EDIT: Find the story of adding an on-board HackHD and the video here.
I had bought this really cheap 27MHz R/C car for around 200 rupees, which is about 5 dollars some time back. It had been gathering dust in a corner of my room since I found driving it really boring and buying batteries made me broke. There was a lack of feel in driving, something which I thought I could change.
The original car was absolutely El-Cheapo – extremely basic 27 Mhz RX-2G based control, microscopic remote, no suspension installed and it used a brushed motor for turning (thus no proportional control – only extreme left or extreme right). The drive system was even creaky and not oiled.
While cleaning my room, I found it and began thinking about what could be done – for starters, I could add a simple suspension – The car had space for adding springs, but none were installed, so I installed a couple of tight springs, thus giving the car a nice ‘springy’ feel. Next I went completely overdrive and replaced the AA batteries with my own dual 3.7v 30C Lithium-Polymer packs in series to give 7.4v ‘flat’ pack.
But still, I was not satisfied. So I went ahead and added a Arduino! Installed a 6 channel radio (HKT6-A) and repurposed the transistor-based H-Bridge from the receiver since I did not have any spare L293D motor drivers. At this stage, the lack of proportional steering hit me, so I modified the turning system with a spare micro-servo. Next, I opened up the drive system and upgraded the brushed motor for a more powerful one from a toy helicopter. Oiled up the cogs and we were ready to go!
The code at the moment is pretty simple and uses an interrupt-driven approach to get the R/C signals from the receiver and appropriately mixes the channels and passes it onto the servo or H-Bridge. At the moment the code is in development and I won’t be releasing it yet until I finish adding all the features. I have plans to integrate GPS navigation to waypoints, a transmitter calibration function system, adaptive yaw control using FreeIMU, Sonar or IR sensors (whichever I find is more suitable) for collision avoidance and adaptive terrain control (changing maximum speed depending on driving surface). That is it for now, and I will be following up on features added in future posts.
Now for driving experience – through all my upgrades, the station wagon became a Mercedes! It can accelerate extremely fast and cruise at around 3-4 m/s, thanks to the high-discharge LiPo pack and weight reduction due to using LiPos. Turning is a breeze and I love the proportional control! It is extremely maneuverable even at top speed. On slippery marble floors, it has a habit of fishtailing when it builds up a lot of speed and also, it skids on hard reverse or accelerating from stopped condition. But on a slightly rough surface like cement – aww, its just sheer driving pleasure mixed with a dollop of speed!
I get around 35 minutes of continuous driving with my current LiPos. Niice, compared to the 15 mins on AAs.
Enjoy the photos below, till I make the video tomorrow (its night now in India) and upload it 😉 Then you can judge for yourself.