Robotics is a mix of several disciplines. There is computer science to program your robot and keep track of versioning and containerizing your code. You need to know a mix of low level C for real time control and high level code for the general application development. Optionally you need to include Robot Operating System. For the hardware side you need some electrical engineering and some mechanical engineering. When getting started it can get confusing and you might have several false starts and pitfalls. The article serves as a general manual to select your initial parts and to let you know some issues you might run into. It is applicable to robots built using the AMD Kria KR260, the Nvidia Jetson Nano or Raspberry Pi or whatever board you start off with. Particularly I will cover use cases, robot right sizing, and power distribution. I will show where small robots are better and when you need larger robots. I will also cover what components you might not be aware you need in some cases or can avoid in others.
Starter Kits Online
When you search online for robotics classes or robotics kits, you will you will often see kits some basic kits available for $30. First of all these are actually overpriced. These usually come with 2 or 4 motors with wires already connected to the motors themselves, some standoffs, brackets, and two plastic mounting plates. Sometimes but not often they add a motor driver called the L298n. Why are they overpriced? Because you can easily make these out of cardboard or packaging around your house and because when you start adding anything other than your driver board, you will quickly start to run out of space. So instead of using these kits directly, you can order the components separately. Particularly you can get sets of TT motors + wheels, a set of L298n motor drivers, and a set of screws and standoffs. This would be either the same cost as the basic kits or cheaper and it would give you extra components in case your original ones break, especially since the motor wires are very flimsy.
Here is an example of such a cardboard robot driven with the KR260. Ignore the wiring for now, the robot fell and some wires broke so I am waiting for some additional components to arrive.
Why would you add more things other than your Jetson Nano/Pi/KR260? Because for any practical robot you don't just want to drive it, you want to have it do a task. Maybe you want it to navigate and patrol your greenhouse or maybe you want it to harvest strawberries or you want it to clean your house with a mop or vacuum. Two of these tasks don't even do much other than navigation but even there you have the space requirements for additional cameras, or for a vacuum and waste disposal. Navigation itself may require either a depth camera in addition to your regular camera or a LiDAR and distance sensors.
If you already had a plan to make a robot with these additional components you might start off looking for a larger pre-built kit. In this case you would get into the $100-$150 range with aluminum plates and larger motors. Even if the actual plates that come with the kit can't hold your components, you could just add more on top but I still suggest being careful about these. Now due to the larger motors to push this robot, you also need a larger power supply. Here things get much more complex and potentially dangerous and the cost of your robot will significantly shoot up. The next sections show you how.
Power Supply
Some small robot kits come with a battery holder for 4 AA batteries. These are not to power your compute board but to power the motors. The small yellow motors in these kits are called TT motors. They are very common and very cheap but they aren't very powerful. They might look fast and on a completely flat surface they actually kind of are fast when fully powered. But when you put them on carpet, they become slower. If you add more weight, again they get slower.
To get around this, you can add more wheels. Some kits come with 2 TT motors and a castor wheel. These are easier from a build and a controls perspective but more motors add more power. So depending on your task you can use 4 or 6 TT motors and power them with AA batteries. The LN298 motor driver can drive 2 wheels so with a 2 wheel configuration you need just one driver with 4 you can wire the two left motors to OUT1 and two right motors to OUT2 to avoid adding two drivers. Alternatively, you can wire the power supply to your breadboard and connect the L298n inputs to that side of the breadboard to power 2 drivers for 4 motors. And you would need to make similar decisions for 6 or more motors. L298n motor drivers and battery packs for 4x AA batteries usually come in bundles of at least 2 and are very cheap.
Alternatively, you can use the higher power motors. In that case, the AA batteries no longer work and you have a few different options. A common one is Lipo battery. You have to buy the battery and a balance charger and you have to be very careful about how you charge the device because they can cause battery fires. Other options are NiMh batteries or sets of 18650 batteries or LiFePO4 batteries. In terms of costs, the batteries and their related charger would run you more than $150. Then you also have to consider the power distribution. For single motor driver configuration you can get away with just connecting the battery to the driver and then have the driver distribute power to your motors. But if you are using the multi motor driver option, you will also need to add a terminal block because your breadboard will not be enough to distribute power from the 12v battery. Also you are now more likely to need more than one motor driver because the larger motors can't be powered properly by L298n drivers. In my projects where these types of motors are required, I prefer the IBT_2 motor drivers which have only one output. Again, as with the L298s, you can tie two motors on the same side of your bot to the same driver to reduce the number of required drivers so for a 4 wheel drive bot you at least need 2 drivers. The power supply, the terminal block, and external charger are not the end either. Now that you are working with high voltages and more expensive components you are going to need fuses to protect these components and external switches to power them off for safety.
Power Supply for Compute Devices
If you are using a Raspberry Pi, that is the simplest thing to power. You need a USB power bank and it should work fine. Just make sure it is 5 volts and 3 amps minimum(5 A for Raspberry Pi 5). If you add USB components to the PI, you need to consider the power draw from them as well.
Jetson Nano starts to get more tricky because while you can power it from a power bank, it will have reduced performance. This is because on USB, the Nano switches to its 5 Watt mode so you need to make sure any computer vision or other processing done on the Nano can be done in that mode. The KR260, its similar to the Nano. You can get a USB C to DC cable with 12 V support and you may need to use a larger 65 Watt power bank. There are also ways to make custom solutions for both to power them from the same battery that is powering the motors but I would suggest doing that only if you are already much more experienced with electrical engineering. Lastly as with the Pi, the more USB devices you attach, the more the power draw will increase so you may need to calibrate for your application.
Conclusion:
This is not as complex as it sounds but you need to keep in mind the environment your bot is driving in and the load it is carrying. If you are going into a greenhouse or farm you definitely need these components otherwise your motors will start getting fried quickly. If you are driving on a flat surface, even with a slight load you could get away with TT motors only. Personally I think that is the ideal solution due to the simplicity and cost. But if you need to carry more load or drive on uneven terrain, you will need the large motor solution described above. I didn't cover quadruped robots or servo motors here and I didn't cover the details of wiring the motor drivers which are covered well in many other resources, one of which is linked below. Quadrupeds are a niche case where the terrain would not support wheels or when you need to climb stairs, when getting started I don't suggest using them. Servos come in two types, there are 180 degree servos used by quadruped robots or camera tilt/pan and there are continuous rotation servos/360 degree servos which may be used in place of DC motors without needing the motor drivers. They are less powerful than DC motors however and more expensive so the TT motors covered here would serve the same use case better. Still a resource for Bot Bot Kit which uses servos in place of DC motors is also linked below.