weChook Racing: Electric 3Galoo Build Log – Lessons Learnt

In case you haven’t worked out from the lack of us being at races so far this year, 3galoo has not been progressing smoothly.

We’ve had numerous problems with the wheels and driveshafts at the rear of the car, and I thought it’d be a good idea to record what we’ve learnt so that other teams out there don’t repeat the same mistakes.

Without further ado:

Bearing Fits

We had the hubs and bearing spacers for the wheels machined by a local engineering shop. Having checked my drawings with one of the technical specialists at work, I had good confidence that the drawings were correct, and most importantly, correctly toleranced.

Sadly, the parts we received back were not up to scratch. The recesses within the hubs for the bearings were too small for us to fit the bearing, although not by an amount that we could measure with a set of calipers. It wasn’t until I sent the parts to my friendly technical specialist that we realised that they were less than 1/10th of a mm too small – this was enough to completely prevent us from fitting the bearing.

Foolishly, we wrecked one hub by trying to turn out the extra hundredths of a mm with our bench lathe which really was not up to the job – we went from not being able to fit the bearing, to it falling immediately back out.

This all put a massive damper on progress, and enthusiasm – as the first thing that we’ve not done ourselves, for it to go this poorly was a bit of an eye opener. We know for next time – make sure our tolerancing is documented properly, make sure the person doing the machining understands and agrees what is required of them, and if possible, get the bearings to them that you want to fit!

Shaft diameters

Our next problem was with the shaft that we bought to use as the rear axles. To our calipers, the shaft we bought was a constant 18mm diameter the whole way along, so we couldn’t understand why it would only fit part of the way through the holes that we needed it to, and why it slopped around at other points.

Again, a measurement with a higher resolution tool showed us that the shaft was definitely not a constant diameter along its entire length. We were advised to instead purchase Cold rolled bright mild steel, which has a much more consistent outer diameter, and has really reduced the amount of wobbliness at the back of the car.

From this we learnt how much difference an imperceptible change in diameter can make, and therefore the importance of using the right materials.

Tolerance Stack up

The design we came up with introduced a lot more ‘critical tolerances’ than it needed to, meaning that many dimensions on many parts needed to be machined perfectly for the design as a whole to work.

The redesign at the rear end used a shaft that we knew would fit well into the I/D of the bearing with no further work, reducing the number of ‘critical characteristics’ by two.

This approach of designing to minimise the ‘critical characteristics’ of any given part makes the entire system more robust, and easier to manufacture, which is a big win!

Hopefully this has been of some use to someone who’s looking at building their own car!

weChook Racing: Rockingham Season Opener 2016

Having skipped out on the Goodwood Test this year (for a few reasons really – we hadn’t finished making anything yet, and Goodwood is a less important circuit to get right these days due to the relocation of the final), 2016 opened for weChook Racing with the season opener at Rockingham.

For those that don’t know, the Season Opener has traditionally consisted of an extended test session in the morning (over three hours this year) followed by two F24 format races in the afternoon. This means an 80 minute race with 2 mandatory driver changes – a slight problem for us!

We’d been pretty lazy in the off season – 2galoo had been put in storage after the 2015 International Final, and had barely been touched since. We did a few quick checks on Tuesday evening (we pumped up the tyres!) before tossing it on the roof and strapping it down.

We drove to Rockingham on Wednesday morning, and after bumping into everyone’s favourite commentator on the road, we arrived just in time to join the start of the scruiteneering queue. 2galoo flew through the checks – including the new impact foam regulations that had caught out a number of teams at the Goodwood test –  and received its MOT sticker, giving us plenty of time to get out on circuit.

ITS GAV!

We had two major objectives for the test – the first was to try out the eChook Nano (read about it here), the bluetooth data logging and telemetry system that we have co-developed with Driven. Our second objective was to extend our understanding on how to use our gearing to maximise race efficiency.

We hit the circuit early in the session and completed 12 laps. Ian drove the first few laps in ‘constant current’ control mode, using the gearing to keep the current as close as possible to 25 Amps. Afterwards, we switched the strategy to run consecutive laps in each gear. The eChook worked admirably, until the phone used to log the collected data fell off the dash into the depths of the car and dropped its connection.

MORE GAV!

After completing the first planned stint, Ian bought the car back in for a few checks – we were particularly interested in the motor temperature after running a few laps in high gears with high current consumption. Thankfully, the temperature weren’t too high, although this doesn’t mean it wouldn’t start cooking if we ran a whole race at those speeds!

Having realised we weren’t collecting any data from the first stint, we decided to send the car back out in the last 30 minutes of the session. A quick battery change later, and 2galoo was back out on circuit, fitting in another 10 laps. I’ll be writing a separate blog post on the data we collected later on.

 Still DecoratedLined upOn track
After a quick break, it was time for the first of the season opening races. As alluded – we had didn’t have enough drivers to actually compete in an F24 format event, so we used the race as another test session. We followed a similar pattern as we did in the morning, a few constant current laps followed by a lap in each of the gears. This consumed far more current than we would normally do during a race, so Ian retired the car after about 50 minutes and 16 laps when the voltage got a bit low, in order to protect our best set of batteries. We matched the fastest lap that we achieved during the international final weekend and had got up up to 2nd place at one point.

After the first race we’d done all of the testing we needed to do, and collected a lot of good data, so we elected not to run in the second race. We had a great day overall, the weather was great and 2galoo ran smoothly and reliably – a fitting sign off after what is likely to be the car’s final event.

This feels like a return to normality after the end of the 2015 season – Congratulations to Dave (and the newly extended Cullimore Racing team) for a pair of victories – Jet II really is the real deal and the design work that has gone into it is the inspiration behind what we’re doing with 3galoo.

The newly arrived Bluebird looked highly impressive – I’m sure it will be a threat in whichever class it ends up entering! The rebranded Minion/ Scooby Too looked very impressive, and completed a whole lot of laps in practice. Probation IV showed up with a new and dapper set of orange bodywork, that looked just a bit like a boat.

Probation IV

Thanks to the GP staff for another cracking event! We’re looking forward to the next race, and to joining them at STEMtech in June.

Now we just need to finish 3galoo before the Goodwood heat!

weChook Racing: 3galoo Design: Wheels

The first thing we decided upon for Electric 3galoo was a change to smaller diameter wheels – 16 inch rims down to 14 inch. The main reason we hadn’t done this previously were concerns over the cost and availability of tyres that fit this size rim, but after discussions with Matt from Renishaw (https://twitter.com/Hunter_Concepts) we decided to take the plunge.

The main advantages of smaller wheels are aerodynamic. The steering envelope is reduced, meaning the total width of the car can be reduced (or the same width can be maintained with less cambering of the front wheels), and the top surface of the car can be lower, reducing the total frontal area.

Plot showing estimated aerodynamic vs rolling drag for 2galoo

Plot showing estimated aerodynamic vs rolling drag for 2galoo

The con of smaller wheels is higher rolling resistance. Rough calculations say that at F24+ speeds, aerodynamic drag exceeds rolling drag by at least a factor of 4, so it shouldn’t be too hard to get a win in the trade off.

As well as reducing the diameter of the wheel, we wanted to make them narrower. The widest point on Electric 2galoo is at the centre of the rear wheel, at 560mm. As well as being well over the minimum track width of 500mm, having the widest point on the car so close to the back is aerodynamically very disadvantageous – we found it impossible to make a smooth curve for the bodywork that came back to point, as seen on Reprobation and Jet.

In order to reduce this width we needed to forego spokes, replacing them with solid carbon disks. We’d also have to replace the standard bike hubs we’d used on our previous cars with something a bit more bespoke.

Our original design (made before we’d actually got our hands on the rims we planned to use) is shown in exploded view below. We planned to fit some foam cored carbon sandwich panels inside the rim, with a hub bonded and bolted around them. We would have had the same wheel design at the front and back of the car – the front wheels would have been bolted through in a similar fashion to 2galoo, whilst the rear wheels would be attached to a brake disc holder to enable driving/braking torque to be transferred to them.

Initial flat wheel design

Initial flat wheel design

Once the rims arrived, we noticed a few problems with this design – the inside of the rim was angled, which would make it very difficult to get a good bonding surface between it and the carbon discs. The outer surface of the rim however was vertical,  making it a perfect bonding surface. This led to our second design iteration – instead of bolting the hub around the carbon discs, the discs would be attached around the hub.

Second flat wheel design iteration

Second flat wheel design iteration

This reduced the complexity of the hub, reduced the number of parts we’d have to turn, and increased the bonding surface area on the rim, hopefully resulting in a stronger final product (in fact, my calculations say that each bond should be able to support 865kg – slightly more than we’re planning for 3galoo to weigh). This still allowed us to keep the front and rear wheels identical – a big benefit when it comes to keeping spares.

If anyone would like a closer look, the drawings for the first hub is here: Hub and the second is here: NewHub

Next up, the chassis!

weChook Racing: How we use data in the pits

Having covered how Ian uses our measured data whilst out on circuit in the last post (read it here: http://wechook.com/?p=518 ), I’m now going to cover what we can do with it when we’re not racing – be it in the pit lane or once we’re back home.

The first step is getting the information from the car to my laptop. As long as we remember to put it in, the telemetry board will record all measurements to a text file on an SD card, which can then be easily transferred across to a computer. The system also transmits data live wirelessly during a race, but this is of little use when the car goes out of range or behind a tree – pretty much everywhere apart from Merryfield and Dunsfold Park.

For the information to be valuable during the constraints of a race day, all the information has to be pulled together quickly – there’s not a lot of time to make changes in between the end of practice and the start of the race so every second counts. In order to maximise the utility of our data logging, I wrote some code in MATLAB that will read the data files, and generate a report with useful plots and calculations. I’ve uploaded two of these reports, from two different races at Rockingham to the website:

As an aside – I heartily recommend that any aspiring young engineer go out there and get some experience using MATLAB – it is easy to pick up and there is a huge wealth of help and support available online. As a data analysis and visualisation tool it far exceeds Excel, and will make a piece of work look far more professional! I use it extensively at work to perform simulations, automatically generate reports (automating a task that used to take hours keeps my manager very happy) and design control algorithms. From experience, I can also say that if I’d learnt to use it whilst at university, it would have made my dissertation project a whole lot more manageable, due to the Gigabytes of data that I was dealing with from incredibly high resolution measurements of impact data.

Sales pitch over! Once I’ve worked my magic with MATLAB and generated a report we can work out how much current and power we were using at any given point, and how fast we were running the motor. Using this approach with data from a run in practice, we can determine whether we can complete a full race distance at that pace without flattening our batteries (I’ve done plenty of battery testing, so I have a good understanding of how much energy the batteries have available).

Based on the data from the Rockingham heat, we were able to plan our power usage for the Lap Race – we estimated how much shorter it would be than the standard hour and then determined how much more quickly we could discharge the battery. If you look at the two reports linked above, you can see that we drew just under 25Ah from the batteries in both events, but at a higher average rate in the lap race.

Also shown in the reports are traces of throttle position and motor speed. Comparing the throttle trace from the Lap Race to that from the heat earlier in the year, it can be seen that Ian is performing fewer gear changes, and spending less time at part throttle. It can also be seen that motor speed tailed off much more quickly at the end of the Lap Race – we’re putting this down to the fact that we were using our best batteries in the Rockingham heat, but we saved them for the F24+ decider on the International Final weekend.

We’re planning to extend our data collection next year to include wheel RPM (from which we can calculate vehicle speed, and determine which gear we were in) as well as motor temperature, to avoid the risk of cooking another one! With this data we plan to be able to run an improved race strategy in the 2016 season – instead of targeting a constant rate of discharge from the batteries, we will be looking at how we can most effectively convert each unit of energy into speed.

Which brings me nicely onto the subject for my next post: Constant Current vs Constant Speed control!

weChook Racing: How we use data on circuit

Seeing as we’ve been espousing the virtues of data collection of late, I’ve decided I’d best write at least a bit about some of the things we do with our data.

I’m going to split this into two posts – the first covering how the driver uses the information during the race, and the second discussing what we do with the logged data in between sessions and race days, as well as what we’re hoping to achieve in the future.

From the Rockingham heat onwards, our cars were fitted with a screen that showed the driver a live readout of battery voltage, motor current and motor speed. Voltage isn’t much use on a moment to moment basis – it fluctuates with the current that is being drawn, meaning there’s no simple way to estimate the charge left in the battery

Motor RPM is also tricky to use – we know we need to keep the motor in its ‘happy range’ in order to keep power consumption low and stop the temperature from getting too high, but it’s difficult to plan a race using motor speed – without a good model of the motor, we don’t really know whether we need to hit 1750 rpm or 1800 rpm to make it to the end of the race!

That leaves battery current as the most useful resource to the driver. We’ve done plenty of testing, which shows that our best batteries have a capacity of roughly 25 Amp-hours, when discharged at a high current. For comparison, our worst batteries have a capacity of 22Ah, which can make a big difference when trying to reach the end of a race.

With 25Ah at our disposal, and an hours worth of racing to complete, the maths isn’t too hard; we need to hit an average of 25A over the course of the race to make sure we get to the end – simples!

With a single speed, relay controlled car, this is achieved through selecting the right gear ratio – get it wrong and you won’t reach the end of the race, or you will get there but at a slow pace. Choosing that gear ratio can be tricky – for me it came down to experience and voltage measurements. I’ll discuss more on this in the next post though!

Electric 2galoo had the luxury of a wide range of gear ratios, and a speed controller. By shifting up and down the gears and by varying the throttle input, Ian was able to target a constant rate of power consumption. At the International Final, this allowed us to control the rate that the battery went flat very nicely – gaining us a place on the last lap as the competition ran out of juice!

2galoo's current consumption from the international final

2galoo’s current consumption from the international final

We’re currently developing a data logging product that will be available for sale to all greenpower competitors – read more about it here – http://wechook.com/?p=511 . If you’re interested in investing in one, get in touch with us on twitter (@Ramjet_gpt) or on the greenpower forum here: http://www.greenpower.co.uk/forum/discussion/3398/introducing-project-echook-nano

 

Introducing Project eChook Nano

Hello all!

The weChook Racing and Driven teams have recently launched a joint project (Project eChook Nano) to develop a standalone system capable of logging important telemetry data from a Greenpower car. Both of our teams feel like we learn a lot from our current telemetry setups and that making this type of information more easily available for other team’s vehicles would be incredibly beneficial and would really help with the engineering and learning aspects of Greenpower racing.

Our aim in developing this hardware is create something simple and affordable that will allow those teams without electronics experience to collect live data from their car for analysis during races, and as something to study in between events. It will be based around an ArduinoNano, and be provided with the base software to perform standard logging functions, whilst giving the students the opportunity to implement their own code to customise the functionality as they see fit.

The hardware is designed to interface with an android app that Rowan has posted about on the greenpower forum here: http://www.greenpower.co.uk/forum/discussion/3335/data-logging-and-driver-information-display-android-app-offer. The hardware on the car communicates with the app via bluetooth, and can provide instantaneous readouts to the driver, as well as logging the information for later analysis. The app will also use the phone’s sensors to supplement the information gathered from the hardware.

A further aim of the project is to provide the ability to live stream the information to web interface via the phone’s 3g connection, allowing information to be viewed live from the pit wall. An exciting prospect to try to understand why a competitor car is accelerating past yours but consuming less amps….perhaps time to get the chain oil out during that next pit stop 😉

We’re designing with the following I/O (and some of our suggestions on what they can be used for):

Inputs
• 2 x Voltage (12V, 24V)
• 2 x RPM (Motor, Wheel)
• 3 x Temperature (Different bits of the motor, battery)
• 1 x Current (Motor)
• Throttle Position
• Brake
• Cycle View & Launch buttons (for use with the app)
Outputs
• LED x 3 (visual status indication)
• Bluetooth Output (interface to the app)
• 2 x PWM output (Fan, Motor controller)

Our primary intention is for this to be a passive component, that can be added to a car with minimal disruption, and will not affect the actual running of the car – we don’t want to be responsible for taking someone out of a race! The pins are there however to receive a throttle position input, and output a PWM signal to a motor controller. Teams can pick and choose what sensors they feel are necessary for their learning, though we would suggest current consumption is the most interesting!

We’re are currently working hard to get the base system cost less than £40 to make this accessible to as many teams as possible. Sensors are not included in this figure but most are cheap components (bar the LEM current sensor which can be found for ~£18). Due to the open source nature of this project we aim to provide teams with all the information required to source and put together the hardware themselves, but initially we will provide a ‘build kit’ so we can get some hardware out there in the field and get keen teams testing it as soon as possible.

At the very least, we’ll be running the system on Electric TubeOfGlue (the weChook racing team’s development vehicle) for the season if no other teams are interested!

Please get in touch with us on the greenpower forum (http://www.greenpower.co.uk/forum/discussion/3398/introducing-project-echook-nano#latest) or on Twitter (@Ramjet_gpt) if this is something your team would be interested in having or even being involved with. We have captured our ideas here but it would be great to hear from others on what is most important to their team.

Best Regards from the team, Matt, Ian, Rowan and Ben!

eChook Nano Schematic

eChook Nano Schematic

weChook Racing: International Final Day 2

Day 2 started with a nice lie in. The car was pretty much ready .to roll, and with all the running on day 1, we had no real need to go out in practice, giving us plenty of time until 1 o’clock when the F24+ International Final & Corporate Challenge would start.

With the transponder fitted and the batteries nicely charged, we had a good look around the car for last minute improvements to be made – we ended up settling on redoing the tracking (again) and making wheel covers out of duct tape. On of the hardest things in Greenpower is quantifying improvements, but we think the wheel covers must have made a difference – despite being a longer race, our average speed in the F24+ Final was greater than it was in the lap race, and our fastest lap was 2 seconds quicker, despite using a lower amount of power per lap.

We used the ample spare time available to us to watch the F24 race – a particular highlight was Viper dashing of the line and overtaking the pace car before the exit of the first corner – I suspect that driver wasn’t really listening at the driver briefing. A cleverer strategy would have been to hang and get up to race speed over the last quarter of the formation lap, ensuring the race proper was started at top speed.

Seeing as we’re planning a new version of 2galoo’s bodywork before the 2016 season we  decided to give the current edition a bit of a send off, by giving it some additional decoration… with help from my sister who was visiting, and from some of the JLR guys as well. We’d like to hope that Gav appreciated our support!

We <3 Gav (we also <3 Nash)

After another precarious trip up the banking, and a failed attempt to goad Dave Senior into a pushing race to the grid, we lined up in 6th place, behind Jet, Reprobation, F-eV, Bullet and Rotary Racer – all big names! After rather rudely snubbing Nash in our on grid interview (sorry again about that!), the grid was lined up and ready to go.

2galoo shot off the line when the flag dropped, just about reaching 2nd place before the first corner. When the car next came into view from the pit lane, it had been overtaken by Jet 1 and 2, along with Reprobation, and was in close formation with Rotary Racer. We managed to hold them off for the first 3rd of the race, but their lap times held strong when we hit the same mid race dip that we experienced in the Lap Race on day 1.

Probation and REC-349 had both dropped back a fair distance at the start of the race, but began to drag us back in in the last 15 minutes. With time for only 3 laps remaining, both of them caught and overtook Ian up the hill (we really need to look into some lightweighting for the driver) and began to pull away.

We crossed the line with only 4 seconds to spare before the flag dropped, which pushed us into the longest race that 2galoo had completed. It appears that Probation had pushed just a bit too hard to get ahead of us before the end, as its speed dropped significantly as the hour mark passed, and we retook the position – unfortunately REC-349 was just a bit too fast for us.

Across the line!

Across the line!

We finished the race in 11th place overall, and 9th of the cars competing in F24+ rather than the corporate challenge. It was a bit disappointing to finish outside of the points, but we were very happy with 2galoo’s performance, and had a lot of ideas on how to improve our performance for 2016 – both in the car and in race strategy. We also made some good contacts over the weekend, with whom we’re hoping to push on to greater success next season.

The F24+ championship concluded with Reprobation 2 points ahead of Jet, an almighty effort from the Renishaw team to beat a car that still looked untouchable at the start of this season. Driven bettered their previous best ever season performance by finishing the championship in 3rd place, just ahead of the two Bullet cars from Silesian.

Electric 2galoo finished the season in 8th place overall, just behind Minion and ahead of Project E. It was the 3rd highest place new car, and weCHOOK Racing was the highest place all new team. Thanks to building a new car mid season, we also managed to finish 25th with Electric Boogaloo!

Next stop: I’m not sure really…. Goodwood maybe?

An important message

An important message

weChook Racing: International Final Day 1

The end of our first season came up quickly. It was less than a month since Electric 2galoo had been finished, and we’d already taken part in 4 races and finished on the podium twice, leaving us sitting in equal 5th in the F24+ championship, with Rotary Racer.

We arrived at the circuit in good time, and were directed to our garage. We had  great location, in between the Portuguese University, Silesian University and the two teams that had travelled over from America – the now established Team USA with ARES, and the new team from the University of Alabama with Shock.

It didn’t take long for us to get through scruiteneering – we got there just before the queue got too mad! With our final sticker off the season on the car, we were ready for a few laps in practice. After our numerous calamities and failures at previous races, we were keen to put as few miles on the car as possible, so we only completed 6 laps in practice to make sure everything was running smoothly.

We ran the stint as planned, and had minimal drop off, but were not overly happy with the pace of the car, being no faster than Electric Boogaloo had been the last time we had visited Rockingham. In between practice and the race we did some serious fettling – specifically retruing the wheels. Just pushing the car along the ground, it was possible to feel an improvement in how the car was running.

Current log from our stint in practice

Current log from our stint in practice

Once we’d worked on the wheels, we downloaded the onboard logs from the practice laps, to check our current consumption was in a good range. Everything looked good – once the number of laps was announced we did a few quick sums, and realised we could up our power consumption by a couple of amps for the race.

After all that, we still had plenty of time to go for a wander and and chat to the other teams in attendance. The story of Shock, from the University of Alabama, rang true for us – the two guys had built their car in the shed in two months. They’d also got it shipped across to the UK from America, so they were just slightly outdoing us there! The car looked very well made, if not a little large (just like our first car… but Boogaloo wasn’t really well made). We had a good chat about how they’d designed their car, and how to make sure they get to the end of the race.

I accidentally posed in front of the American flag

I accidentally posed in front of the American flag

It got to 30 minutes before the race, so we strapped in the race batteries (not quite our best pair – we were saving them for the International Final on Day 2) and taped on the bodywork. Ian strapped himself in and we wheeled ourselves out to the circuit. Our ridiculously huge turning circle meant we took a bit of an awkward route out to the grid, but we made it eventually.

Ian was very excited for the start of the race

Ian was very excited for the start of the race

2galoo was lined up near the back of the grid for the lap race – only the corporate entries were behind us, but we made a good start and overtook a good number of cars from the flag dropping to the first corner.

The first 20 minutes went smoothly, we were 15s a lap faster than in practice, and we had a very gradual drop in lap time. Half an hour in, we experienced a sudden (and still unexplained) lap time drop of 10 seconds, then spent the rest of the race back at our gradual drop off of about a second per lap. This phenomenon would return to haunt us on day 2, in the F24+ final proper. Regardless, we were reasonably happy with our performance, finishing ahead of cars from Renishaw, JLR and Lockheed Martin, and overtaking Minion on the final lap, as their batteries just gave up before the end. Jet 2, driven this time by Dave, beat Reprobation to the line, but only just, having run very low on remaining power at the end of the race!

12094866_10208138173758411_9055269882491743929_o

PSEM had a difficult time – they spent their last lap going at less than walking pace, eventually making it into the pits after being lapped a number of times. It turned out they’d hit the batteries way too hard, and in doing so had overheated the motor – it was at 80 degrees when i got to it with a laser thermometer, and it had been off for a good while by that point! We had a good discussion about race strategy and using gearing to manage current, before they set off on a marathon upgrade session – they were still in the garage long into the evening when we had cracked on with the beers!

With the end of the F24+ Lap Race, day 1 of the International final was pretty much done for us, so we prepped what we could on the car (That car has been tracked so many times now that we’ve got it down to a fine art) and made sure day 2’s batteries were on charge, before retiring to the campsite, for some beers, food and sleep!