Victor- you have the tallest first gear of all the CRXes. Which means 9.6:1 for first, and as you stated, 4.87:1 for second and 3.05 for third.
So for a 22.8" tire it is about a 0.95 foot radius. So 129 peak lb-ft of torque for the 30kW motor. Let's assume that there is no derating of torque at 0 rpm. Again with 140 peak lb-ft for the 45kW motor. 129 lb-ft * 4.87 multiplier = 628 lb-ft 140 lb-ft * 4.87 multiplier = 681 lb-ft (30kW motor)at a 0.95 foot radius = 628lb-ft/0.95ft = 661 lb of thrust. So if the car weighs 3000 lbs, then it has a gradability of 22%. Which is steep. (45 kW)at a 0.95 foot radius = 681lb-ft/0.95ft = 717 lb of thrust. So if the car weighs 3000 lbs, then it has a gradability of 23.9%. Which is steeper still. now derate both 20% at stall. Notice the motor curves don't show stall. Victor's site is fairly honest about it. Max torque at 1000 rpm. It isn't uncommon for a controller to do this. See my section on torque speed graphs below. You get about 17.6% and 19.0% respectively Then add another 500 lbs of batteries and humans to go to 3500lbs. You get 15.1% and 16.3% But go to first gear in the 30kW motor car at 3500lbs and 20% derate at stall. 129*9.6/0.95*0.8/3500 =29.7% 140*9.6/0.95*0.8/3500 = 32.3% (just for "Sheer's" benefit, as I think this is close to the QM) You probably don't have to think about wheelspin until you hit 40-50% gradability. Your 30kW motor can now outclimb the single speed 45kW. Or for a hill the 45 can just climb (same wheel torque), you can run 16.3/28.1 times the current or 58% the motor current for the same grade. But I bet the smaller, lighter motor is cheaper. And makes the same peak power as the big one, just for 90 seconds instead of 180 seconds. And climbs steeper hills if you use first gear. In this case, as is often the case, the *short term* power limit is the inverter, not the motor. For efficiency tradeoffs ------------------------------------------------------------------- Look at http://www.uqm.com/Technologies/specsheets/CaliberEV53.pdf Funny, the efficincy plot doesn't go below 1500 rpm? or here: http://www.uqm.com/Technologies/specsheets/PowerPhase100.pdf this goes all the way down to 500 rpm, and 7% efficiency has been lost just by 500 rpm But that's BLDC, not AC, you say. http://www.solectria.com/downloads/ac90candd.pdf look at the efficiency with respect to RPM and torque there. the metric mind plot shows 70% and falling by 1000 RPM, off from 88% for one of their AC systems. ------------------------------------------------------------------- This is great for number crunching for efficiency improvements, but there are a few streets around here that I personally have measured at 17%. Driveways and ramps can be more than this. From a stop, 2nd gear with the 45kW motor won't climb it. But the 30kW motor with first gear will. You will just have to shift. AC doesn't fail you in the middle with a single speed it is at either end. The motor overspeed end and the roll backwards down the hill end. Either pick one of those to avoid, or buy bigger $ilicon. The motor isn't the transmission, it is the IGBTs that are the transmission, and they aren't free. And they come in multiples of 3. Seth (who can't leave a thread well enough alone)
