Wouldn't it be great if we knew exactly when/where our car tops out?? so we can gear up (larger pinion).
Also, wouldnt it be great if we knew when our car wasn't topping out (or motor voltage stops increasing because load is too large), then we know we need to gear down (smaller pinion)...

Well, recently ive been experimenting with.....


Basically, if you own an easymax you will see it has six pinholes, these pinholes give me direct access to the cpu's programming port, which can also double as general I/O.

Recently, ive been mucking about with an experimental version of the easymax firmware. Ive set 2 of those pins to control a high pitched buzzer (as pictured above). When the voltage across the output of the easymax increases and equals the voltage across the input of the easymax (that is when the motor voltage equals the panels mpp voltage), the buzzer would sound.

This is very good as we can gear the motor to top out just before the end of the race (gear so the buzzer sounds just before the end of the race), or if its a two lap race, we can gear it to top out somewhere in the second lap. If the buzzer doesnt sound at all, it means we need to gear down.

The buzzer consumes 12mA of current whilst operating, but i can PWM it and cut that current consumption down to 2-3mA.

What do you guys think?

Sounds very good considering it is something we have had some issues with.

How long do you think it would be before such a system could become operational on a car? eg would it be ready in-time for Melbourne?

Redlands wrote:Sounds very good considering it is something we have had some issues with.

How long do you think it would be before such a system could become operational on a car? eg would it be ready in-time for Melbourne?

Well its completely experimental at the moment. I dont want to release new and untested firmware without it been fully field tested and bug free. I had problems in the past like this, where i release firmware that has only been bench tested, then in the field, it does some other random thing.

Great idea Tony. I must admit, I really like this one.

At the moment, the only real way of approximating your motor voltage is if you get yourself a radar gun or something else to determine what your speed you are traveling at and then working backwards using gear ratios, wheel sizes and motor speed constants. Even then your max power voltage will still vary depending on panel temp or sunlight % (under lower sunlight conditions).

With this on the other hand, all you have to do is listen for a buzz. Genius.

miseli

Hi all

Yeah this seems like a real breakthrough, especially in light of the problems that we have been experiencing with our personal gear ratios. If there is a possibility, we would definatly be interested in trying this system out at nationals.

Cheers
C.C

Conitsiotis wrote:Hi all

Yeah this seems like a real breakthrough, especially in light of the problems that we have been experiencing with our personal gear ratios. If there is a possibility, we would definatly be interested in trying this system out at nationals.

Cheers
C.C

Ill be happy for you guys to test it out for me.

Conitsiotis,

Be prepared to bring a good range of gears. If you want your motor voltage to be up and around your panel's max power voltage at some of the lower sunlights you'll be needing gear ratios of up to maybe about 10:1 with your current setup. A 5:1 through to a 10:1 would be a good range to have.

I will be interested in seeing what kind of a difference this will really make. If you change gearing, you might potentially be able to improve the efficiency of your electronics by maybe 5 or even 10% for some of the lower sunlights over just sticking with the one (say 6:1) ratio for all sunlights. The difference seen will also depend on the electronics unit used.

If Belridge or Morley are anything to go by, I think changing a gear or 2 might indeed be worth the hassle if you're up against a strong opponent and the sunlight drops below a certain level. These two schools seemed to have close to optimal setups and did rather well in the lower sunlights at last year's nationals (seeded 1 and 2). One of them would have almost certainly ended up winning if the sun hadn't of come out.

miseli

Proper gearing not only runs your electronics more efficiently, but also your motor.+

Your motor losses increase exponentially at the low end (geared to high), so finding the sweet spot on your motor is also important.

The faulhaber has 0.89Ohms internal resistance. If we run the motor at 8 volts max from a 10 watt panel, we will have 1.25 amps running through it. Thats a loss of I²R or 1.25² x 0.89 = 1.4 watts.

Now if we gear to run it at 16 volts from the same panel, we would have 0.625 amps running through it, so our losses are I²R, 0.625² x 0.89 = 0.34W of losses.... So we have saved over 1 watt, which is 10% more power getting used, rather than going to waste.

Now the figures ive calculated above are for the motor voltages at the end of the race. The motor has lower voltages, and higher currents passing throughout the start of the race, so the losses and difference are even greater.

So basically, when we run maximisers, we still need to find an optimum gear.
And during low light conditions, our motor voltages struggle to increase because of the lower power, and the I²R losses have more of an effect here. So we still need to change gearing, to get the voltage up.

You're correct there Tony and resistive losses are also definitely something to look out for.

As you have calculated above, there can be quite a loss at the higher currents. But you'd have to have a ridiculous gear setup at the higher sunlights to give you so much losses though.
As you have also pointed out, the losses of a motor are even greater at the start of a race, but the gear setup to give you max power voltage towards the end of a race will be subjected to the higher currents at the start as well.
As it stands, most cars that don't change their gear ratios have got their cars set up quite well for the good sunlights and the motor losses are around the lowest that are possible with the panels that are being used.

At lower sunlights there can be some differences though, but the currents flowing into the motor at top speeds will however be a lot lower so the resistive losses will also be that much lower.

Since cars hit top speeds at just about the bottom of the hill in low sunlight, cars will run at their top speeds for most of the race until they get around to the hill.
For a 500mA panel in good sunlight, this means about 100mA at 20% sun if you're near max power voltage. 0.1^2 x 0.89 gives a 0.0089W loss. If you now say you have your gearing set up to give you 200mA and half the voltage, that's 0.2^2 x 0.89 or 0.0356W. There is obviously still a significant power loss when comparing the two, but in relation to the panel power being supplied it is somewhat lower.
If your panel say puts out 7.5 or so watts at 100% and about 1.5W at about 20%, that's a 0.0356/1.5 x 100% or 2.4% loss of power and 0.0089/1.5 x 100% or a 0.6% loss of power when running at optimal settings.

In summary, the better your gearing is set up for the conditions, the lower your motor resistive losses become. Motor losses are also another key reason why having a higher voltage/lower current panel is more optimal than one that is configured the other way around.

miseli

I just recorded a video of this in action, however for some reason the camera MIC didnt capture the high pitched sound generated by the buzzer. Maybe its out of its frequency range . So i programmed the LED to turn on with the BUZZER, just so we can see, normally the LED wont turn on like this.







BTW my light box was set to 25%.

TonyB wrote:Ill be happy for you guys to test it out for me.

Sounds good, we think this is a great idea. I look forward to testing it out (and maybe even using it? ) in Melbourne.

I can also see what you and Miseli are saying about finding the optimum gear ratio. The problem is this is a very difficult thing to do. On-track tests are not much good because the light is always changing.

This is a fanstastic additional feature to the development of your EM3. This would definitely serve more purpose to teams that have had limited/no testing, so they can find their optimal gear setting given it is a consistenly sunny day.
Love that motor, its a screamer.

Yes that motor is a Maxon RE-Max 221020. Its the same motor OLOL used.

Its a very high RPM motor with very low internal resistance. But in saying that, you need very high gear ratios (small pinions) to get the torque out of it. Its got half the resistance the faulhaber has, but at the same time, its got half the torque constant per amp.

Yeah, i remember you mentioning this. We did test it but unfortunately did not have the correct gears.