CIM motor question

[first_newbie]

Isn't the max amount of CIMs on one robot 4? If this is the case why do some teams have 2 gearboxes with 3 CIMs each? Do they use one miniCIM?

[Tom Line]

It depends on the year in question. The number of cims allowed has varied over several years. 6 were allowed this year, which is why we had 2 on our hi-lo and 4 in our drivetrain.

I believe 6 were allowed in 2014.

I feel very odd answering my own team member's question on an internet forum.

[theCADguy]

2013 was the last year we were limited to 4 CIMs on our drivetrain. Since then, we actually have been allowed 6 total.

Although in 2014 (Aerial assist) Team 20 did use 4 CIMs and 2 miniCIMs on our drive in order free up CIMs for our launcher.

[Richard Wallace]

The most recent FRC Game Manual is here. R18 provides a table of the legal motors. It is on page 36, in section 4.7.

With a little searching you can also find FRC Game Manuals for previous years. As earlier posters have pointed out, the rules have evolved over time.

[Whippet]

Actually, the first year we were allowed to use 6 CIMs on the robots was 2013. This was also the same year we got to start using MiniCIM and BAG motors thanks to the revamping of the VEXPro line of robot parts.

[BBray_T1296]

MiniCIMs were designed as a drop-in replacement for the CIM. They certainly work in parallel with each other.

The MiniCIM is widely regarded as 2/3's of a CIM, as it has roughly that much available power ratio.

This being said, the MiniCIM and CIM are very similar early on in the power curve, with all but the more strenuous situations being handled just as easily by the Mini as its larger counterpart. This leads many teams to prefer the Mini in systems, as they find the torque advantage of the larger not worth its additional weight.

[cbale2000]

Originally Posted by BBray_T1296

This being said, the MiniCIM and CIM are very similar early on in the power curve, with all but the more strenuous situations being handled just as easily by the Mini as its larger counterpart. This leads many teams to prefer the Mini in systems, as they find the torque advantage of the larger not worth its additional weight.

Do you have a link to those power curves? I've seen the one for the CIMs but haven't been able to find anything on the MiniCIMs.

[kyle_hamblett]

Originally Posted by Whippet

Actually, the first year we were allowed to use 6 CIMs on the robots was 2013. This was also the same year we got to start using MiniCIM and BAG motors thanks to the revamping of the VEXPro line of robot parts.

After seeing the limited list of legal motors for 2016, it seems like the miniCIM and BAG motor were determined to replace the RS775 and RS550.

[FrankJ]

We have used the RS775s. The CIM, although an honorable motor, is no RS775.

[tr6scott]

Originally Posted by Tom Line

I feel very odd answering my own team member's question on an internet forum.

I would feel honored if I found a TORC team newbie hanging out here.

[Scott Kozutsky]

Originally Posted by theCADguy

2013 was the last year we were limited to 4 CIMs on our drivetrain. Since then, we actually have been allowed 6 total.

6 CIM drive was allowed in 2013 but was generally not used due to lack of available parts (no COTS gearboxes) and worries about main breaker. I know for a fact that 610 (world champ that year) ran a 6 CIM single speed and 254 ran a 6 CIM dog shifter with PTO to their climb.

[AllenGregoryIV]

Originally Posted by kyle_hamblett

After seeing the limited list of legal motors for 2016, it seems like the miniCIM and BAG motor were determined to replace the RS775 and RS550.

What do you mean? We will find out what is legal on kickoff like we do every year. All we know now is what isn't legal (BB775 and BB550). FIRST could decide to make all commercial gas powered lawn motor engines legal, I doubt it but that is part of the joy of kickoff. You never know.

[BBray_T1296]

Originally Posted by cbale2000

Do you have a link to those power curves? I've seen the one for the CIMs but haven't been able to find anything on the MiniCIMs.

A while back I tried to generate a theoretical curve using at stall and free speed data, and it was the conclusion I reached. Not sure if I have access to my spreadsheets anymore.

I have heard some dynamometer data but I realize that is a terrible source.

Sorry I can't really answer your question, perhaps someone who has actually put one on a dyno could help.

[theCADguy]

Here is a spreadsheet that I made about a year ago to generate power curves based on motor specs such as free speed, stall current, etc. Basically, you can make curves for pretty much any motor out there if you have the specifications available. Here's the Excel file:

motorCalc.zip

To use it, put the specs into input box on sheet 1, and it will then run a macro to calculate the speed, current, power, and efficiency at different torque intervals.

After the macro runs (might take a few minutes if you want a high resolution graph), go to the Chart1 sheet. Then use the select data tool to get the correct data ranges for the curve. (The ranges vary based on your motor/graph accuracy) Apologies if its not the most user friendly sheet, since I was a beginner at Excel/Visual Basic when I made it.

I tested its output against the existing CIM motor curve, and it seems to be accurate.

[GeeTwo]

I found this link to a 2014 motor curve spreadsheet which includes mini-CIM on this post. The front sheet lists the stall and free numbers and does some theoretical stats. Go the the tab named after each motor (e.g. MiniCIM) to find a power curve.

Edit: Ninja'd!