scout main frame design [updates]
Updated: Jan 6, 2020
The first thing I decided when it came to the new scout robot was there's no more space for messing about. This robot would have to be designed, I'd need to spend some money making this thing a reality.
So of course, the first thing I did, was build a frame without designing it.
Hey, you can't have it all okay...
No in all seriousness, I didn't design the frame of the scout robot before building it. But I did start and get somewhere, so let's go through that. I have a FIRST robotics background, the team I was on was a rookie team which meant we didn't have much funding and always had to be creative. If you were on FRC you'll likely remember those pretty great versa-frame stock, brackets, predrilled metal pieces we used to build our robots. You'll likely also remember versa-planetary gearboxes. I knew how to build-with and cut versa stock, I knew versa-planetary boxes were pretty good gearboxes so I started there.
On another post you'll see I'd already guessed what actuator specs we would need after doing some research on MIT Cheetah 3. So I'd already ended up with the 260Nm actuator with a Neo motor, and versa planetary 100:1 gearbox.
This is what the actuators look like, if you're more interested there's another post on them. I knew I'd need to mount at least four actuators to the frame and the rest would be on the legs themselves based on the design of chipONE and Cheetah 3. These robots have four actuators mounted to the frame as one axis of the shoulder joint that can spin the leg or move it out and in with respect to the frame.
Starting with some preliminary sketches, mostly to get ideas down and see what I needed to order from VexPro to get the frame started, I decided on using 1"x1"x1/16" pre-drilled versa-stock because it's used a lot in FRC and no one wants to sit there on a drill-press making holes. As a first attempt at the frame +/- 1 inch precision would have to do. The rough frame size came from the Cheetah 3 robot, roughly 25" long and 16" wide. That was the initial size at least.
The frame should be as simple as possible, easy assembly, easy repair, nothing besides what is needed, minimalist. I sketched out the laziest frame in the entire world on my paper. There's an upper frame, a lower frame, they're exactly the same, and they'd be connected with the actuators themselves, four of them, one at each corner.
There are four aluminum bars running long ways on the frame, two on the top and two on the bottom. The bars connect to an actuator at each end using the vera-side-mount plate. The side mount plate (shown below) mounts to the gearbox on one side (the flat side) and the 1"x1"x1/6" stock on the u-channel looking side.
There are 8 of these mount-plates total, two for each actuator, one on the top one on the bottom. Both connecting to a piece of stock running long-ways. So now I had a rectangle with two motors sticking out either end of it towards my face.So there was a left side, a right side, and now it was time to connect them together. Four smaller cross-pieces run the width of the frame and bolt to T-brackets. (I'm honestly trying to do my best to explain this but the pictures probably do a much better job).
Much guessing was happening...
So it probably looks weird that the cross pieces are sitting ON TOP of the bars running long-ways instead of in-between like in the first sketches and pictures. That's because when I starting putting this together, 16" seemed really wide (actually it was slightly bigger than 16" because the T-brackets added an inch or so to the overall width). In an effort to not make any more cuts to metal, I simply mounted them to the top instead of in-between to shorten the overall width. It looked wide, I made it look thinner.
The last diagram represents me attempting to lay out where the other electronics and other batteries and such could go inside the robot when the frame was finished.
This frame is as light as it can possibly be, the actuators are structural there are no extra components. And when I said I didn't design it, I mean it past the few initial sketches just to figure out what amount of parts I needed. The rest was just me spending time on the vex-pro website and looking at my options.
In the future, I'll want to do real-time updates of my build process, day-by-day. Apologies for the dumps, this is me trying to catch up to where the project actually is now.