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Getting Motors Running
These new motors are hot!
As I mentioned, I picked up new motors for the 'bot a couple weeks ago. I mounted wheels on them two weekends ago but I haven't started to add all the stuff to get them mounted to the base yet. I couldn't get them to work off the bat with my old motor controller setup but I think it's because they require a good deal more amps. I ended up just connecting them to a couple AAs to see what they're like and they're sweet! I got them through a Jameco catalog; part number 311976CE. They're Johnson Electric 1.2 volt, 0.363 amp dc motors at ~4.6k rpm and 130.4 g-cm (!!!) torque. A steal at $1.50 each.
I picked up a single stepper to test out as well but I'm overwhelmed by the amount of hardware it appears that I need to run this thing. More on that when I've got time to test it out.
I've been fighting with the Robostix to get it to work with my Pololu mdsmc and I think I may have figured it out; the USARTs on the Robostix were defaulting to 38.4k baud and the mdsmc can only autodetect to 19.2k baud. A quick modification in Hardware.h (part of the code that comes in the Flash-LED project for the Robostix) and I think I should be able to get things to work. I got some advice on using portc for the reset line but I don't think it's working correctly. Watching the amps on the reset line on the BASIC Stamp, the line clearly drops out until I set it high but that doesn't happen on the robostix. I'm still strugling to find out why.
November Begins
It's been a while since I've updated here but I think I'm ready to start again.
Building a robot from scratch has been a slow moving process up to now. Order something, plan more, order something else, plan for something else. I'm incredibly close to a point where I can just hack hardware and software all day and it's quite exciting.
I had defined the motor mounts with motors that were way underrated for my purposes originally and so now I have larger, high-torque dc motors which I get to try out tomorrow (Garth called me out on not having strong enough motors). Fiting the new motors in to the old lego mounts should be tight but I think they'll fit in one way or another. Getting the hot glue off the old parts... not so easy. I got a stepper motor to try out for turning my motor mounts as well but stepper motors better have some sort of standard 6-pin connection that I can look up because I've got no idea what all these 6 pins are supposed to go to and this thing came with no instructions. I expected PWM connections, at least. I have my own glue gun now too! Not only that but I've gotta try out my Coldheat soldering tool too. I hope I'm better with that one than I was with the real soldereing iron.
I'm still having lots of problems learning C and avrlibc and the robostix platform. I think I'm just going to give in and ask all my stupid questions on the gumstix list this weekend. I need to make progress. I also got a usb thingie (technical term) for watching serial data. I tried to get that to work last weekend to no end. Also no instructions. Fuck.
Goals for this week? Break old hardware, insert new hardware. Get motor controller working with robostix and that small test motor. Millions of times easier now that I have real headers. You should have seen me gluing single board-headers to wires. I'm silly.
Robot Planning
I've recently decided to use a an external plastics cutting service for parts of an up-and-coming robot (I haven't decided on which service yet) and I needed to figure out the exact size that I was going to build to. This was somewhat obvious since I only have a controller and a couple motor mounts to judge it's eventual size. I sat down with a 3D-modeling tool that I had just discovered a couple weeks ago, SketchUp 5, and started scale-building the parts that I had. With my known parts in SketchUp, I make a rough guess of how large I wanted the base to be and I've been working from that ever since. I have two points to this incredibly tedious story; understanding the scale that you're trying to build to is important and SketchUp 5 absolutely kicks ass.
The first essentially explains iteself. Everything from buying parts to figuring out what motors to use requires a decent guess at how large your creation is going to be. Having a more concrete guess at the exact size will (hopefully) allow you to dodge the little mistakes and oversights later in the project.
SketchUp 5 showed up on my feed reader sometime about a month ago and since then I'd been through all the tutorials and have generally played with the thing for a couple hours. It's an awesomely simple 3D package which makes it great for people like me that are just trying to churn out a rough idea for a project or some 2D CAD drawings for a laser-cut service. They show some very high-end drawings on their site (as all 3D drawing packages do) and I'm sure that's a realistic possibility with SketchUp - it's just way beyond what I'll ever need to do with the app. It takes a couple passes to learn the intricacies of how the tool works once you get off the ground but that's pretty standard for a 3D package and the learning curve is is much lower than any other tool I've tried. Below are some examples of what I've done today in just a couple hours (with lots of measuring and researching going on in the meantime):
LEGO and Motors
This post is the first in a series that chronicles my first attempt at making a robot from scratch. I keep a log of notes in my favorite organizational tool, Backpack, and this serves as a backup mechanism as well as an informational repository for myself and others. Usually I will post more than one of my Backpack notes in a single post so any problems and subsequent solutions will show up on the same page. To see other posts in this series, visit the robotics tag.
17 July, 2005 - LEGO Wheel Research
I am unable to find packs of “49.6×28 VR” lego wheels online (I know I have some back on the east coast). Ordered a newer collection of “large” technic wheels, connectors and gears from lego for $28.97 ($33.92 total).
Technic Wheel Pack 5219 would be a good set of larger wheels but is unavailable from lego online.
Hobby Engineering has some mini geared motors that might work well but I have no idea what RPM (62|93|134|246) I should try first. A trip to millbrae this week might be good. I don’t know if that’ll do me any good without motor mounts though. I still have no idea how to mount those motors or where to find mounts. I can probably ask at HE.
19 July, 2005 - LEGO Wheel RPMs
64 RPMs? That’s crazy slow – it only travels the circumference of the wheel * 60 in a MINUTE. I don’t know what I was thinking but I’m going to start with the slightly higher RPM.
21 July, 2005 - First Batch of Motors
I picked up some motors from Hobby Engineering today. Those geared motors with different RPMs that I referred to before are tiny! I think I was so struck by their size that I decided not to get one for testing which, in hindsight, was a bad idea. I did, however, get my hands on four basic motors and two slightly smaller motors. I asked about motor mounts and the guy at HE was incredibly unhelpful. I really should have picked up a 134 RPM geared motor for testing. You probably get what you pay for from these things and the geared motors are $23 each. I paid $2 a pop for the non-geared motors.
26 July, 2005 - LEGO Shipment
After about a week and a half I finally have the assorted lego wheels, connectors and gears that I ordered. The largest wheels in this selection of “large wheels” aren’t all that large but they’ll work just fine for my needs.
I got a nice surprise in the selection of gears; a perfect cannidate for my wheel-motor mount. Of course I only got one of them in the batch but I think I should be able to find some more on ebay or some other single-part site. (base: 2856 and top: 2855)
30 July, 2005 - LEGO Sizes
Come to think of it, the lego wheels are really quite small. I’m going to have to work out some scale information in some kind of visualization app before I continue because I probably don’t have a very good grasp on what kind of base sizes I can drive with these small wheels. I suppose it’s more of a question of how powerful the motors are but I still can’t imagine driving a huge vehicle with teeny wheels even if the motors work just fine.
Next steps: Visualize scale of wheels and base size.
