Simple shooter verses Arm--seeking advice

We are a second year team with very limited resources. We are trying to decide between a shooting feeder bot and a robot that uses an arm to pickup balls and deliver them to other bots. I am leaning towards the arm because we can use it to push the bridge down and to pick up balls. To be honest I am leaning towards an arm because I have no idea how to build a shooter. Still, I would love to build a simple shooter–but how? Has anybody come across a picture of a very simple feeder bot shooter? I am not worried about scoring baskets, I just want something that can suck up balls and shoot balls in the direction of alliance bots that can score baskets. Also, I am interested in thoughts about whether as a second year team without a lot of technical expertise should be focusing on a shooter or an arm that can pickup balls and manipulate the bridge–or maybe we should focus on something else entirely.

an arm would be far more complicated and difficult to use then a shooter for picking up balls.

for a shooter that simple all you need is a spinning wheel, plenty ideas if you look around CD or look up videos/ pictures from 2006/2009 competition.


This is our OCCRA robot from this year which was completely student designed and built in a 6 week period. (see attached pic) It sucked up 6 12" balls off the ground and put them in up to 5’ high cylindrical goals. I guarentee that if you built something like this to score on the 2 point goals you would have a great season. Just make sure you don’t go outside the 14" zone.

A shooter is much more difficult mostly because you need to precisely aim it. There will be many uncompetitve teams this year with shooters that perpetually miss. Don’t be one of those teams. In contrast, being able to score 3 balls in the 2 point basket EVERY TIME will get you very far into elims at most regionals.

Regards, Bryan

As a fellow Michigan team let me say thank you for this post. I am going to show this photo to my students tomorrow. Do you have an email address we can contact you at if we have further questions?

Sure I’ll PM you. But I’ll publicly say that the entire robot was made using an old kit chassis, 1.5" extruded angle, 2" pvc rollers, and urthane belts (found on Mcmaster.)


for the bridge, all you really need is something that flips down on maybe a window motor) that has a roller on the end. You wouldn’t need an entire arm system which is a…well…pain. Shooter is simple enough, a baseball pitching machine style shooter would work wonders if your just trying to feed balls to one side of the field. Add a camera and some math and you have a scoring bot

This is going at the simplest of the simple, and though I wouldn’t suggest doing it, it’s always an option.

Have 2 wheels angled at a 45 degree angle pointing upwards in the front of your robot, with a little room less than the diameter of the ball behind the wheels. You can now use the wheels to suck in balls, and shoot them up into the lowest basket.

Like I said, I wouldn’t suggest doing it, but if you’re out of ideas by week 3, then it may be something to look into.

The issue with all of these robots that require sitting in front of the baskets is the ease of traditional defense being played on them. When you move to spit something up there, you can get pushed out of the way. If you need to be in a certain position (not the key) to shoot, then someone else can simply park themselves there.

Wouldn’t this be impractical/impossible due to rule/field restrictions? The fender juts out into the field so much that it wouldn’t be possible to place the balls directly into the hoops, at least that is how I interpreted your suggestion. Correct me if I’m wrong

From the front, it is very difficult (though doable–just have to jump about a 4" gap). From the alley side of the court, it carries a risk of penalties, though it’s quite doable. From the other side, however, there’s plenty of room to make a 2-pointer without risk of penalties. The math works out such that a 14" appendage could half-cover the near 2-point basket at full extension.

We called this ‘corner scoring’ (i.e. the corner between the base and alliance wall) and initially thought it was a good idea. In discussing it we realized that it is VERY easy to defend a robot that goes to that corner because the defender can trap you without pinning you. Not that it wouldn’t work, we’re still planning on having the capability, I’m just offering our conclusions on the subject.

It would be possible to build a robot similar to the one BJC posted, but without needed to move the belt assembly, just have the balls get pulled in on the ground at one end of your robot, and exit the top on the opposite end with enough velocity to score from the front of the base. Everything is fixed in place and you’ll only need 1-2 motors outside of your drive train.

Didn’t say anything about how easy defense of that strategy would be, now did I? Even if you don’t pin them, it’s easy to defend. 11" over-bumper reach trying to get over 33" of robot and bumpers, not gonna happen, besides the chance of pinning penalties against them…:smiley: