Electric racing car update

R

Rickharris

Senior Member
OK took car out today for the first time under load. (and with student drivers)

RAF Scampton kindly loaned 4 schools a bit of thir air field for the day. about a half mill course so not long straights to gather speed but good shake down and practice for the kids.

The car ran exceptionally well - of the 4 we were the only car to have zero mechanical or electrical problems and it just ran all day straight off the trailer. (Good engineering - perhaps!)

Even though we changed drivers 12 times in the 4 hours and they were slow at first to get them out and back in we managed about 30 miles (had time off for lunch and strip out batteries measure voltage and replace just for the practice. So didn't do badly.

The leader table suggests if we can crack 50 miles in 4 hours in the real race on Sat 15th Sep we will qualify for the finals in October.

Missed instruments though - no time to get together after return to school too busy trying to just get things into a running condition. Hopefully for next years or perhaps the final if necessary we can get a basic instrument set together. (Looking forward to seeing the offerings from various people now that we can post pictures)

Only used a single set of 2 batteries and by the end they were very tired - measured 12.01 volts on one and 11.8 on the other when we got them home should have checked when we stopped as I wanted to know if they recover after resting but forgot. On charge now ready for Sat - Commercial charger - seemed easier in the long run.

Motor never got so hot you couldn't touch it - but did get uncomfortable to keep hand on it after running for 30 - 40 mins. Will try to arrange some form of water cooling for the race if have time.

One very impressed engineer.
 
S

sevs3

Member
Nice!!!

Nice work Rick. Some pics would be great! We also ran our car for the first time with the motor this week. only reached about 17kms though (This was a 1:1 drive for testing), but we have a plan being drawn up to reach 45km+. I dont think we will be able to run for an hour though :p
 
B

boriz

Senior Member
Some thoughts:

Drag, current limiting and regenerative breaking.

The wiring, and the motor coils, and the battery itself lose energy to heat when the current is high. Limit the current to improve efficiency. It may result in slow acceleration but will pay off in the long run. Keep the current and aerodynamic drag right down and then all you need to worry about is losing energy to breaking.

If you are using PWM, limit the duty. Try 40% limit, then 60%, then 80%. See which performs best on the set course. If mostly straight with soft bends, then 40% is prolly best. If small course with many slow corners than maybe 80% is best. The limit must be adjustable so that you can ‘tune’ the car for the course.
 
B

BeanieBots

Moderator
Capacity meter.

Rick, I've completed & tested the simplified capacity meter.
Only requires 08M + 1 op-amp no critical components and no shunt resistor.
It's good for about 3% once calibrated and setup which is more than good enough for your needs. A little fiddly to setup but that's the price for a simple circuit.
It uses a 1mA FSD meter as the display so looks just like a fuel gauge.

Problem is, I can't get a legible filesize that this forum will accept.:mad:
Interestingly, pdf gives the best results so far. MUCH better than gif or jpg.

It's getting too late in the day now but I'll try and do a circuit description and comment the code some time tomorrow. If all else fails, then back to hosting sites :(
 
B

BeanieBots

Moderator
Rick, I've posted full details for a capacity meter in the Projects Misc folder.
It should be ideal as a 'fuel gauge' for your car.
 
R

Rickharris

Senior Member
First Race Over

BB excellent, many thanks I'll get on to that later this week.
In the mean time we have (I think for a first time out) done quite well in our first race Yesterday (Sat 15th)

My expectations were if we finished 4 hours we would have done very well indeed - we did better!

The Thursday practice went well - of the 4 cars we were the only ones not to have mechanical or electrical troubles during the day - ALTHOUGH - when we got the car back to the workshop we found that the drive shaft securing screws had worked loose and the shaft was all but falling out (OUCH) must buy locktight.

So Friday spent stripping the rear end down and realigning it ready for Sat.

The car passed the inspection on Sat OK and the race started well. We were remarkably consistent throughout the race in terms of speed. 3 Laps in a girl slipped the drive chain and tried to park on the edge of the track - Problem was the edge is banked and her car fell over - she put out her hand and fractured her arm it seems - she went to hospital but was back by the end of the race arm in sling and all :)

Race stopped for 10 mins whilst Ambulance took her off the track.

I calculated the day before we could do perhaps 60 miles on 2 battery sets and would need to do between 45 and 60 miles to stand a chance of qualifying for the final.

In the lap timings - apart from the first session which was spoiled by the accident we consistently lapped 6 or 7 laps per 30 mins apart from battery change period that dropped 3 laps (need to sharpen that process up), We were placed mid field (in 26 runners about 2/3rds of them had several years race experience), throughout the race. It seems the race was somewhat slow even for the leaders who have all produced much better times about +20% at other tracks - the track isn't totally flat and there was a stiff wind blowing directly up the straight which may have affected things but it was the same for all of us.

We complete 45 laps - 67.5 miles to finish 11th out of 26. NO mechanical or electrical problems during the day at all just a bit of bodywork loss fixed with gaffer tape at the next stop. The motor ran exceptionally cool with just a jerry rigged heat sink and good air flow - we cut the sides to make a couple of air scoops - I guess that didn't do much for the aerodynamics either - A cool motor indicates 1. you are not pushing it, 2. A well balanced and free running car 3. Good driving discipline.

I think a body rethink in better materials will add perhaps 10% and a bit calmer would also help, may need to look further at aerodynamics in more detail as well.

This means we may qualify - They say the top 10 from the race should go through and that we were right on the cutoff line. There are 2 more races to go before the final so fingers crossed My best guess from the leader board at present is that there are 23 other cars above 67.5 miles and 36 places so that leaves 13 left to take unless the other races performance is exceptional we should get in. We will know better next week.

Obvious tactic - find the fastest track and compete there! to push up lap numbers. because all tracks are not equal some cars effectively have a penalty from the track they race on.

Race photos here http://picasaweb.google.com/rickharriss/GreenpowerRace07 we were number 4.

Overall we can improve things with the platform we have. When we start to push the motor we need instrumentation to monitor the situation (thanks BB) - We need to push up top speed to nearer 30 mph - Max speed attained 26.5 Mph, average speed over 4 hours with 6 drivers + changes etc 17.6 MPH distance covered 67.5 miles. peak speed and ave speed from the cycle computer Uncalibrated so may be a little out but not much.
 
B

BeanieBots

Moderator
That's excellent for first time. Well done Rick and well done to your drivers.
Interesting about the motor not getting too hot. Would suggest that you can push harder. There are some major improvements you can make on the car which have already been covered so I'm expecting exceptional results from you next year;)
Keep us posted and don't forget to play the rules as well. You've already spotted the trick about picking the track to race on. The information you bring back from this event will be worth gold to you next year so make sure you note everything even if it seems trivial at the time.

A quick not about battery recovery.
Did some test a few days ago on 38AHr SLA units.
Discharge down to 12.2v (I'm kind to my batteries)
After 1 hour recovery, <1% extra.
After 24Hrs recovery ~8% extra.
Not something I would bother including in the equation.
 
R

Rickharris

Senior Member
BeanieBots said:
That's excellent for first time. Well done Rick and well done to your drivers.
Interesting about the motor not getting too hot. Would suggest that you can push harder. There are some major improvements you can make on the car which have already been covered so I'm expecting exceptional results from you next year;)
Keep us posted and don't forget to play the rules as well. You've already spotted the trick about picking the track to race on. The information you bring back from this event will be worth gold to you next year so make sure you note everything even if it seems trivial at the time.

A quick not about battery recovery.
Did some test a few days ago on 38AHr SLA units.
Discharge down to 12.2v (I'm kind to my batteries)
After 1 hour recovery, <1% extra.
After 24Hrs recovery ~8% extra.
Not something I would bother including in the equation.
Click to expand...
That's interesting a number of teams put used batteries back in and did a few more laps, as changing a battery set took about 8 to 10 mins you loose at least 1 and perhaps 2 or 3 laps whilst stationary.
I could only conclude that they had changed their initial set early as performance dropped and were now recovering the last dregs.

A couple of battery questions that arose from the day:
1. Why do they recover - it suggests mechanical changes as they discharge.

2. Our batteries performed very well - 2 in series driving a 24 V motor. BUT the dropped off from driving at something like 17mph to a crawl in as little as half a lap - very sudden. On measuring voltage off load they show 11.08 volts or there about. It looks as if their current supplying ability declines abruptly but why - internal resistance?

Their voltage wasn't a lot better this morning after standing in my garage overnight either so not much recovery there!
 
B

BeanieBots

Moderator
Sounds like one of them might have a dead cell:eek:
11.08v off-load strongly suggests it was taken too low.
When a battery is forced to exceed its maximum possible current (or gets reversed), it produces gas on the plates which acts as an insulator pushing up the resistance very rapidly.
If this happened, it will almost certainly have vented and lost electrolyte and hence capacity. Besides doing a capacity (or "drop") test to find out, you should be able see tell-tale white residue around the vent caps. If there is any, the battery should be replaced for competitive use.

Recovery is a function of their design and will differ between types. Thicker plates, as often found in deeper cycle designs will recover more due to the time it takes to diffuse to deeper levels. It's all one big balancing act.

Oh, and don't leave them in that state in your garage overnight:mad:
It won't do them any good at all. A deeply discharged lead acid battery will sulphate very quickly and add to your resistance problems.
Also, take them off-charge at least one hour before use. A full battery has a slightly higher internal resistance than one which has had its surface charge removed (and associated gas). Try it. Take a full battery off the charger, put on a heavy load and watch as the voltage drops initially and then actually goes up after a few minutes!

For the race, give the driver full control but for testing I would recommend having a minimum volt cut-out to preserve the batteries. This could be set quite high at around 12.0v to start with. Don't forget, in series the battery is only as good as the weekest cell.
 
R

Rickharris

Senior Member
All good points I will take heed - The batteries went on charge that night - well one did they have all been charged now and will keep them on a cyclic trickle charge.

Our position has be changed slightly we officially did 73.5 miles and are 41st out of 127 so should qualify for the final.

Now to get the capacity meter working :)
 
B

BeanieBots

Moderator
Well done:)
Quick thought about the capacity meter.
You don't actually care about correct ampHour rating, just how much % left.
So, don't bother with the rather painful calibration process.
Just hook up a counter (I found the free Kellogs 'walk-o-meter great) to the PICAXE 'reset' output and count the pulses under race conditions until battery is "flat". Then just scale that number to give FSD PWMout value.

Alternatively, get the PICAXE to record it in EEPROM with a little progette to download the number later.
 
R

Rickharris

Senior Member
We are in the final

Updated position:

We qualified for the final at Goodwood 14th October. The 1st, 2nd, 3rd of each regional heat (12 heats) go through automatically, the next 36 go though on the basis of the mileage they do in their best heat. We managed 73.5 mile and came 12th in the mileage race (41st overall out of 158).

We have qualified 48th in total. So currently rebuilding the body work to try to be a bit more slippery, trying for some more sophisticated instrumentation if we have time (thanks to those who contributed) and generally trying to make sure the car will complete the 4 hours in the race.

Watch this space! :D
 
P

papaof2

Senior Member
Minor "slippery" suggestion - wash and wax the body. It will be smoother and might help a tiny bit.
John
 
R

Rickharris

Senior Member
papaof2 said:
Minor "slippery" suggestion - wash and wax the body. It will be smoother and might help a tiny bit.
John
Click to expand...
We are working on 2 parallel concepts:- The bamboo and rip stop nylon shrunk tight and doped for a sharp crisp finish.

The aluminium sheet version of what we already have.

The original bodywork was PVA glue and wall paper for speed of build but with almost 3 weeks in hand we should be able to get slipperier.
 
R

Rickharris

Senior Member
Dippy said:
Putting the driver on a 2 week starvation diet would help more.
Click to expand...
How very true - the driver weights were all pretty much the same as were their lap times - showing around 17 to 18 MPH on average over the 40 mins.

We have 2 reserve driver who we promised a drive if we got to the final but they are both somewhat chunky - why? well 7:30 in the morning - in the school minivan - filling your face with chocolate biscuits because "they are nice"!. Oh well a bit of Formula 1 driver training called for I think.

Question 1 - can you get out of the car unaided in 10 seconds - if not you can't drive.
 
J

joe of loath

Member
ah! i assume this is for greenpower? congratulations on your excellent placing! i'm from team "R"podS (8th on the leaderboard, at the final just look for the weirdest car there. ;) )
was this your first attempt at racing this year? if so brilliant! you finished ahead of one of our veteran teams.


just a few minor pointers,
lap times are more a driver skill thing than driver weight, as driver weight is only a problem accellerating, we foun that my lap times where ok, (i'm the heaviest driver), and our best lap for a few races was by our 3rd biggest. now however, as our newer drivers skills improve, our lightest driver has the best lap times.

good to meet someone with similar interests however!
joe
 
T

Tom2000

Senior Member
Howdy, Rick,

I just read your insrtructable and the comments to date. (Thanks for the link, Jo C!)

Thinking about the comments about centrifugal clutches... I'm not sure your vehicle needs one, but the mention gave me an idea.

You mentioned that you're using an on-off motor control, and that when off, the motor provides a lot of drag.

From all of those, I thought about an overrunning clutch, something like you might find in a bicycle's rear hub. When you "unthrottle," the car would freewheel, without the motor's drag slowing you down.

I don't know where to find a suitable assembly, or even what to look for. I'd suggest actually using a bicycle hub, but I don't think one would handle your required torque. But you might prowl through the catalog and consult your experts. Maybe there's something suitable available for not much money.

Good luck in the next round!

Tom
 
R

Rickharris

Senior Member
joe of loath said:
ah! i assume this is for greenpower? congratulations on your excellent placing! i'm from team "R"podS (8th on the leaderboard, at the final just look for the weirdest car there. ;) )
was this your first attempt at racing this year? if so brilliant! you finished ahead of one of our veteran teams.
Click to expand...
Thanks =- Yes first year the car is a basic seagull kit as we were sponsored by e2v to build it. Next year we should have a custom car and a much improved seagull as well.

Saw your car - I find it difficult to believe you get such a significant advantage from the pod body - but then again you are well in front of us :).

We spent quite a lot of time discussing driving skills and approaches our drivers were very consistent - hopefully as a result.

I have plans for
a) free wheel
b) gears
c)electronic (picaxe of course) speed control. we shall se how it works out.
just a few minor pointers,
lap times are more a driver skill thing than driver weight, as driver weight is only a problem accellerating, we foun that my lap times where ok, (i'm the heaviest driver), and our best lap for a few races was by our 3rd biggest. now however, as our newer drivers skills improve, our lightest driver has the best lap times.

good to meet someone with similar interests however!
joe
Click to expand...
Our driver size problems are actual more to do with fitting in a very cramped space but we will squeeze him in some how :)

See you at Goodwood will you be at the Hog roast?
 

Attachments

Last edited:
R

Rickharris

Senior Member
Tom2000 said:
Howdy, Rick,

I just read your insrtructable and the comments to date. (Thanks for the link, Jo C!)

Thinking about the comments about centrifugal clutches... I'm not sure your vehicle needs one, but the mention gave me an idea.

You mentioned that you're using an on-off motor control, and that when off, the motor provides a lot of drag.

From all of those, I thought about an overrunning clutch, something like you might find in a bicycle's rear hub. When you "unthrottle," the car would freewheel, without the motor's drag slowing you down.

I don't know where to find a suitable assembly, or even what to look for. I'd suggest actually using a bicycle hub, but I don't think one would handle your required torque. But you might prowl through the catalog and consult your experts. Maybe there's something suitable available for not much money.

Good luck in the next round!

Tom
Click to expand...
Spot on - see above post - Problem I foresee are bike chains are fairly weak under extream stress - as an HPV rider I have broken several. BUT I see a free wheel as an advantage as boost and coast is the way the shell eco-marathon drivers get such high MPG.
 
J

joe of loath

Member
awnsers to a few questions up there: yes a bike chain will do for f24 but not for formula catapult (our half inch industrial chain only just stood up to the snatch of a starter motor),

a bike freewheel works well, and you can attatch it to the gear hub on the drive wheel.

and we have to haev the double-pod construction because otherwise i wouldn't fit in with the batteries and motor behind me (i'm 6'6" and with a season of f24 to go :) )

and we found actually a speed control can be quite lossy (not sure about custom ones). as long as you have some gears there's no need for it.

if you need an explanation just come and have a look at "R"podS at the hog roast :D... oh one of our team members made quite an interesting picaxe instrumentation box thingy that gives you speed, battery voltage, motor draw and motor temperature. just ask for alex and he'll tell you some stuff (but its not in the car yet because he keeps having to show it to important people). and i think one of our other teams, rotary racer has a picaxe speed control in their car. look for car number 9.
 
Last edited:
J

joe of loath

Member
congratulations on your performance at the final! i spotted a few of your team members in the pits... but alas, i think i missed the car. (too busy prising myself out of the side of ruby in the streamliner race)
 
R

Rickharris

Senior Member
joe of loath said:
congratulations on your performance at the final! i spotted a few of your team members in the pits... but alas, i think i missed the car. (too busy prising myself out of the side of ruby in the streamliner race)
Click to expand...
Thanks:

We had a puncture in the first half an hour that cost us 30 mins to change the tire - If someone can tell me how a drawing pin gets onto a race track I will be very interested, the tire was OK at the start - then some driver problems caused us to run the first set of batteries flat on the track (the driver missed the pit entrance) so we lost more time in waiting for the recovery - STILL we finished and weren't last (62 provisionally ) but I think we lost perhaps 20 miles.

According to our instrumentation we did just over 62 miles in the 4 hours.

Roll on next year.

Picture of the improved body below.
 

Attachments

Last edited:
C

Coyoteboy

Senior Member
Hehe good results!
I'm fairly sure that if you get that body better shaped you should see some gains.Take some hints from the world speed record recumbent bicycles - they've been refining them for a long time.
 
D

D n T

Senior Member
Electric cars rule

Rick, with regard to gears and bike chain.
We use standard racing bike/ moutain bike 7 speed clusters and the bike chain handles it, although you have to allow about 500mm between centres to allow the chain to swing the full range of gears, vary the drive spocket to vary speed range of the gear cluster. Remember that the smaller you sprocket the faster you get to your top speed but that top speed will be lower than that of a larger drive gear with the same cluster, although, with a larger drive sprocket you will take longer to get to the top speed. On the track you have shown you are probably better of using the larger sprocket because it seems you have a long flowing track that you can let the motor wind out on. Remember to keep the motor revving in its optimal range to be most efficient.. You probably already know that.

Hey SEVS are you ready for the EV challenge in a couple of weeks?? What is your team name I will look you up on the day.
 
R

Rickharris

Senior Member
Thanks for the information - we certainly lack top speed - there was a speed trap at the start finish line - we crossed registering 33 MPH the lead car 55MPH !!

Aerodynamics allow the motor to be lightly loaded and so can be run harder so we intend to raise the gearing slightly to give a top speed of 35 MPH on this car and us it for the starter drivers next year and build a lighter, much more streamlined car for the real contest next year -

The way I see it gears will only be useful if there is instrumentation to be able to use them to the best advantage.

In all fairness we did meet our target which was to finish. Next year we would like to be in the top 3 for one of the heats and finish in the top 10 in the final.

Shell eco marathon cars also have some important messages to follow. The rules for green power forbid a covered cockpit so some aerodynamics have to be compromised.
 
R

Rickharris

Senior Member
Mmm we debated that 55 looked a bit quick. Their lap record at 4 min 2sec says an average speed of 34 mph - I should have worked that out before!

Our average speed of 21.4 is just on the expectations for a standard seagull. Suggesting that apart from punctures and driver errors we should have done 85 miles - Durn it!, We could have won a prize perhaps.
 
R

Rickharris

Senior Member
Rickharris said:
Mmm we debated that 55 looked a bit quick. Their lap record at 4 min 2sec says an average speed of 34 mph - I should have worked that out before!

Our average speed of 21.4 is just on the expectations for a standard seagull. Suggesting that apart from punctures and driver errors we should have done 85 miles - Durn it!, We could have won a prize perhaps.
Click to expand...
Video of finals http://uk.youtube.com/watch?v=Gjb5zmvsZf0
 
Last edited:
S

sevs3

Member
D n T - Were you at the scrutineering last sat? We had a big problem friday before scrutineering, where our motor controller decided that it wanted to try and cook everytihng :S It has been a mad rush to construct a new one, and im glad to say we will be running a picaxe motor controller. I just got it working last night so i will be rushing out to see if it can handle the power of the motor we are running. What category are you running in? We are in the Yuassa, so first race. Just look for a car that looks like this: http://www.alroh.com.au/media/frontpage.jpg :p

I have to say Rick that your new body looks schmick and im very impressed at your distance!!! I dont think our car will run for the full hour that we have to go :p For gearing, have you seen the shimano internal gear hubs? search nexus 8 on the shimano website. Only thing ive found is that they seem to have a high rolling resistance... I do recal reading that they are quite efficient on a forum, but then who knows what test the people were running...
 
M

moxhamj

New Member
LOL sevs3, that 'electric' car should easily max out at 2KpH and will also ensure a lovely smooth track for those in the next race!
 
You must log in or register to reply here.
Top