Rookie Team --- need help (CIM Motors)

What are the pros and cons of using 2 CIM motors for our drive system vs. 4 CIM motors? What are most teams doing?

We are also missing one small piece for our bumper assembly kit.
The part is “am 1143 = 10-32 3 prong tee nut”. Any advice on finding an extra one. We have 31 of the 32 we should have received.

Many teams opt for 4 or even 6 CIMs on their drivetrain than 2 simply due to total deliverable power. Pushing power, acceleration, etc. Regardless, it’s a better idea to do four, especially considering that’s what the kitbot chassis is designed for and (I believe, may be wrong) that’s what comes in the rookie kit.

As to the missing piece, you can find it just about anywhere, including a local hardware store. It’s a standard part.

https://www.amazon.com/10-32-T-Nuts-50-Pcs/dp/B0002ZPELS ?

4 CIMs = Good
6 CIMs = Possible, but complicates things for minimal gain.
2 CIMs = Everyone else can now push you. Don’t do this.

Lesson learned: Always inventory your entire kit of parts before the expiration date :frowning:

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You definitely want to go with 4 cims on your drive base this season.

Do you have a real hardware store near you? They will have the Tee Nuts in stock and you might even find them at Home Depot or similar store in your area. Though you may not really need it as I bet Andy specified the packing size to give an extra or two. Either way not really worth making FIRST make AndyMark ship you a $0.37 item.

In our early years we did 4 CIMS (two to a gearbox) The past few years we have been using 6. One year we used 4 CIMS and 2 Mini CIMS (2 CIMS and 1 Mini per gearbox) This year we will be using 6 Mini CIMS (3 per gear box.)

For a Rookie team be safe with 4. Also remember that each CIM will need a motor controller. Speed and Torque will depend on what gearing your gear box has and what sprockets you use if using chain.

While Ether is right, the correct course of action would have been to file the discrepancy with FIRST, if you put “ask Nathan about missing am-1143 from ChiefDelphi” in your order notes at checkout on the next AndyMark order you place (probably the one for those additional CIMs) I will make sure we throw one in for you.

Good guy Nathan to the rescue.

Go with 4 CIMs. Make your robot weigh 110 to 115 lbs. That will let you push and decrease how often you get pushed.
As a rookie, when your struggling with everything else you can go play defense and run into someone. It’s fun, and this year, probably effective.
Watch out for the pinning penalty and listen to the other team coaches during the match about who to go push on.

As for the tee-nuts.


or
https://www.fastenal.com/products/details/37963?term=tee+nuts&r=~|categoryl1:"600000%20Fasteners"|~%20~|categoryl2:"612585%20Furniture%20Fasteners"|~%20~|categoryl3:"600087%20Tee%20Nuts"|~%20~|sattr02:^9pound10-32$|~

We have been using 4 CIMs for well over a decade.

Seems to work well enough

^^^That’s just about perfectly said.
Only thing I would add is the 6 CIM drive will add a lot of weight. But, if you want to go for maximum defense (potentially a 3rd bot role) you could invest in a 3 CIM gearbox (1 for each side) and learn about chain or belt drive.

If you do opt for the powerful 6 CIM drive, you will want high friction wheels to match (Colson wheels are the go-to for that).

Go with 4 CIMs in your drivetrain. No more. No less.

2 CIMs is quite literally the “rookie mistake” that each team makes once, and then learns from their mistakes. 2 CIMs offers very little power to your drivetrain, which hurts your acceleration. More importantly, having only two drivetrain motors means a lot of load on each motor when they try to move your robot around. The result of that is they draw lots of current, which can put you at risk of tripping your 40Amp circuit breakers that power each motor.

6 CIMs offers you a lot more power in your drivetrain, but it comes at an increased risk. Using 6 CIMs presents risks regarding your total current draw (as opposed to the per motor current draw risks of 2 CIMs). If your whole robot is drawing too much current, you run the risk of your total voltage dropping into the “brownout” range of your roboRio. While brownouts aren’t nearly as big of a deal as they used to be, it’s still better to avoid them. There are certainly ways to get advantages out of running a 6 CIM drivetrain, but as rookies you have enough on your plate already. Don’t worry about buying a gearbox that can fit 6 CIMs, integrating into your kit chassis, selecting the right gear ratio, and putting the software safeguards (voltage ramping and/or current monitoring) required to run 6 CIMs.

4 CIMs is the happy medium. It’s a proven solution run by most FRC teams for the past decade+. 4 CIMs are practically bulletproof as a solution.

As noted, using 6 CIM drivetrains add considerable cost to do correctly. Between new gearboxes, a set of traction wheels to take advantage of the added torque, and new motor controllers that can handle current limiting, you can easily add $500+ to your drivetrain cost over using the kitbot. Not worth it for the majority of teams.

Our team has mostly used 4 CIMS for the drive-train. At least since I have been on the team. I know last year we used 4 cims and got up to around 27-28 ft/sec.

…are you sure about that? Robots are very hard to control at even 20 ft/s (and usually that requires 6 CIMs for a decently weighted robot). AFAIK 27-28 ft/s would be pretty much uncontrollable and have terrible acceleration.

That’s delightful! Great service!