So this is of topic but what is a good amount of time to spend loading(auto)?
The limit is going to depend on the design, but pretty much as fast as it'll flow. You want to ease it open to get a little "settling" weight in- maybe a kilo, then smoothly open up to full flow. All I've seen use a 5 gal water jug as a hopper, so max flow rate is what'll run out the neck. As I noted in my last post, the one we used at State was on the order of 10 seconds. The type of mechanism used to hold the sand back/let it flow can either allow that "full" flow rate, or reduce it somewhat. Full flow is on the order of 10 sec with ....normal "sandbox" sand.
A thing to keep in mind- at any tournament with two loaders, watch, early-on; know which is faster (if there's a significant difference)- three guesses which you want to use- and the first two don't count....
Does anyone have plans for, or know a link for plans to building an Auto-Loader? I'd love to build one for our team to test with.
I don't have time to chase down this morning, but I believe I've seen plans on-line- a little searching might turn something up. There are certainly a lot of videos out there where you can see overall design, which is pretty straightforward. Key is getting details on open/shut mechanism...
I'll check w/ our local schools to see if plans exist; the units have been around for years, so plans may have dissapeared.
I agree with Len... Plans are out there somewhere, I've seen them also... i've built several over the years, and have a few thoughts to share:
The spout of the water bottle doesn't have enough slope, so you need to put a funnel inside the hopper to make the bottom (which is actually the top) a steeper angle.
Use a flexible Fernco rubber plumbing elbow with worm clamps to transition from hopper to PVC chute
I prefer a spring loaded knife valve, cut into the top of the chute as opposed to a flapper valve mounted to the end of the chute, because a flapper tends to throw sand back, on to the floor when it slams shut.
Use a really good grade of sand blasting sand, like black diamond. Yes, it's expensive ($15 / 50 pound), but it has not dust and is a little larger grit, so it doesn't slip past the knife valve
Spring load (Extension Spring)the knife valve,pinned on one side, with a lever handle on the other, then attach the handle of the valve to the release lever pushed by the contestant with a detachable link (archery release, or 3 eyebolts aligned with a pin through them works well.
Connect a string to the release, that the E/C can hold on to, so that when the structure fails, the E/C can trigger the release, and the knife valve slams shut immediately, removing that issue of how much sand do I remove?
If you are really serious about building one, let me know, and I can send you picks of how ours it put together... Not to say it can't be improved some, but it has worked for us for 10 years now.