Building an autonomous truck from scratch: Part 1

With each blog post on this site, I’ve made an effort to not only explore new areas of engineering and computer science, but also to try to increase the technical level of the topics covered. Continuing with this trend, the latest project I’ve been working on is by far the most complex yet; I’ve decided to build a self driving car. Because of the amount of time it will take me, I will be posting the project in multiple parts. In this post I’ll cover the vehicle platform I have chosen.

I spent a good deal of time creating the specifications I would need for the foundations of my car. Now, I obviously do not have the financial, legal or intellectual means to create an autonomous automobile out of a full size vehicle, so I had to consider the alternatives. I could either build a chassis from scratch, giving me great control over its design and capabilities, or I could buy a remote control car and convert it for my use. I concluded that building the vehicle from scratch would be far too much hassle than it was worth, and so I began researching RC cars. Much in the same way multirotors can be split into distinct categories based on price, RC cars vary in quality depending on how much they are worth. As with anything, beyond a point you can only expect diminishing returns, but you get what you pay for the most part. In the context of budget RC cars, this is represented largely by what motor the vehicle comes with, and the durability of the materials used. (See my “How to: Quadcopter” post for more information on the differences between motors). I found it was all too easy to slowly begin looking at more and more expensive cars, many times greater than my budget. I must admit, the temptation to buy an outrageously powerful monster truck was difficult to resist, but at that point I realised I needed to review my priorities.

These are the list of requirements I had for the vehicle:

• Low cost
• Large cargo capacity
• Slower top speed than me
• Proportional steering (servo-based)
• Some off roading capability
• Representative of a real vehicle
• Looks good

(Ok, I’ll admit the last one was not a proper requirement but I still definitely considered it).

After I considered all of these factors, only two vehicles that I had come across in my research fit the bill: the WPL B1 and the WPL B24. Not much seemed to separate these two trucks other than their cosmetic differences and the presence of a spare wheel on the B24. Upon closer inspection, however, I discovered the bed of the B24 was ~10mm longer than the B1’s. Since the truck would need to be functional first-and-foremost, I ended up ordering the B24.

A couple weeks later, the truck arrived from China. The variant I opted for was the kit model, as I would be supplying my own electronics. I also figured I would have a greater understanding as to how the truck works if I built it myself. 

The first step was to assemble the cabin. This was fairly straightforward as it was a case of snapping body panels onto the main piece. For a little extra detail, I cut small squares of reflective plastic and superglued them onto the wing mirrors. I decided to omit the seats and steering wheel, at least until I know how much space I'll need for the electronics that I'll be putting on board. 

Next was the chassis. It was slightly more involved to build than the cabin, as all the parts needed to be lined up in the correct positions before the two metal strips could be screwed together. 

Assembling the differentials and axles was one of the most rewarding steps of the build, as it proved to be a good challenge. Once they were assembled, it was extremely interesting to see how the servo would steer the front axle whilst maintaining power delivery to the front wheels. I thought the hybrid metal and plastic leaf springs were a great touch, keeping the cost of the model down but still giving a considerable range of motion for the axles. 

Connecting the motor to the transmission was the most difficult part of the build. Firstly, the motor barely has enough tolerance to fit, making it extremely hard to push into place. Secondly, I decided to open up the transfer case to add extra lubricant to the gears. Of course, the transmission managed to spontaneously disassemble itself, and I had to spend a good length of time trying to fit the small gears back into place, while my hands became more and more coated in grease. Luckily, I was able to get it back in one piece. I then screwed the motor and transfer case into position on the chassis along with the bed of the truck.

The rear diff -- note the driveshaft and transfer case to the right

Next I assembled all of the wheels. I was then able to add the spare tyre to the truck, before screwing the rest of the wheels onto either end of each axle. 

All that remained was to clip the cabin onto the hinge at the front of the chassis, and I had a finished truck!

The forward-opening "hood" of the truck

I'm really happy with how the truck turned out. For £24 shipped, the WPL B24 represents great value for money. I'm especially pleased with the drivetrain and scale details, as although they are plastic, they do a great job of emulating a real truck. I hope to begin work on the electronics of the truck soon, once all of the components arrive. Keep a lookout for future installments in this series.

To keep up-to-date on this and future projects, join the mailing list by pressing the “Subscribe” button at the top of the page.