so we’ve been prototyping a shooter mechanism, using a CIM and the kit wheels from last year…only problem, we dont have any (easy) ways of powering it, toughboxes only give us around 300 RPM, so we took out a few gears and got it down to 4:1 wich should give us around 1200 RPM(hopefully)
now ive heard(read) about other people just directly driving the wheel off the cim motor how can this be done?
1200 RPM should be enough right? if not we can use chain reduction(upduction:D)
so the question is…what other ways are there to do this?
(yes i read the other thread, this is more from a assembely standpoint though)
we’re using a CIM on a 9:1 Banebots planetary. Gives us more torque so the wheel doesn’t slow down as much as each ball goes through, and still keeps a hefty RPM on the wheel. Also theres the added benefit of really easy direct mounting since the output shaft is a simple 1/2" OD with a 1/8" keyway. Though we are actually going to use a sprocket combination with it to give the possibility of high torque or high RPM based on what our testing shows.
You might consider using only a belt or chain drive, with a reduction ratio of about half the inch diameter of the wheel. ie. 4:1 for an 8" wheel. With the smaller pulley/sprocket on the motor.
one CIM in a toughbox chained to a sprocket(which is bolted) on a 5/8 shaft.
(using two kit wheels from last year, bolted together(not attached to the shaft at all!!! just the compressin of the wheel-bolts and the plastic hubs are enough to hold it on the shaft nicely)
works pretty well, we are getting around 6ft maximum distance, and at 4ft were getting around 80% accuracy
A couple of years ago, for Aim High, we decided to just direct drive the wheels with a connector we designed to fit with the keyed shaft. It took some time to design the right parts but it worked well. It was a last minute addition and due to weight we didn’t get to use it, but it worked really well. It’s just another option.
Not sure why you would go through a toughbox?
A direct drive from the 2.5" CIM is more than enough speed to get you more than your 6ft max distance with a 6" wheel.
But if your system needs alot of torque a direct drive CIM may not cut it. Attached directly to a 6" wheel I think it would get you much further (20 feet or more), but if you don’t want that distance it helps to gear down and limit your distance but be able to fire balls at an even higher rate.
Might want to check out Joe’s “Nothing but Dewalts” White paper.
The combination of 3:1, 4:1 and 12:1 with servo shifting on the fly, plus the fact they are a fraction of the weight of the Banebots gearboxes make them a lovely addition to any FRC robot. We ran them last year on our drivetrain and were very impressed. You might even see 4 or 5 of them on our 2009 bot :rolleyes:
The tip velocity of the shooter wheel is proportional to the wheel diameter. Larger wheel = faster tip velocity = further shot. You can’t ask us for RPM without telling us your wheel diameter.
2 Wheels (top & bottom or right & left) will result in the ball leaving the shooter at double the velocity. (With a 1-wheel system the ball is “rolled out” of the shooter, with 2-wheels the ball is “tossed”.)
Recharge time will depend on your gear ratio. Luckily the CIM has tons of power, so you should be fine if you’re gear ratios are somewhat reasonable.
System rotational inertia will also affect recharge time and will affect how much speed the wheel loses during a shot. More inertia = less speed loss = more repeatable shot. How much mass do you have spinning? Hint: If you don’t want a heavy system but still want a high rotational inertia put the mass as far out as possible (make the wheel heavy at the edge.)
How far do you want to shoot? If you’re looking for a short range shooter you might find that a lower RPM wheel will be more accurate in the ranges you want, and will result in a faster fire rate (the wheel don’t need to slow down).
We found that the compression on the ball will affect the shot distance. Experiment. We like 1.75" of compression. Your mileage may vary.
What type of shot do you want to make? A fast ball? A lob shot? This will greatly determine how fast you need to launch the ball. What angle will your shooter be at?
Overall… the secret is PROTOTYPING! Design is an iterative process. Do some basic design in your head. Build it. Test it. Improve it. Repeat until satisfied. This is the secret to the entire 2009 game. The teams who do really well this year will be the ones who experiment a lot.
well, the farther we shoot the ball, the less accuracy we have(unless we use the camera and everything) so we went for 4ft as our scoring distance, at less than 4ft it works just as well,
IMHO - More so this year than any other. Combine a new field surface, new mandatory wheels, new restrictions on size/bumpers with a “weird” game object, and it makes for a lot to learn. Maybe our team is just slower than usual this year…
Let’s be honest… it has been a long time since I’VE put any serious thought into drivetrain turning.
We made some simple couplers by taking some aluminum round stock, drilling out a hole for the CIM shaft, drilling and tapping two side holes for 1/4" bolts (to squeeze the coupler onto the keyed – or is it flat? – part of the CIM shaft), and then threading the other end of the hole. Add some threaded rod, and ta-daa! A direct-drive coupler for the price of a few bucks and a bit of time.
Although it may be a bit overkill, you could always use FP motors in a DeWALT gearbox, and just limit the output in your code. We used these on our '06 shooter, and it worked perfectly… although we didn’t limit output alot… :rolleyes:
