Our FRC team has a lot of kids interested in robot software this year but most of them have very little experience in programming so I’m looking for some fun projects we can do using the XRP to get them started.
We came up with a couple of ideas but I’m sure there are plenty of others out there. It might be nice to get a list going somewhere since plenty of other folks are probably in the same boat that we are. I’d love some creative ideas for teaching PID.
Here’s a couple of simple to get started:
Escape from the box: set up some 2x4’s (or other barrier) on the floor with only one possible exit. Write code to escape from the “box”.
Draw a picture: insert a dry erase marker in the hole in the center and draw a shape. A square would be a good one to start with but obviously anything goes here.
Line following: start with simply following a line. Perhaps create a contest to see who can go from the beginning to the end faster.
I did this by putting some holes inline with the motor shafts so I could attach some big wheels. Then use the IMU and encoders to keep the robot balanced and stay in the same spot. A stretch goal can be to make it remote controlled as well!
I assume that you are using the holes through the frame that you added to this design as a bearing surfaces for the extended axles. If so, then the holes need to be carefully aligned with the location of the motor output shafts. How are you locating those holes in the new design?
Nope, not using the frame as a bearing surface, the motor axles take the entire load. I know this isn’t necessarily best practice, but the robot really isn’t that heavy, so I’m not personally too concerned about it (I’ve not observed any negative effects). So no careful measuring needed either, the old eyeball-micrometer works fine if you make the hole big enough
If you want to print a 3D frame, in the printables for the project go to the files and there is an alpha “holey” frame that has the holes built into it.
Thank you. I had seen the ‘holey’ frame but somehow missed that it included the holes for extended axles.
Are the holes in the channels of the ‘holey’ frame sized to be self-tapping for M3 screws?
I game piece that is cheap and vinyl floor tile friendly is disposable cups.
We use them in the game we play at the end of our course in the current robotics curriculum.
I will likely keep the game as we switch over to the XRP platform.
We used to build the robots from scratch with arduinos, laser cut chassis, 3D printed parts and such, but are switching over to XRP robots for this competition.
I just modified it for xrp robots, so there could be some mistakes
The rules don’t limit you to only powering with the XRP’s onboard batteries. So for instance if you wanted to run a 12v fan to blow game pieces around, what would be legal but the circuit would only be able to run a maximum of 18v. We used to do the competition powered by rechargeable “9v” batteries so “18v” was two of those. I still have a ton of those batteries so I figured I’d leave that in.
The limiting component is the motor driver chips. They have a recommended operating voltage of 11V with an absolute max of 12V (see section 6 of the datasheet).
!!! However, DO NOT use a 3S lithium battery or any other kind of battery with a nominal voltage close to 11V or 12V !!!
The “nominal” voltage of a battery is usually less than the maximum voltage of a battery. For lithium-ion batteries, for example, the max voltage per cell is typically around 4.2V; so for a 2S lithium battery, the max voltage would be 8.4V (fine); for a 3S lithium battery, the max voltage would be 12.6V (not fine!). For another example, a 12V NiMH battery pack, the max voltage is typically 14-15V.
Additionally, motors create back-EMF all the time, which sends power back to the board and briefly raises the voltage of the power rail even more. So you want to ensure you have some buffer for that and other effects that could cause the voltage to rise.
So it’s fine if you want to use battery packs with higher voltage, just by aware that the max voltage is usually higher than the nominal voltage, and do your best to not exceed 11V. If it hits 11.1V, that’s probably fine, but we cannot make any guarantees above 11V, that’s your risk to take.
Hi, I am interested in this balancing project for my students. Do you have more info? CAD parts, sample codes, Github repos, etc. Please advise. Thanks.
Sorry, I don’t really have anything shareable. The wheels I used are no longer stocked, I don’t have the original CAD files for the adapter shafts I 3D printed, and the code is very hacked together in a way that most likely won’t work for others. It really needs to be redone from the ground up to be a properly shareable project.
