Our team is planing on building a tennis ball shooting robot for our host organization. It is going to have to go through camping conditions, dirt, mud, sand, and alital bit of water . It will have people with limited to no robotics experience operate and maintain it.
I want it to have a super simple electronics and battery interface so that it can be charged/change batteries super easily. It also needs to have fail safes because it will be in operation near kids and were trying to incourage them to join our team, not fear us.
Put the electronics in surplus military ammunition boxes, the lids can be removed for operating and they have a watertight seal. Also, they are easy to come by, surplus center almost always has them.
Edit: these are a bit wider, and I have first hand experience with them and know that they are good boxes. The ones I linked to before are only 4 inches wide and look rather thin compared to the .50 cal boxes
You donāt want dirt & mud in your transmission, so I suggest building something with minimal chain & protected gearboxes. Also, if your motors are going to be running constantly, you may want to find some way to cool them.
I was planing on using a vex cortex with joystick and partner joystick. For motor controllers I was thinking of using victors and vex spin controllers. Anything better than this that you can think of? And is there a good alternate to CIMs for drive-train?
Also thanks for the suggestion for the ammo box, what would be the best way to waterproof any holes for wires, hotglue? And any ideas on keeping the battery away from derbies without putting it in a metal box ,dont want it shortcircuting:ahh:.
When I used them for a similar purpose I cut a piece of plywood that fit in the bottom of the box and attached foam-core board on the four sides to create a box within a box. Unfortunately I never finished them (maybe I will this summer) so I have no photos for reference. For wires I would recommend a silicone based sealant . Your local boating supply shop should have something suitable. If the silicone proves to be too weak, you can try polyurethane instead, but then you sacrifice the convenience of soap and water clean-up. Blends of the two are also available.
Something similar to this would work well for electronics, and you can find one to mount the battery within. I would use caulking to waterproof any holes you might need to cut.
These cases are meant to be exposed to the conditions you described, and come in nearly any size you can imagine.
Consider competitions such as IGVC as a resource: www.igvc.org This is a university level competition that is run outside on a grassy field rain or shine.
Please use silicone sealant that is rated for use in an electronics environment. The stuff you normally get at boating shop and your local hardware big box store
are not. The sealant off-gases acidic compounds as it dries and hardens and this will corrode electronics.
RC is a good suggestion, as receivers are tiny and anything 2.4 ghz is very safe, reliable, and plug & play. A v-tail mixer sold for airplanes is also a ātank drive mixerā for arcade style driving.
Traxxas brand RC cars have waterproof housings for receivers that can be had on ebay for $5, very useful guys.
Iād recommend you take a good look at things that require grease/lubrication and try to minimize them. Exposed chain on this will be a dealbreaker in the long run.
Also, I would like to change my recommendation to Sugru. Not only is it designed to be compatible with electronics, but it also molds like playdough and comes in green (and red and blue andā¦)
little kids+nobody around that knows robots well+pinch points=lost body parts. Lets face it, the kids you want to recrut are the ones that will take the chaingaurd off to watch the chain and those same kids will likely forget to put it backā¦
to put it nicely: if there is something dangerous you can get to, kids WILL get to it sooner or latter. chains and gears have to be accessible so they can be greased. chains and belts have to be accessible so they can be put back on if they come off or break. If you have to have these things, bolts with unusual heads (and maby a lock washer or lock nut or both) is a good idea to slow kids down.
also, stay away from small bolts as the heads strip faster the smaller they are and donāt have wires within drill length of boltsā¦ we donāt want someone thinking they are being smart and drilling out a striped bolt and accidentally electrocuting themselves/shorting it out/ stopping the robot from working.
If you are going to be around little kids you might want to consider firing something besides tennis balls. And you certainly want to carefully consider exit velocity, firing safeguards, etc.
For that eventual day when someone gets hit (and it will happen) you want it to be something soft and/or very low velocity. A high speed tennis ball could actually do some serious damage.
Agreed. You could start with a set of Nanotubes as the basis for a simple 4WD or 6wheel drop center with the front wheels unpowered. With no chain and all the gearboxes enclosed (except for lightening holes) you can enclose the tubes with Lexan (or even tape if you clean it well enough) to keep the gearboxes safe and fingers out. If you add fenders over the wheels and a solid belly pan, that should keep most of the crud out.
I wonāt speak to the electrical side, as others are much more qualified.
Weāre working on this approach for a baseball pitching robot at the request of the local minor-league baseball team. Iāll post photos when done.
Thanks everyone for your help!
Iām thinking we will use the ammo boxes for the electronics and the pelican boxes for the batteries. Any holes Ill cover over with Sugru. To shoot, nerfballs, and cover the whole thing in lexan. And also I think we will use tamper proof screws so that no-one can unscrew anything.
Do you know if the RC receivers have the right pulse width to Jaguars or Victors? Also does anyone have any experience with tamper proof screws/bolts?
Victors were designed to use the same PWM signals as RC servos. Jaguars will work, but wonāt get the full range of outputs unless you recalibrate them. You might need a signal booster, depending on the receiverās ability to supply current.
I think that tamper-proof hardware isnāt really appropriate unless you intend to be leaving the thing unattended for any length of time.
. It will have people with limited to no robotics experience operate and maintain it.