Hey I recently made this bot to throw a tennis ball for my dog Rufus. I wanted it to throw a pretty far distance so he could get some exercise. and i wanted it to be able to get around in my yard.
I made the chassis first it is a standard 4 motor drive tank drive. i tested it out with a few bricks on it to make sure it would work in the grass and it did. then i worked on the actual shooter. it started as an arm with only a few wheels on it to balance it out well and then some more to give it more mass to hit the ball farther. It originally has a 60-12 drive on it and it spun pretty fast.
Then i made the trigger it is just a servo to move the two bars up which have the tennis ball on them and they introduce the ball to the arm at about 45 degrees to make for a max flight time and distance. there is a rubber band on the trigger system to aid the servo in lifting the ball. the band is place so that when in the down position the servo is not fighting the band but after the servo moves the arm up a bit the angle of the arm allows the band to give the servo some help. the string stops the arm at 45 degrees and the cross beam make it so that when the trigger is in the down position the ball doesn’t fall off of the trigger.
after some test shots the bot fired about 30’ so i made the gear ratio 60-12 then 36-12 for a final ratio of 1-15 i also added some med wheels for more mass on the arm and now the ball fires about 45’
so what do you think? i am open to constructive criticism or any ideas you may have to improve performance. i don’t really expect this to play with my dog but i just used that as a challenge.
i can try get one up it is pretty slow getting up to speed but once it is there it is deadly. i made something similar at school that was only a 1-5 ratio like the first edition of this and a kid used it despite the “Don’t Touch” sign an it took his finger nail clean off. i used three motors. because it fit nicely i would have like to put like 6-8 but it would have been hard to get them all attached and out of the way.
here is the link to the video. the first shot was with a kinda dead battery so i swapped it out with a fresh one for shot 2 which accidentally hits the ceiling of my porch. ooopy doopy
I prefer “That stupid kid” the sign clearly stated that it is only to be touched by me and he violated that completely. It made me mad that he touched it cause he could have broken it or something and it was my project for the class. I do feel bad that he got hurt but he was pretty stupid to do it.
You mentioned the arm hits the ball at a 45 degree angle and i think that you could get more distance at a steeper angle. I think distance only starts going back down after a 55 to 60 degree angle. Just my two cents on the topic.
One other thing is the point of contact between your arm and the ball. When the arm hits it deforms the ball slightly and dissipates some energy. If you made a cup of sorts that equally distributed the force of the collision over the entire side of the ball you could have a more efficient collision which could add more distance.
It is interesting that you mention this. After watching the pretty poor quality slow motion hit of the ball i noticed that the trigger system which is set to stop at about 45 degrees actually tosses the ball a slight bit when it stops so quickly due to the string so i would say that it is hitting the ball at about 50-55 degrees as it is.
I like the cup idea as well.
To balance the arm i have an axle that i sanded the two ends down so they are smooth circles not the squares. this ensures everything is perfectly balanced. i place the axle ends on two level surfaces.then i start trying to balance it out first with wheels (they are just to get close) then i add two shaft collars to both axles (cause I’m going to need them later) then i use gears to get even closer) after the gears i try to get the non-hitting side just slightly heavier so that i can fine tune everything with a standoff and two small bolts. you may notice the pattern usually goes one standoff every other hole but on the last little bit of the arm there are three in a row. after i balance it out i just add equal weights to both sides. in my first version the axles on each side were equally spaced from the axle so i would add two small wheels here and two there. but for v2 i moved the non hitting side out 1 space to allow for med wheels to be used.
it takes some time you have to be patient but if you don’t then your machine will rattle itself apart. Have you ever scene a helicopter crash or a wind turbine get blown apart.
One of the basic laws of projectiles is that complementary angles have the same distance (55 would have the same as 35, 60 as 30, etc.). Distance is based off of the sine function, and at an altitude of 0m the projectile goes 0m at 90 and 0 degrees, then the maximum is at 45 degrees. Granted, around 45 degrees the angles are about the same, but they are different and the further you get from 45 the more the distance decreases. So launching it at 45 degrees is optimal.
hmmm…
i wonder if this design system is practical for clean sweep
just rig up a “line up” belt to feed balls to the “puncher”
and hit the balls at a lower velocity so they wont fly out…
It could be used but not that practical, even after changing it so that it has a line belt it takes to long building up speed to be useful and hitting an orange ball like that (which is the only thing worth the effort for, green balls at 1 point each is just a waste of time) may not always get it clean over each time. But it’s a nice idea though, you could use it to see how far you could shoot a green ball but other then that in its current state it’s just limited to ping pong balls or other small objects. Nice robot though, I like the video (imagine hitting a flaming ping pong ball at night, zoooom! Instant flying ball of fire!)
it was a wiffle ball in the video cause i was in my screened in porch and if i used a tennis ball it may damage a screen or something.
As for clean sweep i thought of that too. the 1-15 ratio only adds a few feet to the 5-1 ratio when hitting a tennis ball like maybe 15-20ish and the 1-5 ratio gets up to speed really fast.
Plus once this thing is going it takes more than just one hit to stop it. if you kept the controls in the on position i can see this thing only needing maybe1-2 seconds to get back up to speed to fire again.
