| 02/22/2012 Getting closer. Bell is back together, arm spaced and all locked down. Have to prep the brushes and break it in yet then off to the dyno room one more time. Later tonight or tomorrow after work. They are calling for snow again so this is up hill all the way. 65 miles one way to the track and on the back roads. Grrrrrrrr 02/21/2012 (b) Repairs going smoothly. Bet it doesn't come out twice. I soldered them in. Shims that is, turned out to be the shim and not the magnet. While we have is stripped to the bone I'm pulling the bushings and installing bearings too. Guess it's time for brushes as well. Magnets are potted and I'll let them set a day or so. Have other fish frying so Friday is still iffy but looking better. 02/21/2012 (a) I suppose the good news is I got dyno data out of this armature. The bad news is...blew up the block. A shim let go. I think I can fix this as there is no damage to the armature but it did make a racket. Vibration I suspect. Data is in the amended table below for the date of 2/18 Question is going to be, can I do it before Friday and have it in this or a better state of tune. This is the first of the three that responded to advanced timing like one would normally see, more RPM and less torque but still best RMS power and motor efficiency came in at 25*. Even a slight bump up to around 27* and it under performed the narrow crown motor. 02/18/2012 Motor Performance Standard Bugenis Bugenis Parma Narrow Crown Standard Crown Peak RPM 60,402 65,126 61,418 Peak Power 154 182 176 RMS Power 91.0 104.1 107.7 Time to RPM 2.4 2.5 2.0 Stall Torque 842.5 932.5 946 Efficiency 38.2% 38.6% 42.1% Eff % RPM 74.9% 71% 69% Hit Current 68.59 65.78 63 Peak A/T 15.5 14.98 16.58 50% A/T 13.4 14.7 15.9 Car Performance 60' .1154 .1033 330' .3449 .3172 660' .5556 .5170 MPH 48.10 50.23 That made my eyes bug out! Oh I was pretty sure there was a teen in the combination but what got my eyes to pop was the way the car hammered the short end of the track. Then expecting it to leg it on the back half...it just kept pulling!! The evening wasn't without it troubles though. The track had been cleaned before I arrived and the shut down glue worked up. Maybe about an hours worth of cars now had traversed the track in both lanes and the amount of shut down glue carry back was just crazy. Of course this contaminates my roller and my board which is a mess to clean up not to mention my tires and braid. Needless to say the first pass stunk up the house. No problem....did what I needed to do....house keeping. Next pass she lays down a low .520 and we are on target and ready to do the gear sorting. I made a set of charts to speed this part up for the evening so I didn't have to hand analyze each pass. We cover the gear range and trade a little short time for a little MPH with next to nothing for ET change. Even try the narrower tires and that was a laugh. All gear combinations gave up .521 to .523 ET's. I settle on the 13/54 combo. It provided the most "balanced" passes. Now I wait. After the race I strip the track's back half, scrape the front half to a dull shine, clean the braid and run the slot. Clean my board and roller, again, and put the race tune on the motor/car. That's when she starts bust'n out these teen passes. To be perfectly geared for this track I would need a 55 crown or a tire 1 tooth shorter LOL. ************************************************************************* Okay, on to something else. Mr. G's observation that crown and possibly winding pattern difference, in as much as it effects rotor mass, may be influencing power out put of the narrow crown motors. A thought worth a look...so I did. Here are some points to ponder; 1.) In and of itself rotor mass can neither make nor detract from power input or output. Nothing on either side of the electrical equation is going to change. That is to say for X watts of input power and Y% motor efficiency output wattage is unchanged by the inertia moment. 2.) All motors are subject to the Time Constant rules. They all spool up in the same predictable manor which is easy to calculate and directly measure. 63.2% of the no load speed per time constant of the remaining value of no load speed. What is not fixed by any rule is the exact SEGMENTED TIME VALUES of the time constant. This, for a given power output, is the sole domain of the inertia moment. If your having trouble getting your head around this given this example a try. Your car weighs 100 grams and 10 grams of that is tire/gear weight. Rotational inertia. You find a pair of tires of the same dimensions and grip/hardness etc., that weight 8 grams and because your in a class with a minimum weight you have to add back the 2 grams you lost as static weight. Car still weights the same, motor still makes the same power but you've just reduced the inertia moment of the entire car and it goes quicker. Okay, a dyno doesn't know what's loading the motor so it's ignorance is our blessing. For that lower rotor mass the motor spools up quicker and as out put power is calculated from the input measurements of current, time segments verses rpm, voltage and flywheel mass it can and will show a bump in output power. The question then is how much of a bump? Easy as pie. Take the spool up rates of the two armatures and convert the values for RPM to time into the % of no load RPM to time. Integrate an RMS value for the entire rage and the difference, in percent, is the amount of the power increase the dyno showed is coming from the change the rotor inertia moment. In this case, 0.5% of the 28 watt increase in peak power, or 0.14 watts. That's the good news, not much. The real question still on the table is how much of the improvement came from the iron and how much came from the crown geometry? Next motor will tell us that. |
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| KMR Kahale & Martin Racing |
| 02/17/2012 .1033-60', .3172 mid track .5170 ET @ 50.23 MPH |
