Sunday, November 9, 2014

Mini Cart / Build Madison

Build Madison is almost over, so I get to sleep soon. I found a helper for the mini cart project, a design which will also be part of the MOARbots framework. The mini cart has immediate appeal--it can use cheaper motors and batteries, and more can fit in the arena for large multi-robot events.

Here is the mini cart alongside the regular cart.

The mini cart motors were pulled from a misc. motors bin, so they aren't exactly the same. Also, one
of them had been previously used and wasn't in good condition, so this prototype really only can turn one wheel on. The point however was to prove that it is possible to use el-cheapo small toy motors, with 3d printed gears, to move a cart.

I spent most of my time though working on an omni wheel design. I found some tackier heat shrink in large diameters that works very well for tires. Other than the tires and axles (small finishing nails), everything else is 3d printed. The triangular shape allows for two halves to fit together snugly to form the final wheel assembly. This design has very little room for error, which especially problematic given the variance on prints. A redesign should be coming soon.

One more thing: the MOARbots project has a wiki now. It is minimally populated but it will be growing A LOT especially as I get ready for a set of UW students who will be working on this project for independent study credits. I'll link it often in the future as well.

Thursday, November 6, 2014

MOARbots, the ESP8266, and more omniwheels

This project finally has a title.

MOARbots: Modular, Open-Source, Affordable Robots.

Progress on MOARbots is as follows:

I learned about the ESP8266 through Hackaday and decided to purchase a few. It is a $5 WiFi chip and programmable microcontroller to boot. I haven't been through the recently translated datasheet yet, but it seems to clock at 80MHz and have 16 GPIO pins, 2 of which are broken out on the boards I purchased. It will require tons of development to be usable for MOARbots but the community is very interested in it to make Internet of Things happen at a low cost point, so I won't be alone.

I decided to make a micromini version of my omniwheel bot, based around three Pololu motors I got for free. The motors are far too expensive at $15 to be part of the framework's suggested bill of materials, but for now this is a good project to test out my designs for small 3d printed omniwheels. I'm working through some designs, and here's a render of iteration #1.

Hand forming steel wire made sense for circles, but not squares. I didn't want to take the better part of a month to build a CNC wireformer type machine, or to bother making simpler hand jigs for preset sizes or shapes, so I've rethought the design and will aim to use small finishing nails, which are cheap and widely available and don't need to be formed.

After the monthly Sector 67 meeting, a few people test drove the 2-wheeled cart. Despite the very simplistic control scheme (pre-programmed forward, left, right, stop routines), users were able to drive the cart pretty smoothly, even getting interesting drifting action at top speeds. The battery was barely drained even after a solid 20 minutes of driving, and with the addition of a heat sink the L298 motor driver was doing just fine (the heat sink is very necessary though). So this iteration of the cart is a success I think, and I will just need to buy some more L298s before I have everything I need to assemble 6 more.

Saturday, November 1, 2014

Omniwheel Robot 1

Before giving a talk at the university, I decided it would be a good idea to...spend 20 hours straight working at Sector on a omniwheel robot prototype. I only got a half hour sleep before the talk but I guess I must have been coherent based on the response from others.

See my slides on Google Drive at this link.

Here are some photos of the omni wheel bot.

Omniwheel before assembly of beads. The wooden block is a jig for mounting the press fit gears on the motors. The vertical mount design isn't great, as weight of the robot causes the mount to flex downwards a little, which pushes the gears together more tightly, which increases friction. That will be changed in the next version.

Some of the beads before mounting. I loaded them up on a piece of wire and coated them with Plastidip (black) or Flexidip (red, pictures on the full assembly below). It is better than nothing but still not a great solution. So far my best solution has been to skip tires entirely, and run the robots on rubber mats. I'm still looking for a good tire solution though.

The fully assembled omniwheel bot. I tested it with the power supply, and it does move. It draws a bit more current than planned (5 amps or so) but I think with a little redesign I can make a lower current draw version.

I got a bin full of more stuff donated to Sector, including some really nice motors to play with. The primary goal is still ultra-low-cost stuff, so I will start looking into sourcing cheap motors. My framework will come with practical notes, including 'buying guide' type notes for some parts, as well as design files, code, and everything else.