Rolling and Aerodynamic Drag Test Track

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TonyWilliams

Well-known member
Joined
Feb 19, 2011
Messages
10,107
Location
Vista, California USA
I drove to my uber secret test hill for testing of tire and aerodynamic drag. Here's an general description of the course to roll down:

Code:
Sign *   Nomenclature   *  Elevation * Miles
1 - No Parking Bike Lane    * 1400ft * 0	
2 - 7% grade.....           * 1325ft * 0.2	
3 - Call Box......          * 1300ft * 0.1	
4 - Watch Downhill Speed	 * 1272ft * <0.1	
5 - No Park Bike Lane       * 1240ft * <0.1	
6 - No Park Bike Lane       * 1177ft * 0.2	
7 - No Park Bike Lane       * 1089ft * 0.2	
8 - Call Box @ Parking Area * 1076ft -neg-	
9 - 7% grade.....           * 1069ft -neg-	
10- Watch Downhill Speed    * 1360ft * 0.1	
11- No Park Bike Lane       * 1000ft * 0.1	
12- 60 mph.....             *  853ft * ? (1.5 miles from first sign)
13- Lowest point(no sign)   *  810ft * ?
14- Bike Lane....           *  850ft * ?

So, I did several runs today. The first was stock and reached 84 mph @ check point 12, and 36 mph on the uphill section at check point 14. Elapsed time from a dead stop was 1:57.9 minutes. I tried rolling starts from numerous speeds. The cool part is that with the HUGE drag at the high speeds; it should be easy to measure changes in drag, both for mostly linear rolling resistance, and the aero drag.

I taped a box on the same spot on the "wing" that vortex generators are typically put on airplanes (see pic below). I expected some small change, but it actually limited the speed to 73 mph !!! Woo hoo !!

Now, I can swap out tires, change ride height, tape on aero mods, and other fun projects. Let me know what I should check next!


53cd8681c386d0f0f6b04d5ad25881db.jpg



SA-160VortexGenerators03.jpg
 
Herm said:
How about different tire pressures?.. but document tire temperature when you do that.

Sure, that's easy. I'll swap to the old stock wheels and tires, also. Yes, document it!!

I've got to find some yarn to tape on the windshield so I can feel like a glider :lol:
 
If we had an accurate way to measure energy going in-out* of the battery you could find out how efficient regen is.

*that was a hint for Enginier.. a module with a good coulomb counter in it.
 
Nice project!

thimel said:
Please do several runs with exactly the same conditions to see how reproducible the results are.
I will second the thought to repeat runs to help reduce any noise. 3 runs on any setup would give you a good idea of how consistent any particular result is.

Looks like a few other good suggestions (tire pressure, stock vs Juke wheel/tire setup) there.

Since the box on roof (LOL at the unbelievable butter!) was so effective at reducing speed (no wonder roof racks kill efficiency), might I suggest folding in the side mirrors?
 
We need to get you set up for EV-CAN and CAR-CAN logging,
along with GPS data, all simultaneously logged into your PC.

That should greatly simplify your data gathering, and
allow yourself and others to explore and analyze the data.

Other than a Windows PC to run CAN-Do, you need:
1. A USB connected GPS "hockey puck"
2. An OBD cable with custom connector(s)
3. A 2-channel CAN logging interface system
4. A USB connection to the PC for the logging data

#3 and #4 can be done in several different ways,
and I am working on improvements.

I have supplied LEAF Logging Systems to several
groups of investigators. If interested, please ask
for details.
 
I begin every days driving with ~2000 ft total descent in the first 7 miles.

When I start off with a charge of no more than ~90%, regen does almost all of the required braking.

Interestingly, this is true Summer or Winter, as the increased friction of denser cold air very closely offsets the lower regen capability of a cold battery (4 bars on this drive for the first time this yesterday).

When I begin at higher SOC, I find opening all the windows on this part of my trip increases drag enough to spare my discs a lot of wear.

This is a lot less comfortable in the Winter than in Summer, of course.

I'm sure that throwing a small drag chute out of a window, and then pulling it bag in when I reach the Millville plain at ~500 ft., would increase my brake pad life significantly...
 
garygid said:
I have supplied LEAF Logging Systems to several
groups of investigators. If interested, please ask
for details.

Ok, let's talk about this at the next OC meet this Saturday. I need a better timing method... maybe lap timers like we use in racing.

I tried 3 runs this morning (keep in mind, climbing 600 feet over and over KILLS that poor battery... I can only do it maybe 8 times max), but on the third run, a friendly Sheriff's Deputy showed up to watch what was going on. So, I only got two runs:

Code:
Sign#        Run1           Run 2
           Time-MPH        Time-MPH
 2           0 - 0            0 - 0
14     0:52.6 - 81      0:51.9 - 81
16     1:38.5 - ..      1:37.8 - 33
Peak GPS  125.9kmh         126.4kmh

My trial runs today were with the Michelin MXM4 tires, size 215-45-17, 36 psi. Stock LEAF (3350lbs / 1350kg) plus payload of me (220lbs / 100kg) and equipment (66lbs / 30kg) and the wheel / tire combination weigh more than the stock Ecopia tires (18lbs / 8kg).

Mass: 3654lbs / 1657.4kg
Relative Air Density: 96.68%
Wind light and variable (below 3 knots)

METAR KMYF 1453Z 11004KT 10SM SCT026 13/09 A3003

Elevation: 1100 feet - 335.28 meters
Air Temperature: 55.4F - 13C
Altimeter Setting: 30.03 inches - 1017 mbar (hPa) - 14.75 lb/in2 (psi)
Dew Point: 48F - 9C
Density Altitude: 1148 feet - 350 meters
Absolute Pressure: 28.856 inches Hg - 977.18 hPa - 14.1728 lb/in2 (psi)
Air Density: 0.0739 lb/ft3 - 1.184 kg/m3
 
Herm said:
If we had an accurate way to measure energy going in-out* of the battery you could find out how efficient regen is.

*that was a hint for Enginier.. a module with a good coulomb counter in it.
I too would like to see regen data from these great tests. Hopefully we won't have to wait for Ingineer.

The Gid meter already reports dynamic battery voltage that can be logged. Just like voltage drop (relative to OpenCircuitVoltage) is a direct measure of battery loss during discharge, the voltage shift up during regen should be a good measure of battery loss during charge. I agree we need either dynamic kW or current logged to plot how the loss varies with regen. Since this is dynamic data, perhaps garygid already has identified its tags.

Of course there are significant losses in the inverter and motor that would be in addition to the battery loss. If you do pairs of downhill runs in both Neutral vs Eco we can derive the total mechanical energy going into the regen system from the velocity profiles, which you are already deriving from your waypoint times. The difference between the mechanical and electrical measurements should be the regen efficiency.

My more crude measurements indicate I am getting overall regen efficiencies in the range 75-79%.

Abasile, who has a lot of downhill experience, has reported that the regen limit can cut back over time scales of fractions of a minute, and it can decline almost to zero as you approach 80% SOC. I have confirmed this latter effect on my recent trip to Idyllwild. Just like QC power tapers down as SOC rises, tracking the increase in battery charging impedance, it seems likely that battery regen losses will increase with SOC. All of this might complicate getting reproducible data.
 
Run 3 and 4, with 50 psi (vice 36 psi) in the Michelin MXM4 tires, plus about 60 pounds for a passenger. Air temperature is up to 68F / 20C, which should favor going faster.

The speeds and times were nearly the same.
 
With the simple single-channel logging that the GID-Meter does,
logging the EV-CAN bus messages, we have frequent Pack
Voltage and Current, and times down to (probably) a few
milliseconds. That gives us Power, and ultimately, Energy.
True, we do not know how good the Current measurement is,
but the voltage has Ben verified, I believe.

We also get RPM (related by tire diameter to
speed), but I have not yet identified a trip meter,
which might be in the CAR-CAN data.

Adding GPS logging at the same time, one gets some
often useful information, about once per second.

If someone wants to play with the 3-bus plus GPS data,
I can post a log file of an 18 minute test drive.

There are even some GPS receiver devices that provide
data 10 times per second, up from the more usual
once per second.
 
garygid said:
With the simple single-channel logging that the GID-Meter does,
logging the EV-CAN bus messages, we have frequent Pack
Voltage and Current, and times down to (probably) a few
milliseconds. That gives us Power, and ultimately, Energy.
True, we do not know how good the Current measurement is,
but the voltage has been verified, I believe.
This is very good. I am sure the current measurement is plenty fine for our purposes. When I suggested some time ago adding some integration functionality for those of us without a data-logging Windows laptop, I seem to recall that was not practical because the software environment of your meter's processor did not provide a decent time-base with interrupt delays, etc. Is that still true ? In data-logger mode you have the time in your lap-top and even more accurate time from your GPS dongle.

Maybe some day data-logging to my iPad ?
 
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