CounterStryker BB 2015
Jun 14, 2015Public
Photo: This is the new bot I'm working on for Bot Blast. I saw Counter Revolution at Robogames this year and thought that two counter rotating blades was an interesting solution to the terrible gyro dance problems I had with Chop at motorama last year. I decided to see if I could take that concept and expand on it, by using only a single weapon axle and support system as well as my favorite form of weapon locomotion - the friction roller.  To capitalize somewhat on the mobility improvements I needed a bot that could keep its wheels on the ground and I've been wanting to do another truly invertable bot for a while. I decided big, separate, expendable wheels like Sewer Snake uses might be worth a shot.
Photo: Here I've tilted the bot back a little so you can see the friction roller sits between the two blades. What you may not be able to see is that one of the blades doesn't actually have any teeth. I am concerned that if I put teeth on both blades, I'll have severely limited bite because the teeth will be crossing each other at more or less random intervals. I decided to give up a little bit of stability by having one of the blades not have any teeth. I'm hoping that having it attached through the friction wheel will mean energy in the toothless blade won't be a waste - it should at a minimum keep the bot spun up better and in the best case actually contribute to the hits. We'll see I guess.
Photo: Because I'm using a friction roller system, both blades need to have a continuous outer ring. To maximize bite I wanted an asymmetric blade, but I couldn't use the profile I used for Chop because it isn't continuous around the edge. I found that if I filled in all the holes on the non-tooth half of the blade I could get most of the counter balance I needed so that is what I went with.   I will also be making a symmetrical blade in case this one isn't strong enough. There is a pretty big hole at the same point as the tooth so I'm a little worried that it might crack the ring there.  You can also see that I installed wedgelets this time. I'm  planning to spring load them so they stay on the ground and they should help a lot with the lack of bite I got with Chop / Weekend Warrior
Photo: The bottom of the bot is pretty different from what I normally do too. It's still my old stand-by of .094 garolite plate, but I needed a way to mount the weapon rails in the middle of the base without potentially just cracking the middle chunk of the base out of the robot on a hit. I decided to try using big aluminum "washers" that help spread the load over the garolite base.  I hope they'll be enough.
Photo: The blade axle is set up a lot like the one on Devour was. It's a .5" ti shaft and each blade has a hub with a needle roller bearing in it. The two counter rotating blades are separated by needle roller thrust bearings and a UHMW spacer. To tension the two blades against the friction wheel I can add a rubber washer between the weapon rail and the outermost thrust bearings.  The whole mess is retained with shaft collars.
Photo: Well the first step in a new build is dismantling of the old bot, but in this case Kyle already did some of that for me with Ripto UlTImate.
Photo: So his blade hit the front plastic piece and just pulled the bolts right through the base. Countersunk garolite is not very strong and I knew that when I did it. Notice that the screwed together frame parts held together though.
Photo: The side frame rail cracked right at the cross brace but didn't break. It was a brutal hit, so I'd say it did its job.
Photo: That wheel doesn't work anymore. Judging by this pic I think kyle must have gotten under the frame piece and hit directly up from the bottom. Probably while I was gyro dancing everywhere. Ouch
Photo: That wheel doesn't work anymore. No surprise I guess. $12 down the drain!
Photo: He also clipped th ebot in the back a couple of times. These didn't cause any significant damage which is good because my lipo battery was behind that wasll and the foam. I had it as protected as it could get I think.
Photo: The plastic held up great I'd say.
Photo: ouch
Photo: So, on to the new bot. I'm sure you're all thinking "why does he build frames like that, obviously they can't take a hit!".  Well no, they can't take a hit from a 12 pound with a scary vertical disk. They can sometimes take a hit from a six pounder, and I'm hoping with the screwed together battery box in the back and the big foam shock absorbers on the outside it will hold up ok. Well, that and the big blade on the front of course :). Also, they go together really fast. So fast in fact that I forgot to take pictures until I had it done... which took about four hours.
Photo: I haven't done the axles or hubs yet but you can see the wheels are HUGE
Photo: This is closer to what the frame will be like with the blade on it.
Photo: And then I mounted the drive motors too. The axles are still temporary until my second mcmaster order comes in, and the belt alignment on that side is a little wonky, but all in all it's coming together.  The weapon motor wil mount between the two drive motors (snugly) and the blade assembly will attach at the extra holes at the front.
Photo: Tonight I worked on the drivetrain. Doesn't that hub look a lot like a dave's hub? Well... it's not, and I can tell you ol' dave is earning his pay making hubs for all of you.  In my case I wanted to use an off-the-shelf axle as much as possible, but wasn't satisfied with a set screw being the only thing holding my wheels on laterally. The result was one of my two fun lathe parts for this project... this hub.  The last 3/16" of the bore is tapped 1/4-20 for the 5/16" shoulder bolt axle.  The rest of it is counterbored to slide over the shoulder bolt itself. This lets me tighten it onto the shaft and use the threads to transfer the torque instead of a set screw.
Photo: It's set up so that there is a little gap between it and the robot. I probably could have left a little nub sticking out there like the dave's hubs do, but I'll just slip a washer in there and that'll be good enough.
Photo: A washer then goes over the threaded part of the shoulder bolt and I tighten a nut down to smash the whole assembly together. The wheel is wider than the space alotted to it (by quite a bit, actually) so it is smashed in between the two flanges pretty tightly.  I can make it slip with my hand but I doubt the little 1000 RPM motor will have enough torque to make it slip. If so there's always more washers to make it tighter or I can just tap a bolt into the hub flange so it sticks straight into the foam. I doubt that will be necessary
Photo: Here's what it looks like when it isn't installed in the bot.
Photo: And from the end. That flange is where I could add a little screw sticking into the wheel if it is necessary.
Photo: Here I added the other hub and installed it on the other side. Took me about 35 minutes to do the second hub. I've also filed the flats on the shaft and added set screws for the left side. I'm not ecstatic about using set screws instead of a keyway but the way the width is set up a keyway would require me to take the side of the bot off to install it. I might stll do it because really, that's only three extra bolts... I'm going to get it working with the set screws first.
Photo: You can see that the shoulder bolt head (which is 7/16" diameter) fits just barely inside the .5" hole for the bearing on the far side. I'll probably put a cover plate over both of the axles because I don't want the battery rubbing on anything moving.