And a week of nothing happened. Multiple reasons for this: epic partying at the Media Lab, waiting on parts, and deprivation of waterjet access.
However, July is approaching, and so my time will be slightly more constrained with the beginning of a new internship (alongside my Media Lab job). So I’d better get some bot work done while I still can, eh?
The big news item for today is: Pop Quiz 2 drivetrain test is a success.
Drive pods installed! Each motor is epoxied into place into its mount (not very serviceable), and each drive pod is retained by two screws and the “channels of drive pod holding” machined into the chassis, like the design.
And here is Pop Quiz 1.91666666667. I duct taped all the parts the bot would conceivably need, plus some extra things to get it to somewhere around 1 pound. There were things missing, such as a giant blade, but overall it was ready for a test drive.
Here’s the video.
I approve. The bot is actually a little bit too squirrelly. It’s also running on 11.1 volts out of 14.8, so it will be even faster when done (I doubt the ounce or two that I’m short will actually make a difference). The BB controllers seem to like the motors enough, and I didn’t get any thermal problems from either controller or motor. I’ll probably just dual-rate the drive down on the transmitter… or just drive really fast. It’s somewhat slower than Test Bot just by the feel, but because the bot is so much smaller, is harder to gauge the heading.
I have a feeling that frankenmotors will be an integral part of my bots from here on.
So, what’s left to do on Pop Quiz?
1. Get Ti
2. Put Ti and carbon fiber on God Machine
3a. Wind motor
So now I would like to introduce my crazy non-robot summer project for the 2008 season.
In the summer of 2007, I designed and built Snuffles the First, an absurdly over-motored electric scooter. R&D from that led to the (as of yet unfinished) Snuffles the Second, a slightly less over-motored electric scooter that I designed with more practical uses in mind. The fun part was, of course, the over-motoring, as I could barely stay on the thing and none of my friends could.
But a scooter can only inspire so much awe. Past “HOLY FUCKING SHIT THIS THING IS NUTS”, I didn’t really get much in terms of reactions from Snuffles the First. So what, it’s a Razor scooter with motor cancer.
This, of course, needs to be fixed. I need to go bigger, more awesome. One step further up from a mere scooter.
So, for the 2008 summer build season, I am proud to announce PROJECT LOLRIOKART.
Yes, it’s exactly what you think it is.
- 15kW motor power, brushless DC
- 8″ pneumatic tires, front and rear
- 54 volt, 30(?) AH nickel-cadmium battery pack
- 25MPH top speed, conservative estimate + room for expansion
- Hijacked grocery store shopping cart chassis
Wait, brushless DC? What the hell is that by the back wheels? That’s a brush motor!
Right, because that picture is epicly outdated. Instead, I have one of these.
It’s a brushless Etek. The metrosexual successor to the indefatigable Etek, but still a good performer. It’s currently on loan to me from a friend who is temporarily stopping his Etek-powered moped project. Rated for four kilowatts of output power, it should be plenty to get me moving. I’m running it slightly higher than 48 volts owing to the battery packs. Drivetrain parts are arriving this week, and consist of a 3.5:1 #40 double chain setup. Unfortunately, I couldn’t quite dig up a differential, but the rear is quite open and serviceable, so I could shove one in if i find one. Meanwhile, solid-axle-induced wheelspin for the masses.
This makes my 400 amp DC controller totally useless, so I obtained a 72 volt, 200 amp controller that should hopefully feed the Etek well enough. A 300A+ controller would be optimal, but… yeah.
Speaking of batteries…
I spent the past week reviving the old nickel batteries. Out of five packs, one had about 50% dead cells, and so I decided to cannibalize it to replace the failed cells in the other packs. Two were completely healthy and sprang back to life after maxing out my charger at 7 amps for an unknown amount of hours.
Here’s the deal. The amp-hour counter on the charger consistently overflows and starts from 0, and I have never been there to watch it. The charge time is always around the 650 to 700 minute mark. That’s over 10 hours steady at 7 amps, which would make these ~60 to 80AH nickel cells. However, I suspect that the charge counter rolls over at 32767, which is conveniently the size of a 16 bit integer for most microcontrollers. The displayed capacity is always about 2000mAh after it’s done. So these could be 30AH cells.
Or, judging by the charge time alone, it could have rolled over twice, and actually be 60AH cells?
Either way, 30 or 60AH is an asston of capacity. I will need a dedicated charger, because my charger can only handle 24 volts and 7 amps.
After the cells were equalized, I started disassembling the packs which needed rescue.
I disassembled the dead pack, and it almost punched me in the stomach.
These cells are bound together by metal end plates and a steel strap spanning them. There is SO MUCH pressure that I could not even begin to get them back together by hand. I don’t know why these cells need such intense binding pressure, but they do begin to bulge slightly when allowed to sit.
Doesn’t sound kosher, but whatever.
After transferring the requisite cells, I had to somehow put them back together. For this, a pickup truck cargo binding thingie came to the rescue. I used the ratcheting handle to slam the cells back together along with the back plates to a state which allowed me to squeeze on the straps and tighten everything down again.
One of the packs required a 12 inch wrench on the end of the handle to bind. I was afraid the strap was going to explode. But it all came out fine.
While the packs were fresh, I had a little fun with them. This is a neat 12 volt revolving light, as found on tow trucks, that I found hiding in a corner at MITERS.
I foresee a handy functional decorative item for the LOLrioKart.
With the batteries slow-cooking to completion on their final equalizing charge, it was time to begin on the mechanics. First off, those little rubber casters had to go.
I decided to replace all the wheels with large pneumatic casters that were hanging around. Even though using the stock rubber casters would add to the surrealism, there were significant downsides.
For one, the ride would be horrific.
15 horsepower would blow off the rubber almost instantly.
The vehicle is going to weigh about 400 pounds with me in it, and I could easy exceed the capacity of the casters, leading to epic fail.
So the choice was made to make custom mounts and steering brackets for the pneumatic wheels.
The stripped chassis, before I also removed the bottom shelf thing. I took the opportunity to stick a wire wheel on the grinder and remove some of the (quite extensive) body rust. What I was left with was tubing that was mostly smooth and could be measured up for modification.
Even more spare goodies from the Media Lab go into this project. Here’s an Epic Switch for the main battery.
And here is the State of the Onion as of two days ago.
I am awaiting parts for the drivetrain as well as some barstock to make the steering arms. Originally, this was going to be a 100% scrounge-beg-and-hijack build. However, I just couldn’t bring myself to build something not to my spec, and so I actually got parts for it. Big industrial stuff is very cheap, however, and it won’t impact the bot builds.
Hopefully more progress this week. The parts for something this huge don’t need as much precision, so it’ll go quickly.
I’m not alone on my epic project endeavour. Here’s one of the other MITERerers finishing up his epic amplifier and horn. I have no clue which decommissioned air raid warning station that thing came from, but it’s gigantic, almost 20 inches across at the end. He’s building a custom amplifier for it, in order to do who knows what.
Fun stuff. Anyways, bot on.