motor powered launcher

Just curious, has anyone tried a motor powered launcher like this one, or any other type in toss up this year. We don’t have pnumatics and I was wondering if anyone tried a motor powered launcher.

Obviously vex pro has more parts so we would have to improvise.


We tried a prototype last week, I was working on the choo-choo in CAD today.


And have the beginnings of the real thing. It’s hard to see from that photo but it used a small turntable driven by a 12 tooth gear.


The students want to go with pneumatics though so I doubt we will finish it. It’s also pretty violent when it fires.

Two questions:

  1. do you use 1 or 2 motors
  2. how many rubber bands / elastic tubing are you using.

At least I’m not the only one with this crazy idea.:smiley:

I like it though.:slight_smile:

One 393 motor is used to pull back the launcher, the final gear ratio is not decided but the prototype used 5.5:1 (ie. small turntable)

We used the latex tubing, probably looped around 20 times, the launcher used a 1x5x1 C channel strengthened with a 1x2x1 C channel (different from the CAD, that’s just for working out some geometry issues). The robot is designed to handle beach balls only (a strategic move based on previous game observations and, well, because that’s a different strategy and looked fun), it was launching a beach ball from the bump over to the goal zone consistently. Anyway, as I said the students wanted to also try pneumatics so it has now been modified for that. The advantage of the choo-choo mechanism is that is does not run out of air :slight_smile:

The launcher need to be built to be robust, there is a lot of stress on the launcher as it waits to fire, you need to keep safety in mind with these types of mechanisms.

Thanks for the specs, and the quick response.:slight_smile:

We will, if we decide to do it, we will start with a low amount of elastic and work it up till it is the correct amount. Probably with the amount of stress, every thing will be double and triple checked for robustness and durability.

Thank you jpearman for your time and ideas.

Use pneumatics if you can cause it’s always better than using motors… but having two pistons is recommended for a catapult! Having at least two tanks would be enough… if you can not afford two pistons you could use one piston but it would need to be built right in order to work efficiently. :slight_smile:

Why do you say this?

Pneumatics add weight.
Pneumatics have a limited number of catapult launches.
Pneumatics potentially have a different amount of force each time if a pressure regulator is not used.

The motor is not used to launch the catapult, it moves the catapult to the pre-launch position, elastic force is used to power the catapult.

We use pneumatics on both of our bots for a catapult. Never have I seen such imaginative placement of reservoirs in my life, and this is for a 24 in^3 and a 15 in^3 bot.

One of our builders prototyped something similar to what Team JVN of build blitz did. It looked awesome.

Well obviously the more tanks you have the more weight it will be but the parts themselves don’t weight that much. Best to have double acting pistons versus single acting cause more power, also you will not be firing the catapult the entire match unless necessary. The catapult would just get weaker as the psi decreases! The pneumatics kit comes with a pressure regulator to control the amount of pressure being used, low to high setting… Using pneumatics has a advantage cause you can use motors for various other things.

I smell am accidental cortex smasher…

My original post said we don’t have pneumatic components, nor will we be getting them this year. We want to make sure we have enough funding to go to worlds if we qualify. I was wondering if anyone had an effective way of using motors to complete the task. If used correctly, it could have the same amount of force as pnumatics, but has no chance of running out of air, and doesn’t add the weight of pneumatic storage tanks. I simply was wondering if anyone had any other alternatives than pnumatics so we wouldn’t have to purchase them. We would plan on using them at major tournaments such as the state championship/world’s, so we would have to use them a lot. We wouldn’t want to run out of air.

Well think about it, a match is not that long and only lasts 1 minute and 45 seconds. If you had 2 piston catapult the psi would drop by 20 psi shot but that’s if you had one tank, or if you had 1 piston catapult it would drop 10 psi per shot with one tank. Pneumatics are worth it if you have the funding for it! :cool:

Or you could build (my personal favorite) a 0 piston, 0 motor catapult! It drops 0 psi per shot with any number of tanks, so it lasts infinitely longer than it’s piston-using counterparts. It also can launch an amazing 0% of the distance! It’s super effective!

It is a matter of time, we want to get something with our current parts, without shipping time and waiting for it. If we use this in a match at world’s, we might need to fire it quite a few times throughout the match, assuming the stash fills up early in the match. Had we wanted to do this from the beginning, we would probably use pnumatics. At this point we want to actually use innovation, with the parts we have, and not just copy the standard pneumatic design.

Not to mention with your math you could only fire 5 times, effective.:smiley:

Where are you getting these numbers?

you just fire the catapult with the bike pump attached

Sure. If it was linear…

I’d like to see that in a tournament. Driving your robot around and running on to the field to pump up your robot with a bike pump would be a sight I have to see. Not quite sure it would be in 18x18x18 to start, not to mention other rules in would violate.

That’s our current design. We want to improve, other wise this thread wouldn’t exist.