weChook Racing: Goodwood Test 2015

As ever when we travel to Goodwood, the event started on Saturday afternoon. Driven kindly offered to take Electric Boogaloo in their van, as our intended transport vehicle was suffering from being an Alfa Romeo, and could not be trusted to get there in one piece.

Goodwood Van

Once the van was seen off, we piled into the ST with our tents and set off down the M40. A couple of hours later we arrived at our usual campsite (which is just shutting down, what will we do?!) and pitched, before heading off to the pub for dinner and some triple cooked chips.

For the first time in 5 or 6 trips to Goodwood we managed to get up and set off at the time we planned to. Unfortunately I then got a bit lost, and wasted all that time we’d gained! Once we eventually got to the circuit and set up our paddock, we went straight for the scruiteneering queue before it got too gargantuan, and settled into the routine of telling people ‘No, the car isn’t actually finished yet, we’re going to do some bodywork soon!’.

Scruiteneering was a bit of a challenge; I don’t think any of the guys were used to seeing a car with so much still exposed! Fortunately, the two of us know the rulebook inside out, and after a few discussions, we were given our MOT sticker, with only a couple of things to sort out before the next event.

IMG_9316 (3)

With that, we were ready to get out on circuit! Ian wedged himself back in, and we trundled over to the pit lane. After a final quick check of the electrical system, Electric Boogaloo was ready to go!

At this stage we really had no idea how well the car would go. It had had a few runs up and down the road, never really getting past 20 mph, and not doing any representative cornering. Would the steering be any good? Would the chain come off? Would the whole thing just fall apart once it got up to speed? We just didn’t know!

After a nervous 5 minutes, the car came blazing through the final corner, and past us down the main straight, with barely a sound considering the exposed powertrain. The second lap time around it looked even quicker, putting in what was at the time the third fastest lap.

Ian came back in at the end of the third lap, and a few issues were immediately apparent. Firstly, the motor was rather warm. Secondly, there was a puncture. We rushed back to the pits to sort these issues out, with an inner tube ‘borrowed’ from Driven, and a saw to increase the motor cooling. We just about got it all sorted to get the car back out before the end of the session, but were bought back in again before we could complete a whole lap.

With a few laps under our belt, and no breakdowns or chain-offs, we were feeling pretty satisfied! Better still, some of the smirks from the start of the day had turned into begrudging compliments, having seen how well the car was going.

The afternoon saw more of the same. We set our fastest lap at 30.3 miles per hour, but suffered from quite high current consumption and motor temperatures – somewhat inevitable running a car with all the aerodynamic qualities of a brick! Ian still managed to do plenty of overtaking though!

We managed pretty much a race distance over a couple of stints on track, with no mechanical failures (almost unheard of during my time with Driven!), and we learnt plenty about how much steering lock we need, and how the gearing/motor controller can be used to our advantage. We developed a pretty extensive to do list in order to have the car really ready for Rockingham, which is now just a few short weeks away.

Away from the track, it was fantastic to catch up with all the other Greenpowerites that we haven’t seen since the National Final, and chat about cars with people as enthusiastic as we are! I was particularly impressed with the work done to Probation IV, it could barely be recognised as the same car from last season. As ever, Dave looked imperious in Jet, and we were keeping a close eye on the aero-mods he was trialling to see if there were any ideas worth… appropriating.

Thanks to Greenpower for organising another slick event, and I’m looking forward to the next one! Hopefully we’ll see you all there!

weChook Racing – Greenpower Motor Testing part 2

Introduction

After testing two brand new Greenpower motors (http://wechook.com/?p=321) we borrowed the two motors that had been fitted to Project E and C-XeVolution for the last season.

We were aiming to determine how effective these motors were compared to the new pair and to each other.

 

Background

Over the course of the season, the two motors fitted to C-XeVolution and Project E had both covered hundreds of miles, so we wanted to determine whether there had been a significant gain or loss of performance from the extensive run in. Unlike C-XeV’s motor, nether of this season’s motor’s has been significantly overheated, however the motor from C-XeVolution did get warm at Castle Combe and the International Final, due to the hills.

 

Test Procedure and Equipment

The used motors were tested using the same equipment as the new motors. This time, we decided not to attempt the highest current draw using the heated seat pads, as the results were not reliable enough. In order to test at the higher currents, its likely that we’ll have to add more bulbs.

 

Results

Shown below are two plots. The first shows a comparison of the 4 motor’s efficiency plotted against motor rpm, the second shows efficiency plotted against battery current.

Plot 1

RPMpart2

Plot 2

Currentpart2

Conclusions

When plotting the motor’s efficiency against current, C-XeVolution’s motor is comparable to the second new motor, however it must run much more quickly in order to achieve this efficiency. Evolution’s motor’s performance appears to be tending towards that shown by C-XeV’s motor in the last test report, suggesting that the extra heat it experienced at Castle Combe and Goodwood may have started to cause some damage.

Project E’s motor also appears to need to run at a higher speed in order to achieve its peak efficiency, although it is more efficient than the first new motor over most of the tested speed range.

It suggests that, if we had managed to the run the motor at ~2000 RPM, rather than ~1700RPM, we would have been in a much more efficient range.

 

Further Work

Further testing of the new motors after a more extensive run in will allow us to see how efficiency is affected by distance and thermal cycling. The motors will be cycled using a power supply to start with, and then run in anger once the rest of Ramjet is complete.

We also need to develop a more reliable method of testing the motor at higher duty, in order to better compare motors at the speeds they tend to experience during a race.

weChook Racing – Greenpower Motor Testing part 1

Introduction

As part of the development process for Ramjet, we have been testing a pair of brand new motors, as well as an old (and heavily abused) motor that was used in C-XeV –  Driven’s 2012 competitor.

The aim of the testing was to calculate the comparative efficiency of the two motors, and develop an insight into how the motors perform at different speeds and powers (and see what a really bad motor looks like as well!).

Background Information

During a Greenpower F24+ race, the motor is run using two 12V Lead Acid batteries wired in series to generate the required 24V. Bench testing has shown that an average current draw of ~22Amps or less is required to reach the end of a race without over discharging the batteries, or ‘falling off the cliff’. If the battery is discharged to the extent that the voltage begins to collapse, lap times at the end of a race can be severely compromised. This can be seen in C-XeVolution’s performance in the Greater London F24+ Heat, when compared to Project E. (504 compared to 711: http://bbk-online.net/gpt/lap213.htm)

Over the course of the race, Project E lost 6 seconds compared to its fastest lap, whilst C-XeVolution dropped nearly 40 seconds. In the race, C-XeVolution was consistently consuming an average of 24 Amps, whilst Project E was consuming 21 Amps.

On a race by race basis, current consumption is controlled by gear ratio. In order to most effectively select a gear ratio, a good understanding of the motor must be gained. Adding further complexity to the mix is the fact that the profile of each circuit varies so wildly. At Dunsfold Park, Project E’s current consumption stayed consistently between 18 Amps and 23 Amps, whilst at the National Final in gusty conditions, the current dropped as low as 15 amps on the main straight, and topped 35 Amps uphill. As such, simply investigating the motor performance at the intended average current would not be enough.

Test Procedure and Equipment

The electrical lab-car, built at the start of the year to develop and test Driven’s 2014 electrical system, was used to test the motors. The test motors were attached to another, spare motor, which acted as a generator powering a number of bulbs. The number of bulbs in the circuit, and thus the torque applied to the test motor, was controlled using a separate arduino board.

Using a current clamp and a voltmeter, we recorded the power into the drive motor, and out of the generator across a range of different output currents. We also used a tachometer to measure the motor’s shaft speed. It’s been assumed that at a given rpm, the generator’s efficiency will be same, independent of the motor being used to drive it. Thus by comparing the two new motors on a plot of efficiency against rpm, we can eliminate the efficiency of the generator from the equation.

Following the first test session, the motors were run in, unloaded and from a power supply, for 3 hours and 12V and 3 hours at 24V. Once the motors had been allowed to cool down after this, they were tested again. We decided to add some more load to the test rig for the second set of tests, to understand the efficiency at lower rpms/higher currents. These loads were not as stable in their power consumption as the bulbs however, and so there is less confidence in the results at a higher current.

Results

Below are three plots. The first shows the motor/generator system efficiency against motor RPM, and the second shows efficiency plotted against current output from the generator, which is broadly analogous to load on the motor when racing. The final plot is a repeat of the first, but with C-XeV’s motor included.

Plot 1

RPMnoCXeV

Plot 2

CurrentnoCXeV

Plot 3

RPMwithCXeV

Conclusions

Compared to the two new motors, C-XeV’s old motor ran at a significantly higher speed when unloaded. To achieve the same current output from the generator, it would require more current from the power supply than the new motors. Due to the higher speed of the generator, its voltage output was higher, masking somewhat the motor’s inefficiency. It is inarguable however, that it is less efficient at the speeds experienced during a Greenpower event that the two new motors.

When comparing the two new motors, there is a noticeable difference, with Motor 1 having an efficiency 5% or more greater than Motor 2. The margin increases towards the top end of the powers seen during a Greenpower F24+ event.

After the run in period, both motors showed a lower peak efficiency. The gap between the two motors at lower speeds decreased, and the peak efficiency for both motors appeared to be at a higher current. The second set of tests also showed the folly of allowing current to reach 30 amps or above. Efficiency quickly dropped off and the motor began to noticeably heat up.

Based on this testing, it appears that the motor’s peak efficiency lies between 13 and 16 Amps. It is also known, based on Peukert’s Law that a batteries effective capacity decreases the more quickly it is discharged (Have a look at wikipedia: http://en.wikipedia.org/wiki/Peukert’s_law, or Chipping Sodbury’s page: Greenpower Science).

To me, this suggests there may be an alternative race strategy, that involves running less aggressively, at peak motor efficiency and a low battery discharge rate, for a portion of the race, before moving to a low efficiency, high power mode for a blast to the line. Whether this strategy is quicker over the duration of a race would depend on the battery’s Peukert Constant, the change in motor efficiency at different currents, and the overall aerodynamic efficiency of the car.

Further Work

Further work will involve further running in of the motors, before another testing session, and performing the same series of tests on the motors fitted to Project E and C-XeVolution (Driven’s last two cars) for the 2014 season for comparison. Both motors have been well run in, and neither has been significantly overheated, which will make for an interesting comparison both to the brand new motors, and the very much overheated motor from C-XeV.

A new work stream opened up by this testing is to investigate the possible effectiveness of a split strategy, running slightly slower at a super high efficiency, to allow a final blast towards the end of a race. In order to determine the worth of this strategy, a better understanding of the battery and motor performance will be needed.