Hi everyone!
I’m new to the forum and it’s my first post - go easy 
. I’m not sure this fits ‘robot’ criteria specifically, but it also doesnt fit the RC (Remote Control) world.
The ‘cheap’ project has escalated, as I’m sure many can appreciate! It has now become a remote controlled kids ride-on project which I’d like to have dual controls for control when riding and via remote. For the purpose of providing background and works done so far please see below (yes it’s detailed - hopefully easy to follow). I still want to keep this a budget project, i.e. A few quid, not a hundred quid.
My son had a ride-on car bought for him a couple of years ago (he’s 6 now). This had a 6v battery, 6v RS 390 motor (20-35w), a kids ride-on gearbox and LED lights and speaker for MP3 and car engine noises - it’s one wheel driven and hits 1-2mph on a flat smooth surface with him on it.
- Battery upgrade. I replaced the 6v SLA battery with a 12v SLA battery. Everything worked ok, still a bit slow.
- Motor Upgrade. I bought an RS 890 motor (200w) and replaced the RS 390 motor. Had to remove some of the gears in the gearbox and was fiddly but went well. It works.
- 12v to 24v conversion. I added another 12v battery in series to create a 24v circuit. Surprisingly, existing circuitry held up and it was FAST! However with no ESC (electronic speed controller) it was all or nothing when on the acclerator pedal (an on-(on) rocker switch under a foot pedal) and was a bit lethal, plus the 7a thermal fuse kept tripping when on rougher terrain.
- 36v upgrade. Oh dear! I thought “well the motor should be able to handle up to 36v and has been tested at 48v by others, maybe I’ll add another 12v battery”. I think you can see where this is going. It flicked on but then no signs of life. In my infinite wisdom I removed the fuse and tried again… It set on fire and melted the entire circuit. Wiring melted, on-switch melted, pedal switch melted… It was a smoky mess!
- Removed old circuit. I didn’t understand how the circuit was comprised so I unpicked all the melted wires and attempted to replace key parts, this didn’t really work so I cut away most of the wiring for now. Needless to say, wasn’t working.
- Added speed controller. I bought a cheap DC speed controller (https://www.amazon.co.uk/dp/B075FTQ2ZH/ref=cm_sw_r_cp_api_i_.kRREb56W1PPT) and wired up the now 36v battery and the motor. I kept it very simple and didn’t connect any of the old circuitry, I bought 6mm2 cable (overkill perhaps) and wired battery and motor to the ESC, using the existing slots in the dashboard for the potentiometer (pot) dial and LED display screen showing 0-100% of power usage (volts). Worked a treat. On-off was controlled by the pot as was the speed. Was still lethal as there was no other way to control the speed or turn it off, so it ran away a few times. To give you an idea of the power, it was built for a 15KG rider and with me on it (90+ KG) was able to hit around 12-15mph…
- Traction issues. Driven by one plastic wheel was a problem (wheel spinning on all terrain), solved by cutting an old bike tyre and fitting - worked much better than expected and has held up very well.
- Stability/control issues. With all that power through one wheel, the car would pull violently when under higher power and would wheelie.
- 2 rear wheel drive. Options are to power the axle or to power the other rear wheel. I went for powering the other rear wheel because, well, for one MORE POWER and two the axle is a fixed steel bar and I would have to completely change the structure of the car (also more expensive). I have purchased another RS 890 motor, gear, fixing bracket, ride-on gearbox and tyre adapter (all for about £25) - This hasn’t arrived yet.
- Remote control. I wanted to add controls which would power on/off the car, as well as control speed (Steering we can talk about later, it’s not something I’m considering until after I have a basic remote control version up and running). I purchased a 12v remote controlled DC relay, the idea being this can be used with a simple IR remote like a car keyfob to start/stop the ESC. This is yet to arrive but does present a problem as the ESC, although able to handle 60v and 30A, runs at around 1v I believe, not enough to power the relay. (Relay yet to arrive)
- Resolve relay power issues. I decided that running on one of the 12v batteries would work well enough, so why not re-wire all of the LEDs, speaker etc. and power it via a DPST on/off switch which essentially powers on/off both the 1v ESC circuit and now the 12v LED, speaker, MP3 circuit to one of the 12v batteries. Worked a charm, whilst still having all 3 x 12v powering the ESC/motor.
- More control/usability. To add more control and prepare for the additional motor, I upgraded the ESC to this: https://www.amazon.co.uk/dp/B075FTL53W/ref=cm_sw_em_r_mt_dp_U_PTRREbYKWQEFV which should now handle up to 100A and adds reverse/forward. Power to motor is controlled by the on/off switch, a forward-stop-reverse switch and the potentiometer which ranges from 0-100% of power. I have an on-(on) replacement rocker arriving tomorrow for the acclerator pedal so all being well plenty of ride-on controls and pretty much back to original functionality.
- Upgraded traction and other bits. I’m currently upgrading all wheels with new tyres, to help with the 2WD when it’s in place and grip when steering. The charger port now allows for charging without having to entirely remove all batteries and charge externally, this is a switched jack so I’ve also ensured the main circuit disconnects when plugged in. I also moved one of the batteries to under the bonnet to help with weight distribution.
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The remote control problem. Finally! I want to be able to control the ride on speed with an RC (remote control) controller, ideally a transmitter/receiver like this: https://wheelspinmodels.co.uk/i/298083/. This would replace the job of the potentiometer, however based on my research it’s not a simple plug and play:
14a. The potentiometer (100K) controls voltage on the ESC from 0-100% of the circuit voltage, which I believe is 1v.
14b. An RC receiver sends PWM pulses to an ESC normally to determine motor speed, however the usual ESCs are built specifically to recognise this and as they are primarily for smaller remote controlled vehicles, they don’t cater for the higher amp and voltage motor.
14c. I’d like to think I can add an input, in parallel to the pot, add a relay to the pot to disconnect when I assume control, and take over speed control.
14d. I believe replicating the inputs and outputs of the pot, ‘processing’ via an arduino or similar and presenting back to the ESC may work but I’m out of my depth here.
Next Steps
- Remote control. Figure out how to remote control speed with RC remote (see ‘Q’ below).
- Accelerator Pedal. Fit accelerator pedal switch (arrives tomorrow)
- Add relay. Fit relay switch (https://banggood.app.link/8vq1kOMHb6) when here
- 2WD. Fit 2nd motor when here
- LED Display. Find a way to move the LED display from the ESC circuit board into dashboard (help welcome here - I don’t know terms for mounts/wiring types etc.)
- Steering. Consider a motor or servo for steering control (maybe - after this RC build)
Ok, so what do I need help with specifically?
Q: How can I control the ESC remotely, without changing the ESC or overhauling the build/project?
If you need more information please ask. I have photos for the various stages if that helps. Assuming I can get past this stage with your help, there are a few tweaks I’d like to make to the circuit as well as the steering challenge to make this fully remote controlled.
Thanks in advance!