Wednesday, April 25, 2012

Mech: Visualizing a simple walk sequence

I've added color and sequencing to the simulator. I've also added a cockpit (red) and an engine (grey) to the mech to show better what it will look like.

The simulator is good enough to be able to simulate many possible walk sequences. I wrote a function that tries many many actuator combinations to come up with a walk sequence that fits a few basic criteria:

  • Starts with both feet on the ground
  • Does not drop the cockpit height below 8'
  • Maximize stride (I've not yet modified it to maximize efficiency)

I then fed the computer-chosen result through a function to show the sequence and spit out some diagnostics about the walking movement:

  • Stride length: 6.7'
  • Actuator displacement through a single step: 1.4'
  • Efficiency (stride/displacement): 4.79

I noticed in the course of doing this that the certain actuator positions increased efficiency. However, I suspect they also rely on greater actuator strength. Right now I'm counting all actuator displacement to be made equal. In reality, the difficult of moving the actuator isn't just in the distance it travels but also the force on it. To compute this function automatically I'll have to add a ton of statics equations to the simulator.

Notice that in addition to the simple walking sequence I've added the crouch distance. For this configuration it stands with a hip height of 8.7' and a minimum crouch distance of 4'.

Wednesday, April 18, 2012

More mech simulator

Added some more functionality to the simulator. In particular colors. We can see now the two legs and the actuators that control them. We can also execute commands to lengthen or reduce the length of those actuators. I'll be adding stats and auto-calculation of the structure next. This one will be particularly interesting. I've not yet decided if I'm going to calculate it or have the machine find it by trial and error. After that probably a third dimension.

Monday, April 16, 2012

The beginnings of the mech simulator

I decided I needed some computer aided design, beyond the excel spreadsheet I was using. I need a mech simulator. The mech simulator has several goals:

  • V1: Show the mech based on the dimensions and actuator positions

  • V2: Indicate bob-height when walking

  • V2: Indicate stride when walking

  • V2: Indicate max/min height

  • V2: Indicate foot colissions when running walking sequence

  • V3: Export information to open-scad for 3-d rendering and model printing

  • VNext: Load calculations

  • VNext: Inertia calculations

After a bit of playing around I found the best way was just to specify new joints and place them at distances from previous joints. I wanted to make something easier/cheaper and more specific to this project but there was no value in not making it general. This joint-adding approach makes it easy to write out the dimensions of whatever you're making. It works for single-leg-bone designs. It works for parallel-leg-bone designs like what I will probably use.

I still have to work out the dimensions myself, but once I have a sequence of commands and information about walking I'll be able to play with that much more dynamically.

Eventually the V2-VNext features will allow me to expand and finalize my designs while still being able to react to fuck-ups I make.

Wednesday, April 11, 2012

So I've decided to build a mech and I want your help

There's a lot of work to do.
1. Statics analysis on how a two-bone leg is different from a one bone leg. I can eliminate an actuator by doing design A and don't think it changes the force equations much but I don't know. At some point I'll do the statics equations but anyone can do that right now. (see diagram)
2. Research availability and prices on hydraulic cylinders/actuators that have built-in encoders. As in a measure of how far the cylinder has extended. All the exterior encoders I've seen will mountings, calibration, etc. It must be something with a price, at least a quote if not an add-to-cart style for purchasing. There's a lot of industrial parts makers that do not actually handle distribution and we need a distributor.
3. Other large-scale walking robots. Especially bipedal. I haven't seen any that actually walk. If there's not a video of it moving it's a BS project. Best I've seen is a 6-legged logging robot that's build not to damage foliage as it moves through the forest.

Pick one. Tell me what you find out.