Parts list:
Motor and drive train combo: 2 x 550 30000RPM Gearbox with 12V Motor,Electric Motor with Gear Box for Kids Electric Cars and Motorcycles High Speed RS550 Drive Engine Match Children's Ride on Cars https://www.amazon.com/dp/B076Q3XTWB/ref=cm_sw_r_cp_api_i_PiZADbZK937A2
Transmission to wheel adapter: Transmission Gear External Gear Accessories Connect Gearbox Motor and Wheels for Kids Powered Ride-Ons, 550 Gearbox Accessories Kids Ride On Car Replacement Parts E https://www.amazon.com/dp/B076HW2W98/ref=cm_sw_r_cp_api_i_TlZADbWF68M45
Variable speed controller: RioRand 7-80V PWM DC Motor Speed Controller Switch 30A https://www.amazon.com/dp/B071NQ5G71/ref=cm_sw_r_cp_api_i_LjZADbQSB11QY
Connectors: Amass 10 Pair XT60H Bullet Connector Plug Upgrated of XT60 Sheath Female & Male Gold Plated for RC Parts ... https://www.amazon.com/dp/B074PN6N4K/ref=cm_sw_r_cp_api_i_nkZADbG4NVM0E
Spade connectors: Supco T1112 Quick Disconnect, High Temperature, 12-10 Gauge, 1/4" Female Tab (Pack of 15) https://www.amazon.com/dp/B0071NC78C/ref=cm_sw_r_cp_api_i_olZADbX56T2WB
Battery terminal: https://www.ereplacementparts.com/contact-plate-holder-p-154719.html?osCsid=ijjl2im5cg4p7n3dm3k1cbpjv6
Voltage meter: MICTUNING MIC-VM DC 12V LED... https://www.amazon.com/dp/B078LVLHNF?ref=ppx_pop_mob_ap_share
Note: no affiliate links. All straight links!!!
This all started off with my wife saying that Lightning was a little too slow! I said no problem I got this.
So my first step was to investigate what was the best way to go about this. After a while of researching the best way, I realized that they are more or less oversized versions of my rc cars that I race. With that in mind I was able to do everything.
I started the conversion using just one of the motors. This was so I could make sure I was mentally doing it all right. While the transmission was close to the stock one, it was not a exact fit. I ended up having to trim away some extra plastic and make the opening larger.
Now that the motor and trans is in for the right side I had to start looking at the wiring. The wiring that is in there stock was 18 gauge and while technically will handle the 18v I wanted to be sure we did not melt any wires. I swapped it out one by one using the same 12 gauge wire I use in my RC cars.
The first wires I did was the battery connector. I found the connectors online and used a epoxy putty to make the socket. This ensures the connection is good to the battery.
I then proceeded to replace wires in the harness one by one till they were all replaced. Once it was all setup stock it was time to add in the speed controller. This allows me to turn the speed down (by adjusting the voltage.) I put it online between the battery and the rest of the wire harness. I did it here because it was not able to handle flipping the polarity for reverse. (Popped a fuse finding that out lol. )
Once this was wired up I was able to add in the “fuel gauge”. I put it in what is the “gas cap” on the car. This is a simple dc voltage meter. Nothing fancy here.
Once all that was wired. I needed to make a “Y” splitter for the motors. I know this puts them in parallel all the time and down the road I might change that but for now just forward and reverse was good enough.
Since this car was a single drive motor previously I had to completely make a new hole for this second motor. This was a bit simpler then making room for the first motor.
One thing to note on wiring the second motor. You will want to do it in reverse of the first one as it is spinning the opposite direction of the first motor.
After this was done they only thing I did was relocate the dial for the speed controller from on the speed controller to on the back of the car under the rear fender. This was so I can adjust it without having to remove the seat to adjust it. One thing I may still add is a master power switch. I know this car has one but due to positioning I had to put the battery meter before that switch.
One thing that is still a work in progress is I bought a mltoys brake reduction system. The problem is I was not sure which wire it should go to. This is not the typical plunger switch gas peddle. It is a 6 poll rocker switch. Once they get back to me with that I will get it installed so it is not as jerky on starts and stops.
I'm doing almost the exact same thing in the next couple weeks to a F150 Power Wheels. I'm going to be using 2 18v batteries in parallel. I decided to be safe and add a fuse to the positive of each battery (30a). I'm combining the two battery leads into a distro block, and from there into a 40a breaker switch so to prevent damage to any of the components down the line should the system draw too much from both batteries at once.
40a Breaker
https://www.amazon.com/gp/product/B000K2K6YS/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
From the 40a breaker, I head out to two places just like yours.
One lead heads to the step down to run lights on a dash switch. Again, I added a 10amp fuse inline on the lights to prevent any weirdness there.
The other lead heads to a voltage regulator that will then head into the motor wiring harness (shifter, pedal and then motors).
After looking at your diagram, I'm not seeing anything that looks off. I think it will turn out great! I would recommend adding an inline resistor on the brake pedal (orange wire) to limit the instant off on the motors to help prevent the wear on the motors. I choose
https://www.amazon.com/gp/product/B008MLL3JQ/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
I'm also adding a volt meter on the dash to let the kiddos keep an eye on their battery life. The battery controller chip (same as yours) will cut off at 16.5, but I figured they'd at least know when it was time to head home when it hits the high 16's.
Other parts
https://www.amazon.com/gp/product/B07929Y5SZ/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B071NQ5G71/ref=ppx_yo_dt_b_asin_title_o06_s01?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B01EFUHFDU/ref=ppx_yo_dt_b_asin_title_o06_s01?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B07TYSP7KV/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1
Seems like it would work. You could put a PWM controller on them to get speed control and slow them down to a quiet level.
I've found a bunch of people using DC motor speed controllers like this one:
https://www.amazon.com/dp/B071NQ5G71/
I got this specific amazon listing from the description of this video:
This is a common problem. Common enough that no-name Chinese vendors sell exactly what you likely need on Amazon.com for example: https://www.amazon.com/RioRand-7-80V-Motor-Controller-Switch/dp/B071NQ5G71
You can add a PWM Speed controller inline with the second battery which would let you control how much extra voltage is applied with a knob. This is the one I used: RioRand 7-70V PWM DC Motor Speed Controller Switch 30A https://www.amazon.com/dp/B071NQ5G71/ref=cm_sw_r_cp_api_glt_fabc_KKTDHRRE44XGY3HJ9ZJC?_encoding=UTF8&psc=1
For my project, I wired two 18v batteries in parallel to double the capacity, then added the above PWM to reduce the voltage until my little one can handle >12v.
I have a spare DC speed controller sitting around. Was used for a week before I purchased the ML toys variable pedal/speed controller kit. You're welcome to have mine. Just pay shipping
It's the exact one /u/FlickeringLCD posted https://www.amazon.com/dp/B071NQ5G71/