Quote:
Originally Posted by jimmers205
What are some examples of generic and adaptable drive bases? How would I go about designing a drive base?
I have seen a lot of diamond cross-hatches on the bottom of robots. What are the advantages of these? What material would this bottom be made out of and how is it attached to the rest of the chassis?
Thanks!
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What type of drive base to design depends a lot on your team's resources, especially in terms of fabrication capabilities. A drivetrain that makes a lot of sense for one team may be very hard for another to construct. There are numerous examples of many styles of construction out there. Look at COTs options from VexPro, Andymark, and Team 221 for inspiration, and search terms like "West Coast Drive," "Sheet Metal Drivetrain," "Box Frame Chassis" "Tube Drivetrain" "Parallel Plate Construction," and so on for numerous examples of custom work. Base your early work closely on inspriation from these examples, paying close attention to what exactly makes these designs effective, and then branch out from there.
Just a few specific things to look for and consider in your drivetrain design. I'm sure others will chime in with more. Here I'm assuming a basic 6WD drop center, some of this may not apply to other styles.
- The drivetrain is the most important part of your robot. If it fails, your robot fails, plain and simple. Err on the side of caution when it comes to structure decisions. As you get more experienced, you'll learn more about exactly where you can and cannot cut corners.
- You're generally going for complete rigidity in your drive frame, as well as leaving options to mount extra features to. Analyze how the individual joints of the frame interact, and make sure that it can't bend or flex too badly. Common bending problems to look for include torsional rigidity (twisting across the frame diagonal), parallelogramming (pivoting at the corners to go from a rectangle to a parallelogram), and impact resistance (how well will each of your individual frame members resist deformation when directly loaded)
- Actually do the math when selecting your gearboxes and motors. Optimize your robot for the distances you plan to be travelling regularly.
- Determine the materials and fabrication techniques that make the most sense for you to use in the construction of your drivetrain, and assess the limitations imposed upon you by these resources. Sheet metal sponsor? Build a sheet metal drivetrain. No lathe? Try to design around COTS axles as much as possible. And so on.
- Live axle or dead axle? Cantilever wheels or dual-supported wheels? Each have their pros and cons, and the choice is often driven by construction technique.
- Even if you go with a custom drivetrain, assess how you can use individual COTS parts effectively. Many custom drivetrains will use numerous small COTS parts throughout them to save on fabrication time, gearboxes being among the most common.
- Make sure you have a plan for driving each of your wheels effectively. If you are using chain, make sure you have a solid tensioning system. If you are using belts, make sure you have a tensioning system, or that you design for exact Center/Center distance, and have the resources to hold those tolerances
- Don't forget about your bumpers. Please, please, please don't forget about your bumpers. It's much easier to integrate a bumper attachment system into your frame from the start, than to tack one on at the end. This applies tenfold if you go with cantilevered wheels. Some teams have even been using the bumper as structural members of their frame recently.
- Consider the gearbox options available to you, and how you plan to integrate this to the drive. Direct driving a wheel saves weight, and can improve drive reliability by ensuring that a wheel per side will always be driven, but actually integrating a gearbox at the wheel can be a design challenge.
Based on how you worded your question, I guarantee that the thread below me is going to be filled with posts recommending you stick with COTs options. While a COTS chassis may well be the "best" decision for your team depending on where you're at entering the build season, and while there are numerous solid options on the market (Versachassis, AM14U, Drive in a Day, C-base, SuperLight Chassis, etc.), that doesn't mean that you should just abandon the idea of doing a custom drive. The offseason is a great time to practice and learn design, and practice is the only way you'll step up to do one in-season (or, by getting forced to by design constraints, completely unprepared to do so...that was fun...). Assess design quality honestly and realistically compared to COTs options when selecting your competition drivetrain, the most reliable part of your robot, but by all means, work to improve your skills all that you can.
The diamond hatched bellypans you are seeing are made from raw aluminum plate, typically cut on a waterjet, and attached using rivets or screws. A bellypan which rigidly connects the corners and sides of a drivetrain together helps with torsional rigidity, parallelogramming, and gives you an easy to use, low down place to mount electronics. The diamond plates you are seeing are flashy and one of the most weight-efficient ways of doing it (1687 did one last year), but they're also quite resource intensive (you need a dedicated manufacturing sponsor or the ability to cut it inhouse. The machine time on these plates is often better utilized elsewhere). Teams have used solid metal, plastic, fiberglass, and even plywood in the past for similar effect.