pic: 2471's car drive for BunnyBots 2016



This is the drive train for one of the robots Team Mean Machine will be entering in the 2016 BunnyBots competition. It drove like a champ with preliminary code the other day, but I’ll post some video once the software is in a more refined state.

To same time and money, it is basically our 2016 drive in the back, and our 2015 drive in the front. So it has four CIMs in the back and two minis in the front, all geared for 17fps.

Questions and comments are more than welcome.

How’s the turn radius on the drive train?

423 has also made a number of robots that handle like cars by taking a mecanum chassis and replacing the rear wheels with omnis. It drives like a car even though the front wheels don’t actually pivot - I can attest to this because I drove on it to classes a few times. In the end, any chassis where the center of rotation is between the rear wheels will drive like a car.

So this is basically the mullet of FRC drives.

I think the only time I’ve seen a “car drive” style have success in a competition was 2008. What exactly is the competition like that you will be in?

One the software is updated, it will be able to turn in place.

This year’s bunnybot rules are available here. A major component of the game is going around a figure 8 race track. However, we mostly chose this drive design because we had the components laying around, and we thought it would be cool/entertaining.

How intensive is the machining on your turning modules? Those look like they could be pretty simple to make. Also, I feel obligated to mention that while this might handle similar to car, it’s still using independently driven wheels and two independently steered wheels. It’s probably more mobile and can do tighter turns than a car using some version of Ackermann steering.

Here is the first prototype module of this design. I am very happy with how the design turned out. We built 10 modules in the first week or so of build season 2015. They were made almost entirely on a manual mill and manual lathe. They survived four competitions and hours of drive practice, and are still in fighting shape.

Also, I feel obligated to mention that while this might handle similar to car, it’s still using independently driven wheels and two independently steered wheels. It’s probably more mobile and can do tighter turns than a car using some version of Ackermann steering.

As mentioned above, it will be able to make any turning radius including turning in place.

Do you have any more pictures of the module? I’m mostly interested in how you did the top of the caster box and radial/thrust bearing setup.

how do you know that the figure 8 racetrack is a major component?

Here is a cross section view of the module. Hopfully it answers some of your questions.
The top of the castor box was a 1/4’’ plate of aluminum with the tube of the castor bolted to it from all sides with 0.5’’ 6-32 bolts. the main coaxial was then pressed into the top plate up to a flange, and the turning sprocket was pressed around the flange and bolted to the top plate of the castor box.
The bearing setup was just two igus plastic bushings and a steel washer.

Strategic analysis and human role play of the game.
Of course, its impossible to say for certain what will be a major component at this point.

As promised here is me driving this robot for the first time with the new software:

video

I was surprised by how well it cornered at speed, even though I shouldn’t be… Race cars are made this way for a reason.