it makes sense to use 3 minicim or 2 cim motor for drive base
For the chute door?
There’s a good amount of past discussion on the pros and cons of each option. Try using the search function to read up on the topic and come back with more specific questions.
The bottom line is, like most engineering decisions, the right answer depends on your priorities and neither option is better at everything. You may not want to make your decision until after kickoff when you know what strategy you want to pursue.
In addition to the CIM and Mini CIM, there are also now NEO and Falcon brushless motors that have similar mounting to a CIM with more power and higher efficiency. You should probably also consider those when deciding.
I researched but don’t understand
What don’t you understand? You’re going to have to be more specific or we can’t help you. All the information you need is out there
I’m going to simplify this a bit–it seems like you’re a rookie.
The correct answer to your question is, “it depends”. There is no actual correct answer to which is better. On top of the question you asked (motor type and quantity), there is a second question to ask, “which gearbox should I use?” Unfortunately, that has the same answer of “it depends”.
The two drivetrains will have different masses, similar available power, and different current draws.
As Ari noted, there’s other available motors–my team last year ran 2x or 3x NEOs to get under the weight limit, but we tend to prefer a 3-MiniCIM these days after changing from 2-CIM.
@omerakblt, have you by any chance heard of the JVN Design Calculator (or any other similar calculation tool)? It may help you with the decision. It might not.
Also: “better” may depend on factors other than pure engineering of what you want on the robot. For example, ability to obtain motors and/or gearboxes could force you one way or another in this situation. Or speed controllers–a 3-Mini-CIM system uses an extra speed controller per side compared to a 2-CIM system.
Thanks ı understood
As @AriMB and @EricH have stated, there are many options and the option you should choose depends on many factors. You need to perform the analysis for each one to determine which one(s) is optimal for your application.
In my day job, designing electronic circuitry for industrial equipment, I have made up very large spreadsheets that do the performance calculations for the different options (up to 10-12) so I can compare the various factors of interest.
Definitely! A 3 motor setup also uses an extra PDP slot per side. This is not a concern for many teams, but this may be a deal-breaker if you build complex robots.
Similar at start, yes. However, I haven’t seen anyone point out power at the 2-minute mark.
At 120 seconds of runtime at peak power, a CIM puts out about 202W of power as heat builds up and increases friction.
At 120 seconds of runtime at peak power, a Mini CIM puts about about 190W.
VEX hasn’t published similar testing for NEO and Falcon 500, but I’m confident they’d put up better numbers since brushless architecture will be more efficient.
The appeal of six motors is having the additional power available to gear more aggressively without overtaxing your motors or having to configure and plumb shifters. The appeal of the Mini CIM is that you save nearly four pounds compared to six CIMs and lose much less power than you might think.
4 CIMs: 11.2 lbs, start at 1348W, 808W @ 120 sec peak power
6 Mini CIMs: 12.96 lbs, start at 1290W, 1140W @ 120 sec peak power
6 CIMs: 16.8 lbs, start at 2022W, 1212W @ 120 sec peak power
@Billfred didn’t know the peak power over time data was there. Thanks.
This is a topic I spend a chunk of time talking about in the drivetrain presentation I’ve been giving for a few years, and finally uploaded to our YouTube.
We used 2 mini-CIM per side of our drivetrain this year, and the little robot did just fine.
There is a whole bunch of “it depends” going on, here.
Agreed. I’ve been involved with building eight competition robots with 4-CIM drivetrains. The biggest determinant of their drive performance was definitely weight, even the first few years when we screwed up the gear ratio.
This presentation is very good. Thanks for posting it.
Can I ask where the 2020 ilite simulator is? I have been unable to locate it.
@JesseK has a link to his github with 2020 candidates in that thread
Can you let me in on the joke? I don’t get it.
2015 Q&A question (courtesy of FRC900): “Chute Door?”
GDC answer to same question: “Yes, Chute Door.”
The real question was asked and answered one Q&A later but the sheer comedy became a running gag. Still is.
One of the questions asked on Q&A in 2015 (IIRC) was simply “CHUTE DOOR?”. The CHUTE DOOR was a field element that year, part of the HP feeder station. The GDC responded, "Yes, CHUTE DOOR.