For the love of CIMs (A question about CIMs and gearboxes)

I love the CIM motor. I really do. However, the only thing I don’t like is that you can only use 4 of them. And for the most part, most gearboxes only allow 2 inputs, still capping you out at 4 per robot.

So my questions are:

  1. Have you ever been able to use more than 4 CIMs on a robot?
  2. What are your thoughts on a custom gearbox with 3 CIM inputs, and one output?

The CIMs would be in a triangle formation around a central drive gear. This could allow for a smaller gear reduction, or a robot that is both faster, and more powerful in one.

And just for the fun of it:
3) What would a 4 CIM gearbox be like? What would the advantages be?

  1. YES. 2010 allowed 5 CIMs. Also, 2006 (and 2007?) had a motor type known as the Big CIM (bigger motor, but for the size not quite as much oomph as you might expect), of which type I remember 2 being allowed. (330 only used one big CIM–it powered our 2006 shooter wheel.)

  2. Eh. More isn’t always better. OTOH…

118’s V6 drivetrain. Now THAT was a DRIVETRAIN! 4 CIMs + 2 FPs. One gearbox. Power to all 4 wheels, which were in a coaxial swerve configuration. Not sure what year… I want to say 2007. Not sure how they powered their turreting arm… But it was quite a feat of engineering.

While it unlikely that we will be able to use 6 cims next year consider this, a 6 motor drive train with 4 cims and 2 banebots(775’s or 550’s). 973 used them(3 in each gearbox) until the 775’s started shorting out. There are quite a few teams that have used 6 motors in drive. 8 motor might require another stage of gearing.

148 has done this(6 motors in 1 gearbox).

They were legal in 2007–1618 used them in their drivetrain to free up a small CIM for the (horribly-overpowered-like-some-yutz-in-the-marketing-program-specced-it) arm. They were powerful and torquier than the small CIMs, but still had less available power. That was your six-CIM year (technically, anyway).

Six-motor drive seems to be most popular when one of the smaller kit motors is made to act like a CIM. The overwhelming majority of teams that go this route seem to use the AndyMark AM Planetary, which takes a high-RPM motor like the Fisher-Price motor (originally) and gives you a speed and mounting interface that’s close enough to the CIM that it’ll work for our purposes. (Each motor has its spot on the curve where it’s most beneficial, but all the motors will contribute one way or the other.) Indeed, that’s what 148 did in 2008 to put the Fisher-Price motors in with their CIMS.

I don’t have a picture, but what 2815 and 1398 did in 2010 with their six-motor drive (two CIMs and a planetaried F-P per side, shifted) was add another idler gear in between one of the CIMs and the F-P. You could plausibly squeeze all three together with a large enough input gear (and planning the rest of your drive system accordingly), but we went this route to make room for the shifter hardware. Even single-speed, I think we would’ve gone this route for packaging reasons–our robot that year was designed to go through tunnels on the field.

  1. In 2010 we were allowed to use a 5th CIM motor. This was because of some other motor changes that year. Many teams used the 5th CIM for a hanging mechanism or kicking mechanism. Otherwise, 4 CIM motors have been a staple of the KOP since 2005. (Excluding the ‘big’ CIMs of 2005-2007)

  2. A gearbox that accepts three CIM motors as inputs isn’t all that uncommon. Many teams will design a gearbox to accept 3 CIM motors then run an FP, 550 or 775 through an AM planetary, Cimulator or CIMsim transmission to make it’s output interface like a CIM motor.

From what I’ve seen, adding a 5th and 6th motor to the drive will help with acceleration and allow you to gear for a higher top speed with a single speed drive train. You’re pushing power will still be limited by the CoF of your Drive train, but it’s ability to accelerate more quickly and sustain a higher top speed may be advantageous in some games.

  1. I believe others before me have posted some of the coaxial swerve boxes that used 4 CIM’s in a single box. There are a few advantages to this, but many of them have to do with the packaging of a coaxial swerve or similar Drive train.

Gearboxes with 4 to 6 motors really only seem useful for swerve drives, or at least that’s what it sounds like to me. I was wondering though, has anyone in FIRST ever built an adder-subtractor drive like tanks use? This would also have the potential to use many otors in one gearbox. I’m honestly not sure if it would have many benefits, but it would be a cool challenge.

Eventually having so many motors in the Gearboxes will cause a high enough voltage drop on the battery that performance will suffer. Unless your manipulator is Intermittently operating or doesn’t use much current adding more motors to the drive-train may hurt performance, especially if you get to the point where the 120 Amp breaker is in danger.