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Simple Trug Kit Car
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Simple Trug Kit Car – winner of the Corporate Challenge 2009
Designed to be the ‘Mirror Dinghy’ of Greenpower to be built from plans, modules or as a complete kit. Available, when developed, only through Greenpower and an alternative to the excellent new F24 metal kitcar.
Chassis - Laminated, moulded, plywood tub using vacuum bagging. Many schools already have the inexpensive equipment required.
Body - Zotefoam Cheap and non toxic. Formed using a radiant heater and easily glued together.
Transmission – Single gear fixed to adaptor plate. Gear ratio can be changed for different circuits.
Electrics – Current limiter to avoid damaging motor and conserve battery energy. LED readout.
Modular Construction – Steering module, rear axle/transmission subframe, rollbar/battery security module. Teams can join these up with an aluminium, composite honeycomb or wooden chassis of their own design and dimensions. Body can be wheels enclosed or wheels exposed.
Designing and building a car from scratch is a tough mountain to climb. It is hoped that in making available the ‘hard to do’ bits, more teams will be tempted to become involved. -
Yes the current limiter will be available. It worked perfectly on Sunday even stopping the car in practice when one of the very old batteries fell below its working voltage. It will help safeguard batteries and motors. It is a small black box designed by Simon Garland which, in addition, gives current indication and incorporates the brake light circuit. Just plug the indicator and the brake light into the unit. If the brakes are used together with throttle the motor will cut out until the brakes are released.
Once again, we don’t want to take the fun away, so hopefully the current limiter will come either as a built unit or as a kit of components for students to solder up.
No idea of delivery dates or cost yet. Suffice to say it will be cheaper than buying new motors. -
Like the idea of the current limiter.....we've got one of Gareth's excellent amps gizmo on board that works a treat but our first driver out saw red mist and totally ignored the LED's and drove round the first hour with all the red LED's flashing drawing over 30+ amps! Idiot. So the unfortunate second driver had to come in very early for a battery change which then compromised the rest of the race having to nurse them to the end which they successfully did, using the LED read out properly. Would appreciate a shout if these become available.
CC -
"old man" .......yeah right, you're as lively as the next ;-)
"Suffice to say it will be cheaper than buying new motors" Big smile :-)
A PCB, plan and component list would be worth a few quid to many. (or even just the PCB artwork)
Need anyone to try out a home build version? -
Chris and Peter
The website Grahame was referring to was the Greenpower A-Z Technical Handbook. There is no magic and there are no secrets. Follow the advice, put it all together and 125miles is the result. We had some energy left over in our batteries, probably enough for another 4 laps. Have another read and see what you can, or didn’t do.
Michael -
When you say you had enough left for 4 laps, do you mean at the pace you were running through the whole race?
If the car were to be geared up to use that extra power in the 4 hours (ie further up the aero curve) would it actualy translate into an extra 10 miles or more like 5, maybe even 2.5?
Josh -
4 more laps at the rate we were using it. We ran conservatively. Hard to say how that would translate if we geared up as that would also depend on the weather on the day. We were carrying a couple of rolling resistance faults and fair to say that had I not been driving, the car would have done at least one more lap.
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In case anyone is wondering, it seems that aerodynamics is significant in all this.
"Gosh".
Great result though, and a great idea. Look forward to the future, again....
RGE -
Chris
I would not recommend anyone ‘bakes’ their batteries. 50 degrees C is not that hot. The A-Z ‘Battery Care’ page says:
DO:
Keep batteries in a warm place (max 50 deg C). You will increase their capacity
Keep the spare set in an insulated container using space blanket or loft insulation. Protect from airflow, wind chill, on the car
DO NOT:
Leave them on a cold concrete floor
I did not see any insulation around the batteries on any of your cars and I guess you probably didn’t charge them up in the airing cupboard at home or insulated them in Quarantine. Sunny it was at Goodwood but it was still cold.
By necessity, notes in the A-Z are brief but the information is all there. Any knowledge I have went into the document. As I said, there are no secrets.
Michael -
Many years ago I contacted Yuasu about the 096/4, so pretty much the same applies to the TT100's.
For every degree above a given point, a battery will gain 0.5% capacity per degree centigrade. So, if you camp out before the final, chances are your batteries will be around 10 centigrade the next morning. If you have a good airing cupboard, and a good box to keep them in, you might get to 30 centigrade = 10% 'extra'.
Batteries have a very high thermal inertia - previous experiments raised the cell electrolyte to 37 degrees, then stored overnight in our 3" insulated box, then raced in uninsulated cars, then boxed back up on the way home and left, box temp rose to 28C then slowly dropped. Does it help? Probably. Should it be allowed? Maybe not. Pain to organises and manage YES.
However, in the interests of a level playing field, does this not count as 'external energy input?'
Admin?
RGE -
RGE
AERODYNAMICS
You are correct, aerodynamics do make a huge contribution. Simple Trug, like the 3 previous Trugs has a blunt nose rising to the front axle line and then tapering to the tail. This gives a nice low pressure area over the cockpit opening minimising drag of the driver. It even sucked off our front number in the CC! Have a look at the 2009 Grand Prix cars. They all have this same shape. Many Greenpower cars are a wedge the wrong way round.
Another advantage is a high internal front rollover bar reducing the height of the rear external one, hence less drag and a comfortable ‘legs bent’ driving position.
WARM BATTERIES
You can only have a rule if you can police it otherwise you invite cheating. The scrutineers can see if ice is being used for cooling the motor and counts as external energy input. Warm batteries and insulation is good practise. Remember 10% extra capacity does not translate into 10% more miles which I am sure you knew anyway. -
Thanks Michael. My only problem is that I needed to have 8 batteries for each car (and we had three) to do the day (Practice, Opener & CC) and there is no place with that relatively high temperature that I can keep 24 batteries on the boil!
FR-2 does have 2" thick foam sides to its battery compartment but not on top, underneath and to the front which is only shielded with a deflector plate. Not sufficient I appreciate.
I do have a 12 volt heated blanket so I'll use that next time.
Thanks for the help.
Chris -
All good stuff. We are re-jigging our digital dashboard slightly after tripping over ourselves in the CC and are looking at the car shape too. Plenty more MPH in the chassis yet!!
RGE -
Hmmm.....stitch and glue plywood chassis, high front roll bar situated at the drivers bent knees, rear wheels supported on both sides.....
Michael you've made me realise the good points in Plume's first car that perhaps I dismissed in projectile!!!!
congrats on an excellent bit of design and engineering.
Tony. -
Tony
It is not actually stitch and glue. The ‘U’ shaped tub is laminated from 2 layers of 1.5mm ply (that only bends in one direction) The sheets are glued using a roller. Having put them together, they are then folded over a Styrofoam mould and held roughly in place with double sided Velcro before going into a big PU bag. The vacuum pump is connected and left to suck out the air for 12 hours whilst the glue dries. External air pressure applies a uniform force over the whole surface just like a vacuum packed piece of meat.
The curvey seat shape is made the same way.
For more information on products, materials and the process see www.bagpress.com
The deep sides and curved sills with 50mm radius make the structure very stiff between the axles. The sills also allow air to escape freely from under the car. Obviously the 3mm skin to the tub is not enough side protection and so a steamed 7 lamination ash hoop runs along the insides at elbow height and around the nose of the car.
Michael -
Supporting the rear axles on both sides in a frame rather than a cantilever arrangement has the following advantages:
1) Lighter 9mm diameter axle.
2) Already in turbulent air from front axle.
3) Provides shoulder roll protection allowing use of helmet wide rear rollbar which means less rollbar exposed to the free airstream and lower frontal area.
4) Better use of internal car space. -
7) can use standard pre-made wheels
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Congrats on the car. I noticed that you mentioned aerodynamics as being a key aspect (amongst others) of the success of the car. I'm interested to know why you chose not to enclose the wheels, particularly the rear wheels seeing as they were mounted in a frame?
and before i forget...
8) can use vee brakes on the rear
9) gives a mount point for disc brake calipers -
Item (2) above explains why, you'd gain nowt. The front wheels have already done the damage, so to speak.
RGE -
The aim was to build a simple and effective car with reasonable aerodynamics, low weight and low rolling resistance. We did not want to use complicated machinery, nor exotic or expensive materials.
The ‘core car’ is designed to be developed. You can fit a gearbox, instrumentation, radios, fairings, alter the wheelbase or track, enclose the wheels, change the shape, colour, what ever you like. We encourage teams to use their imagination but have a starting point of a safe vehicle which is simple to build and easy to drive.
The last thing we want to do is discourage the scratch built cars. If anything we have proved that you can build a competitive, successful, simple car with a standard configuration. -
Have you any price indications for the speed controller/sensor/logger you might be offering? I ask as I'm selling our digital dashboard to a couple to teams who want it, and don't want them to invest in something that does not do what yours seems will, does that make sense??
Gareth -
Gareth
No idea on price yet. As a commercial product it will of course have to include its share of overheads which presumably yours will not. The aim is to make it cheaper than the cost of a new motor. As well as the protection it offers there is a performance advantage. Instead of heating up West Sussex (Goodwood) all that wasted battery energy can be used to make the wheels go round.
Michael -
Some more facts on our Current Limiter.
With a limit of 50 amps, the car was coming out of limit after 35 seconds which would put an unlimited car 170 metres ahead.
To get to 95% of max speed an unlimited car takes 36 seconds. Limited takes 53 seconds.
You lose 17 seconds each time the limiter is in use. At the Corporate Challenge with 1 start and 2 pit stops this cost 51 seconds. This is nothing compared to the extra capacity it gives the batteries all of which can be put into greater speed/distance. -
Currently (groan) you are at the mercy of TSR as Michael is not in a position to price up his current limiter circuit.
TSRs dashboard will tell you what current you are drawing and your drivers can use this to make appropriate gear selections. If they'll sell you one, its a neat bit of kit to have.
Michael's curcuit does this too but, as described above, it restricts the current to below 50A thus prolonging motor and battery life and allowing gentler starting. A neat bit of kit too but I suspect that it may prove costly. More costly than a fresh motor per season? Probably not. -
Spot on SKS, all it does is show you how much current you are drawing and then IF you can do something about it (change down/up a gear or changes a sprocket after practice) it helps you get there. It has worked sooo well on TSR-4 (up until the corporate challenge when some/all drivers must have pushed the upper limit) that we don't bother logging the car anymore, but NOW WE WILL to find out who does it!! Some of the lap times were clearly a bit too enthusiastic which cost us a place or two. 4 should have beaten 2 and they both should have gone further than they did. On a good day it helps you hit the available capacity spot-on but it does rely on drivers doing as they are told by the dash board. Can also double as the sensor for a data logger (picaxe one) and that basis is really that it can be understood and adapted by the team. Could be used for battery capacity testing, all sorts really, with just a few lines of basic code per application. Ideal extension task for a team member.
Electroads gadget will be in a different league and does something similar (measuring current draw) but is more advanced as it includes at least a speed controller/pwm and ????
RGE -
We have used TSR's digi gear for two seasons on FR-2 + Rohloff with success and would highly recommend it (but as experienced by Gareth's team, someone was mesmerized by the pretty red flashing lghts and didn't back off with the expected consequences!) We are fitting the same to the new FR-4 which will be running with a NuVinci. Car nearly finished.......but it's a bit big! I got into it no trouble and I'm 6 ft and not that svelt! I designed it with a view of getting the team mothers interested in driving for the Corporate Challenge but it wasn't ready in time. Got a queue forming for the 2010 event though!
CC -
Love the idea of the mums racing! We're working on something similar for our new car to both of the above with perhaps some new features. If it turns out okay after this season, we might consider selling to raise new funds - not much more info I can give atm I'm afraid but just to let you know.
pb -
We are very sorry but despite hundreds of hours of work, the current limiters are still not available. At the moment they are commercially unviable and the circuit is now being redesigned. They will not be released until we are satisfied that quality and reliability is assured.
Michael -
If you can scrounge a vacuum pump you can use thick plastic sheet made into a bag with gaffa tape, that's what I use it's very effective. I just push the vacuum pipe into a corner and seal with tape once it starts to be evacuated it self seals to some degree.
About to mould a new seat so I'll get to use it again with plywood and polyurethane glue.
Ashley
