I’m going to try and keep this short and simple, but it might not be.
We’ve taken a ton of tips from our other discussion and thought a lot about them. We’ve decided that our robot would be a simple 4-wheel tank drive with a 6-bar lift and a simple mobile goal intake. The idea has proven to be okay, but our chassis is suffering greatly. We have ordered mecanum wheels for easy maneuvering, but we haven’t gotten them yet and I won’t see them for at least a week because of Thanksgiving break. Because of that, I can’t really build the chassis without wheels. We didn’t get those dreaded regular wheels because they have only brought sadness to us when we use them. Our only option was to use some sprockets and tank treads to act as wheels for the time being, but OH MY GOD THEY’RE SO ANNOYING. I can’t build a simple drive train because the wheel takes up so much space and I need that space for the mobile goal intake. I’m stuck. Help. Please.
I would highly recommend against using mecanum wheels because they are by far one of the slowest options, second only to using actual tank treads. Omni-wheels are usually the way to go for a tank drive. To measure out your base, I would recommend just looking at the wheel specifications and measuring space with a ruler. Another great way to preplan your bot, without the needed parts is to use CAD, which is very helpful in measuring exactly the right spacing. Building your chassis without the right wheels shouldn’t be too hard, just make sure to remember that the wheels will add some extra height. Just remember the diameter and thickness of the wheels and you should be fine.
@RoboTurtleLord thanks for the help! Unfortunately, we can’t get omni-wheels at the moment and we’ll have to store those mecanum wheels somewhere else. The main problem I’m having is that because the tank treads are so wide, it changes the width of the area that I want to make the place for the mobile goal intake. Essentially, I can’t build it because it makes the space too narrow to correctly implement a 4-bar that will lift up our goal. (It was inspired by the OSIZR reveal’s mobile goal intake)
A good place to start would be to use a gap of 5 holes to substitute where the wheels would go. I find that anywhere from 4-7 is a good length. Unless you are thinking about using external gears or sprockets to chain the wheels together, 5 holes should be plenty. Our mobile goal intake works well even with a 7 hole gap for wheels on both sides.
Additionally, as we have found, the mechanism that OSIZR is a lot tougher to make stably. By supporting and manipulating all of the weight from only the center of the intake, there is much more strain put on the linkage. We have found that by integrating the 4 bar mechanism into our chassis, we can make a much more stable lift. This also means, that having a narrow space between the wheels of your chassis will not affect your mobile goal lift. Look at 9065c’s reveal video to get a better understanding fo what I am talking about. Essentially, the lift will move horizontally as well as vertically so you can grab a mobile goal outside of your base and then move it in.
However, If you do want to stick with a OSIZR type lift, you will want to use as little space as possible within the chassis, and may even want to leave the back wheel unpowered, as teams like 1961x have, to have more space for your mobile goal lift.
@RoboTurtleLord good point! I understand what you mean; my only problem is that I don’t really understand how they got their goal lift to move like that. I’m a beginner builder and it’s really confusing to try and see how they did it. I’m guessing they painted some of their parts black to match their name? Either way it confuses me a little bit more because in OSIZR’s reveal, they showed off a really easy 4-bar with a simple space for the goal. Thanks for the tips, though!
@Easton I did; I understand the mechanics of the mogo lift (it works the same as our toolbox’s “lift”, in the fact that it operates nearly the exact same way but with different pieces) and I just can’t pinpoint what I need to do. From what I’ve seen, I’ve already taken some leftover pieces and cut them to the desired length I want the lift to be.
Maybe think about it as a regular 4 bar, on its side. When you are making a 4 bar for a vertical lift, you have one “bar” attached to the chassis - where the motors are located and the linkage is powered.
You then have the two “Powered Bars”- which are the bars being powered by the motors and augment the rotational movement from the motors.
Finally, you have the “linear bar” which is connected to the angular bar. This bar, thanks to the linkage, stays parallel to the first bar while also providing horizontal and vertical movement.
Now, just think about this in relation to a MOGO lift.
The “Bar” with the motors is attached to the base.
The two “powered bars” are simply attached to axles powered by the first bar
the final bar will be parallel to the base, and is just the carrier of the MOGO.
To get a better understanding of what I am saying, look at some of these videos.
We managed to get our drive train down to 5 spaces (both c channels facing the same way) with
bearing - washer - 4.6mm spacer - gear(not hs) - 4.6mm spacer - omni-directional wheel - .25in spacer
for the other shaft with a gear replace the wheel with two .5in spacers
I don’t understand all the hate being thrown at Mecanums. We’ve used them for two years straight, head-to-head tested them against omnis on the field and there’s no difference between the two except on strafing with x-drives. Anywho, straight axle to internal high speed motors is what we’ve used. With a good weight distribution, they’ll have the speed and torque to move mobile base across court quickly and easily climb obstacles; 10-point pipe.
I agree that mecanum wheels can be used effectively, however one thing that you need to keep in mind is that at worlds (possibly below that now) they use an anti static spray on the fields, this unfortunately causes higher levels of friction, which makes the drive motors overheat more often. This happened to my previous team during starstruck and was incredibly frustration since it never happened before during testing.
We went through that drama last year. Our first robot was +24 lbs of pure steel and we tried to run it with 4 high speed motors straight to the mecanums. So much overheating. As far as strafing friction goes, I can load the robot with a mobile base and constantly strafe and turn with it till batteries are almost dead on my living room super plush rug-really high friction-with no overheating.