PolyBOTS

BotMobile Design

Building and designing on the fly

-Authored by Yuri.

As I am writing this, I am working on the new Polybots sports car / robot called Botmobile.  The Botmobiles predecessor was Panzer and Deth-Chair.  In short, Botmobile is a frame with 4 wheels, 2 driven, 2 steered.  And a Chair is attached on top for user to sit and control the robot.

Let’s go into the design part.  The key of designing on the fly is to know what you are building.  The plan of all the parts and all joints.  If it’s unknown what part is going to be used, a sufficient space must be left.  For best results all parts should be laid out on the ground or table to know exactly what goes where.  The key here is not to start with the caring members (frame, chassis) but with the parts that attach to it.  The reason is, you have the parts, you can only modify them slightly, but a frame does not exist, so you can make the frame the way you want it.  You always want to leave enough options for later to not redo anything. The same procedure above was used on the Botmobile.  Most parts where present and accounted for.  The motors, wheels, batteries, chair, and raw materials (frame members) where all accounted for.  The build had to meet minimal requirements, like maximum width of 33 inches, so it could go through a door.  Minimal requirements where to ease the design, and should be made for any project. Now that most parts are laid out, and you know how you want to built the caring member.  Before you start, try to visualize where the loads are, and how much are they.  Let’s say a truck battery is 40lb uncharged,   where is it sitting, have you put enough support for it?  Or let’s say a robot would go over uneven terrain, would it bend too much?  Those questions and similar should be answered.  You don’t want to use just any materials; you should size up the materials properly.  Last thing you want is too be too weak or being too heavy.  For many projects, you would require putting in an order for materials and parts.  Last thing you want to do is get too expensive parts and on the other hand too cheap.  You have to shop around a bit, and not only on McMaster, but on other websites or places.  McMaster practically has most parts, but not the cheapest.  I am going into it, because you will be or maybe given a budget.  Being a smart builder, you would want to spend the entire budget, Yep, all of it, but not at one time.  If you do your shopping, you be able to get surplus materials, better parts, and many more goodies.  As an example, let’s say using McMaster and getting a square bar aluminum would cost 8 dollars per foot, using another site you find same identical bar for 3 dollars/foot.  Getting 30 ft, you would save 150 dollars, good savings, now you can get that Lithium Ion battery or larger motors, or better wheels.   Then spending the budget, don’t cheap out on major components, if a part cost a bit more to get stronger, faster, durable part.  Use the budget and saving to get it.  The key here is to have detailed and planed out list of parts and materials to the last nut and bolt.  Then you can upgrade and improve the project to the limit of the budget.  Then you get all the stuff you want and some more. So, now key is not quitting.  You went so long, and no one screwed up your little or major project.  Now its building part, the key is to stick to the plan, and try not to deviate too much.  Remember, you have no more budgets, and the success lies in the plan you made before.  Hopefully you worked all the details of your plan before.  Otherwise, you will end up with half done project, or a part supplier for another project.    Guess where all the parts came for the Botmobile, guessing from failed or disassembled previous project, if yes then you guessed right.  There were only some parts not from Polybots that I myself invested in.  Batteries, terminals, some wires, switch.  The total runs up to about 50 dollars, that’s a personal limit I have for a project or a club. So you finished the project, does it work?  If yes, congratulations. If no, your contraption is going to be fixed up, or just taken apart and placed in a parts bin.  If it works, chances that it will be taken apart are a lot lower.  Congratulations, you have finished.  Try doing another one.