Getting more range out of a 4 wheel shooter

Technical Technical Discussion
#1

I’ll try to describe what we have as best as possible. Essentially, we have two SETS of wheels that are mounted horizontal of each other. These wheels are mounted on a CIMple box with the default gear ratio which has a CIM-U-LATOR w/ a BaneBot 775 going into it. Both of the wheels are setup this way.

When we run both sets at full speed, we max out at probably 10 feet with our 8 foot height but are never able to go above 8 feet and can never get farther than probably 15 feet if we do not go for a high basket.

Any help would be greatly appreciated and if you have any questions feel free to ask.

#2

Why do you go through two reductions via gearboxes? For our shooter, we have our 775’s going into our CIM-U-LATORs and then directly driving our wheels. We get perfect power, distance, and control over the ball, and have yet to find a problem.

Pro tip: If using this setup, never run the motors at 100% power. 85% power works beautifully, and won’t destroy the motors (or the balls).

#3

It wasn’t really my decision. The impression that I have gotten from why that decision was made is that we had already made a shooter with CIMs going into the CIMple box and the person building it didn’t want to take the CIMple box off of the bot. I had actually suggested removing the CIMple box from the equation but it was basically said that we didn’t have time for “that type of change”.

#4

the first thing we did this year was to do a test with our 2009 lunacy bot which is geared the same as yours is now. we got about the same performance you are reporting. I think you just need more speed, 2 775s is enough power to throw a ball a long way.

#5

The CIMple Box uses a 12:56 reduction. Assuming you are using 6" wheels (just for example purposes), you’ll be going approximately 921.66 rpm, which would be 15.36 rotations per second. If you take out that reduction of the CIMple Box, your wheels will be going at approximately 4301 rpm, which would be about 71.68 rotations per second, which is about 466% faster than your original speed with the CIMple Boxes.

tl;dr? Taking out the CIMple boxes will allow you to shoot much farther.

Show this to the person building the shooter.

Hope this helps!

#6

“There’s never enough time to do it right, but always enough time to do it over.” Guess what, you have a week to do it over, because 5 weeks wasn’t long enough to do it right.

The CIM-U-LATOR runs a 2.7:1 reduction; the 775 turns at 19500 rpm with no load. This gives 7222 rpm going into the CIMple box (about 2K more RPM than a CIM). The CIMple box has a 4.67:1 ratio; this means that the output is spinning at about 1500 rpm. Torque-wise, however, you went from 166.4 oz-in stall torque (motor only) up to almost 2100 oz-in (motor through two gearboxes). That’s a bit more than you should ever need for a lightly-loaded shooter! (Your total reduction is about 12.61:1; that’s a wee bit on the high side for something that needs to spin fast.)

Pull the CIMple box out, and your speed goes up by about a factor of 5, your stall torque goes down by the same factor, give-or-take a bit for loading and speed. That should give a much longer range, while still allowing you to load and fire easily without jamming up.

#7

Best thing would be to remove the the cimple box.

You can also add more mass your wheel to make it go farther.

#8

Alright I’ll forward this on to our coach. I was unaware that the difference would be THAT large. Thank you for your time and for the information.

#9

The RS775-18 runs at 19500 RPM with no load at 18 Volts.

It runs at 13000 RPM with no load at 12 Volts.

#10

Which explains why it was running faster than a CIM after going through the CIM-U-LATOR… I pulled the specs from the BaneBots website, but didn’t see the 12V free speed listed.

The ratios, however, still stand–removing the CIMple box from the equation will have a significant positive effect on the speed, and a corresponding drop in torque.

#11

It is not directly listed, it is listed under the Kv (1083 RPM/v)

#12

Banebots spec for 775-18 at 12 volts:
http://banebots.com/docs/M7-RS775-18-AT12V.pdf

#13

For what it’s worth… we have a similar two-wheel sets setup as you. However, we’re powering them with 2 RS-550’s, one on top and one on bottom. They go through a 7:1 reduction to the shooter wheels. At about a 45 degree angle, we can hit the backboard for the top basket from midfield (that is, when the ball doesn’t hit the ceiling in our shop!). That’s running both sets of wheels at full speed by plugging them into a battery for testing.

#14

What is the diameter of your wheels?

What is the tread material on the wheels?

How much are the balls being compressed as they go through your wheels?

How are you feeding the balls into the shooter? (by hand? consistent feeder mechanism?)

In order of magnitude, we saw four ways to get more distance on our shooter:

  1. More linear velocity speed on the shooter wheels (spin them faster, or use bigger wheels)
  2. Grippier tread material on the wheels
  3. Higher compression of the balls between the wheels (to a point)
  4. Making sure both sets of wheels contact the ball at the same time when fed
#15

What is the diameter of your wheels? 8 inches

What is the tread material on the wheels? 2010 KoP wheels (Rubber?)

How much are the balls being compressed as they go through your wheels? ~3 inches

How are you feeding the balls into the shooter? (by hand? consistent feeder mechanism?) Consistent feeder

I talked to one of our mentors and he is worried that we will not have enough torque not having enough force on the ball to make any difference.

Video from yesterday can be found here: http://www.youtube.com/watch?v=N-KTmL2Hc3U