Solar Freaks

Last year we had some discussions with regards to RC solar cars. Just thought ild open up a thread so we can discuss the general build options/rules that we are going to base the cars on.

I was thinking we follow the same set of rules as the AIMSC, however we omit the guides (or they can even stay) and add our own active steering and speed control??

Any thoughts...

Sounds great Tony.

I built a demo model last year and tested the car using a standard hobby battery. Couldn't get it to run off the solar panel with the automax installed. Speed controller wasn't liking the output. Is there any way which I/ we can get past this Tony?

On another note, what I found with my demo RC was when taking sharp turns it tended to flip even with a drag plate of approximately 50cm^2 (0.5 radius turn & no ballast/ 3 wheeler). So I suggest that we should lower the drag plate down to 1/2 to 1/4 of the national regulation just to keep the center of gravity lower. The drag plate should not be removable, simply because I'm sure we will not cheat on this aspect and the strength could be used else where. No guides since they will definitely catch on to something on any uneven racing surface. Also if possible use a lighter ballasting formula to increase speed!!!

Marc, has the location for the national event been finalized? It was held at UTAS last time, right? Any tennis courts around the uni or will we use the car park area which was suggested last year? Please define the racing surface and race course.
Suggestion for race course!
1.Pure sprint over 20m + (testing speed)
2.Zig Zag course (testing movability of the car)
3. Something crazy (testing drivers skill)

Should be interesting if we can get a few cars up and running for the nationals!

Hmm, I'd forgotten about this. I'll have to start working on it.

We should probably work out what sort of RC everyone is using so we don't all end up trying to use the same bit of the spectrum.

Adhering to the AIMSCC rules somewhat sounds like a good idea.

If the 2011 electronics ballasting formula is used then it ought to give a bit of an advantage to the lower powers if the race course has plenty of cornerng, braking and accelerating. No arguments from me there although they may struggle in the lower sunlights if BEC is used.

I am probably in agreement that it might be worth lightening up the ballasting to some degree. This year's AIMSCC formula requires teams to carry more because otherwise it would be rather difficult (it still is in some cases) to make up a low to mid powered panel to fit in under the no-electronics formula with the considerable weight reduction that is being offered.
Since the RC cars will however all be using electronics, the weight can brought down by a bit. I'll have a play around with my simulator and look at a new lighter formula that maintains a similar power advantage/disadvantage to the current one if that's what we want to go with.

I think that things like the drag plate should be kept unchanged if possible. There would almost be no point in having a drag plate if it were reduced down to 50 or 100 square cm.
Having the 200 sq. cm would be a good challenge in my opinion and keeping in line with the AIMSCC rules as much as possible leaves the possibilty open for relatively easy conversion to running on the track.
Having a 200 sq. cm drag plate doesn't necessarily mean that the centre of gravity can't be kept low. There shouldn't be any problem with the Scorpio panels and there's nothing in the 2011 AIMSCC rules stopping heavier panels such as the Engelecs from being kept nice and low on the car.

It might be worth defining a minimum course cornering radius or vehicle turning circle.

Probably the biggest thing that needs to be sorted out is deciding what we want to allow with the electronics system. Should capacitor banks be allowed? BEC or non-BEC? Etc.
Finding an appropriate ESC for the maxons/faulhabers might also be a challenge.
From memory I believe that Tony once mentioned that he would be able to make the Automax plug directly into an Rx and output a varying voltage to control motor speed (if this is the path we want to take).

Once we have come to an agreement on things then perhaps we could modify the current AIMSCC regulations and make up an "official" set of RC rules.

jhg wrote:Marc, has the location for the national event been finalised? It was held at UTAS last time, right? Any tennis courts around the uni or will we use the car park area which was suggested last year? Please define the racing surface and race course.
Suggestion for race course!
1.Pure sprint over 20m + (testing speed)
2.Zig Zag course (testing movability of the car)
3. Something crazy (testing drivers skill)

Yes Jun, this year's nationals will again be held at the Utas like in 2008. There are tennis courts at the venue which might be able to be used. Otherwise, as you have mentioned, a section of the car park could probably be marked off. The car park surface consists of a reasonably fine grade of asphalt and the tennis courts are of hard court form which would probably be quite good to race on.

Having several different areas to test the cars in would be good. Some sort of a sprint and having to traverse a race course sound feasible. I don't know if we can already define a race course. We'll probably just make one up on the spot.

Marc

Hey Guys,

Yes the Automax can be programmed to accept a servo signal, which can be used to control output voltage. When full power is applied, or 100% throttle, the Automax can be programmed to deliver max power to your motor whilst tracking the arrays MPPT. Tracking is not necessary if full power is not applied.

There is another option, where the Automax can be used to charge a capacitor bank, and a conventional ESC can then be plugged into the capacitor bank. The storage will need to be quite large.. as seen on page 2 of this (rc-solar-car-t19-20.html) thread. This method is probably more effective as the panel will always be making power even when we slow down or stop. It'll also give good acceleration.

I think in any case in order to make a more efficient system, we will need to use a switchmode BEC, as opposed to a linear regulated BEC. The Automax has a linear regular at 5V, however, its limited to 100mA, and with input voltages around 15volts we will probably be stressing it too hard. Switching BECs can be sourced really cheap from overseas, http://www.hobbyking.com/hobbyking/stor ... duct=14310, and can be up to 95% efficient. These will be perfect to run the onboard electronics, and it wont matter what the panel voltages are.


Because we are running on rough surfaces (compared to the track) we might even need to consider rubber tires or even shocks. I think this will be necessary to prevent wheel spin on acceleration, esp if we run a capacitor bank.

TonyB wrote:There is another option, where the Automax can be used to charge a capacitor bank, and a conventional ESC can then be plugged into the capacitor bank. The storage will need to be quite large as seen on page 2 of this (rc-solar-car-t19-20.html) thread. This method is probably more effective as the panel will always be making power even when we slow down or stop. It'll also give good acceleration.

Yes, I think that this should be the way to go as it easily more efficient. The first method just doesn't make the best use of what the panel can supply. How much did those 55F supercaps set you back and how did the car in the thread end up turning out by the way? How did the brushless fare at the power that you were running at?

TonyB wrote:I think in any case in order to make a more efficient system, we will need to use a switchmode BEC, as opposed to a linear regulated BEC. The Automax has a linear regular at 5V, however, its limited to 100mA, and with input voltages around 15volts we will probably be stressing it too hard. Switching BECs can be sourced really cheap from overseas, http://www.hobbyking.com/hobbyking/stor ... duct=14310, and can be up to 95% efficient. These will be perfect to run the onboard electronics, and it wont matter what the panel voltages are.

Looks like a good little switchmode BEC there and at a decent price too. Do we want to have the solar panel drive this or hook up say a 9V instead? I know that it technically wouldn't then be a BEC anymore and a switchmode unit not really necessary, but if we use a separate battery to run the electronics and steering servo, all the available panel power can then go towards driving the car. The battery and electronics could then simply make up part of the ballast that will need to be carried anyway.

TonyB wrote:Because we are running on rough surfaces (compared to the track) we might even need to consider rubber tires or even shocks. I think this will be necessary to prevent wheel spin on acceleration, esp if we run a capacitor bank.

Tyres of some sort will be a must. Not only to prevent wheel spin but also to provide the necessary traction for the car to corner. Since car park and tennis court surfaces tend to reasonably smooth, one should probably be able to get away without any shocks.

Marc

Hey all,

So how were we thinking of setting up the RC electronics? Perhaps we could set things up similar to the block diagram below (modified from Tony's diagram in the other thread).


Ok, so having the 9V battery there doesn't make it a pure RC solar car (regardless of whether it is used or not the Tx will still be powered by batteries), but it does however allow all the available panel power to go towards driving the car.
Without it the panel will not only drive the motor but also the ESC and Rx plus a servo (which I am guessing will consume an average of maybe 100-200mA with a moderate amount of stick play). If this is the case then the cars could really struggle at the lower sunlights.

What are everyone's thoughts?

Marc

Im happy with your suggestion..

I would be interested!!