One of the first things to consider when designing our robot is the chassis – the mechanical platform including wheels and motors – to which we will attach our electronics, sensors and other body-parts.
We want to be guided by a few simple principles
- Keep it simple
- Don’t re-invent the wheel
- Spend your money wisely
- Prototype early
It is easy to find robot chassis available for sale on the Internet whether with two, four or six wheels, and with varied levels of quality and cost. In order to get to a point where we can start with the coding (which is likely the part where we will be spending most of our time) it would make sense to choose something that doesn’t cost too much an that is easy to assemble.
This simple four-wheel drive chassis, made up of two sheets of perspex seems like a perfect candidate. It only costs about £15 and seems like it would make a decent platform for prototyping the electronics and software. The main drawback of this chassis is the materials and quality of the gears and fixing of the wheel to the shaft. These parts are all plastic and depending on the weight and acceleration of the robot this joint between the shaft and wheel may break and start to slip. If your robot is heavy you might want to look for some metal gear motors instead with a more robust fixing to the wheel.
To control the motors we are choosing a DC & Stepper Motor HAT from the company Adafruit. We chose this motor controller board for a number of reasons. It can conrol 4 dc motors in two directions and it is fitted with industry standard components.
It seems robust, but most importantly, it has good example software available for download which will help to get the first version of the robot up and running quickly.
At about £20 it might be slightly more expensive than some other options but spending a bit more on a decent motor controller that is well supported seems like a reasonable thing to do.
The next thing to decide is how to power the robot. There are a number of different battery solutions to choose from, whether LiPo, NiMH, with different voltages and mAh ratings. Safety is also a factor to consider when choosing a battery solution as incorrect usage of especially LiPo batteries can cause them to overheat with dramatic consequences.
After doing some research, the best option for us seems to be to stick with the tried and tested and go for a typical RC car battery solution. These are typically 7.2V NiMH batteries, although there are also LiPo alternatives. For us, at this point it doesn’t really matter what the capacity of the batteries are as long as they are safe and don’t cost too much including the chargers.
The chosen battery is an Overlander 3300mah 7.2v Sport Stick Pack which cost £14 and the Fusion Vector NX86 Delta Peak AC/DC Fast Charger for £23.
What would you recommend as a good starting point for a robot chassis? Feel free to put a comment in the comments section below.