[ausev] Transmissions

[Ken Thomas]

People do use direct to drive shaft coupling for daily driving. Daily 
drivers are Grassroots EV's specialty.

It sometimes appears that direct drive shaft is avoided, but that is 
because often times a conversion is done on cars with transaxles. These 
are usually front wheel drive, front engine cars. Since cars with 
transaxles do not have a drive shaft, it makes it easier to just mount 
the motor to the transmission (transaxle).

AC motors and DC motors are not functionally different. The difference 
is that AC motors are electrically commutated and DC motors are 
mechanically commutated. The advantage of AC is that the motor timing 
can vary with RPM. DC motors generally operate at a fixed timing. That 
means the motor is most efficient at the RPM it is timed for. DC 
motors, however, are not "doomed" to fixed timing. Jim Husted of High 
Torque Electric manufactures a variable timing ring for DC motors. With 
this, the only RPM limit for DC is the inertia of the copper commutator 
bars. Efficiency is where ever the timing is set. (The advantage of DC 
motors is that the controller only has to provide one "phase", or DC. 
Therefore, for the same amount of power electronics in the controller, 
a DC controller can deliver three times the current of an AC 
controller. Current translates to torque which translates to 
performance.)

Regarding your AC and DC motor set up, a variable timing ring on the DC 
motor would satisfy that goal.

Also, Keep in mind that John Wayland's White Zombie, which is a big 
league drag racing machine, is also extremely efficient running errands 
around town. The battery pack capacity is only 32 AH (very small for a 
daily driver), however, John drives it to the track, races, then drives 
it home. Well, yes, he charges at the track, but it is a 20+ mile trip 
down the expressway. The battery pack is small so it is not having to 
drag a "ton" of batteries down the track. Fitted with a larger pack, 
the White Zombie would get very impressive range as a daily driver.

Also, Again, Dennis Berube's Smoke Screen drag truck is also his daily 
to work & errands driver - even with a small pack.

Here is a link to Jim Husted's timing rings:
http://hitorqueelectric.com/gallery/v/Variable+timing+rings/

And here is a link to Grassroots EV:
http://www.grassrootsev.com/

Regards,

Ken




-----Original Message-----
From: Jim Watson <osious at gmail.com>
To: AustinEV News Announcements and General Discussion 
<ausev at austinev.org>
Sent: Wed, 4 Feb 2009 2:30 pm
Subject: Re: [ausev] Transmissions


This helps alot! Especialy the motor with a universal joint connector 
on the shaft. It looks like this is great for drag racing. So why don't 
people do it for regular street cars for commuting to work or to the 
store. Let me guess, if your motor runs at high revs it uses more 
power. The higher revs and power drain the less distance you can get 
out of your pack.

So,... what if you mount a DC motor directly to the drive shaft with an 
AC motor connected to the rear of the DC motor. My thinking on this is 
to possibly create higher efficiency at higher RPMs. The two motors 
would not be used at the same time. The DC would be used just for 
acceleration and coupling, then the AC motor would be used for higher 
speeds. In a since the switching would create a vertual transmission. I 
know this would mean two separate controllers, and some crazzy wiring. 
But I am wondering if this configuration may yeild greater milage 
because there would not be a lot of friction causing parts in the 
transmission. Maybe I dont even need the DC motor if there is an AC 
motor in the mix. I think the AC motors are more effiecient at higher 
RPMs but they also drain more power at higher RPMs.

With your experience and knowledge about converting cars, what would 
you say about this?

Thanks

Jim



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