Does Your Team Use 4 CIMs on Your Drive?

[JamesCH95]

Originally Posted by Dad1279

I'm sure that depends on the application, wheels, gearing, etc......JVN spreadsheet is your friend..... we will confirm with testing.

Back to OP, check the following chart (thanks to team 358): http://team358.org/files/mechanical/...nRefTables.jpg It clearly shows the advantage to 4 CIMs in a conventional traction drivetrain.

Precisely why I said YMMV.

I really like that spreadsheet, it is what I use quite frequently when picking gear ratios for drivetrains.

This just occurred to me: with 4 CIMs in a drivetrain you will run into two limiting factors in a pushing match. The drive train will be traction-limited, extra motors won't help here because you simply can't get their power/force to the ground. The drive train will be current-limited, i.e. you'll start popping breakers before you lose traction. The issue here is that with 4 CIMs you run the risk of popping the main breaker (120A) before you pop the individual (40A) breakers. Adding two more motors will not improve performance in this situation either because the main breaker will go before any of the individual motors will.

Extra drive motors might help a small amount with acceleration and other dynamic situations, but IMO 4 CIMs can accelerate a full-weight robot very well, even with high gearing.

[Chris is me]

Originally Posted by JamesCH95

The issue here is that with 4 CIMs you run the risk of popping the main breaker (120A) before you pop the individual (40A) breakers. Adding two more motors will not improve performance in this situation either because the main breaker will go before any of the individual motors will.

For what it's worth, the 120A breaker can sustain 160A for about a minute before tripping. The auto-reset breakers are much faster acting.

[JamesCH95]

Originally Posted by Chris is me

For what it's worth, the 120A breaker can sustain 160A for about a minute before tripping. The auto-reset breakers are much faster acting.

Interesting. Do you have a source for that? I'm curious.

Odd that it's dubbed a "120A" breaker if it will allow significantly more current for such a long period of time.

Edit: NVM, found it in the breaker spec sheet here: http://team358.org/files/electrical/120aMainBreaker.pdf

[GilaMonsterAlex]

Definitely go with 4 CIMs. Like someone already said, we have so many other options that there's no reason not to use 4 CIMs.

Last year we used 4 CIMs, Toughbox(12.5:1), and 8" wheels. We played defense, and were super quick and tons of torque (very technical terms). We never popped a breaker, and we were at max weight.

[Cory]

Originally Posted by JamesCH95

Extra drive motors might help a small amount with acceleration and other dynamic situations, but IMO 4 CIMs can accelerate a full-weight robot very well, even with high gearing.

I suppose it depends on your definition of high gearing, but we have had robots in the 18-20 FPS range that accelerate sluggishly.

If you want to run a max weight robot at those kinds of speeds your acceleration will suffer with only 4 CIMs.

[JamesCH95]

Originally Posted by Cory

I suppose it depends on your definition of high gearing, but we have had robots in the 18-20 FPS range that accelerate sluggishly.

If you want to run a max weight robot at those kinds of speeds your acceleration will suffer with only 4 CIMs.

Good point. A 2-spd transmission will really help getting to those high speeds I imagine.