Archive for December, 2008
Quadruped Prototype Machining
Checking vertical alignment prior to drilling
For those who are just venturing into machining, tapping small holes such as 2-56 is nowhere near as hard as it sounds, and horror stories of broken taps ruining parts can be easily avoided if you take your time and do everything carefully.
Tapping 2-56 Holes
(experienced machinists can skip on ahead)
- Make sure your pilot hole is drilled perpendicular to the surface, and free from metal chips before tapping
- Use lubrication. I used WD-40, although there are specialty tapping fluids available
- Use a tapping block to ensure the tap is perpendicular to the part’s surface, and cocentric with the pilot hole. You can easily make one by drilling a hole the size of your tap’s shank into any firm material large enough to keep the tap straight. I don’t recommend using wood, metal is the best choice. Unfortunately, wood was all I had available and I found it absorbed the WD-40, and the tap did bring some sawdust off.
- Make sure your part is firmly held in place so that it’s easy to keep the tapping block firmly on the surface. For thin parts, using a vise is a very good idea.
- Make sure that you back off a quarter of a turn often while tapping, when you feel increased resistance. This will break the forming chips and keep them from clogging your tap. I usually did three half twists forward, then one half twist back and it seemed to flow nicely
- Keep in mind how deep you have to tap. Typically twice the width of the screw you are using should be enough to properly secure your part. Just me mindful of the type of tap you are using, since a plug tap will have to go a bit deeper than this, and a taper tap will have to go much deeper.
- Clean the tap often. The chips will build up and stick, especially with the use of lubricants.
- Wikipedia has more information on tapping, and if you look around there is a lot of wisdom floating around on the net, but hopefully I have brought some of the best points togethor here
First Leg mock-up (minus gears, bearings and shafts)
Jeep Stuff
This is just a placeholder for the “Jeep” category until I figure out how to place things better… And now some pictures for your viewing pleasure!
Climbing a Rock
Lined up on the Ridge
Quadruped Robot Introduction
Sometime in the mid to late 90s, I got the idea to build a quadrupedal walking robot. Ideas bounced around my head constantly since then, but school and work got in the way of “free time”. Over the years I gained more knowledge and experience in electronics and robotics design, and constantly refined the ideas I had in my head. In mid-October 08, with the local diving season comming to the time of year where it no longer takes up most of my free time, I finally began to get concrete design work done on the robot. The picture below is what I came up with.
Concept Sketch of Spyder (aka Bert) the Quadruped
An admittedly ambitious project, this Quadruped is to be named Bert and/or Spyder, I haven’t really decided yet. It will be powered by 3 PortEscap gear motors per leg (a sum total of 12), due to a lucky surplus find a couple of years back, at BG Micro. Each joint will have bearings for smoothness (another surplus find, care of the the Electronics Goldmine). The frame will be rough cut from from Aluminum by the Big Blue Saw. Although it’ll add a bit of cost, it will save me an imense ammount of time making some intricate parts and fancy shapes, so I decided it would be worth it. The rest of the machining to be completed on my Dad’s Sherline mill and lathe.
The brains will be a Gumstix computer I picked up a while back and have been playing with, and eventually I plan on creating a head to go in the center of the robot, however I haven’t quite decided how I want to go about this. The entire robot will be powered by some LiPo batteries, which hopefully should provide a good life time.
Waterjet Cut Parts
After a couple of months of design work, I finally sent the files off to have the core, and one leg water jet cut. I only ordered one leg to start with in order to make sure everything works out properly before committing to building the other four legs. Today I got the water jet cut parts back, and they look nice! All the parts came connected as one big piece, so some dremel work was required to seperate them without damaging the parts, and I’ll have to take care in filing the connecting bits flush to the part.
Another issue with water jet cutting is the kerf diameter, or diameter of the waterjet stream, in this case approximatley 1mm, so some corners that I had cut to that diameter will need to be filed into square points, but that’s no big deal.
Bunch o' Parts
To the left you can see some of the parts that will make up one leg of the robot. I’m still waiting on some small parts such as teflon washers to use in the joints, but that should be arriving any day now. You can see my H-Bridge in the mix, I’ll need 6 of those dual H-Bridge boards on the final robot.
All in all an exciting build!
H-Bridge Fundamentals
An introduction into basic H-Bridge theory and operation, this article covers the fundamentals you need to know to make a working H-Brigde with N and P Channel MOSFETs
H-Bridge Prototype Build
Driver Board with solder paste
Re-flowing this design is a must, as I’m employing “Direct FET” packages from IRF. The package is basically a metal can with the bare FET on the bottom side. This is supposed to allow for very good heat dissipation, and minimal packaging loss (read: Low RDS-on). I’m expecting this PCB to handle approximatley 10 amps per channel (it will handle two motors) continuous if properly cooled, but for the next few projects I have on the go, it will be much less. The PCB is small itself, measuring a little over 1″x1.5″!
"Completed" Controller with PortEscap motor
Unfortunately, it appears that ths 9s12 I put on there has a maximum bus speed of 16 MHz, however the internal serial bootloader I was hoping to use to load code needs to ramp the PLL up to 24 MHz for proper operations, so testing is on hold until I get a 24 MHz capable part, hopefully early next week.
Edit: 14 December – I borrowed a BDM programmer from a colleague, and managed to load code into the 9s12, and currently have the motor driver actually driving a motor, complete with ramping up and down in speed.
“New” Blog
Posted by Roko in Randomness on December 11th, 2008
Bluehost upgraded the machine that my website is hosted on, so I thought I’d give wordpress another go. (Previously it would always get suspended for exceeding CPU quotes).
With the upgraded machine, it seems to be running much nicer right now. If you run into problems, let me know. Expect new content to filter in as I progress on my random projects.