I am having a competition with friends where we buy cheap $10 RC cars. Modify it and then race it. I’ve only taken a semester of circuits but not enough time to learn it all. I am very interested in circuits and thought this could be a learning experiment. I wanted to push my cars motors to its limit without worrying about the motors lifespan.

1. What I first did was take the rc car completely apart and add one double A battery in series with the other 3. With this I could definitely notice a huge power increase but felt too easy.

2. I ordered a boost converter and used a 9V battery to power it. The output I set at 12V to the circuit board then to the motors. What I noticed is that the rc car seemed to surge but not go anywhere. Noticed measuring current going into boost converter was higher than current leaving the boost converter but voltage being higher. I believe resistance is constant so voltage is directly related to current. (Higher current = voltage) but seems to have an issue working.

3. The last option I haven’t tried is using an H bridge.

I have already ordered other motors but what else can I do to make my rc car faster?

 

Ideally look at the voltage of the motor and power it with another 3V higher, an H-bridge will give full voltage to the motor in both directions,using Nicads which can be controlled by pwm easily for slow start to maximum power.

 

The current available from a standard (rectangular) 9V battery is pretty low, much less than an AA cell and will probably not be sufficient to power your car.

 

... Another possible approach ... depending on accessibility.
If the gears between the motor drive shaft and the wheels are exposed sufficiently, it may be possible to change the gear ratio. A slightly larger diameter motor gear engaging with a slightly smaller diameter wheel shaft gear would produce higher wheel rpm, at the expense of reducing starting torque and initial acceleration.
Here is a related informational article ...
RC car gears

 

what else can I do to make my rc car faster?

Chop unnecessary parts off the car to reduce weight.
An H-bridge won't do anyting useful for the car unless it has to be reversible.

 

9V battery has really lame current. Try a lipo, it's not all about voltage.

 

I am having a competition with friends where we buy cheap $10 RC cars. Modify it and then race it. I’ve only taken a semester of circuits but not enough time to learn it all. I am very interested in circuits and thought this could be a learning experiment. I wanted to push my cars motors to its limit without worrying about the motors lifespan.

1. What I first did was take the rc car completely apart and add one double A battery in series with the other 3. With this I could definitely notice a huge power increase but felt too easy.

2. I ordered a boost converter and used a 9V battery to power it. The output I set at 12V to the circuit board then to the motors. What I noticed is that the rc car seemed to surge but not go anywhere. Noticed measuring current going into boost converter was higher than current leaving the boost converter but voltage being higher. I believe resistance is constant so voltage is directly related to current. (Higher current = voltage) but seems to have an issue working.

3. The last option I haven’t tried is using an H bridge.

I have already ordered other motors but what else can I do to make my rc car faster?

Ideally look at the voltage of the motor and power it with another 3V higher, an H-bridge will give full voltage to the motor in both directions,using Nicads which can be controlled by pwm easily for slow start to maximum power.

I am not too familiar with H-bridge. How does it work? Based on what I searched online it shows that it can change polarity but nothing about voltage increase.

 

9V battery has really lame current. Try a lipo, it's not all about voltage.

Which I realized today as well. I took the voltage going into the boost converter which was at 5V and current 4A. The the voltage and current out had 7.8 volts but 2.8 amps. Significantly lower current which would be causing motor to be weaker. I will probably have to throw away the boost converter idea and try something else.

 

Seems like you took 20 W input and got 21.8 W (7.8V x 2.8A) output. That is magic. With a properly designed motor, it should go faster. Then again,maybe your numbers are more than a little off.

 

I took the voltage going into the boost converter which was at 5V and current 4A.

How did you measure the current? I don't think a 9v can put out 4 Amps. I think your original idea of adding AAs is pretty good. Maybe go for 6 AAs? Not sure how much voltage the rest of the circuit can take though.

 

How did you measure the current? I don't think a 9v can put out 4 Amps. I think your original idea of adding AAs is pretty good. Maybe go for 6 AAs? Not sure how much voltage the rest of the circuit can take though.

Sorry I didn’t explain. I originally tried a 9V battery which was not sufficient enough current. So using 4 AA batteries in series my multimeter read 5.5V which the batteries could have been low or my multimeter wasn’t reading all 6V. Using that method The current measured approximately 4 amps. Voltage out was higher and current was at 2.8 amps. What I will try is wire 2 batteries in series. Ground to the board and positive to the wire connected to the positive going to the motor. Then in this case I will possibly not damage the board and still control the motor. Or my idea could be completely wrong.

 

The current measured approximately 4 amps.

Did you measure this in series with the motor? That sounds really high for a little RC car motor. Was the motor free-wheeling or stalled? If you just put the meter probes across the battery when measuring amps, you are just shorting out the battery.

 

I am not too familiar with H-bridge. How does it work?

It works like this.

 

In my old slot car days we used to de-wind or rewind the motors to give it that extra kick.

De-wind = remove a couple...few windings.

Although, I have no idea how much extra current your controllers will handle.

 

You need more voltage, and more current. Stacking batteries in series will get you voltage, and using batteries that can supply a lot of current will get you current.

Basically current makes the motor go, more current = more power and speed. You need more voltage to push the current through. Power going into the motor makes it spin, but a spinning motor acts like a generator and causes it to fight back against the power you're putting in. This is called back EMF. Basically the faster the motor spins the more back-emf it makes, basically higher resistance and it becomes harder to push current through, so the faster it spins the more voltage you need to keep the current flowing. The cheapest/easiest way is to stack batteries in series. 9V are horrible for current, AA will give you a lot more but at some point you will hit the current limit of the AA. Google for things like "energizer AA datasheet", look at the datasheets for different batteries (alkaline, lithium, carbon-zink,and see what types of AA give the most current. If you really want to boost it up, go with LiPo as mentioned above.

You can use a boost circuit to boost the voltage, but there are 2 problems; (1) you'll need a big boost circuit to get a lot of current, and (2) you'll need a battery that can supply a ton of current, so might as well just use more batteries.

Edit --> As @ElectricSpidey mentioned above, a motor with less windings will spin faster, at the expense of torque. A motor with more windings will make more torque, but not spin as fast. If you're really dedicated, you can experiment with different winding counts to see where the happy medium is that gives you the best performance.

 

Does a powerful RC car spin its tires like a real powerful car?
Are powerful RC cars All Wheel Drive?

 

... Another possible approach ... depending on accessibility.
If the gears between the motor drive shaft and the wheels are exposed sufficiently, it may be possible to change the gear ratio. A slightly larger diameter motor gear engaging with a slightly smaller diameter wheel shaft gear would produce higher wheel rpm, at the expense of reducing starting torque and initial acceleration.
Here is a related informational article ...
RC car gears

I purchased a new motor online 3V 24,000 RPM. After wiring it to the board

How did you measure the current? I don't think a 9v can put out 4 Amps. I think your original idea of adding AAs is pretty good. Maybe go for 6 AAs? Not sure how much voltage the rest of the circuit can take though.

You are correct I did take the current measurement incorrectly. Dumb mistake I forgot to do. But instead of adding the boost converter I put the rc car back to stock but replaced the rear drive motor with one I bought online. Wired it to the board like the original motor. When picked up and at full throttle the motor spins quickly but when I put it on the ground it jerks. From what I’ve read online it could be cogging. Not quite sure how to fix this issue now or revert back to the original motor.

 

I purchased a new motor online 3V 24,000 RPM. After wiring it to the board

You are correct I did take the current measurement incorrectly. Dumb mistake I forgot to do. But instead of adding the boost converter I put the rc car back to stock but replaced the rear drive motor with one I bought online. Wired it to the board like the original motor. When picked up and at full throttle the motor spins quickly but when I put it on the ground it jerks. From what I’ve read online it could be cogging. Not quite sure how to fix this issue now or revert back to the original motor.

Sounds like gearing ratios too high,, try the motor on a lower voltage..

 

Typically, the maximum power generated by an electric motor is somewhere around the mid-range rpm. If your rpm operating point is at either extreme, one being the stall torque at zero rpm, and the other at no-load rpm, the motor power transferred to the load will be minimal.
... So, no matter what motor you have installed, the operating rpm must be in the right 'neighborhood'.
... Inline with Dodgydave's previous comment, it sounds like your motor is not turning normally, but may be stalled out.

 

Which I realized today as well. I took the voltage going into the boost converter which was at 5V and current 4A. The the voltage and current out had 7.8 volts but 2.8 amps. Significantly lower current which would be causing motor to be weaker. I will probably have to throw away the boost converter idea and try something else.

For any circuit, the power out will not exceed the power in, unless there is an additional power source. Many years ago I did create a winning dragster package for somebody by substituting a 9 vol radio battery for the 2 AA cells.
The battery life was very short, but it did win races, which were only a few seconds. So there are trade-offs.