On Jul 26, 2014, at 12:01 AM, Cor van de Water via EV <[email protected]> wrote:
> Ben, you are right. *if* you can find a 6:1 rear end > (the highest that my vehicle can be equipped with is 4.2:1) The car has an 8" rear end, which will go up (down) to 4.11. There's a shop in town that'll build a custom 9" rear end with 6:1, but it wouldn't be cheap. > then at 12.65 MPH the drive shaft is doing 1000 RPM. > Just a random data point: my previous truck (S10) when doing > a constant 55 MPH on level road, no wind, consumed 15 kW to > maintain the same speed. > Scaling that down to 1/4 of the speed: 14 MPH should take way less > than 4 kW since the wind resistance is not linear (I believe it is 4th > power of speed) so 5 hp at 1000 RPM is a good continuous power rating, > as long > as the higher RPM rating is equally higher. Then I think I'm probably okay with a pair of AC-51s and a 4.11 rear. Power in the AC-51 increases linearly with speed at slightly greater than unity: 5 @ 1000, 13 @ 2000, 22 @ 3000, 31 @ 4000, 40 @ 5000 45 @ 6000, and then back down to 40 @ 7000. (Those're all from eyeballing the graph, so not exact.) If an S10 needs 15 hp (and I'm freely interchanging hp and kW to make the math easy) at 55 MPH, the Mustang shouldn't need *much* more than that -- and I'd place my bets on it needing less. At 55 MPH with the 4.11 is 3000 RPM; with a single AC-51, that's 22 hp. The single motor would be okay, but it might not be happy climbing hills -- not that we have many in town here, but Sedona and Flagstaff and the Grand Canyon and lots more are only a half a day away. At the slow end...1000 RPM is ~19 MPH. Five horsepower might not cut it by itself, and 15 MPH school zones might be a problem -- with a single motor. But doubled with a second motor it should (I think) be fine. 500 RPM is at ~10 MPH, and the two motors, I'm guessing, should still be capable of 5 hp combined. Intuitively, it works...I'd think five flesh-and-blood mustangs would have a hard time pulling the car to 20 MPH, but ten of them should be fine -- it'd be like carrying two riders at a gallop. Couldn't keep it up all day and would need a good rubdown afterwards, but definitely doable. At 6000 RPM where power peaks, it's 110 MPH -- more than enough speed, at least without handling upgrades and perhaps an upgraded driver. Plus, those types of speeds would presumably be in hybrid mode anyway if 90 hp isn't enough. > The saving grace for EVs is that the "continuous" trip is almost always > less than an hour (Tesla excluded) so you can typically look at 1/2 hour > rating of compnents such as motors and those are way higher than 24/7 > continuous ratings. Indeed, the car is going to have a battery in the 10 - 20 kWh range. Anything much over half an hour on the road would be in hybrid mode. Still, I'd rather not burn up the motor early by constantly stressing it. Seems like throwing a pair of motors at the car does, indeed, solve the gearing problem, and a second AC-51 is definitely cheaper than the custom transmission and not that much more expensive than a custom rear end. That it would give very characteristic "Mustangy" performance (to use David's term) is good; I'd rather spend less money and have more power than spend more money and have less power! Also, now that I understand this a lot better, I'm going to re-run a bunch of those battery calculations. I might be able to shave off some of the Ah specs if I assume that the system as an whole doesn't need more than 1000 A rounded up for a bit of overhead for age / temperature / whatever. Thanks again, b& -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 801 bytes Desc: Message signed with OpenPGP using GPGMail URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140726/13e221b1/attachment.pgp> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
