent. One would have to be adapted to rear derailleur though.

With their very small size coupled with the silence, they would scarcely be noticed.
.

 

[Cyclezee]

I agree John, though there is an attraction in a two Tongxin Nano motor bike, relatively light, free rolling and silent. One would have to be adapted to rear derailleur though.

With their very small size coupled with the silence, they would scarcely be noticed.
.

Or Tony, a second Torq1 front motor fitted to your T radical? You have alreday done the hard bit.

J hn

 

[flecc]

The thought had momentarily passed my mind John, but it would make a bit more noise and be fairly obvious if only from the performance. The weight would be a bit much too as you've said, needing two eZee batteries as well as the two motors it would be heading into old Powabyke territory.

In fact the T bike doesn't get much use as I'm quite happy with the Q bike's performance and capabilities.
.

 

[Cyclezee]

In fact the T bike doesn't get much use as I'm quite happy with the Q bike's performance and capabilities.
.

Does this mean you might retire the T bike and put it out to grass

J hn

 

[flecc]

It'll get summer pleasure use John, it was never intended or equipped for bad weather of course. It's laid up in the garage now where it spent last winter.
.

 

[Cyclezee]

Tony,

I think your T bike is one of the best thought out and engineered hub motor e-bikes around It would be nice if Ezee took on some of your ideas and put them into a production bike.

J hn

 

[frank9755]

John, the only controversial point in your post above would be 'one of'!

Unfortunately putting a the Tongxin in a rear wheel with decent gearing would be a challenge. They do a threaded motor but it is centred on the axle (possibly needs to be because of their two-part axle). This, and limited axle length means that it would only work with a very narrow freewheel - perhaps a 3-speed. When I put a 7-speed on mine there was hardly any axle showing out the end!

The wire comes out of the non-freewheel side so someone with the right engineering skills might be able to lengthen the axle but I'm not aware of anyone having done it. Maybe it would be as simple as taking the motor apart and replacing that side of the axle with a longer one - but I know little of the innards of the motor so can't judge how feasible that would be.

Frank

 

[Cyclezee]

Point taken Frank. It is almost an insult to say Flecc's T radical is anything other than THE BEST My excuse, ......I am but a mere mortal

J hn

 

[Mussels]

Maybe I should look at a 9-speed hub (no way I'm paying for a Rohloff at those prices) for the back wheel to get a bit of extra range out of the gears?

I found that reducing the gearing on my Wisper helped a lot with hills, I rarely used the top gears so didn't miss them.

 

[flecc]

The wire comes out of the non-freewheel side so someone with the right engineering skills might be able to lengthen the axle but I'm not aware of anyone having done it.

Frank

It can be done Frank, there's almost 22 mm internal diameter on the inner multi freewheels so an extender is possible. As you may know I had to have strength extension on both the Q and T bikes for that same short and weak spindle reason, the T bike one being spindle threaded as well.
.

 

[frank9755]

Yes - of course you would have had to do that to put a front motor in the back! I've not read your site for a while; I shall have a look...

 

[subevo]

ive got a giant lafree with an ezee liv front end attached.(bought a brand new ezee liv to rob the parts from which cost £700)therefore twist and go action combined with pedal assist.it has worked great and can fly up hills at up to 18mph.but recently the ezee liv 36volt battery pack broke after 11 months.so i just bought some cheap sealed lead acid ones 3 off to make 36volts.not as good but i only use it to boost up hills on way home from work.ive now done 6500miles with my original lafree bought 4 years ago.with around 2000 miles on the twin motor setup.the lafree refuses to die.ive now recouped the cost of the ezee liv on fuel savings on my car.

 

[Cyclezee]

Very interesting post Subevo and a bold move to buy a new bike just for the parts I assume you are using the original Lafree battery to drive the crank and the Ezee battery to power the front hub. I would imagine that setup would put quite bit of extra strain on the frame. Is it a stepthru Lafree or Gents model?

I'm sure people would love to see some photos of your creation if possible.

J hn

 

[subevo]

its the gents model with crossbar.i will take some photos and try and post.ive not done this before.