Roko.ca

Cave Diving Photos on WIRED

Roko — Tue, 15 Sep 2009 20:45:06 +0000

Some amazing photos of rebreather cave diving on the WIRED website…

http://www.wired.com/wiredscience/2009/09/gallery_cavediving/

Quadrupeds Need a Whole Lot of Motor Controllers

Roko — Fri, 05 Jun 2009 04:35:02 +0000

Blank PCBs

It’s

Motor Controller in the Leg

been a while since my last update on the Quadruped’s build progress, but I finally got my PCBs back for the motor controllers. Since the robot has twelve motors, I need six motor controllers in total (Each of my controllers controls two motors). They’re an updated version of the h-bridge I prototyped last fall, and used in my mini sumo robot. Although definately more than is really required, the motor controllers boast ultra-low RDSon Direct FETs, and HC9S12C32 micro-controller to handle the control and monitoring of the h-bridges. The black soldermask really enhances the look of the PCBs mounted in the robot.

Each leg has it’s own motor controller to manage the two motors in each leg, and another two motor controllers will manage the four motors in the core. The leg motor controllers are shaped specifically to fit within the frame on one side. The other side of the upper leg frame will hold another PCB with some sensors (I’m planning on e-field and/or pressure sensors in the robot’s feet and on the leg itself.)

Motor Controller and Angle Sensing Boards

Each

Programming Adapter

joint requires angular feedback for the motor controller’s closed loop system. This is accomplished by using special potentiometers through which the joint shaft will pass. The potentiometer is wired as a simple voltage divider, and as the angle of the shaft changes, the potentiometer will give a different voltage output. This voltage will in turn be read by the motor controller and turned into useful data. The special potentiometers used here were a bit of an obscure find, but luckily they are a stock item at Digikey.

In order to ease the routing of all the connections on a 2 layer PCB, I decided to offload the large BDM header onto a separate board, which can be screwed onto the leg frame when I load the motor controller firmware. Several pogo pins then make the programming connections to the test points on the controller PCB. I decided to get creative with the shape, and it turned out pretty neat.

I’m toying with the idea of putting a customized boot loader in the 9s12 controller, and giving the main processor (the Gumstix) programming control over all motor drivers. This way, instead of individually updating firmware on the motor controllers as I continue development down the road, I can instead just load one hex file into the Gumstix’ file system, and it will automatically update the firmware on all six motor controllers.

LiPo Batteries

I also recently ordered the batteries I will be using to power the robot, 4x 2000 mAh LiPo batteries. I will be running then in a 2-series 2-parallel configuration to get 4000 mAh at 7.2 volts to run the entire robot. I still need to design and build a board that will fit underneath the batteries in the core of the robot, which will be responsible for battery protection/charging as well as power and control signal distribution to the four legs.

Still a lot of work to go, but it’s getting closer to walking…

Some Random Stuff

Roko — Sat, 09 May 2009 16:45:44 +0000

U-Blox GPS and Satantel Antenna

One of my friends working on a GPS project of his own managed to aquire some Sarantel Helical antennas, and got some for me as well. I’m planning on using them with the U-blox GPS module I have had sitting around. (I originally bought the GPS module for a MUAV autopilot I’ve been slowly designing, but when I got busy with work it got put aside and technology outpaced my design. For the MUAV autopilot I’m now intending on using a smaller, lighter GPS module which has freed up this one for service on my Quadruped). I’m still mulling around on choosing an LNA to throw in between the radio and antenna to improve sensitivity, so the PCB design is stalled until I make a selection.

Teaser Photo

Although the GPS is “technically” able to attain a GPS lock indoors according to the literature, I’m not going to count on that. The camera will be used for indoor navigation and world modeling (I’ll post more on the progress of that later), while the GPS will be used primarily for outdoors navigation. The main reason for this is I’m thinking of having a go at the Robo Magellan competition put on by the Seattle Robotics Society. Although for the general flat environment a small walker is at a huge speed disadvantage to the larger wheeled or tracked rovers that typically enter, I’m more interested in the technical challenge of designing a robust and adaptive walking/navigation algorithm for the robot than winning.

Mini Sumo Brain

As a bit of an unrelated note, here’s a picture of the populated circuit board for my mini sumo. Now that there’s no pressing deadline to get the robot working, I’ll have more time to fiddle with this board and get FreeRTOS up and running on the LPC2138 to manage the data and computational requirements of some of the more complicated sensors I’m throwing into this sumo robot for no other reason than “because I thought it would be a good technical challenge”

2009 Western Canadian Robot Games I

Roko — Tue, 05 May 2009 18:23:00 +0000

The HC12 Motor Controller Board modified as a sumo controller

I spent the second half of last week scrambling to get my mini sumo robot, 1.21 Gw into a working condition for the robot games. I populated the circuit boards mentioned in an earlier post but as I grew low on time I decided to put those aside for this year. Instead of trying to teach myself a new architecture (LPC2138), I decided to concentrate on programming the robot using a board I was familiar with, my HC12 based motor controller design. (This was the prototype motor controller for my Quadruped walker, so I had some base code already written for it, which went a long way towards getting my sumo robot programmed in a little over a day)

331 Grams!

I made the decision to forgo edge sensors for this competition, and instead chose to make the robot as aggressive as possible, the theory being that if I push the opposing robot off the edge before my robot gets to the edge, I won’t need edge sensors. In the end, I managed to get a working robot, measuring 98mm wide by 97mm long, and weighing in at only 331 grams!.After I finish the actual controller board I intend to use on this robot, I’ll have to make some weights to bring it closer to the 500 gram limit.

In the end, I placed first in the advanced mini sumo category, though I had some good competition! For more videos, check out the WCRS website. I will try to post my own pictures and videos when I get a chance.

Mini Sumo PCBs…

Roko — Tue, 28 Apr 2009 17:57:49 +0000

Bare PCBs

After

Fitting the PCB in the body...

a rushed PCB design marathon, I got my PCBs in last week, built by the good folks at APCircuits. The stencil came in shortly after. Since I made the PCBs into a panel, I had to cut them appart and file down the edges so that it would fit in the chassis. Overall the PCBs turned out nicely. I built them up and can sucessfully load code into the LPC2138. (No pictures of the completed circuit board yet). Things are comming togethor nicely.

You’ll also notice on the silk screen that I have given this robot a more creative name than Mini Sumo Version 6. I now call it “1.21Gw,” pronounced, of course, much as Doc Brown pronounced it in the timeless classic (no pun intended) “Back to the Future”

Now to finish it up and write some basic code for the robot games this weekend.

Angry Sparrows (Aka fixing a driveshaft)

Roko — Fri, 17 Apr 2009 00:57:19 +0000

The needle bearings from one of the u-joints.. This wasn't the worst

Last

The shaft of one of the worse u-joints.. This one had no needle bearings left.

year my front drive shaft started squealing. After a frustrating time trying to get it fixed by the dealership under warranty, I eventually pulled the drive shaft and replaced the u-joints and centering ball myself. As you can tell from the pictures taken shortly after my last trip to the dealership, they were rather destroyed.. It’s actually a pretty simple process, and a cheap u-joint tool from Princes Auto helped a lot… If only getting a dealership to do a proper warranty repair was this easy….

So, if you hear the angry sparrows a calling from your drive shaft, and lubricating does not help, replace those u-joints!

If you’re looking for a write-up on how to do this, I recommend Stu Offroad’s writeup: http://www.stu-offroad.com/axle/driveshaft/driveshaft-1.htm

It’s not a robot until it looks like a robot.

Roko — Thu, 16 Apr 2009 06:34:26 +0000

Flycutting the outside of the Chassis

The long weekend was a busy one with lots of progress made on the mini sumo. I sat down in front of the mill, and machined the robot’s body out of a single piece of 1″ thick Delrin, a task requiring a lot of care to not mess up, as one slip up has the potential to ruin the entire part, and hours of work.All in all, I think it turned out very well. Delrin machines very well, although does require a vacuum cleaner close by to continually clean up all the chips that accumulate, especially considering how much material I removed….

I also spun the two aluminum motor mounts, and cut the stainless steel base plate that seal off the bottom of the body. Still a lot of work to do on the chassis, and the circuit design is progressing slowly.. Now it’s just a race against time to get the PCBs made, circuits debugged, and a rudimentary program written up to get the robot running for the games. It’ll be tight, but I think It will be ready…

Here are some additional pictures…

Bottom view of the Chassis

Front view, with motor mounts and hub vissible

Milling out the inside of the Chassis, where the electronics and batteries will go

Adventures in Mold Making Part II

Roko — Wed, 08 Apr 2009 21:34:54 +0000

Removing the prototype tire from the mold

After

The first tire.

16 painful-to-wait hours, I cracked open the mold to check out the first prototype tire. It turned out very nicely, and much better than my previous adventures so many years ago. (Maybe when i get a chance I’ll dig up some of my old stuff to use as a comparison).

The traction on these tires is amazing, and the dark blue colour looks cool, however I think I’ll use a bit less pigment next time. The tricky part will be maintaining a consistent amount of pigment, since I only have one tire mold and will have to mix up a new batch for each tire I make. Making another mold would take valuable time away that I need to work on the chassis and electronics design if I’m to have any chance of finishing in time for the WCRG…

Note the air bubble that caused a missing piece in the tire.. Since this was a prototype tire that I plan to rip apart to test the strength, I wasn’t too concerned about fixing that part while molding it.

Adventures in Mold Making Part I

Roko — Wed, 08 Apr 2009 04:00:21 +0000

Somewhere in this piece of Delrin is a mini-sumo robot chassis.

It’s been a while since my last post, but I’ve been working away hard at designing and a little bit of machining for my Mini Sumo. It’s proving to be quite a challenge to fit all the electronics and sensors I want into the small package of a mini sumo robot only 25mm tall, but I think I’ve figured out how to shoe-horn the electronics in there.

I’m planning to do some fairly sophisticated sensors, but that’s a topic for another day, and likely after the games as I likely have to run a temporary brain for this competition as time is too tight to get a PCB turn.

The finished tire mold

I have made decent headway on the chassis, having made more wheel blanks, and made a mold so that I can cast my own polyurethane tires. The mold itself is made from Delrin on the mill, held togethor by four screws, and kept in alignment with 6 dowel pins. The center slug was spun on a lathe, and forms the bottom of the mold, as well as a means to seat the wheel directly in the center of the mold. A top plate from scrap polycarbonate is screwed on to keep the top finish of the wheel nice.

Delrin is a really nice material to work with on a hobby mill and lathe, and it was relatively easy if somewhat time consuming to bore out the 25mm diameter hole for the robot.

Brushing on the Mold Release

6 or 7 years ago was the last time I cast polyurethane for sumo tires, I reckon, so I figured what I had lying around was no longer good. A bunch has changed since then, and a stop to a local mold making shop with some samples had me settled on Smooth-On Reoflex 30. Other people have used various Reoflex durometers for sumo robot tires as well. Feeling in a spendy mood, I also decided to buy some blue pigment.

Excitedly, at the end of the work day I got home with the polyurethane in it’s shiny box, which I’d bought over lunch hour, and prepared the mold. After collecting all the things I would need to cast my tires, I found that the really Old AIrbrus lying around wouldn’t spray the mold release agent anymore, so I cheated and used a brush instead. After waiting for the mold release to dry, I clamped the mold pieces together, popped in a wheel, and started mixing some polyurethane.

Ready to pour the polyurethane!

This new stuff works better than what I’d used previously, and was less viscous and as such did not get as many air bubbles trapped in it while mixing. An added benefit was that I could use some over-sized syringes I had lying from an old ink-jet cartridge re-filling kit.

A word of caution when using pigment for polyurethane, however: The “SoStrong” pigment.. Is, just as the name would imply, oddly, So Strong. I used a few drops, which was a few drops too many. The end result was a very dark mix. But, as this is a prototype tire that I plan to rip appart to test strength, I wasn’t too concerned.

Now the tire is sitting in the mold. With a 16 hour de-molding time, It should be ready tomorrow roughly around lunch… We shall see how it turned out then.

For now, here are some other links you may find useful with regards to polyurethane sumo tires:

Jon Hyland’s Seeker3 Sumo - He has some very good pictures of his awesome robots, including some more details on molds
Dave Hyland’s “Making Marauder’s Tires” – Jon’s brother has more good details on casting polyurethane
WCRG’s Molding Tires

Mini Sumo Motor Mounts

Roko — Fri, 27 Mar 2009 04:13:46 +0000

Well, it’s been a while since I’ve updated, and I have gotten a little bit of work done on the robots in between ice diving adventures, and working on the Jeep. Most of the progress made has been playing with software (Investigating webcams and OpenCV for Spyder’s machine vision) and hardware design (PCB layouts for Spyder’s many circuits.)

Motor Mount Prototype

Today

Motor Mount Prototype

, however, I sat down and got some machining work done for my mini sumo. I was wrestling (no pun intended) with the idea of how to mount the motors, and eventually decided to make a flanged sleeve for the motor to fit inside, which will then be securly attatched to the frame of the robot. The first attempt turned out pretty good, although not quite perfetct, as I didn’t properly square it off in one of the steps. It’s useable, but I’ll have to decide wether or not I want to make another one.

So, things are slowly comming a long. I’m afraid I won’t have all the circuitry I wanted to put into the mini sumo done in time for the robot games (chiefly goverened by the long lead time for budget PCB’s from batchPCB), but hopefully I can at least get something that will run arount the ring. I suppose as a backup, I do have my H-Bridge prototype board I could use to control it.. Complete with high-efficiency H-Bridge, and a powerful little 9s12 to control it all… Hmm..