/diy/ - Do It Yourself

[Anonymous No.600415]

Hey guys
I wanted to know how I can calculate the efficiency of a small model car with a solar panel and an electric motor.
n = usable energy / invested energy

so i think it might be simple for the solar panel:
energy of sunlight*surface of panel*time

i find it difficult to calculate the output energy that the tire puts on the ground though. Could you guys help me out to find this out?
what would the energy be at tire? force*velocity*time ?

could i put a string around the tire and attach it to a newtonmeter and see how much force it can produce?

[Anonymous No.600422]

>>600415
why not just look up physics resources?
What am I? Your personal calculator?

[Anonymous No.600431]

>>600415
There are a few different ways to do this.
You approach is good.

>energy of sunlight*[area] of panel*time
This is right. note: the time you want to use is from stopped to when you measure the distance/velocity

>force*velocity*time
not quite
Energy= Force*Distance
Since electric motors have a flat power profile, you can hook a force-meter [or fish scale or something] and measure the force.

You can also use:
Kinetic Energy = 0.5*Mass*Velocity^2

[Ananamoose™ No.600435]

>>600415
>could i put a string around the tire and attach it to a newtonmeter

just saw this part. It would be better to attach the newton-meter to the back of the car see how hard hard it pulls. This will prevent errors due the the torque from the wheel being applied at different moment arms.

[Anonymous No.600442]

>>600422
i looked a little but found nothing that explains me how i find out the power put to ground
>>600431
thanks for you clarifications
>Energy= Force*Distance
>Since electric motors have a flat power profile, you can hook a force-meter [or fish scale or something] and measure the force.
but i want the power at the tire to ground, the final power output. i think there's quite a loss between electric motor and wheel (friction?)
>>600435
ok thank you. but when i attach the newton-meter until the vehicle stops then that would be the maximum force of my vehicle but not the one put onto ground (since it has a veolcity...)?

[Anonymous No.600447]

>>600431
>This is right. note: the time you want to use is from stopped to when you measure the distance/velocity
sorry i dont get this, could you explain it to me?

[Ananamoose™ No.600453]

>>600442
i think a picture will clarify things

The force it pulls with while stationary is the same as the force applied while moving. If you let it go, it will keep accelerating until the force of friction equals the force of the motor.

>>600447
You want to start at 0 and measure how much energy is added to the car as motion [this is the useful work]. Therefore, you want to start the time with no energy and determine how much of the energy as sunlight got converted into kinetic energy of motion in the car.

Are you going to actualy do this, or is this just theory?

[Anonymous No.600461]

>>600453
lol thanks for the picture. actually i got what you meant but when i attach a newtonmeter and read the force at maximum then the velocity will be 0? but in reality my vehicle is moving so therefore the force i read when the car is not moving is not representative? or do i get something wrong here?
>Are you going to actualy do this, or is this just theory?
im actually doing this. have a picture of my vehicle. its actually a solar-hydrogen car

[Anonymous No.600466]

>>600461
so say, let's say i get a force of 20 Newton, how would I proceed?

[Anonymous No.600482]

Why not just time the car going a few meters and weigh it to find the work?

[Ananamoose™ No.600489]

>>600461
Ohh yeah, I saw your thred a few days ago.

bretty cool.

I didn't realize you had the added step of splitting H20. That makes things a little more complicated.

The most practical thing I can think of is measuring the output current and voltage of the fuel cell over a full discharge. If you can do calculus: integrate the area under the curve [with Current*Voltage on the Y-axis and time on the X axis].
If you cant do calculous, just take the averge current times the average voltage times the time it takes to use up your stored hydrogen/oxygen.
Energy = Current*Voltage*Time

Its very difficult to measure the efficiency of a vehicle using the physics definition. Because, once you reach top speed, you're not really doing work any more.
F=m*a
W=F*d
If speed is constant a=0 so,
F=0
W=0

That's why cars are rated in miles/gallon [km/liter] and not percentages.

You can assume the motor has ~90-95% efficiency if you want to include that.
Total Efficiency = (Efficiency of Step 1)*(Efficiency of Step 2)*(Eff.... so on

[Ananamoose™ No.600490]

>>600482
Because work is a dot product
If the system moves perpendicular to the applied force: no work is done.

[Ananamoose™ No.600492]

>>600461
>>600489
You might also try /sci/, they're bretty good at this stuff.

[Anonymous No.600502]

>>600489
thanks
ill look into integrating, actually i just learnt it recently, lets see if i can apply it.

so maybe i should find out how long and far i can drive with the produced hydrogen? but how would i convert that into an efficiency (%) from the solar power that shined on my surface area of my panel?
>>600492
asked the question there too still awaiting answer/suggestions

[Ananamoose™ No.600513]

>>600502
>but how would i convert that into an efficiency (%)
This would be very difficult to do.

In physics terms efficiency=Work done/Energy in.
Work = Force * Distance
Work = Current * Voltage * Time
Work = Mass * Gravity * Height
And a whole bunch more that dont really apply.

This is further complicated by friction, You usually dont consider energy lost to friction as work done. When the car is travelling at full speed, all the energy going to the motor is being used to overcome friction [electrical, mechanical, drag]. Therefore, in physics terms no work is being done.

You can 'cheat' and claim those losses as work done, but you're still going to have a hard time figuring out the Force to use in:
W=F*D
It's going to drop as the fuel gets used up. You could take several measurements at different levels of 'charge' and average them. Then do a couple runs and find the average distance traveled over a complete discharge.

[Anonymous No.600519]

>>600490

>dot product

Someone knows vector math on 4chan?!

[Anonymous No.600520]

>>600513
Thanks for your answer
It really seems complicated...
So if I wanted to find out the force I would need to find out air resistance, inertia force, friction force, rolling friction force and (gravity)? Then add them up and declare it as F?

[Ananamoose™ No.600531]

>>600520
>So if I wanted to find out the force I would need to find out air resistance, inertia force, friction force, rolling friction force and (gravity)? Then add them up and declare it as F?

It would be a lot easier to find the force using a newton meter.

[Anonymous No.600533]

>>600531
Yes but force is zero when car is travelling at constant velocity? I will find out the force with a newtonmeter on friday but it doesnt represent the same force as if the car was moving.

[Ananamoose™ No.600536]

>>600533
>Yes but force is zero when car is travelling at constant velocity?

Net Force = (Force from motor) - (Force of friction)

Typically you use Net Force when calculating work, but that's going to be zero for a vehicle traveling at constant speed on a level surface. If you project requires finding a % efficiency just be sleezy and use (Force of motor) for F int he equation. Make note of it in your presentation or paper or whatever.

I slightly less sleazy solution would be to drag a mass behind you. The mass should have an approximately constant drag once you get it moving. You can measure this whit a newton meter. It takes more force to get it moving than it does to keep it moving. The force of drag is material dependent, so your track will have to be all the same material, and you'll have to measure the drag by pulling the weight around on that material with a newton meter.

That would make the math much simper.

[Anonymous No.600547]

>>600536
I guess I'll calculate it first with just the motor force and if I have left time on my hands I might try what you suggested.
Although I don't know how I would accomplish the drag and calculate the net force out of it...
Could you maybe make a picture if you have time?

[Ananamoose™ No.600559]

>>600547
The friction force of the weight is very nearly independent of speed.

You can use the reading from the newton meter as you F in:

Work=F*D

[Anonymous No.600659]

>>600559
Thanks a lot
Will try this tomorrow

[Anonymous No.600884]

Keeping it alive

[Anonymous No.602058]

>>600559
ok couldnt do it earlier because i could find something that moves at constant velocity (like a remote controlled car) to pull my vehicle.
but the concept is right, right? (pic related)

gonna ask some friends tomorrow if they still have some remote cars somewhere that can pull 5 Newtons (i tried it with my hands, i got about 5 N but its not exact i guess)

[Anonymous No.603297]

Keeping alive