Cim-Sim gearbox for shooter questions

This could have already been discussed, but I could not find the thread for it. Any how, we are using a AM Cim-Sim gearbox on our shooter and had absolutely no luck with it at the Alamo regional, which changed our strategy to becoming defensive, which did pay off. Is anyone else using that set up for a shooter, and if so what are some tips/tricks that make it work.

Thank you for any advice or help.

We’re using it and it worked well. I know a ton of teams are using it. What about it didn’t work for you? I wish you’d posted yesterday, I would’ve stopped by your pits to help out.

Thanks Kevin, we were busy with everything and i didnt even think to, or find you. All we get is a launch of about a foot in front of the bot, and horrible lag of the motor when the ball is introduced into the hood which I think it a big issue to the problem.

I thought I snapped a picture of you guys. I’ve attached it here. I love the bump travesal sstem, by the way. Questions I can’t answer from the pics:
How many and which motors into the CIM-sim?
How many and what diameter shooter wheels?
How much compression are you running? (How much space is there between the wheels and the hood?)
Are you running the motors at full speed when the ball dribbles out?
What, exactly, do ou mean by a horrible lag of the motor when a ball goes in?





what motor(s) are you using ?

what size wheel ?

Jag or Vic ?

what’s the total gear ratio from motor rpm to wheel rpm ?

are you running the system open loop or closed loop ?

how many amps are you pulling when the wheel is spun up to speed ? is this at 100% PWM or some lower value ?

We have a similar set=up, except we are pulling the ball from the bottom and shooting over the top.

We are using 2 CIM-sim’s on our shooter. 2 FP and 2 AM motors total.
We are direct driving the wheel, so there is no speed reduction from the gearbox output.

We are running 2 8" AM hard plastic wheels, spaced about 2" apart. All is assembled as a single unit so all motors, gearboxes and wheels are linked with a single shaft.

We have about 2" of squeeze on the balls.

For shooting from the top of the key, i think we are running about 55% speed. Using Victors.

I thought I snapped a picture of you guys. I’ve attached it here. I love the bump travesal sstem, by the way. Questions I can’t answer from the pics:
How many and which motors into the CIM-sim?
How many and what diameter shooter wheels?
How much compression are you running? (How much space is there between the wheels and the hood?)
Are you running the motors at full speed when the ball dribbles out?
What, exactly, do ou mean by a horrible lag of the motor when a ball goes in?

Thanks we worked hard on the system for getting over, we based it on the NASA Rocker Bogie system.
To answer the questions:
-2 Fisher Price motors
-Started with 6" now has a 4" in it
-With the 6" it had about an 1.5" almost 2" of compression, although it happens early and the exit is a little less then at the beginning.
-it bogs the motors down quite a bit as the ball drops in
-Each motor is hooked up to a jag each and the motors run at full speed when the ball is introduced.

what Fisher Price motors are you using? there are 5 different legal FP motors this year

what is the gear ratio from motor rpm to wheel rpm ?

how fast is the wheel spinning ? -or- how many amps is the motor pulling ?

if i adjust for the different wheel sizes (8" vs 4") and speeds (55% vs 100%), we both have similar surfaces speed at the wheel, but we may be about 10% faster.

More importantly, we may have about twice the power input, depending on which FP motors you are using. The AMs are 180 watts and the FPs we have are 170, so we have almost 700 watts total.

-We are using the 2 new FP that were in this years kit.
-Gear ratio off of the output of the gear box is a little over 1:1, a 24 tooth sprocket on the gearbox to a 22 tooth on the wheel.
-honestly could not tell you how fast the wheel is spinning or the amperage.

What is the reduction in the gearbox?

If you’re only running about 0.5 to 1" of compression now, you really shouldn’t be bogging those motors down, even if those are the weaker FPs. You really shouldn’t be having problems if you have 0673 FPs. Do you have any guess how much current the motors are pulling when it’s running without any balls? It should be something less than 10 amps. Anything more means you have some serious mechanical binding somewhere.

Frankly, your system looks like it should manage better than a foot or two. I’m leaning towards there being some significant mechanical resistance somewhere in your system. Your sprocket-chain connect there is a possibility. I’d also look at your bearing system for the axle of those shooter wheels and make sure you don’t have any resistance anywhere. Some of my kids had a shaft collar rubbing against an aluminum retaining plate. It warmed up the shaft nicely and also slowed done the shooter a good bit.

I guess the other thing I would do is make sure both motors are actually running and pushing the shooter in the right direction. You can check that by unplugging one of the motors at a time and making sure the wheel still turns and in the correct direction.

EDIT: Now that I see you’re runnig the new 170W FPs, you might as well swap those out for a pair of the BaneBots RS-550 motors. Those are 250ish watts but otherwise physically identical to the FP motors. That’ll atleast give you a little more speed and torque.

I’ll assume that means FP00968-9013

-Gear ratio off of the output of the gear box is a little over 1:1, a 24 tooth sprocket on the gearbox to a 22 tooth on the wheel.

Well, if everything was spinning freely with no friction,

16700	motor free rpm
5	gear reduction
0.917	gear reduction
3642	wheel free rpm
60.7	wheel free rev/sec
4.0	wheel diameter, inches
1.05	wheel circumference, feet
	
63.6	wheel tangential free speed, ft/sec

That ought to be plenty fast.

How tight is that chain ?

honestly could not tell you how fast the wheel is spinning or the amperage.

That’s a critical piece of info to diagnose the problem from afar.
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As of right now the wheel and the sprocket set up spin extremely free and no binding in there, the motors are both spinning and in the right direction, weve checked that a lot. But pretty much as the ball drops in from the top the motors bog down and the ball just kind of flops out with no energy at all.

This is turning into a stumper. The only advantage the rest of us have over you is that our 6" and 8" wheels have more rotational inertia than your 4" wheel. So your 4" wheel doesn’t store as much energy and more of the energy for the shot has to come from your motors.

This might explain everything, though. Your wheel would be losing most of its energy at the beginning when it’s just pulling the ball and starting to compress. Then it’s running slower through the high compression and you don’t have enough compression afterward to make up for it. If you don’t have good grip on your wheels, that’d likely make things even worse, wasting what little stored energy you have in friction while the wheels are slipping.

I think you’d probably be best off by increasing the grip on your wheels and trying to increase their rotational inertia. You can do that by increasing the mass or the diameter of the shooter wheel. Or both. Or by attaching a separate flywheel to your shooter axle somewhere it won’t interfere with firing the ball.

Also, also, were you getting the same symptoms with the 6" wheels? Why’d you switch away from those? We’re running:

  • 2x -0673 FPs (~600W)
  • CIM-SIM direct drive
  • 2x 6" AM performance wheels
  • ~1.5" compression

We’re getting pretty good distance out of this setup, shooting from the key at about 70% drive on the motors.

  • 2 9015’s
  • 2 CIM-Sims through 2 Gates belts with no reduction
  • 4X 8" past KOP wheels
  • ~1.5" compression
  • 60° launch angle

It’s working great for us. I think we need 50-60% to shoot from the key. We keep our gearboxes nice and greased. Grease would fly if you added anymore.

The 6" actually worked a little bit better then the 4", we switched to the 4" on Saturday morning to try it and it we actually took a step back. We had a mentor from the GatorZillas come over and he said we had way to much compression early, as in when the ball first hits, and not enough on exit; this was with the 6" in. So we tried switching to a smaller wheel to try to counter that. We cant just turn the hood around, otherwise we would have done that.

The 6" wheel is the AM white plastic hard wheel, and the 4" is the plastic one that was on the FIRST Choice list.

Our team is using Cim-Sims with the 9015 motors, one on each gear box. But we have a shooter with two pairs of wheels with one gear box for each pair of wheels. The hood drag is too great in your design. The wheels may have sufficient linear velocity, but the the hood is keeping the ball from getting up to speed. In short, there probably is a lit of slippage of the wheels against the ball.

With our design, we have four 5 3/4 in diameter by 3/4 in. aluminum wheels in our shooter. Two disks to a axle. Once we spin up, the balls move through with very little decrease in speed of the wheels. We shoot 32 ft. with an arc 16 ft. high.

I’d look at ways to cut down on the drag in the hood.

Dr. Bob

Chairman’s Award is not about building the robot. Every team builds a robot.

Your problem with the 6" wheels may have been too much compression too quickly. Your problem with the 4" wheels is definitely the lack of compression through most of your shooter. I understand that you can’t flip the hood around or anything at this point. I think you still have options for increasing your exit compression now that you have 4" wheels. You need to make up a liner for the exit side of your hood. This can probably be a piece of lexan that fits inside the hood, and a few spacers made of wood or something that push the lexan away from the hood and closer to your wheel, increasing your compression. You might also benefit from friction tape on your wheels to make them grippier, and I still recommend a flywheel or heavier wheels so you can store up energy and your wheels can maintain a higher speed as the ball goes through.