HELP with racing car nstrumentation

#41
sedeap, we appreciate that you cannot give away the secrets of your friends invention, but could you give some data?
We all know that there is no such thing as a "free lunch" so where is the catch? Static electricity is generated by friction literally ripping off electrons. To do that requires mechanical power. Hence, does this collection method add to the vehicle drag and if so, how does the increased drag compare to say adding a generator to a wheel?
 

sedeap

Senior Member
#42
:::::::::::::::
BeanieBots:

Unfortunately that isn't my field of Specialization, but as I understand, the Air (and the dust or polen in it) passing over this surface do the magic when the object is in movement. Not good enough for static devices i think.
That surface probabily be rugged enough to "catch" more friction, but look like pretty flat at naked eye.

The whole process is under development and testing right now, but I think the tricky part is in the duty cycle of the coated surface, and the average speed of the air to make it work, obviously the whole surface must be isolated from the ground, and direct sunlight pull up the power collected (perhaps due to doped Polivinyl) like one low power solarcell.

The entire project is based on Tesla's discover, about "Cosmic rays antenna collector", "Radiowave electricity", and "Low electromagnetics fields close to Ground dust of the Earth", "Air dielectric capacitor". as my friend says.

This sounds like drunk chinese to me, but he's involved in that and becomes rush excited when talking about it.


:eek:)
 
Last edited:

D n T

Senior Member
#43
Rick!! lets chat.

I run an EV team at my school and am the electronics nerd behind two other teams.

Our instruments have previously consisted of a bike speedo and an amp meter, however, that is not enough and I want more technical anyway.

Enter PICAXE stage right!
I am currently working on a Program/ circuit to read, calculate and display:
Amps, Average Amps, Motor temp, as well as send all this out to a waiting pit crew and pit chief sitting around either another LCD or a laptop.
Amps - what the car is using right now, hall effect from allegro or honeywell
Average Amps - what has been used through out the race, allowing an optimal average to be maintained to ensure that your batteries are used at the best drain rate
Percentage throttle- mainly because4 I had some space, although I want to replace that with,
Gear- Yep, we have 7 speeds to keep the motor reving at its optimum.
Motor temp- be cool, go better, thermister in motor casing

Gears are for accelerating, cruising( behind a slower competitor while waiting for a passing opotrunity), or going into a corner and being ready to power out of it.

Cooling the motor.
Can you get a thermal syphon going?
Can you mount a fan on your vehicle to drive a small pump using the air flowing past your vehicle, it could be argued that the power from your batteries is making the car move and the fan attached to the car would not move if the car was stationary.
Use a large aluminium plate as a "rear spoiler" and mount the motor to it, ours hung under the car and the air flow kept it and the motor noticably cooler than without it.

Make the car big enough for you to ride it, it helps in motivation, I built my own and Im addicted to the whole EV thing, as soon as the council build paths all the way from my home to my school, thats how I'll be going to and from everyday!!

If any of the above is of any useful, email me and I will send you the program and cicuit to date, I need some help[ on it if you like to share. I'm not going to post it because some oif my competitors have been know to visit the worlds foremost pool of PICAXE knowledge as well.

golsson@student.ecu.edu.au

Have fun!!!


Edited by - D n T on 13/07/2007 11:19:54
 

bcj

New Member
#44
Hi, been watching this discussion with interest.

Am intrigued by what appears to be the assumption that you will be best to accelerate to speed as fast as possible then hold that speed. I also note the comment that if you draw a high current at the beginning of the discharge you effectively reduce the overall capacity of the battery.

I would have thought you would have been best to accelerate slowly and steadily at a controlled current drain thus conserving the total capacity of the battery. Using this approach you should be able to reach a slightly higher maximum (and sustained) speed.
When all is said and done what you really want is the highest average speed over the entire 4 hours which does not necessarily mean reaching any particular speed quickly.

This approach may also enable you to use lighter duty components in some areas thus conserving weight - currents are lower, transmission does not need to handle as much torque etc.

Edited by - B C Jones on 13/07/2007 12:06:57
 
#45
B C Jones, you've almost answered your own question but you missed a crucial bit out which is "with the power available".
Ramping up to speed takes time, to get that time back means having to go at higer peak speed. Higher peak speed means lower efficiency. Lower efficiency means having to reduce speed (for the same number of joules)which in turn means longer time taken over entire distance.
Getting to speed quickly and then holding is a very well tried tested and proven technique. Things get a little more complex with hills and sharp bends but the overall principle stands as firm as following the "racing line". Only digress from optimum when you have to, eg overtaking.
 

bcj

New Member
#46
Somehow I got the idea that a higher drain at the beginning would reduce the overall capacity but perhaps that is just my interpretation and not what was meant.

I agree that getting to speed as quickly as possible and holding is ideal if you don't have a finite capacity - e.g. in regular petrol engined racing. But in a petrol engine, moderate acceleration and a higher top speed is more fuel efficient - now I fully appreciate that electrical systems have different characterisitics (and most importantly efficiencies) than petrol engines but would have thought the same general principles would apply. However with a fixed capacacity anything that affects that total capacity is detrimental. Accelerating hard is also potentially inefficient. If over 4 hours the average max is only say .1 kph higher to make up for the slightly slower acceleration then that may well be an overall gain as the losses due to drag etc would be minimal as the speed differential is minimal.
I have not done the modelling that you obviously have so I will bow to your greater wisdom in this matter but stand by the fundamental that however the car is driven must be to attempt to acheive the highest overall average speed for the full 4 hours with whatever resource is available.

Edited by - B C Jones on 13/07/2007 13:53:09
 

D n T

Senior Member
#47
More thoughts:

Rick, I looked at your pictures, if you use larger wheels you will have less revolutions/ given distance, although you will need to used more grunt too get them moving.
Our vehicles use 26" diameter BMX wheels with a diskbrake mountain bike hub spoked in at the rear and wheel chair hubs at the front ( three wheels) and the drive line used all bicycle gears chain and derailers. The gears mean that other than the initial take off the motor draws less than 12 amps, usually about 8, changing gears at 5 amps.
The initial burst of high power doesn't blow a 20 amp fuse if the driver applies full throttle then zero throttle then full then zero ( manual PWM) with about two seconds between full throttle. I had to train the drivers to accelerate moderately and not try to "burn off" the other racers. Another thing we use is starting at the back of the grid. By doing this the driver can either coast behind other cars and save energy ( slip stream) or pull out and get by when it is safe to. Doing this ment that we got lapped once early on by two cars, but they died out before the end and we cruised on by, one of our other drivers infact dropped pitted and dropped of a drink to the driver while he waited for assistance.
I don't know if you have CRC brand products over there but they make "CO contact cleaner" electronic claening solvent. If you are allowed to carry it onboard, plumb it in using the little straw and some fine copper tubing(automotive oil pressure gauge pipe)so that the driver can use it in an emergency to cool the motor and douse the motor in it at the pits at battery change if you are overheating too much.Just a funny foot note: Some of the student spectators on the test days wanted us to "put NOS on it" ( too much fast and the furious). Because I "know some people", I got a little bottle of it as a favour and connected it up. "FULLLY SIK"
It didn't help with combustion but it did work well running through a coil heat exchanger on the motor and out the back of the car. Some people thought it was funny, or was that just the gas? It cooled the motor down, not to mention the red can of cola that the tube wrapped around before the motor, a chilled beverage holder, just what you need on an endurance race. Anyway back to it.

The construction of the motor. How thick is the outer casing? can you pull the motor appart, put the outer casing in a lathe, use a parting tool and cut grooves in it to increase the exposed surface area of ther motor for cooling? This would increase the contact surface area for the copper cooling tube you are using as well.

We found that the best thing to modify is the way the students percieve that the car should be driven. Once they knew how to drive by the amp gauge they were lasting longer and changing gears better to keep the draw at the most acceptable level.

email me if you like, see previous post.

This is the website for the race We are involved in.
evchallenge.swantafe.wa.edu.au/


Edited by - D n T on 13/07/2007 14:12:52
 
#48
<BLOCKQUOTE><font size=1 face=arial>quote:<hr height=1 noshade>
1) What you want for this year
2) What you'd like this year, but can do without
3) What can wait until next year

Things can be bumped up ( and shunted down ) according to progress.

Of what you want this year, determine what are the priorities -

1) Need
2) Want
3) Would like

Choose one or maybe two projects and throw them to the wolves to attack. I'd consider each instrument as its own project even if they do use the same inputs or control the same outputs. Get them working then integrate later. <hr height=1 noshade></BLOCKQUOTE></font><font face='Verdana, Arial, Helvetica' size=2>

Sorry I haven&#8217;t replied to all of you&#8217;re really good answers, and I am very grateful for them all. With the end of term coming up I have been a little bit busy.

Hippy has a good point, I think that for this year we need to concentrate on the essentials:

I think that the essential instrumentation we need is-motor current, battery capacity (perhaps measured as a voltage level at which we need to change the battery), motor temperature. I think we will measure speed by using a bicycle speedometer.

Battery state and motor temperature are critical to us to avoid trashing either of them (both expensive components to replace).
From all of the discussions that we have had I conclude that the most important feature from a design point of view is to reduce aerodynamic drag, when you look at previous winners you can see that they are all very smooth and Aerodynamically efficient.

Although there are cars in the top 10 but have made been made less aerodynamically.
Because of cost restraints we cannot run the batteries until they are dead-I guess that this limits are lower voltage to around 11 volts. This seems something that we can measure very easily using ADC and make a suitable display. It is very difficult to get students to read instruments accurately. They do respond however to green yellow and red lights, so I think they are large led display is most appropriate. That is: yellow light-things are getting bad, red light-come into the pits.

I guess that in the pits we can measure the offline voltage and make some assessment of the battery condition when we change drivers. Unfortunately we have not the time to do extensive testing at this stage. For our first race I think we will have to see just how we do with the minimum. We can then plan for next year with a better idea of what we&#8217;re up against.

Would like for the future more sophisticated battery charging control and instrumentation showing battery condition

PWM control as an alternative, perhaps automatic cruse control monitoring motor current/speed to give optimum performance with little input from the driver.

I see the driver as just responsible for steering the car.

Telemetery so the pit crew can see what is happening, perhaps burst downloaded as they pass the pits.

Communications with drivers.

Simple to latch on/connect up instruments that give diagnostic information in cases of problems in a race.

Nothing too difficult! <img src="smile.gif" width=15 height=15 align=middle>

But you did suggest a wish list.

Edited by - rickharris on 15/07/2007 08:30:19
 
#49
DnT Thanks for your offer to help - much appreciated.

We are very restricted, unable to open motor or modify in any way. Even the battery pack is supplied.

I expect to cool with water in copper pipe, do you use heat sink compound to improve thermal efficiency? I gather a lot of schools just spray water onto the motor casing (it is sealed). I was thinking I could wrap the motor in steel pot scourers to increase the surface area and trap some of the water to aid cooling.

I think we will draw the line at NOx :) It seems the rules prohibit the use of any cooling method that has used external energy , we can get freeze spray over here that gets to -26 deg C - seemed like a good idea.

It looks like your rules (or perhaps ours) are very similar although you have more freedom.

If you teach DT in Perth, (and this is a long shot), do you know Graham Coulson? He taught at out school for a while a couple of years ago but hales from Perth and teaches there.

Edited by - rickharris on 15/07/2007 08:35:02
 

D n T

Senior Member
#50
Rick,
Ive got some stuff you might want to have a look at ( current measuring gear etc).

Do you have crocodile clips and/or AutoCAD??
because most of it is in these formats

Most importantly, if you drop me an Email I will know were to email you, I might even use the education department email system if it will let me on.
I'm : golsson&quot;AT&quot;student&quot;DOT&quot;ecu&quot;DOT&quot;edu&quot;DOT&quot;au.

Its my old uni email because the ed dept is so tight on what it will let you open that its useless.

IMPORTANT NOTE:
Be careful with your steering levers, we used a joystick steering system and found that the lever was cracking and breaking on the pivot point, we solved the problen by sliding a piece od soild aluminium round bar inside the tube and re drilling the holes. This stopped the steering snapping off when students paniced and pulled the stick back to stop instead of applying the brake. Using your steering system a paniced driver might pull on both bars and have problems.

Catch you later.

Edited by - D n T on 17/07/2007 17:11:38
 

womai

Senior Member
#52
One point that barely got touched (not instrumentation related, sorry) are the wheels. In general, larger wheels have smaller road resistance, so you want to use the largest wheels that are allowed. Also, I'd minimize the width, so if there is any chance road racing bicycle wheels can carry the weight, go for them instead of what you have right now (I weigh almost 100kg and by racing bike wheels had no problem with that for 15 years, so with your 4 wheels your total vehicle weight could be at least up to 200kg. Inflate them as hard as you can though). If you are not convinced, try racing a road bike against a mountain bike...

So in short, go for large, narrow wheels instead of the small, wide ones.

Second, Dr_Acula is right on saying that trying to go use a speed that allows you to go exactly 4 hours is the optimum strategy. Going faster only wastes unnecessary energy in wind resistance. It goes up quadratically.

So if you had only wind resistance and could go 4 hours at 10mph (40 miles total distance) until the battery goes flat, then if you drive 20mph instead you can only go for 1 hour - measly 20 miles total distance. In addition to that, I suspect even a lead-acid battery has less effective capacity at high discharge rate than it has at lower rates, but in this question I am not the expert.

There are secondary effects that make going slower even more attractive: Your motor produces less heat, so you need less cooling liquid - reduces the vehicle weight. In addition, if the motor is cooler, the resistance of its copper wiring is less, so you waste less energy in ohmic heating. Better use that energy to drive the wheels :)

Just my 2 cents

Wolfgang


Edited by - womai on 30/08/2007 20:55:21
 
#54
Sorry for the silence - We are (as UK readers will know) getting to the end of the summer break and so I have been topping up my Tan in France and the south of England.

Racing car development stalled apart from some desk top experiments to reacquaint myself with op amps and a trial at temperature measurement which will be our biggest issue (I think - as a cooked motor will stop us dead and it is easy to do)

We lost some time at the end of term with the team breaking up due to exams and subsequent leaving - I held an open meeting to gather fresh interest, the only requirement was you have to bring a parent as the Head has specified parents must accompany the team as racing is not a risk free undertaking and he will not be responsible for any incidents - ergo parents on site if they have an issue they need to speak up.

How many turned up? 4 students+ parents. Lots of kids interested in driving but not many parents willing to put in the time for their kids!!.

However we should have a team the race we must enter (our heat) is at Darly moor race track nr. Ashbourn on the 15th Sep.

As it stands when we return to school next week we have to initially get the bodywork complete or we have no car to drive - instruments or no instruments, anything else will be a bonus, I view this as a long term project anyhow and do not expect to do at all well in this first entry - more of a steep learning curve.

I appreciate the wisdom of narrow wheels and many go this route - we have been sponsored with a kit car which fixes many design aspects at present and as the cost is in excess of &#163;1000 it seems a shame to look such a gift horse in the mouth as it were.

Improvements need to come in time and I already have half a new tubular steel chassis built to take a narrower wheel and some other issues for later.

keep the ideas coming guys I do read and ponder them all and appreciate your time and effort.

<A href='http://picasaweb.google.com/rickharriss/Greenpower1' Target=_Blank>External Web Link</a> Pictures of the car as we started the body - front done and one side finished now - can be seen here

Edited by - rickharris on 30/08/2007 22:46:18
 
#55
Sorry to hear about the lack of interest. I have to say I'm very surprised at that. In my experience interest for such projects can be so high (including parents) that the problem can be how to limit the numbers without causing too much dissapointment. Maybe meeja studies (that's reading the paper in front of the telly whilst looking at a CD for those not aquainted with the term) has become more popular since competitiveness became a non-PC topic.

Anyway, I agree with your attitude of using the first 'run' purely as an educational excersise. You will get more from seeing other's entries and talking to them than you will from all the text here. The Technogames series which was shown on BBC2 a few years back was a very good example of the rapid improvement from year to year which was attributed largely to simply &quot;taking part&quot; in the competition and taliking to others.

I'm hoping to start some solar-battery projects over the next few weeks. Part of the requirement is to know battery capacity at any given time and adjust loading accordingly. It is a similar issue to yours so if it ends up PICAXE driven, I'll post here for your consumption.
 
#56
Looks a great project. If I was at school I'd love to be involved.

Why the poor turnout? Obv loads of kids wnat to drive a car, but no-one prepared to be pit-crew? Thats so strange. Or is the meeja studies teacher better looking?

btw, how much does it weigh? It looks very sturdy.
 
#57
BeanieBots/Dippy- Thanks - Actually we don't do MS (not academic enough ) - I think it was involve the parents that scuppered the meeting - anyway I didn't try to go further as it was close to the end of term and my fear was as you say I would get too many - rather then too few.

We entered Techno games in it's last outing - swimming (froggo the hopit - LoTR was on at the time) We did quite well and got into the final.

We also entered the solar car and got to the final. We had beaten the eventual winners but they complained the track was too bumpy for their car so they got an extra go (same for all of us I say)

I was very sad the BBC abandoned it as a public service operation they should be sponsoring such schools projects as a part of their service.

I realise many members of the public were spending 100's if not 1000's of pounds on their entries but not all did that well - mostly reliability. Schools find it hard to get that sort of cash together. we spent about &#163;7 and my RC equipment.

At that contest they suggested perhaps they would have a walking/running biped robot contest the following year - interesting to see how things have progressed in 4 or 5 years - Bipeds are now common and in every toy shop and playing football.
 
#58
Mmmm.. ironically we have quite a few overpaid bipeds playing football - and most of those have less procesing power than a PICAXE.
 
#59
We've met then Rickharris!
The track certainly was bad for the solar event as poor old Prometheus found out getting a piggy-back ride on top of Gonzalez and ultimately being disqualified.

You say you beat the eventual winners?
Do you mean you did the 25m in under 4.25S?
What was your entry's name?

It was a great shame that they pulled the plug just as it started to get going. However, the BBC did sort of sponsor schools. They paid me to go to several schools to give &quot;Robotics Master Classes&quot; for several years after the last show. One school even applied 3 months after the cut-off and with a little persuation the BBC still coughed up, so I think they did their bit really.


Edited by - beaniebots on 02/09/2007 22:52:17
 
#60
Technically - Their vehicle got stuck on the track in the heat and didn't finish we passed them to go on to the next round. We were a LOT slower in reality just lucky.

Still gets you on TV!

 
#62
Dippy - The car weighs about 40 pounds without the motor and batteries.

It is entirely constructed from pop riveted aluminum but is quite sturdy. The motor and battery set adds around 70 pounds to the set up - more than the driver I expect.
 
#63
We represented Boston Grammar School - I see a typo for Final read Semi-final

- I don't recall the name we gave our chariot - It was a 3 wheeler using CD's as wheels. worked well though every time - just didn't carry enough solar panel to provide the get up and go (cost limitations and not knowing what the competition would have to show.)

I have a video of that particular program we were in somewhere at school, or at least I had. Also the frog getting swamped by an over animated shark.

Which team were you Ill look it out when I get back


Edited by - rickharris on 02/09/2007 23:02:53
 
#64
Umm...
Well I got more than my fair share of TV coverage!
Phoebius ... Gold Medal ... World Record ... NESTA Prize ...

We never got stuck but the 10mm guide track which was only 8mm did rip off my steering pin. Chris Delph of Whizz-bang fame helped us get it modified and stuck back on.

We came 5th the previous year with a time of 18S over 20m with Heliosonic. The Wife took that one over and got 5.2S over 25m the following year. That is the sort of progress that can be made just by attending and having a good chat with others.

Edited by - beaniebots on 02/09/2007 23:18:41
 
#65
I've just done a quick scan of the entire televised solar events for the last series and couldn't find any reference to Boston Grammar School. I'm not sure that all the 1/4 finals were covered but the semis and final all had interviews.
I'll see if I can find you in the other events.

...a few DVDs later...

I eventually found an entry for Boston Grammer, &quot;Froggo The Hoppit&quot; by James, Robert &amp; Neil in series 6 of the final year. I see what you mean about the shark. Looked like it was going for the kill just before swerving off to avoid what would have been a spectacular collision.
(still nothing for solar though, maybe I missed it)

Edited by - beaniebots on 03/09/2007 09:55:19
 
#66
We were there - Aircraft hanger Nottingham way - Tall balding bloke with 2 students one with ginger hair.

I didn't actually see what happened other than the car stopped - I am sure it was the eventual winner, very low and flat - I was told they caught on a raised join in the plywood track and were to be allowed another run - they were of course very quick and their time allowed them into the final.

Memory fades with age but I am fairly sure that was what happened. I was considerably surprised we got to the semi - but then again a lot of the contestants were left on the line with cars that didn't get started.

 
#67
Ah.., think I spotted you.
Left most lane (the bumpiest) next to &quot;Black Hole&quot; which had very large wheels with circular cutouts in them and won that round. Black Hole came 4th in the first round of the semis with 11.46S
They didn't mention your robot or school though so I may still have your placing wrong.

There were over 70 entries that year but only about 20 or so even moved.
The auditions are just as bad as what you see on &quot;X Factor&quot;. I saw one entry which was a cereal box with two pencils pushed through it and some wheels that looked like they had been chewed by a mouse out of another cereal box. They were very upset that they were not allowed to enter despite not even having a motor or solar panel.
 
#68
Sounds like us - A private school had a very exotic car with a fancy PIC controlled energy release system to ramp up the motor etc. etc. It never got off the line!

We got better press with the frog James Watson one of our students got interviewed which was used. Sadly I wasn't there for that event and James father took them to the show.

Swimming seems more contestable, All be it we didn't have a pool to try the frog in and out local public pool refused outright saying if it fell to bits in the pool they would have to drain it at some ridicules cost to make sure all the bits were recovered.

Still not to be any more.
 
#69
Indeed, there were some very fancy micro based power controllers. The best way to go if you have a solar array for power supply but not for an event like that. By the time the micro has found the peak and adjusted for the change in load the race is over. One guy was running around boasting about how his micro could sample and adjust every 30mS. Didn't have the heart to tell him that my ANALOG design had a slew rate of 100v/ms. Horses for courses as Dippy always says and that was a race course for op-amps not micros. (well maybe a DSP at a push).

Getting back on thread. The good news is that I've just wasted an hour hunting around the house for a FET input op-amp because I need to build a ....
..wait for it ...

a battery capacity meter!

Although, thinking about it, as you aren't using any form of throttle, you would get a fair indication by just using a simple throttle activated count-down timer.

I want to try a very simple (resetable integrator) design that uses only one op-amp, an 08M and a few caps. The tricky bit is trying to get it to work from a single rail. PWMout is used for the 1mA analog meter display so I can't use it for -ve rail generation but PWM might be good enough.
 
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