Pusher Trailer Conversion

[truly_bent]

I have two bikes, one mountain and one recumbent. Because I'd like to switch the electric drive easily between the two, a pusher trailer seems a good option and single track has always made more sense to me than the wider dual track units. A couple of years ago I purchased the CycleBully (20" wheel) plans from the AtomicZombie site, but never built it. Circumstances are such that I'm going to need an electric bike soon and time doesn't permit a build. Seeing Gary's "Tri-Pie" build with it's 16" MP wheel on the BOB trailer has focused my attention on that style again.

I realize that the 16" MP III at 48V is unlikely to be quick enough. I'm not a speed freak, but 20mph max is a tad on the slow side. I was wondering if the MP II with an external controller, perhaps third party controller, and a higher voltage might push the speed to a more acceptable level without damaging the windings.

Another consideration might be to use one of those child "tag along" trailers, with its 20" wheel, but without some serious modifications I expect that would end up looking dog ugly.

Any suggestions would be appreciated.

[Leslie]

Ahh the ole push trailer.   Hey never thought bout the change ability aspect.

I'm not entirely sure but last I read 18" 20" are working faster with more torque than the 26" so you may be still on a good speed with the 16", may have something to do with the gearless.  The only problem is  bearings may take a bit more turns and regen may be awesome at high RPM..

If youre game and you wants the speed a Delta phase mod to the Pie maybe the speed hit you will enjoy.  On the 26" a delta mod can increase your speed substantially at the expense of torque, however the 16" would certainly replace any torqe lost in the translation to delta.

Keep in touch please, Id love to see what you do here.

[Leslie]

Hehehe Gapy, I have not heard from this member in a while.

http://www.youtube.com/watch?v=UBmmXoONXzk

You like?

[Bikemad]

I'm not entirely sure but last I read 18" 20" are working faster with more torque than the 26" so you may be still on a good speed with the 16".

Les, I'm still not sure about the 18", but the speed of the earlier 16" Magic Pies was definitely increased, but this resulted in reduced torque, which was probably not quite so necessary with the smaller wheel diameter.

You might find it strange, however the 16" is made to hit that speed. The windings are different, lower torque but higher speed. Go check out the Tq figs for the 16" and you shall understand!

I don't know whether the 16" MPIII has these higher speed windings or not.

I found this video of a DIY push trailer on YouTube which looks good.

Alan
 

[truly_bent]

Bikemad: I've seen that pusher on YouTube. In fact I think I've seen just about all of them. That particular one uses lead acid batteries for starters. For the money, I think I can cobble together something better.

I've been in touch with Gary at http://www.goldenmotor.ca/ about using the MP II. I believe he's in agreement that "overvolting" either the 16" or 20" with an external controller is the way to go in this case. Unfortunately, Goldenmotor only drives to 48V, so I'm forced to look elsewhere.

I'm thinking two 36V 12AH batteries in series ought to be a good start. Might not get me to where I'm going without peddling, but I need some exercise anyway.

I've just responded to a request from Edward Lyen (http://lyen.com/) for more info. His controllers get great reviews over at Endless Sphere, seem to have plenty of options, and are well priced. I work with industrial control systems, so $200 (plus a bit more for bells and whistles) for a motor controller (110V max) looks like Christmas to me

Zo, the field is narrowing down to one of three possible trailers: BOB Ibex (suspended), Weber Trailer (German quality, can add suspension), or ExtraWheel (no suspension but wins on price). A great spot to check out these and other trailers is http://www.biketrailershop.com

[truly_bent]

Ummm... In the course of surfing the forums I find discussion about how the 16" MP is wound for greater speed than its siblings, but, so far as I've found anyway, this hasn't been confirmed anywhere. I've been unable to find confirmation on the goldenmotor.com site or my local rep's site either. My local rep has no more knowledge of this than I do, which is just a tad disconcerting.

Is this a trade secret? Perhaps it's not documented anywhere so that GM can divest itself from some legal issue. Perhaps I just haven't found it yet. If somebody knows the secret to where this information is hidden, please come forth.

In the same vein, I just discovered this terrific tool at http://ebike.ca/simulator/, but I'm probably the last guy on the www to find out about this (if you don't know about this, then you're the last ).

The point is that the MP isn't listed in the drop down menu of various motors within the simulator, so getting meaningful data out of the graphs for our applications is more a matter of luck than skill. Which of the motors on that list is the closest to the MP please?

Thanks in advance...

[Bikemad]

I will admit that the following files were not very easy to find, but I did eventually find what I was looking for:

Magic Pie performance curve 24V
Magic Pie performance data 24V
Magic Pie performance curve 36V
Magic Pie performance data 36V
Magic Pie performance curve 48V
Magic Pie performance data 48V
16" Magic Pie performance curve 36V
16" Magic Pie performance data 36V

If you compare the standard Pie with the 16" Pie you can clearly see the difference.
In fact, the 480 rpm of the 16" pie @ 36V is almost 80% faster than the 268 rpm measured on the standard Pie @ 48V!
If you look at the screenshot below you can see that the estimated road speed for the 16" at max rpm would be slightly faster than the standard Pie with a 28" rim:


If you increase the voltage on a MkII 16" wheel, it should be plenty fast enough for your needs, but I don't know if the MPIIIs will be the same.

I have attached a copy of my spreadsheet in case you want to play with the various figures from the above data sheets.

Alan
 

[truly_bent]

Thanks Bikemad.
That'll shut me up for a while and puts you one step closer to Godhood of Magic. That is what comes after a PhD, isn't it? 

A couple of notes:
- The 16" has a higher peak efficiency (83.8%) compared against the standard configuration (77.2%)
- The peak torque is very similar for both, but the 16" is drawing about 6 amps more at that point

Comparing apples to apples (both at 36V) the max rpm of the 16" gives 37.4 kph (23.3 mph), while the 20" standard is running at 25.7 kph (16.0 mph). That's quite an increase in speed. At that point, however, the 16" motor is showing zero torque, literally.

My intention is/was to run either of these at 48V minimum. It would be the 20" standard that needs the boost in voltage for acceptable speed.

The jury's still out on which pusher trailer to go with. It was pointed out to me that it would be nearly impossible to mount a hub motor on the Weber single sided swing-arm type configuration. Well duh! That's obvious in hindsight, but I didn't see it at the time. That leaves the BOB Ibex or the Extrawheel as the most likely candidates. I did check out the Aevon http://www.stokerproducts.com/Aevon_Trailers.html, but the price is in the stratosphere.

I'll know better by the weekend.

And thanks for the spreadsheet Bikemad. You're a God... almost 

[Morgen 3Eman]

OK, time to show my ignorance again.  I Know quite a bit about delta-wye transformers, but what the hell are you guys talking about delta  and wye motor windings?
Please make me more knowledgeable. 


TTFN,
Dennis

[Morgen 3Eman]

Oh, and why can't you have a hub motor on a single sided swing arm?

TTFN,
Dennis

[Bikemad]

OK, time to show my ignorance again.  I know quite a bit about delta-wye transformers, but what the hell are you guys talking about delta  and wye motor windings?

Dennis, the hub motors we are using work on the same principle as a simple mains voltage three phase AC motor.

The three phase windings on the GM hub-motors are typically wound in a star configuration, and if you look at the following diagram you can see the two basic forms of connecting the windings in a three phase motor (and generators):

(Star is also referred to as "Y" or Wye)   (From the Greek alphabet where Delta is a triangle)

In the above diagram, If we replace the 400V shown with the battery voltage we are using on our hub-motors, the 230V volts shown would be equivalent to ~57.5% of the battery voltage.
So, with a 48V battery, the voltage across the single winding shown would be ~27.6V in the standard Star connection.

If we were to reconfigure the windings to produce a Delta type connection, the full 48V would be applied directly to the single winding.
With most electric motors, increasing the voltage will increase the speed proportionally, so by increasing the voltage from 27.6V to 48V we therefore also increase the speed of the motor by approximately 74% , but unfortunately this also results in a reduction in the motor's torque.

Check out this post for more details on a Delta modification performed on a Magic Pie.

Alan
 

[truly_bent]

3Eman;
Perhaps I'm being a bit hasty in saying a single sided swing-arm isn't a good idea. A number of motorcycles are built that way these days. However, the Weber trailer wasn't designed as a pusher (neither was the Ibex it's true) and I'm thinking it's unlikely the designers built in that much of a margin at the single connection point. My impression is that they were shooting for weight saving. The BOB trailers are good for a 70 pound load while the Weber is listed at 55.

I guess we could try it. Well, you can try if you like. I can't afford that much for an experiment myself. As encouragement, I've attached a couple of pics of a Weber trailer that has been electrified by pulley method. This is the only example of an electrified Weber trailer I've found so far. No idea of the power of the motor, though I doubt it's pulling as much as the MP. If you're good with German you can find out more from the site: http://www.bobtec.de/. Click on "Fahrradanhänger mit Elektromotor" and go down to the bottom of the page.

Clever people these Germans...

[Morgen 3Eman]

OK, I totally understand pushing too much power thru a wimpy swing arm.  I wouldn't do it either.

But I totally do not understand the delta-wye voltage/torque/speed change with winding drive. I understand the different voltage impressed across the windings by changing how they are wired.    As I understand it, the MP is a basically a  phase synchronous  or stepper motor, driven by a variable frequency drive. Rotation is locked to excitation frequency, while power developed is determined by applied voltage.   If that is wrong, then ignore the  rest, and set me straight on this point.   (And let us understand that I haven't really thought about how a motor is made to rotate in at least a decade.)

If it is a stepper, driven by a VFD, then the higher voltage  impressed across the winding makes me think that more current will be drawn thru the winding, producing  a stronger magnetic field and the torque should be greater.  Where am I wrong?

I also want to admit to you all that I am a cheerleader for direct-drive VFD systems.  They are simply wonderful for pumping systems, be they air or water or solids pumps. 



TTFN,
Dennis 

[truly_bent]

I'm no expert, but intuitively I think it works as follows:
- In Delta configuration, voltage across one winding of 100% battery voltage.
- In Wye configuration, voltage across two windings of 57.5% battery voltage each.

It makes sense to me that there's an increase in power to the motor in Wye configuration. Not so much it's true (115% of battery voltage when added together), but then there are two windings acting simultaneously against the magnets as opposed to one in Delta. Ergo, greater torque in Wye configuration.

The series windings in Wye (greater resistance) would also explain why the Delta configuration (less resistance) draws more current at peak efficiency rpm. (It's been pointed out to me that the word I should be using impedance, not resistance)

With any luck, a real expert will wade in and explain this whole conundrum properly.

[Morgen 3Eman]

Hi Truly,

So we both think that the delta setup draws more current for a given voltage.  If IxE=P, then the delta winding arrangement draws more power.  So how does more power drawn  generate less torque?  It just doesn't make sense to me.  I know for a fact that when a motor is required to produce more power, they draw more current.  And if the RPM are kept the same, then the increased current must produce greater torque to drive the load. 

And the word  you are looking for is impedance, in this case a combination of resistance and inductive reactance. It is still expressed in Ohms, usually with a phase angle to denote the relative values of resistance and inductive reactance.

I guess it is time to use the Google to relearn how motors work......

And I just remembered that there are only three wires from the internal controller on my MP3.  So it must be a delta wired motor, as wye setup has  4 wires. 

TTFN,
Dennis