GoldenMotor.com Forum
General Category => General Discussions => Topic started by: truly_bent on April 09, 2012, 01:32:30 PM
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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.
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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.
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Hehehe Gapy, I have not heard from this member in a while.
http://www.youtube.com/watch?v=UBmmXoONXzk
You like?
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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 (http://www.youtube.com/watch?v=qJG5u-QawaI) on YouTube which looks good.
Alan
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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/ (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/ (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 (http://www.biketrailershop.com)
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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/ (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...
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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 (http://www.goldenmotor.com/magicpie/MP-performance%20curve%2024V.pdf)
Magic Pie performance data 24V (http://www.goldenmotor.com/magicpie/MP-performance%20data%2024V.pdf)
Magic Pie performance curve 36V (http://www.goldenmotor.com/magicpie/MP-performance%20curve%2036V.pdf)
Magic Pie performance data 36V (http://www.goldenmotor.com/magicpie/MP-performance%20data%2036V.pdf)
Magic Pie performance curve 48V (http://www.goldenmotor.com/magicpie/MP-performance%20curve%2048V.pdf)
Magic Pie performance data 48V (http://www.goldenmotor.com/magicpie/MP-performance%20data%2048V.pdf)
16" Magic Pie performance curve 36V (http://www.goldenmotor.com/magicpie/16in%20MagicPie%20Performance%20Curve.pdf)
16" Magic Pie performance data 36V (http://www.goldenmotor.com/magicpie/16in%20MagicPie%20Performance%20Data.pdf)
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! :o
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:
(http://goldenmotor.com/SMF/index.php?action=dlattach;topic=4271.0;attach=5651;image)
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
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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 (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 ;)
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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
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Oh, and why can't you have a hub motor on a single sided swing arm?
TTFN,
Dennis
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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):
(http://myelectrical.com/Portals/0/Images/PostImages/StarDeltaWinding.jpg)
(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 (http://goldenmotor.com/SMF/index.php?topic=2830.msg17213#msg17213) for more details on a Delta modification performed on a Magic Pie.
Alan
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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/ (http://www.bobtec.de/). Click on "Fahrradanhänger mit Elektromotor" and go down to the bottom of the page.
Clever people these Germans...
:)
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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
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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.
8)
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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
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Well sometimes I can be dumb as a post. The 4th termination could be made at the windings. Getting old is not fun.....
But I still don't get the "less torque with delta" business.
TTFN,
Dennis
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3Eman;
I did as you suggested and spent some time searching on Wye/Delta motor configurations. The best explanations I've found so far were in the RC community. Specifically, this Brian Mulder guy at http://www.southernsoaringclub.org.za/ (http://www.southernsoaringclub.org.za/). In his Electric Motors - Part 2 he goes into some depth on windings configuration. Using his explanations as reference, I bounced around the MP data sheets, trying to make better sense of it all.
The question that kept coming up in my mind was, "Why would anybody configure for Wye when Delta seems to be better on most points?". Delta is more efficiency and has better top end rpm. Brian says that Wye has better torque characteristics, but our data sheets show that peak torque for the 16" only slightly lower (albeit at higher power consumption).
I think the missing ingredient is wire gauge. Thinner wire can't handle the amps as well and because Delta draws considerably more current it's most likely to be wired with a heavier gauge. Heavier gauge wire means fewer turns per tooth and fewer turns means less field flux. Less field flux equals less torque.
The higher the number of turns on a tooth, the greater the magnetic field produced for a given current. Stronger magnet field results in more torque and lowers the RPM/Volt number.
I don't know if our 16" MP motor is wound with heavier gauge wire or not, but that could account for the reduced torque even though we see more power input to the system.
The 36V data sheets would seem to agree:
28 N.m = 750.64 watts (31.50A) for the 16"
28 N.m = 583.52 watts (23.66A) for the standard
Here, both motors are producing the same torque, but the 16" is costing us more in power. What we lose here in power is gained in speed because the 16" is rotating at 255 rpm versus 199 rpm for the standard.
:-\
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The 4th termination could be made at the windings.
That's exactly where where it is, click on the image below to see it full size and you should be able to see where they terminate.
(http://www.arhservices.co.uk/GoldenMotor/Startermination.JPG) (http://www.arhservices.co.uk/GoldenMotor/Startermination.JPG)
As I understand it, the MP is a basically a phase synchronous or stepper motor, driven by a variable frequency drive.
As I understand it, the MP is a three phase AC motor where the timing and switching of the phases is controlled by the hall sensors, but the average value of the voltage (and accordingly the current) being delivered to the windings is actually controlled by Pulse-width modulation (PWM) which basically adjusts the "On" period of the duty cycle in relation to the throttle signal.
Alan
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Hi Alan and Truly,
I really meant that I should hit Google, but thank you for your research. I'll never get smart if I have you guys doing all the work!
"Stronger magnetic field means more torque" was quoted, and so does a stronger current through a given winding. Higher impressed voltage across a coil drives greater current through the coil, increasing the magnetic field, which means more torque, does it not?
I'm an old gear head, and it looks funny to read a line where increased power is considered a bad thing......."What we lose in power we gain in speed" ! To me that should read " What we gain in power gives us more speed" is my preferred what to convey that data.
Alan, I never once considered that PWM was still in use for motor speed control! That makes a great difference in how to look at the question. Variable freq has so many advantages, but I guess PWM must be really cheap to build.
Thanks for trying to help me get smarter, guys.
TTFN,
Dennis
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3E;
Glad to be of service :). I'm trying to make sense of this myself.
Alan;
Just to scratch my curiosity itch, can you find out if the 16" motor is wound with a different gauge of copper? You may have to go deep undercover for that one 8).
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Perhaps the torque is affected by the fact that with delta wiring, when one winding is energized, the other two are also receiving power and generating a magnetic field. Wye only energizes two windings with voltage impressed across one phase. I really need to find some time to research this.
TTFN,
Dennis
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This Brian Mulder guy shows how that operates as well. He explains that if each winding has a resistance of 1.0 ohm, then Ohm's law proves the total resistance of the network to be 0.66 ohm.
As you suggest, the winding between the two conducting points has a strong magnetic field while the other two have lesser fields - probably on the order of 1/3 strength or thereabouts. All the windings therefore are contributing to the resulting torque.
I didn't realize this myself, until I read through his tutorials.
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As far as I am aware, each phase wire connection is either switched High (battery +ve) or Low (battery -ve) in relation to the magnetic field adjacent to its respective hall sensor (using PWM to control the duration of the "On" period of the duty cycle).
To make it easier to understand, let's simply assume that the "On" period is 100% of the duty cycle (full throttle) so full battery voltage is being switched.
With star (wye) windings, all three windings will be energised at any one time, one in series with the two other paralleled windings.
Using High/Low switching with Delta windings means that only two windings can ever be energised at the same time, because the third winding will either be High at both ends or Low at both ends and will therefore have no potential difference (voltage) across it.
I found a great animation that demonstrates the basic operating principal of a three phase star wound motor (http://elabz.com/brushless-dc-motor-with-arduino/) that can also be manually overridden by moving your cursor over the boxes.
Alan
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Well, how much dumber than a post can I eventually become? Clearly you can get current flowing through all three windings of a wye, and only two windings of a Delta. But there is actually a third value that a phase wire can attain, and that is open circuit.
To bring a particular phase wire to battery +, the upper FET in its H switch is turned on. To bring that wire to battery -. the lower FET switch is turned on. With both FETs off, the wire is floating, and no current flows through the associated winding in wye configuration. So while the motor pulses are overlapping, current will flow through all three windings, and during the time a single phase is on only two windings get power. And the other way round for Delta.
At part throttle, the phase wires can be at open circuit a significant portion of the time.
TTFN,
Dennis
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Well, it's all moot now anyway.
???
I opted not for the trailer, but to electrify just one of my bikes. They both have 26" rear wheels, so i've ordered a 26" MP II. Not sure which bike will end up "electrified" at this point, but that'll work itself out.
I guess it was the extra $500+ for the BOB Ibex that killed it. Still, the setup i'm going to end up with isn't too shabby to start. Plus the MP II there's:
- Lyen 184110 MIIR 65A controller (does everything except perk coffee apparently)
- 48V 20AH LiFePO4 battery
- Large screen Cycle Analyst
- Various other bits necessary to glue it all together
The controller and Cycle Analyst arrived today. All the other pieces should be in within a week or so. Because I wasn't sure what voltage I wanted to go with, Edward modified the controller to accept any battery pack from 36V to 88V. Absolute max voltage is 110 before the FETs fry.
Another recumbent phreak I met recently wants to build a AZ Cycle Bully as well. The pressure's off now so we're planning on making it a summer project - maybe finishing in August.
In the course of this discussion i've learned quite a bit about these brushless motors and want to thank those who contributed. I'll post a picture when one of the bikes is up and running.
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It Lives!
True to my word, I am posting pics of my little project.
Just powered up today. A little trouble with the throttle connector but she's okay now. I've just finished downloading parameters into the controller and she's ready to rock.
For any of you who can't see too well, the donor bike is a Burley Canto recumbent.
- Cycle Analyst on the bar with cruise buttons and a 3 speed range selector.
- Brakes are linked to the controller for regen
- 6 speed gear cluster with new speed selectors
- Lyen 18 FET controller
- One torque arm installed (lost the bike stand in the process)
That huge pannier bag on the back contains a 48V 20AH (LiFeP04) battery, and a bunch of foam to keep it centered. I have another Arkel bag for the other side. I went with a removable bag for the battery so I could carry it and the charger separately.
Obviously, a little more work needs to be done to improve water resistance of the cable connectors. Actually, it's not as bad as it looks. Everything is pretty well isolated with heat shrink tubing. I'm looking into plastic junction boxes to find something suitable.
8)