Author Topic: Exploring High Performance Motor Build  (Read 10834 times)

Offline toddshotrods

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Re: Exploring High Performance Motor Build
« Reply #45 on: March 13, 2014, 10:19:28 PM »
OK. Back to engineer mode.

Two issues. One small other larger.....

1- A foot operated "shifter" to electrically switch between the two. Do able...
My plans were a little more benign.  For switching, I was planning on electronics based on vehicle speed and throttle position, etc.  Actually though, I think I can simply manually switch (at the handlebars) between a couple modes, because:


...2- The DC motor will not RPM with the AC motor and will sling the comms from their beds.
     You need to uncouple them in "high"...
Since my little 7" motor can safely spin to 7000RPM (Wayland spins WZ's 9" to 6700), it's a simple matter of gearing.  With the intermediate reduction at the AC shaft, between the DC motor and the rear wheel, I can have the DC motor spinning at an appropriate percentage of the AC motor's shaft speed.  Maybe around 70% of the AC motor's speed.  So, at 6500-7000RPM, the DC motor cuts out, electrically, and the AC motor keeps spinning at or near red line.  It would have been on the whole time, and actively pulling from around 5000RPM on the DC motor, and would ideally be in its optimum zone, and be able to sustain that RPM as long as needed.  In theory, from how I see it, there's no reason both motors can't be "hot", until the RPM and/or temp sensor(s) cuts the DC motor.

In other words, I am really using both motors almost all the time, but each one is working harder at different points.  My concern with running the DC motor at or near its limits too long were cooling and commutation - the AC motor steps in and resolves that issue.  Even the way the DC buck converter works, it will naturally start to trail power off as the need decreases/speed increases - the DC drag racers' #1 pet peeve - it peters out as the perceived load diminishes.  My concern with running an AC motor at the top-end RPM I desire is getting enough torque on the bottom-end to even get there, the DC motor resolves that issue.  The AC inverter can take its sweet old time in climbing up to max power, because something (DC) is giving it a shove.

If you see something I'm missing, I'm listening...

Offline mizlplix

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Re: Exploring High Performance Motor Build
« Reply #46 on: March 15, 2014, 12:17:33 AM »
"Since my little 7" motor can safely spin to 7000RPM (Wayland spins WZ's 9" to 6700), it's a simple matter of gearing.  With the intermediate reduction at the AC shaft, between the DC motor and the rear wheel, I can have the DC motor spinning at an appropriate percentage of the AC motor's shaft speed.  Maybe around 70% of the AC motor's speed.  So, at 6500-7000RPM, the DC motor cuts out, electrically, and the AC motor keeps spinning at or near red line.  It would have been on the whole time, and actively pulling from around 5000RPM on the DC motor, and would ideally be in its optimum zone, and be able to sustain that RPM as long as needed.  In theory, from how I see it, there's no reason both motors can't be "hot", until the RPM and/or temp sensor(s) cuts the DC motor."

I can see this strategy will lower the DC motor's top RPM, it will also increase the amperage under drive conditions, as DC motors do not like to "lug".  (At least none of mine did)  But, we are talking about a light weight vehicle here, so in the end,"What the heck"  go for it.   :<bs:

A lot of other side issues crop up in my mind, like pack sag under loading from two controllers, but this is still an uncharted area. My concerns might be needless. (My 130 AH cells @ 130 volts sag badly.  I wish I had the room for a double pack.)

Miz

1930 Ford Speedster, AC50, full manual powerglide, 6.14gears, 38-130AH CALBs.

Offline toddshotrods

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Re: Exploring High Performance Motor Build
« Reply #47 on: March 15, 2014, 05:47:12 AM »
...I can see this strategy will lower the DC motor's top RPM, it will also increase the amperage under drive conditions, as DC motors do not like to "lug".  (At least none of mine did)  But, we are talking about a light weight vehicle here, so in the end,"What the heck"  go for it.   :<bs:...
Actually, you just made the remember something.  I have to pay attention to how long the DC motor is freewheeling, to avoid damaging the comm.  With the gearing as I specified, it would only cut briefly at the end of a standing mile acceleration run; probably not at all in a quarter-mile run, or on the street.  If I ever did something like Bonneville, where the top end RPM could be extended for quite a while, I would need to gear the DC motor so that it stays under the limit, and there is at least some electrical current flowing through the comm (no complete electrical cutout).



...A lot of other side issues crop up in my mind, like pack sag under loading from two controllers, but this is still an uncharted area. My concerns might be needless. (My 130 AH cells @ 130 volts sag badly.  I wish I had the room for a double pack.)

Miz
I can accommodate that easily, because I was designing for high voltage.  If I knock the lower voltage (370v/900a) pack down a bit to stay under a Zilla or Soliton max input, I will have plenty of headroom to accommodate sag.  The LiPo pack would be reasonably stiff too, so, I should be able to provide both motors with whatever they need.

Thanks for the input Miz, I am listening and thinking and applying, to try to cover all the bases...  :Tt0:

Offline piotrsko

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Re: Exploring High Performance Motor Build
« Reply #48 on: March 17, 2014, 12:51:45 PM »
if you power the com and you spin the motor you're going to have a possible run-away  regeneration problem with the series motor

Offline toddshotrods

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Re: Exploring High Performance Motor Build
« Reply #49 on: March 17, 2014, 02:36:08 PM »
I may have described that incorrectly. I meant the DC motor would be actually working, not just spinning with a little voltage applied to the comm.  I will gear so that it never exceeds its max RPM.  Both motors will reach reach their respective max RPMs simultaneously.  The DC motor will have just fallen out of its peak section of the power curve, while the AC motor is working at its best; vice versa on the low end.