This is a universal chassis that I thought up and designed in the last couple months, and is also my first full CAD project.
The concepts behind the chassis are:
1: It can be completely built with only basic shop equipment (drill press, band saw, etc.)
2: It can accept as many basic drive trains as possible (though only a few are shown):
4WD
6WD (dropped or flat center)
8WD (dropped or flat centers)
10WD (with slightly uneven spacing)
Omni (slide style)
The drop or lack thereof is acheived by rotating the center bearing plates 180 degrees. Their holes are 1/16’’ of an inch below the center of the bars, while the holes for the other wheels are 1/16’’ above the center of the bar.
Specs:
Bars: 3’’ x 1’’ x .125’’ 6061 Aluminum
Wheels: 6’’
Drive: ToughBox Nanos with chains to any unpowered wheels
Overall: 35 x 26.9’’
This is version 9, and I am about to start verion 10, which will move from hex to standard axles to reduce costs. Any other suggestions would be more than welcome.
Would you always leave the extra bearing blocks inside the chassis or would you take them out to save weight? how easy is it to get at the transmissions and wheels if you wanted to change them?
I love this idea, very versatile. You can argue that the same things can pretty easily be done with the kit chassis.
Is there a reason for not centering the gearbox and motor assemblies? It’s a minor thing but it makes your COG much nicer. Also I don’t really see the need for the second omniwheel for strafing on the slide drive. I guess it makes you faster at it but not really worth the weight of the wheel, motor, and gearbox especially cause you can use a CIM somewhere else on your robot by not using it there.
I apologize in advance for this massive response, I just wanted to address everyone’s questions/comments.
Thank you, we will hopefully build this as an off-season project to test its viability, in which case I will post results.
I feel that it would be better to leave them in because it allows for faster changes between drives. I intentionally left out anything on the bottom of the robot, with the idea that we could raise the robot and have easy access to the necessary bolts under it. This would theoretically mean that switches could be very quick with a few people.
I would be cautious about 4’’ wheels however, due to the three inch bars. The strength is hard for me to predict, but it is entirely .125’’ aluminum and bolts. The weight should be about 30 lbs, but there is a lot of estimation in that.
Right now it is very much in the conceptual stage, and hopefully we will build it as a test chassis to determine its viability.
Really? Our team doesn’t have much experience with direct drive, so I hadn’t assumed much of a difference.
I feel that the big advantage this has over the kit chassis is that it allows easier access and switching between these different drives without modifying the frame itself at all.
As far as the centering, it was simply difficult to accommodate for a dropped or flat wheel with the gearbox also attached.
I debated the second omni wheel for a while, so version 10 might be able to accept either 1 or 2 strafing omnis. That’s definitely back up on the consideration list, thanks.
I’m not saying the chassis is a bad idea, I actually really like it.
We had a grand total of one keyed shaft on our robot this year. We lost the key half a dozen times. Sure you could put more effort into the design and build such that it isn’t an issue, but hex is just simpler, more easily repaired and maintained.
The bearings are a bit more expensive, but you could not convince me to go back to keyed shafts. More pieces, less strength, harder to deal with over all. The only advantage is that you can use round bearings (without using a sleeve), which are extremely common and widely available.
I’d really like to try out a drive system that goes 1/2" hex -> 1/2" round -> 7/16" hex. It would be a bit of a luxury, but not unreasonably so (especially if you have a machining sponsor to save you the cost of the necessary tools if you don’t have them).
Interesting idea. Just a couple suggestions:
Unless you are planning to weld this, I’d suggest beefing up the gussets between the siderails. Add a few more rivet/bolt holes to them, especially on the insides.
With cantilevered wheels like this, I’m not sure if having the sprockets on the outside of the wheels would be the best idea. If you can figure out how to move them to the inside of the chassis or even to the other side of the wheels without violating your design goals, I’d recommend it.
Finally, I don’t think it should actually be used for competition. If you use it for preseason R&D, the modularity could be beneficial, but for competition, choosing one design and sticking with it is almost certainly better. This way, you don’t have to make concessions on other parts of your robot just to accommodate this drivetrain.
All told, very nice job for your first CAD project. Keep taking on new projects - it’s an excellent way to get better.
Cool idea. Although I like the concept, I feel like weight might become a bit of an issue. You have to carry around all that plate and bearings even if you never use them.
Also, do you have any plans for bumpers? These tend to get left out in most drive train designs until the end. You may have trouble supporting the bumper to what the manual requires (I believe every ten inches) with the three bearing blocks in a row.
“Chameleon Drive” implies the thing blends into the background … yet I totally see all of that drive in all configurations o.O
(Ok, I kid…)
The most basic piece of this ‘drive’ is the H-frame. Your H-frame setup is very verstatile. However, I don’t think the gearbox configurations are. For the 8WD and 6WD tank variants, why not just use the CIMple boxes that come in the KOP? The chain runs are easily tensioned by sliding the transmission, it’s lighter overall, c.g. is lower overall, and the sprocket reductions are adjustable so you aren’t stuck with purchasing ~$100 in gears just to get the right speed for a given year.
For the slide drive (your bottom pic), you may find that the robot doesn’t need to slide sideways as fast as it moves forward/back. If this is what you find, you may be able to use 2 RS-550’s (properly geared…) in lieu of 2 CIMs, thereby putting the 2 CIMs back on the outer wheels for better power characteristics during normal play.
For use as a test chassis, how about emulating AndyMark’s nano tube chassis and running power between the wheels inside the frame? That way, you could have every wheel slot powered all the time, making swapping drive trains even easier (just pull off one set of wheels and put on another!)
If you want to use this for competition, keep the weight rules in mind. Swappable systems like this are really cool, but all of the hardware used in every configuration you bring counts towards your weight limit. So, if you plan to swap between traction and omni wheels at competition, you’ll have to weight both sets of wheels with your robot, even though only one set will be on the robot at a time. See R03 in the 2012 game manual for specifics (it’s been in the manual that way for years, I doubt the rule will change in the future).
One more thought… why not push the two cross bars towards the outside a bit more, and set them up for 3 wheels each? That would give you the option of using the center for a strafing wheel like you have now, or setting it up for a wide drive base design, with no wheels on the long side.
Figure out your bumper mounting. This is something most people ignore until the “end” but the sooner you think about it the happier you’ll be with the implementation.
I’ve found the 6" diameter AndyMark omni-wheels work a lot better when they’re run as duallies – you should consider that for your H-Drive implementation.
I believe you’re sacrificing some functionality at the expense of versatility. “Jack of All Trades, Master of None.” In my experience, it is very very very rare for a team to switch drive styles mid-season. As a result, it might be better for you to CAD several different configuration specific designs, knowing that you’ll be able to do subtle things to make them better than this one design that does all of them. If you prioritize versatility enough that you’re willing to make tradeoffs (they may be big, they may be small) then you have nothing to worry about. Your mileage may vary.
Very cool design. I agree with a lot of the other commenters that this looks like a really neat and versatile test chassis. I would suggest talking with your programmers about sensor incorporation and programming goals. A chassis like this could go from good to great with good iterative software and driver interface development.
Even if it is a test chassis, the addition of good bumper should enable you to have a defensive sparring partner.
As with the above project, it could be a great project to make in the offseason to test different drives, but it most likely is not the practical design for a competition robot.
Also, this may be a good chance for you to learn how to create configurations of your assembly within Solidworks.
We switched from swerve to Mecanum at the LA Regional this year; this was because we accidentally fried our swerve steering motors when calibrating the PID at San Diego and didn’t want to deal with it at LA. We were able to do this very fast because we design our drive train in modules. Each module uses the same of mounting and has everything already built in (except controllers).
I really like a of things about the the OP’s design, especially the design around limited manufacturing capabilities. Also, it looks like it should be able to accept mecanum as well because of the corner gearboxes. Great work!
Just out of curiosity, how much time do you think it would take to change the drive types? It would add a neat dynamic if you could be a 6- or 8-wheel drive for quals, then switch to mecanums or a slide drive in elims so you can triple, or change drives between matches to better suit your opponents and partners.
