# RAV4 EV Specs leading me to flirt with direct drive again



## meanderingthemaze (Jan 25, 2010)

I was convinced by a number of people that with my configuration I should keep the tranny and not go direct drive, but after talking to someone about the RAV4 EV, I'm starting to wonder if I can consider it again. I would really prefer direct drive for a number of reasons. After comparing the specs with my proposed conversion, let me know what you think.

Here are the specs on the RAV4 EV as taken from here:
http://www.seattleeva.org/wiki/Toyota_RAV4_EV


> Data from http://electricdrive.org
> 
> Vehicle Size:
> Overall Length (in.): 156.7
> ...


And here's my conversion info:


> Data from Service Manual for 1969 Datsun L521 pickup
> 
> Vehicle Size:
> Overall Length (in.): 170.3in
> ...


I’m also attaching some scans of the manual in case some other pertinent info might be in there...thanks


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## rillip3 (Jun 19, 2009)

The main reason direct drive is usually discouraged is because you give up mechanical advantage, and the attachment would have to be very precise. Given the instantaneous torque applied to it on starting, if your attachment was off even a degree or two you could easily break the welds. All that has been sorted out for you in the way the transmission is attached. 

What are the reasons that you'd like to go with direct drive? There may be other ways to address those concerns, or if you're very good at that sort of thing, you might decide that it is worth the effort.


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## EVfun (Mar 14, 2010)

rillip3 said:


> The main reason direct drive is usually discouraged is because you give up mechanical advantage, and the attachment would have to be very precise. Given the instantaneous torque applied to it on starting, if your attachment was off even a degree or two you could easily break the welds. All that has been sorted out for you in the way the transmission is attached.
> 
> What are the reasons that you'd like to go with direct drive? There may be other ways to address those concerns, or if you're very good at that sort of thing, you might decide that it is worth the effort.


What has to be more accurate? 

You have to be quite accurate when connecting to a transmission input shaft. A direct connection to a driveshaft leaves a lot more room for motor location variation.


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## rillip3 (Jun 19, 2009)

EVfun said:


> What has to be more accurate?
> 
> You have to be quite accurate when connecting to a transmission input shaft. A direct connection to a driveshaft leaves a lot more room for motor location variation.


Creating a coupler for the motor to the transmission is a well traveled road, and the transmission was designed to have a connection to the workhorse (previously engine, now motor) there. Engineering the connector for a motor to the drive shaft is not as well traveled, and if you don't do it right, you'll break it to pieces, and you do not have the luxury of having a piece engined to fit that exact purpose at that point.

If you have the engineering know-how to do it, perhaps there is a benefit to direct drive, though I'm not particularly aware of one. Otherwise, it's very convenient to take advantage of the years of engineering that went into making the transmission and it's precision assembly to the drive shaft.


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## EVfun (Mar 14, 2010)

If you choose a common transmission with an adapter readily available then that route is easier (shell out about $800 and be done with it.) Having just done a conversion to a transmission where an adapter wasn't available I would go direct drive if starting again! 

The torque to deal with is the same either way, set by the chosen motor and controller peak amps. Here is a nice page of parts needed to couple directly to the driveline. Most towns of 20,000 or more in population will have a driveline shop that can build the driveshaft to the correct length. The needed parts are all pretty common except for the yoke for an 1.125 inch motor shaft. You want to pick up the original engine and transmission mounts to attach the motor(s).


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## meanderingthemaze (Jan 25, 2010)

The reasons I prefer direct drive are:
1. I am used to driving an automatic and like to have my hands free.
2. I want others to be able to easily drive the car.
3. I prefer simplicity and it would be nice to get rid of extra weight, tranny, hydraulic clutch system, as well as more open space in the cab without shifter.


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## meanderingthemaze (Jan 25, 2010)

Thanks EVFun, you know that yoke is exactly what I was picturing manufacturing myself. But I'd much rather just buy one of those.

Anyway, the reason of this post to determine if I would have more or less the same performance as a RAV4 EV given that the specs of the car are very similar. I guess one big unknown is what the torque curve and RPM range is for the RAV4 motor. I would imagine that even though they are both rated 50kW that doesn't mean they will perform the same at various speeds, conditions, etc.

Using Anaerin's trusty speed calculator, I determined I need a ~4.5:1 fixed gear ratio for a 75mph top speed. Would it be relatively easy to modify the differential to achieve that?


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## madderscience (Jun 28, 2008)

before you decide on direct drive, you should figure out what the torque curve looks like on the motor/controller combination you want to use. Knowing that, and the gear ratio and tire diameter can give you a pretty good idea of your off-the-line acceleration.

I kind of suspect that with a 4.5:1 final reduction and a 50HP isn't going to provide you with adequate power for accelerating from a stop or for climbing any kind of hill.

http://www.evparts.com/cms/picts/products/MT5615%20Torque.PDF

That link is to the torque chart for your motor (or something pretty close). It says you get about 90ft/lbs of torque at stall (and it's pretty constant up to 3000 rpm which would be freeway speed with your drive ratio of 4.5)

So if you have 4.5:1 final drive you get 90 * 4.5 or about 400 ft/lbs at the drive wheels. If we assume you have 24" diameter wheels (to keep things simple) your drive motor can push the car forward with 400lbs of force. 

If the truck weighs 3000lbs (just guessing), then you have about 400/3000 or 1.3 m/s^2 of acceleration.

basic physics says v=at, or velocity equals acceleration multiplied by time.

60mph is 27m/s more or less.

so 27m/s = 1.3m/s^2 * t. 

this makes t equal 20 seconds for 0-60mph time. Doesn't seem too terrible, *but...* since your torque is largely constant with an AC system (up to 3000 rpm in your case) you can pretty much just scale this. for example, it will take you 10 seconds to get to 30mph, and 5 seconds to get to just 15mph. That's kind of pokey.

What can you do? note that redline on that motor is 6000 RPM. If you were to change your final drive ratio to something like 9:1 you could basically halve your 0-30 time and still have enough RPM to get to 60mph. You would not halve your 0-60 time since torque drops off on that motor above 3000 rpm.

9:1 final drive ratio is typically pretty close to 2nd gear in most cars. That's why a lot of EV drivers spend most of their time in that gear. The Rav4 EV probably has a similar final drive ratio; maybe even a little higher like 10:1 or 12:1.

Oh, and as far as changing differential gear ratios goes, most rear drive vehicles have or had multiple differential gear ratios available. 3.23, 3.5, 4.1, and 4.77 are common gear ratios but what specific ratios might be available for yours I don't know. Your vehicle's service manual will probably tell you what you have now, or you can measure it by jacking up one wheel, putting the car in neutral and turning the drive wheel once and counting the revolutions of the driveshaft. multiply by 2 and that is the differential gear ratio. Modifying that ratio means buying a new ring and pinion and installing them or having the work done. Not uncommon work but beyond the basic DIY crowd due to tolerances and preloading requirements to get it done right.


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## meanderingthemaze (Jan 25, 2010)

madderscience,
Can you take a look at the PDF I attached to the original post? I must admit I'm not gearhead, and am probably interpreting thinigs wrong. But, it looks like my 1st gear final ratio is 4.5:1. Could that be? Also, should we guess that the RAV4 had a higher RPM range and better torque?

Thanks for the calculations, I didn't follow every step so I'll have to take your word on it.


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## EVfun (Mar 14, 2010)

meanderingthemaze said:


> Thanks EVFun, you know that yoke is exactly what I was picturing manufacturing myself. But I'd much rather just buy one of those.
> 
> Anyway, the reason of this post to determine if I would have more or less the same performance as a RAV4 EV given that the specs of the car are very similar. [snip]


Now for the down side of direct drive... 

You will need more motor and controller. With direct drive you cannot shift and raise the motor rpm to improve cooling at city speeds. Your controller also needs to be able to dish out more motor amps and hold it for longer because you are getting low speed power by using less voltage and more amperage. Amps are what cause heat (resistive losses are amps squared times resistance.) 

Most manufacturers use direct drive because a bit more motor and controller are cheaper than a gearbox and a clutch plus the couplings and mounts to go with it. Most people converting an existing car keep the tranny because it's already there. That usually makes it the least expensive route. Efficiency seems to come out nearly the same either way when the components are well chosen (increase in low speed motor and controller losses vs. eliminating transmission losses.)


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## meanderingthemaze (Jan 25, 2010)

EVfun,
Perhaps that's why they use higher voltage systems, to reduce amps and heating at the low end.

OK, well, I tried. I guess it's pretty clear. I'll need the tranny.


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## Coley (Jul 26, 2007)

One thing having a trans is good for, is that you can test run the motor to check on things in the system by putting it in neutral.

Other wise, you need to jack up the drive end and that can be dangerous, unless you have a hoist.

Drive line angles can be different, even when you jack up just the rear axle.
Makes checking vibration difficult.

Plus a controller runaway is a dread, without a gearbox. It may be hard to pull it into neutral, but it can be done.


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## Ladogaboy (Apr 25, 2010)

Just throwing this out there:

Isn't the AC50 50kw Max power? The RAV4 EV might be 50kw continuous, meaning it might be almost double (100kw) the peak power of the AC50. 

Also, I have to imagine that, with the voltage difference, the RAV4 will see much higher RPM, making a 9:1 or higher gear ratio possible.


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## madderscience (Jun 28, 2008)

Pretty sure the 50KW is max power. 108V at 500A is 50KW basically. the controller will limit the amps to that maximum.

The ratios given in the pdf show the differential ratio ("final drive") as labeled, AND the individual transmission gear ratios. Looks like there are 3 differential ratios to pick from.

You multiply the two to get what I was calling "final drive" by which I meant the ratio between the drive motor and the wheels. 

For example, first gear in the first column in the chart would be a ratio of 4.875 * 3.657, or 17:82 

Going without the tranny would of course mean you only have the differential gear ratio and your best option would have been the 4.875 ratio. 

However it sounds like you have decided to keep the tranny which given the motor/controller combo is the best approach.

cheers


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## meanderingthemaze (Jan 25, 2010)

madderscience said:


> Pretty sure the 50KW is max power. 108V at 500A is 50KW basically. the controller will limit the amps to that maximum.
> 
> The ratios given in the pdf show the differential ratio ("final drive") as labeled, AND the individual transmission gear ratios. Looks like there are 3 differential ratios to pick from.
> 
> ...


Not so fast...

OK, so this is going to turn into a discussion of power vs torque, but the Azure Dynamics AC55 system(http://azuredynamics.com/products/force-drive/TractionMotorswithDigitalMotorControllers.htm)
has much more torque (206 ft-lb peak, 103 ft-lb nom) but doesn't have much more power (59kW peak, 25kW cont) than the HPEVS's AC50 system I have been looking at. 

How is that significant? Could I use the Azure system then, since I should be able to use a lower gear ratio then right since I will have much more available torque? I have a little bit of a hard time understanding the practical diff between power and torque. 

(you have to download the PDF from the above link to see the torque and power curves)

I guess all "automatic" drive systems have the disadvantage of being able to disengage the motor which is why the Toyota problem recently was such a big problem. But I do plan to have a few safety disconnects in place to be able to manual shut off power to motor. Of course, if there were a short that could not be stopped, then I would have a runaway vehicle. Perhaps there is a way to have a machanical disconnect in place almost like a clutch for the connection between the yoke and the motor? Not sure if it's worth the engineering.


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## EVfun (Mar 14, 2010)

Torque is a twisting force. Power is a combination of twisting force and speed. 

Horsepower = torque * rpm / 5252

By extension, if you lower your gearing the horsepower remains the same but at a lower rpm and higher torque. This is the value of a transmission. If you take off in second you have roughly double the torque at the wheels compared to 4th. If you do not have sufficient torque in your motor/controller package you need gears to accelerate acceptably. You need 2 or more gears so you can move the rpm back into your power band.

I'm better at DC (never done an AC conversion) so I will use for an example. I have a 1420 lb EV. With a Curtis 1221B controller I have to take off in 2nd gear (2.06 to 1) if I want reasonable acceleration. That controller has a maximum motor amps of 400 and with that a Prestolite MTC-4001 makes 64 ft-lb of torque. I swap in a 1000 amp Zilla controller and I can take off faster in 3rd (1.32 to 1) gear than I used to in second. 

With the Curtis I feed 132 ft-lb of torque into the differential to take off from a light in 2nd gear. To go freeway speeds I have to shift to 3rd gear to lower motor rpm. With the Zilla turned down a bit (800 peak motor amps) I feed 172 ft-lb of torque into the differential to take off from a light in 3rd gear. The Zilla can easily allow me to drive without shifting. The Prestolite motor is large enough that it can handle the lower voltage at higher currents required to operate at lower rpm (3rd gear instead of 2nd) at city speeds. 

Hopefully this helps more than it confuses.


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## meanderingthemaze (Jan 25, 2010)

What you says makes sense. But I still am not sure if I can do all the calculations myself. The most confusing aspect is the gearing. I don't know exactly how to read the manual specs and figure out the final gear ratio. 

If madderscience is telling me right above, then...
1st gear: 4.875 * 3.657=17.82:1 * 90 ft-lbs = 1604 ft-lbs (at the wheels)
2nd gear: 4.875 * 2.177=10.61:1 * 90 ft-lbs = 955 ft-lbs 
3rd gear: 4.875 * 1.419=6.92:1 * 90 ft-lbs = 622 ft-lbs 
4th gear: 4.875 * 1.000=4.875:1 * 90 ft-lbs = 438 ft-lbs 

The next part would be how much torque is required for "good acceleration" for a 3000lb pickup with radial tires on 15" rims. An estimate would suffice.

Are you saying that the DC motor can have variable max torque, depending on amps(controller)? Is there an upper limit on what the motor can take? I understand that more amps equals more torque, but if a motor has a max torque rating, wouldn't that be the max amps it could take? I guess the big diff between AC & DC here is that with AC motor/controller relationship is more specific. I can't just upgrade to any controller that will push more amps, it has to be suited specifically for the AC motor.


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## Ladogaboy (Apr 25, 2010)

madderscience said:


> Pretty sure the 50KW is max power. 108V at 500A is 50KW basically. the controller will limit the amps to that maximum.


I wasn't talking about the AC50, I was talking about the RAV4 EV:



> Electric Power Plant:
> *Voltage: 288*
> Horsepower: 67
> Power: 50 kW
> ...


It doesn't list what the amperage is, but if it is the same as the AC50 system, wouldn't it be putting out considerably more power? My only point was, the OP was most likely comparing peak power (AC50) to continuous power (RAV4 EV). If that's the case, he is not going to be able to replicate the RAV4 EV's performance with an AC50.


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## Duncan (Dec 8, 2008)

Hi Meandering

_The next part would be how much torque is required for "good acceleration" for a 3000lb pickup with radial tires on 15" rims. An estimate would suffice._

This is easy - you need to know the radius of your wheel and tire, my 14 inch 185/70 are about 24 inches diameter - 2ft - makes the calculation easy!

Using that 
_If madderscience is telling me right above, then...
1st gear: 4.875 * 3.657=17.82:1 * 90 ft-lbs = 1604 ft-lbs (at the wheels)
2nd gear: 4.875 * 2.177=10.61:1 * 90 ft-lbs = 955 ft-lbs 
3rd gear: 4.875 * 1.419=6.92:1 * 90 ft-lbs = 622 ft-lbs 
4th gear: 4.875 * 1.000=4.875:1 * 90 ft-lbs = 438 ft-lbs 

_1st Gear - 1604 ft-lbs at 1 ft radius = 1604 lbs force
2nd gear -955 lb-ft = 955 lbs force
3rd - 622 ft-lns = 622 lbs force
4th - 438 ft-lbs = 438 lbs force

Acceleration
1st Gear = 1604 lbs force, 3000lb mass = 1604/3000 G acceleration = 0.53G 
2nd gear = 955 lbs force = 955/3000 G = 0.318 G 
3rd = 622 lbs force = 622/3000 = 0.2 G 
4th = 438 lbs force = 438/3000 = 0.146 G 

Continual 1 G acceleration = 0 - 60mph in 2.6 seconds 

1st Gear = 0.53G = 4.9 sec 0 - 60 not bad! 
2nd gear = 0.318 G = 8.2 sec
3rd = 0.2 G = 13 sec
4th = 0.146 G = 18 sec

Of course you dont actually get the 0-60 times as vehicle drag increases

The Tesla uses a single speed direct drive set up - but its motor is good to 12,000 rpm!


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## EVfun (Mar 14, 2010)

meanderingthemaze said:


> What you says makes sense. But I still am not sure if I can do all the calculations myself. The most confusing aspect is the gearing. I don't know exactly how to read the manual specs and figure out the final gear ratio.
> 
> If madderscience is telling me right above, then...
> 1st gear: 4.875 * 3.657=17.82:1 * 90 ft-lbs = 1604 ft-lbs (at the wheels)
> ...


You have the gearing torque multiplication right. That is some low gears, the transmission gear ratios look just like the ones in my '66 Datsun 411, but I have a 4.11 final drive with little 13 inch wheels. You will want around 1000 ft-lb at the rear wheels to leave a traffic light and feel "normal." You will likely find 2nd to be the gear of choice as it is pretty close. 1st might be welcome if starting off while pointed uphill. 

Yes, the torque of a series wound DC motor is dependent on the amps you feed it. In the case of a Prestolite MTC-4001 it is about 64 ft-lb at 400 amps and about 140 ft-lb at 800 amps. For series wound DC motors the manufacturers tested max is routinely ignored, but it is true that each motor model has a maximum amp level before damage happens quickly. Most of the 8 and 9 inch motor in use can handle 1000 peak motor amps, an ADC or WarP 9 inch can even take 1400 amps for a few seconds at a time. I'm a little more concerned about my smaller Prestolite (7 inch) and I'm not sure I want to push it quite that high (the manufacturer has charts up to 500 amps but I know it will take more.) Older Curtis motor controllers dish out a max of between 400 and 550 amps, so by using a Solitron or Zilla controller you can get more torque from most of the DC motors used in EVs.

I should point out that just because a controller is feeding the motor 800 amps doesn't mean the batteries are supplying 800 amps. My Zilla in my Datsun is programed to only draw 300 battery amps but allow motor amps to rise to 600. The Zilla can take 120 volts at 300 amps and turn it into 60 volts at 600 amps for the motor. You may notice how that works a lot like torque multiplication through gearing


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## meanderingthemaze (Jan 25, 2010)

Ok, so, I'll figure out the tire size.

But what is the proper torque number of a particular motor to use for the calcs? The continuous or max torque? I suppose that the torque in real world situations will be max if you floor the accelerator, and continuous when you're cruising (more or less)? So, I should use max to know what I CAN get out of the motor if I demand it right? Also, the torque will die off as RPMs go up, so max torque won't be constant, right? 

I mostly will need the high torque at below 30mph speeds. After that if it begins to die off gradually up to 60mph then I should be good. At that speed I don't need to be able to accelerate very much.

Let's see what I can come up with and I'll post to make sure my calcs are correct.

Thanks!


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## EVfun (Mar 14, 2010)

If you are trying to get an idea of the initial take off from a stop you can use the peak torque at 0 (or under 200) rpm. For a series motor that will be the torque made at the controller peak amp level. For AC motor/controller packages you should refer to the manufacturers data.


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