| CPSC 226 | Robot Base Recipes | Spring 2005 |
Here are some hints on how to cook up your personalized robot base that your IsoPod will control. Much of this information was provided by John Vaughn from previous incarnations of this course. Cooking is more fun with friends so be sure to swap ideas with your co-workers. You don't need to wash your hands before you start but be sure to have the right tools and ingredients on hand, and to use the proper tools for the job at hand.
Always wear the safety glasses when using the drill press, band saw or scroll saw. All these tools are basically safe to use if proper procedure is followed. Don't get in a hurry when using the tools. Allow enough time to learn how to do things right without rushing through the work.
Drill press
Drilling holes in plastic is usually much safer than drilling into metal. There is less danger the drill bit, however small, will catch or "grab" the metal and try to spin the piece you are drilling around as the bit turns. This can be very dangerous with a thin metal plate suddenly acting like a whirling blade or tiny frisbee from hell. The main problem with plastic is that the bit will still "grab" the plastic and try to pull it upwards unexpectedly at times. You can avoid this problem by using the "hold down pliers" or drill vice we have added to the drill press. USE IT WHEN DRILLING. I will demonstrate how to use this along with the drill press. For drilling small pieces, hold them in the metal vice while drilling. To drill larger holes, first mark and drill a small 'pilot hole' that guides the larger bit through the material. Use the clamp for larger diameter holes since larger bits tend to catch the material more than small ones. Pay attention when we step through the safety talk concerning using the drill press and follow the guidelines. Using a drill press on our small bases is a very safe operation provided you follow the rules and use common sense.
Band saw
This saw comes with a sharp moving blade that will definitely endanger your fingers if you are not careful. Fingers can be cut more quickly than wood are plastic. Keep your fingers out of the blade path as you cut. Always adjust the height of the blade guard to no higher than 1/16" to 1/8" above the height of the material you are cutting. Hold your materials by the sides. Do not force the material against the blade, a gentle push will do. Do not cut very small items that require you to get your fingers close to the blade. Do not try to cut very sharp curves using the band saw. Use the scroll saw for that. Do not cut thick metal with our band saw. It is meant to cut thin wood or plastics, not steel or aluminum. If you need harder metals cut you will need to use the hack saw and do it by hand or ask for help from me.
Scroll saw
This saw excels at cutting very precise curves in thin wood and plastics. The blades need to be correctly tensioned or they tend to break easily. Don't try to cut fast with this saw. It is meant for slower, more precise work. If you need mostly straight or gently curving cuts, use the band saw. You can detach one end of the scroll saw blade and insert it into a hole in the material and cut out slots or other larger openings in materials.
Portable drill
This tool is pretty safe, but it can still spin things out of control. If you use this tool, you should always use a piece of plywood under your material to keep from drilling holes in the work table, and use a clamp to hold the workpiece and plywood to the table. Please don't drill holes in the nice black work tables. Be sure and store the chuck in it's holder before you put the drill away.
You should never operate any power tool unless someone else is in the room with you.
Other classes use this room besides us, and other students use tools and supplies besides you. When you are done with a tool put it back in its proper place, even if that's not where you found it! Take 2: When you are done with a tool put it back in its proper place, even if that's not where you found it! Put lids back on containers and close drawers. Help keep the Lab clean. Put up any unused screws, washers, etc, where they belong. Use the wisk broom to clean up your work table before you leave the lab (it's OK to sweep stuff onto the floor). Label your "stuff" if you want, or take it with you. Be nice with other people's "stuff" - the golden rule applies here.
Robot Hints and suggestions
I have a couple of "store-bought" robot bases that you can use as a model for yours if you wish. As you will have to do your own customization, feel free to imagine something cool but remember the rules of the final robot exhibition and be sure your robot is appropriate for the festival's requirements. Think carefully about various robot designs and their ups and downs before making final design choices. Customization choices you plan from the beginning are best since you can determine what your robot base will be like before you go much further and it will save you some reworking. Also notice that custom painting/stickers/add-ons etc are best planned at the beginning since adding items later can damage installed sensors, wiring, etc.
External wiring connections coming to the IsoPod should be made via plugs and connectors so that the IsoPod be easily disconnected from its robot base. You've made several of these already. Pairs or triples of wires that belong together (going to the same motor, for example) should be twisted together and usually should be of different colors so you can tell at a glance what is connected to what without dragging out the multimeter for a continuity check.
Motors should be aligned onto the base so your robot drives forward naturally instead of at an angle you will have to compensate for. You want the direction of travel of both wheels to be parallel. This means your motor mounts should be parallel and on axis. Be sure to allow clearance for wheels and base.
Think through placement of sensors as a whole so they don't interfere with each others view or operation. Route wires from sensors so they won't catch on wheels or any other moving part.
Basic robot parts
You should have these parts in your robot "kit":
Miscellaneous
These parts are in the cabinets or nearby:
General Layout
What follows next is a general recipe for building the basic mobile robot base and attaching the IsoPod to it. As you choose placements of sensors be prepared to handle unexpected placement difficulties, problems with clearances, etc. Again, remember the requirements for the contest.
Check out the models and notice how the two motors attached to the motor-mounts, and how the motor-mounts attach to the base. It is possible to use a low-slung lower base by mounting the motors on top of the base, but you will need to do something to have the caster wheel be at the right height. The caster wheel in your kit is different than the ones on the models. You may need to pvc cement an extra block of plastic to the underside of the base to bring it to the right height. NOTE: The shape of the base(s) is up to you to cut, and all the holes in the plastic base are up to you to locate and drill. The rule is: Design thrice, measure twice, cut/drill once.
Advice:
Layout the shape of your base using a piece of graph paper and lay it on the plastic. Layout your parts on the graph paper to make sure you have clearance etc. When you are sure of your design, copy the design from your graph paper to your plastic base plate and use a thin pen to mark the location of the holes on your base. Remember which side is top and which is bottom. Be sure to allow clearance for the various parts to fit together on the base. If you want to cut out any slots or large holes, see me and we will look into using the band saw or scroll saw to do this.
I recommend marking and drilling all your holes one after another so you don't have to drill extra holes later with some of the parts already attached to the flat base plate. After the motors and wheels go on, in particular, it becomes much harder to drill holes easily without damaging existing parts. Some holes must be "chamfered" or "countersunk" to allow flat head screws to fit flush with the surface when tightened. You should chamfer the holes with the appropriate tool found by the drill press. You can use this in the drill press or use the hand twist drill to do this step. The drill is faster but you will need to work carefully to avoid removing too much material. Check your work by doing test fits using a flat head screw as you remove material.
A standard way to mount the IsoPod controller is to mount it on a top level of your robot base. The battery packs ordinarily go on the lower level with connectors going up thru a hole in the top level. You have standoffs for accomodating a second level for your robot. You can find smaller aluminum standoffs in the cabinets to elevate your IsoPod carrier board slightly above the top level. Feel free to use the standoffs from your earlier robot as well.
Congratulations, you are the proud parent of the basic robot controller and base. What you include from now on will depend on exactly how you customize your robot and what capability you want it to have but below are some general suggestions. Don't forget about the contest requirements!
I suggest mounting the QRB1134 sensors using the built in mounting holes so they can be moved up and down for fine adjustment.
The Sharp GP2D12 sensors fit nicely mounted with small wood screws to the edge of the plastic base
I like to braid (or twist) my connecting wires to keep things a little more tidy.
We have a box of "parts" that you may dig through to find something "special" for your robot. You can also feel free to add any extra sensors that you find or that we may have. (The photocells we used for the light seeking robot are a possibility.)
Many customizations are possible with with your robot. The success of most of these really depends on how much quality time you spend on planning, designing, and researching. Ask if you want some ideas or check out the course home page links. Have fun and don't hesitate to try things out.