Solar car, Voltage determines Velocity

[caters]

I have come up with an idea for a solar car. Now I am not going to build it because it would require welding and although my dad knows how to use a welder and a plasma cutter, I still think it would be too dangerous for even my dad to build, not to mention expensive. Even if he cut all the metal himself, the metal would be expensive. Not to mention it could start a fire which would mean no more solar car.

But just because me and my dad can't build it doesn't mean I can't come up with an idea for it. So here is my idea. I was thinking that maybe voltage could determine velocity.

When the car is charging, it is connected to a solar panel via a cord which plugs into the top of the car. Then, wires within the chassis send electricity to the battery to charge it up. Once it is fully charged, it won't overcharge.

There are 4 different situations that can happen with the battery based on amperage and voltage. Those are:

• High voltage and High amps(doesn't need recharged)
• Low voltage and Low amps(needs recharged)
• Low voltage and High amps(needs recharged and is being used a lot(that or resistance is too low)
• High voltage and Low amps(Resistance is too high, even the high voltage can't overcome the sheer resistance)

So anyway, I know that the circuit would be a lot more complicated than I am showing in the image but it will be easier to understand this way and just so you know, I am using electron current(the true current) so polarity being backwards is because of that. Electrons flow from negative to positive. A big misconception to physics students is that positive charges move but they don't, they are too massive. Conventional current though forces students to think backwards is forwards. This world would be a much better place if we just used electron current. Then there wouldn't be this "positive charges move" misconception.

Anyway, here is the simplified circuit(this actually is the original circuit, I will draw a more complicated one just to show how complicated it is):

Basic car circuit.pdf

From the negative terminal, through the negative wires(those black wires), the electrons flow to the 2 motors(LM means left motor and RM means right motor) and the built in multimeter. Then they flow through the positive wires(those red wires) to the positive terminal. This is all in terms of electron current(here negative wires to negative terminal makes perfect sense).

As the voltage on the motors increases, the speed increases.

If the voltage difference is 0, the car goes straight. If it is non-zero however, there is more of a torque on the motor with more voltage. Since the motors are mechanically connected to the wheels, this also means more of a torque on the wheels that are on the same side as the motor with higher voltage(so if the right motor has a higher voltage, the right wheels will have a higher torque and thus a higher rotational speed. And while individual torques on the wheels may cancel out, there is 1 more torque caused by all these other torques. That is a torque on the entire car. This 1 torque(which remember originates from the voltage difference), determines whether the car will turn left or right and like the wheel torques, is also in the direction of the higher voltage(so if the right motor has a higher voltage, the car will turn right).

What do you think? Is this a good idea as to how voltage can determine velocity?

[swansont]

A big problem with a solar car is simply the area available for charging, and if this is insurmountable, the details you discuss are moot. You have a couple of square meters available for solar panels, and if you have an insolation of 250 W/m^2, that's 500 W. Or 0.5 kWh or energy each hour (assuming no losses). That's enough to travel about 3 km. Most commercially-available (in the US) cars have battery capacity  that far exceeds 24 kWh, which you will never reach, and that only allows for a range of about 140 km.

Put another way, the motor is running at 50 kW or so at 100 km/hr. You need a 100 kWh battery. That's what you need to charge up in order to be useful. The problem is surface area, not the electronics.

[caters]

Really? Because I have posted about this on other forums and they all said that the problem lies in the turning mechanism(voltage difference causing a difference in rotational speed between the 2 motors and those motors being mechanically connected and thus causing a torque on the wheels which in turn causes a torque on the whole car that causes it to turn). They all said that the differential speed due to voltage would produce too small of a torque for high speeds and so while you might turn just fine at 5 mph, increase that speed to 45 mph and the car will crash because a small torque at a fast speed would require a turn that barely even looks like a turn and most roads have a 90 degree angle at intersections. So they basically said that voltage difference and a 90 degree turn just aren't compatible at high speeds.

[Strange]

Related to that, controlling DC motors by simply adjusting the voltage does not give you very accurate control over torque, which depends on speed, load on the motor and other factors.

Electric motors for cars use multiphase windings to provide accurate control and feedback.

[swansont]

5 hours ago, caters said:

Really? Because I have posted about this on other forums and they all said that the problem lies in the turning mechanism(voltage difference causing a difference in rotational speed between the 2 motors and those motors being mechanically connected and thus causing a torque on the wheels which in turn causes a torque on the whole car that causes it to turn). They all said that the differential speed due to voltage would produce too small of a torque for high speeds and so while you might turn just fine at 5 mph, increase that speed to 45 mph and the car will crash because a small torque at a fast speed would require a turn that barely even looks like a turn and most roads have a 90 degree angle at intersections. So they basically said that voltage difference and a 90 degree turn just aren't compatible at high speeds.

"Problems with electric cars" is not the same discussion as "problems with a solar car"

[caters]

I know that but my solar car design has 2 motors and electric cars in existence only have 1 motor. And assuming that the surface area problem can be fixed by coating the outside of the car in microscopic solar panels, this voltage controlling the turning direction and speed would be a challenge, but only at high speeds. And nobody would want a highway with a speed limit that is way below the normal highway speed limit just because voltage has a problem at high speeds. Then, you would get nowhere fast. Going to the doctor downtown if you are not downtown might take several hours if you have to go slow on the highways due to a limit of voltage reasonably controlling torque.

 

As to how voltage controls the speed regardless of turning? The more voltage, the higher the speed.

[Strange]

3 minutes ago, caters said:

I know that but my solar car design has 2 motors and electric cars in existence only have 1 motor.

It is not used often because the advantages (cost, weight, etc) outweigh the advantages.

https://en.wikipedia.org/wiki/Individual-wheel_drive

8 minutes ago, caters said:

As to how voltage controls the speed regardless of turning? The more voltage, the higher the speed.

It is not that simple.

[caters]

Why is is not as simple as increasing the voltage increases speed? I have seen demonstrations of a motor connected to a power supply where they kept increasing the voltage and as the voltage increased, the rotational speed of the motor increased. Now yes, it was a small motor like what you would use in a robot but still, increased voltage caused the speed to increase. And given that the 2 motors in the car are mechanically connected to the wheels, when the motor's rotational speed increases, so does the wheel's rotational speed and that rotational speed determines the speed of the car.

[Strange]

16 minutes ago, caters said:

Why is is not as simple as increasing the voltage increases speed?

Because there is not a simple relationship between torque and voltage. Yes, the speed will increase. But by how much?And how will that be affected by the current speed? And by loading? And temperature?

Also, how do you propose to control the voltage?

It would be much more efficient to use a multiphase DC motor where you have have precise control of the torque generated.

[caters]

On 9/8/2017 at 1:09 PM, Strange said:

Because there is not a simple relationship between torque and voltage. Yes, the speed will increase. But by how much?And how will that be affected by the current speed? And by loading? And temperature?

Also, how do you propose to control the voltage?

It would be much more efficient to use a multiphase DC motor where you have have precise control of the torque generated.

I was thinking about maybe using capacitors connected to the accelerator, steering wheel, and brake along with some variable resistors.

Specifically, when you push on the accelerator, because more voltage is needed, more electricity goes from the capacitors to the motors and this adds voltage to what is already there.

When the brake is pushed, less voltage is needed and so more electricity gets stored in the capacitors.

When the steering wheel is turned left or right, the resistors get involved as well as the capacitors. Like with the accelerator, more electricity is sent from capacitors towards the motors. But these capacitors are connected to variable resistors. When the steering wheel is turned left, the left variable resistor has a decreased resistance whereas the right variable resistor has a higher resistance. This causes there to be a voltage difference that causes the car to turn to the left. Similar thing with turning right except which resistor has higher resistance and which one has lower resistance is switched.