So you've seen it in action yesterday. It's now almost fully built.
And what a journey it was. I don't think I would have been able to complete it in my "normal" life due to the amount of troubleshooting I needed to do at various different stages. Being an obsesssive kind of person, I just can't rest until I've solved each problem that crops up, and that had led to some very late mornings in the last few days (despite Covid!).
Let's start from scratch again...
So to make a single turner target, as demo in earlier part of the blog, it can definitely be done for under £20 if you already have most of the stuff like wires etc. As listed before, a Pi Pico cost less than £6; a tiny servo like the one I used are less than £2 each. USB cable, battery pack etc I suspect you'll have at home somewhere.
The other assumption I'm making here is that you have some Ikea furniture you would like to repurpose. Most of the material I've used are repurposed from other bits, as I will show you later.
The programming:
Pi Pico are dirt cheap, and if you have a project in mind, and would like to dabble at programming, then Pi Pico is a cheap way of getting into it.
Happy to share my codes with you, but bear in mind it's not the most elegantly written code ever written, but if you are a beginner like me, then it might actually be easier to follow what I'm doing!
The electronics:
Again, you will need at least a button to interact with the unit. A simple push button? Or even a foot switch, or the combo of everything.
Here, I've used a rotary encoder... one that you can turn left or right infinitely. They are cool, but can be a bit daunting to programme unless you know how it works. I just copied the code from Kevin McAleer who has a Robotic YouTube channel as well as shared codes on GitHub (repository of codes that programmer shares between themselves).
You can buy a LCD screen for a few quid which can display graphics, and they are only a few quid. However most of them are about 1.1" in size, which is probably not the best from a practical standpoint. I've opted for a 20 characters, 4 lines (hence 2004) LCD display. Extra cost which I think is worth it.
I've added a buzzer to the build. I've used one that came with a kit that I bought, but they again are mass produced and are very cheap to buy. Without looking I suspect they would be less than £1 each.
The servos:
When I first started I only wanted a single turning target so I can do some Gallery Rifle style shooting at home without a timer. Then for some reason I decided that it would be fun to have a bank of pop up targets, and here we are! I managed to find a set of 10 servos for about £16, but they normally go for around £20 for 10. Again, added cost, but the end result is worth it.
Note that I have stuck with the cheapest of the cheap servo, the 90R. They are not the strongest, but the certainly did the job as demonstrated in a video earlier in this thread. You can opt for a bigger one, the 995 or 996, as used in R/C cars. A note of caution though, they are not as fast as the 90R. In fact, they are a bit sluggish for the gallery rifle style shooting. I bought a set of 4 996R servos, and they are going straight back to Amazon. They are rated for 0.17s for 60 degrees, which sounds fast. The 90R are about 0.1sec for 60 degrees. The difference in quite stark in real life.
They do of course sell high speed servo, but they are about £18 each. Times that by 10... yeah, I know.
Let's keep the cost down!
The wiring:
This was my Achilles's heel for the past 3 days. A servo has 3 wires, Vcc, Ground and Signal. Times that by 10, and all to be held in a fairly tight space, you can see where I am going with this.
Wires wires everywhere!
Those of you with a bit of knowledge of electronics / Hi Fi will probably have spotted a major problem here.
Yes, noise.
The servos are controlled by electronic pulses generated from the Pi Pico, and it tells the servo which position it needs to be in. These servos, although cheap, where behaving quite sensibly on the "test bench" (aka desk!). But when you extend the cabling for it by about 1m, add some DC wires, which itself generates magnetic field (hope you paid attention at school back in the days!), can create noise for the signal wires. That's why a lot of cables for signals (phone, LAN cable, etc) are shielded. Here, I'm just using cheap old unshielded wire, and lots of it. And running the power and signal in parallel, a recipe for disaster!
What you can get is flapping.
The servo is picking up noise, and it doesn't know what position it is in. A gentle tap to stop the movement also "stabilise" it.
The answer is better cable management, and shielded cable to carry the signal. Again, added cost and a trip out to RS Electronics (but I'm Covid isolating so I can't!). Keep the unshielded part short, and run long parts with shielded cable. The other alternative is a ferrous choke (one of those round metal thing, sometimes tubular shape which looked clipped on) but they seemed quite expensive on eBay at £7 each. Times 10 again...
Another issue I created for myself was short circuiting! That's again down to me trying to keep the cost down, as well as no access to a decent electronic shop (I used to have a Maplin catalogue when I was a kid!) I was just using my solid core wire to "plug" into the socket on the servos, and it may have cause some short circuiting, which manifested last night when I was trying to finish the project off. I must have yanked the cable a bit hard, and something might have touch. The damm thing stopped working completely. I spend about 4 hours taking it apart, relook at the wiring, attempted to solder instead to "plug" the servo to the cables (but gave up after one as the quality of the cable was just shocking), and dropping lots of hot glue on various areas so it won't happen again. If you are building one yourself, have a plan on how you would do your cable management.
Switches:
I've already mentioned the rotary encoder earlier.
Have you thought about how you would start it all up? Press the button on the box and run back to your firing point and get your kit ready before the programme starts?
Or have some sort of remote switch?
I've gone for the latter.
I am sure I can use some sort of RF remote, as I have used in my shooting club at Derby. But that means you will need to press the button, then pick up your guns and get ready etc. It breaks your natural rhythm
A foot switch, that's what you need!
A quick tour of the build.
I happened to have one from an old project (again!), so I repurposed that for this. It used to be a variable speed foot switch for my scroll saw (varying electricity output to the saw and so the speed).
But that would means I will also need 6+ metres (or whatever) worth of cable to run it!
Now disclaimer alert. Don't try this at home!
I used normal mains cable, and 3 pin plug! 🤣
Simply because I have 2 reels of 10m extension cables, and I can't travel out to get myself some normal bell wire cables. Plus, with the extension on reel, I can add multiple of them to shoot from up to 25m! Genius or crazy? You decide.
Other than that, I don't think there is much else I would add. Happy to answer questions on here or PM. And happy for more detail technical discussions on anything related to the project.
Imitation is the sincerest form of flattery...
Code for me too please Adrian....Already banging my head against the wall with a Pico starter kit.