# Solar Car, Voltage determines Velocity

Discussion in 'General Electronics Discussion' started by caters, Jun 15, 2017.

1. ### caters

3
0
Jun 15, 2017
Here is my idea of a solar car(obviously I am not going to build it because it would involve welding and high voltage, both of which are dangerous).

No hydrogen is needed here because it is completely powered via solar power.

When it is charging, the solar panel is connected to a cable that plugs into a socket on the top of the car. This sends electricity to the battery and charges it up. Once it has reached 100%, no more electricity gets into the battery so it doesn't overcharge.

The battery powers everything from the lights to the motors that actually move the car.

I want to focus on the battery, motors, and built in multimeter.

There are 2 motors here, 1 on the left and 1 on the right. They both have a hot wire which branches off of the wire that is connected to the negative terminal of the battery(a hot wire sends current to the component in question). They also both have a neutral wire(neutral wire sends current back to the battery) which connects to the wire that is on the positive terminal of the battery.

The multimeter is also connected by a hot wire to the negative terminal and a neutral wire to the positive terminal. This multimeter is used mainly to know when the battery is getting low so that a person can get to a solar charging station or back home, before the battery dies.

This battery gauge is used for the same purpose as the multimeter but doesn't show actual numbers or units.

Whether or not the battery needs recharged is dependent on the voltage but more important than that is the amperage. If the amps get too low, it doesn't matter what the voltage is, the battery needs recharged.

High amps but low voltage, recharge
High voltage but low amps, recharge
Low voltage and low amps, recharge
High voltage and high amps, doesn't need recharged

Now let's focus on the 2 motors. These determine the velocity of the car via voltage and voltage difference.

If the voltage difference is 0, the car will go straight. If there is a difference, the car will turn in the direction of higher voltage. So if the right motor has more voltage, the car will turn right and if the left motor has more voltage, the car will turn left.

The magnitude of the velocity, commonly called speed is determined by the voltage itself. The higher the voltage when the difference is 0, the faster it goes.

Is this idea of voltage determining speed and direction and thus velocity a good one?

Basically I have this circuit:

LM means Left Motor and RM means Right Motor. With the neutral or black wires I am not trying to show crossover of current. Rather I am trying to show the merging of 2 currents into 1.

2. ### davennModerator

13,618
1,881
Sep 5, 2009
only if you have a charge controller circuit inline between the panel and battery(s)

that really doesn't make sense specially this part
the positive lead from the battery positive should go to the positive terminals of the motors etc
the negative lead from the battery negative should go to the negative terminals of the motors etc

in your diagram the battery symbol is reversed ... you have negative terminals going to the positive wires

huh ?? .... I you need a steering system like a normal car, that is, you need to physically turn the front wheel(s) else it will not turn

3. ### caters

3
0
Jun 15, 2017
But if I want the velocity to be determined by voltage, the motors would be mechanically connected to the wheels so that when the left motor has a higher voltage, the left wheels turn faster than the right wheels and thus the car turns left. Similar thing for when the right motor has a higher voltage. So in other words, electricity from the battery powers the motors and the voltage there determines the rotational speed in the motors and the mechanical connection there determines the rotational speed of the wheels which overall determines the speed and direction of the car.

And while conventional current has negative terminal connected to negative wires, electron current makes a lot more sense to me. Sure, it means that the amperage is negative but so what? It is only the magnitude of it that counts. And electron current has the negative terminal connected to positive wires because of the way electrons flow(negative to positive). So the way I have drawn that circuit is perfect if you use electron current instead of conventional current. I think this world would be a better place if electron current(the true current) was used instead of conventional current. There certainly would be less misconceptions about how electricity works(most common misconception, especially in students new to physics, thanks to the use of conventional current is that positive charges move and that is certainly not true, protons are too massive to move through a wire and it would change the element that makes up the wire which is not a good thing).

4. ### BobK

7,682
1,686
Jan 5, 2010
If you want to control the speed of the two wheels to determine the direction of the car, you need a motor speed controller (PWM) between the battery and the motor for each wheel. Then you need something that sets the duty cycle of the controller. Basically, you need a microcontroller or computer.

Bob

5. ### davennModerator

13,618
1,881
Sep 5, 2009

As I said earlier, the wheel WONT turn unless you physically turn it

sorry, but this is all total garbage

if you don't connect the battery(ies) correctly, the circuit wont operate correctly

6. ### Alec_t

2,860
768
Jul 7, 2015
Unless your wheels have a proper castor steering mechanism (e.g. Ackerman type) you will have in effect 'skid steering', such as is used by bulldozers. This will wear out your ty(/i)res in no time!

davenn likes this.
7. ### caters

3
0
Jun 15, 2017
But then voltage wouldn't be a factor anymore if I had a steering wheel and I really want voltage to be a factor here(and not just in knowing when the battery needs recharged). And the mechanical connection between the motors and the wheels should be in such a way that rotation in the motors causes rotation in the wheels and differing rotational speed is the essence of wheels turning. The difference in rotational speed causes the whole vehicle to have a torque which forces the vehicle to turn in the direction of the faster wheels. In other words, the torques on the individual wheels may cancel out but the overall torque is still non-zero which means the vehicle turns.

Since torque is a rotational force and voltage can be thought of as an electromotive force, 1 force(voltage) causes there to be another force(torque on the motors) which in turn causes there to be another force(torque on the wheels) and all of those cause there to be 1 more force(torque on the whole vehicle).

I mean, if I wanted voltage to be a factor and a steering wheel, the steering wheel would have to practically be a battery that can change polarity no problem. I don't know of a voltage source that can change polarity like that. Current source, absolutely(AC is current that changes direction multiple times a second) but voltage, I don't know.

And even then it wouldn't work the way I wanted it to(negative voltage I didn't want here, just a difference in voltage(still positive voltage everywhere)).

8. ### davennModerator

13,618
1,881
Sep 5, 2009

yes there will be a limited amount of turning ability but you have totally missed the point of why that is a really bad idea

here it is here repeated