We are a rookie team and, thus far, are lost like a ball in tall weeds. We have watched the videos for the game and field and we were wondering if the 6" wheels that came with kit would give enough clearance to go over the bump in the middle of the field as well as climb the ramps.
Secondly, should we upgrade the wheels to a mecanum drive or to omni wheels?
Lastly, Is there any benefit to any of the chassi sizes given in the Andymark kit? In other words, is the long better than the square, but square is better than wide etc.
First of all congrats on making it so far in the build season! Being a rookie can be intimidating, and I completely understand - that’s why CD is here to help. The kitbot wheels will give you plenty of clearance and you’ll be able to comfortably go across the 7/8" bump and ramps on the field. I would recommend not experimentation with omni wheels and definitely not mechanum wheels. This isn’t the year for them, your kitbot wheels will perform much better anyways.
Spend the extra time instead designing the cube mechanism and perfecting it, then getting driver practice. Those two far outweigh small tweaks in the wheels you decide to use with the KOP chassis.
The configuration you choose depends on how you decide to design the intake. If you go with a taller bot, you wouldn’t want the square configuration. If you want to be a good match for a ramp bot, you’d want as small a chassis as possible. Spend a couple days deciding what you exactly want to do and then you can probably figure out what configuration to use.
Our CAD team has finished up with the drivetrain, so I don’t know if they’ve virtually tested the ramp specifically yet. I’ve seen the Robot In 3 Days (RI3D) talk about this and using 6" wheels so I expect they would work.
As for wheels, there’s a lot of “that depends” in there. The easy decision is on mecanum. Mecanum allow you to strafe, but bring with it there are 2 key things you need to take in to account. First, if bots play defense and push, you’ll get pushed around easily. Secondly, if you use encoders to measure distance on the drive train, it won’t work well. Normally, one revolution of the wheel axle means a fixed distance traveled. But the rollers on mecanum will “slip” when you start and continue rolling after you stop.
If you have a 6 wheel, omni’s can be used as front, back or both. They would allow for easier turning, while the non-omni wheels provide the pushing power.
If you’d like to talk about the kop drive train sizes, pm me and we can setup a call.
I would agree that the 6" wheels that came with the kit are the way to go, or a mix of traction wheels and omnis. I think that’s likely the way my team is headed as well. ChiefDelphi is also a great place to be when you have questions - I’m here all the time looking to learn from others.
I also wanted to say that I’m with team 1466 in Knoxville, and we’re only about an hour away from you. If you’d like to check in, stop by to visit, need someone to come by and help, need some parts, whatever, please get in touch. There are several veteran teams in east TN. If you’d like to check in, you can send me a PM here or email: [email protected]
We sketched up a ramp and set of bumpers onto the kit chassis in Solidworks to see how it would go up onto the Platform. The recommendation from that is to have the bottom of your bumpers at least 1.75" from the ground (but make sure the top is no more than 7" from the ground).
One coach in our area had asked about switching to 8" wheels from the 6" ones in the kit - that change would actually make it harder to drive up the slope since the wheels would be further inside the robot.
We rolled some old robots up ramps and feel like 4" wheels on the kit frame won’t be a problem. *Note: the kit comes with 6" wheels.
The kids noped out of mecanum wheels after how poorly they did with the ramps in 2015. If any wheel lost floor contact, it got harder to drive it.
I think we’ll be using omnis on the front, at least, to aid turning.
After marking out a quarter field, I’m definitely thinking that the ramp zones will be close quarters, and so you may need to drive across on the ramp sometimes. Thinking about this, I think we should make a full ramp to practice maneuvering across it. Basically, have them practice driving fast over the ramp (with a turn before/after). The field elements are so massive this year so we have to be a little picky about which ones get built to scale.
We are not a rookie team…but we’re going to use the kit chassis, in the maximum allowable size configuration (32.3"long, 27.5" wide). This requires paying close attention to how you build the chassis, as the kit instructions don’t show this configuration. It’s a combination of the “long” chassis layout for the side rails, and the “square” chassis configuration for the end rails. Be careful, you only get to cut the parts once!
We decided to use this configuration because we intend to make a “tall” robot, because we decided that it is going to be necessary to control the scale, to win matches. A tall robot needs to have the wheels as far apart as possible to keep from tipping, and this chassis configuration is the one that allows that. We will also go to a lot of effort to make sure the weight is distributed as low as possible—that means we won’t go to much trouble to keep the bottom of the robot light, but we will go to a lot of trouble to keep the top of the robot as light as possible, and also to make it so the weight is most often down low (ie a moving arm assembly that is normally in the down position).
The kit chassis is a pretty good product, and using it will let you drive the robot pretty well, and most importantly, allow you to spend more of your time figuring out how to make decent manipulators, and also let you spend more time practicing driving the robot. The kit chassis has a dropped center wheel, so it turns pretty well–think about how having only four wheels in contact with the floor most of the time, makes it act like the wheelbase is much shorter.
Thank you all. We will be going with the 6" wheels and may look at omnis on the front or front and back.
Should we use the 4 CIM motors on the gearbox, or should we only go with 2? I know we are limited to 6 CIM motors, which may come into play with climbing and creating a lift mechanism, but I’m not sure if 2 motors on the gearbox will be enough power for the bot.
4 motors gives you the acceleration you want, without using up too much of your battery’s limited power. If you decide to make a really small and light robot, you could get away with two drive motors, but you probably still want four…
Note that there is not a limit on the number of CIMs this year. Usually teams use either 2 or 3 cims per gearbox (4 or 6 total). Using 2 cims total is not a great idea as it puts a lot of load on the motors.
Haven’t tried it, but kitbots with 4" wheels could not cleanly drive over the scoring platforms in 2015. I haven’t gone back to check, but it seems the platform ramps this year are a bit higher and steeper.
four cim’s is a safe bet for drivetrains, its what my team has used for the past three years and its worked out pretty well so far, as for wheel size I think you could probably make four inch wheels work and definitely make six inch wheels work but you could know for sure with some simple 2D cad. if you need to calculate for gear ratios use the JVN design calculator and that does math for you.
I would echo what others said about using JVN’s calculator for your motor allocation. Would also advise you look at what other teams used on similar mechanisms in the past and see what they chose. We Haven’t used a full CIM motor on a robot in years.
Personally I would go with 4 CIMs on the gearboxes in total. Its probably what most teams will run with. With the unlimited amount, even with available PDP slots. If your concerned about the amount of CIMs for other mechanisms, there are many other motors available and if geared right will work.
If you have the resources, I recommend following Simbotics guide for the “Kitbot on Steroids” and replacing the wheels with 6" Colsons. This will give you a much more powerful drivetrain, put you higher on picklists, and allow your robot to execute in an overall more reliable and powerful way. After all, the drivetrain is undoubtedly the most important mechanism on any FRC robot.
I’m not sure I completely agree with this. Having a great, fast drive train is awesome, but if you can’t manipulate cubes that well to begin with, then you likely aren’t going to be too high on pick lists. I’d recommend spending more type perfecting the manipulator for the greater positive impact on performance than small ones that may make a difference in driving ability. Just my 2c.