Can CIM's compete anymore?

Yes, CIMs can still compete. For >80% of teams, CIMs are still a great drivetrain workhorse.

Can I heart a post twice?

They do beat the NEO on power/efficiency specs within the FRC design space, but by narrow margins that don’t matter much. Very well done engineering to achieve that, and I don’t mind them trumpeting it in their marketing.

(My excitement for the product comes from having NEO-level performance come from a single integrated package implemented on the CTRE programming framework.)

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For what it’s worth, we did last year with a programming team of two and it really only took them a week or two to figure out the NEO and SparkMax. You definitely could have put NEOs on your drivetrain, and it would probably have been less painful than you think. Lots of teams made the switch halfway through the 2019 season and went through the same learning curve. Not a cake-walk, but not impossible.

The ~780W peak power is a crazy number, but it’s not practically attainable. (I assume that’s what you’re talking about with the on-paper performance comment.) Current draw at that point is 120A. The practical differences between the Falcon and the NEO (as I see it) are:

  1. A nominal improvement in efficiency. This means a little more power output for each watt put into it. They’re pretty close though.
  2. Built-in controller. This means fewer points of failure, but the failures you do have will be more expensive.
  3. Higher free speed.
  4. Cooling port, for those who will use it. (Can the Talon FX read the motor temperature? It would be cool to have a solenoid that can trigger to automatically cool your motor.)
  5. Spline shaft. Incredible feature or expensive gimmick? Time will tell.
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Arguably the more interesting feature is a user replaceable shaft… I would love to see multiple options here.

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Some of the Sparks were SparkMax running with PWM, so it’s even higher then 18.6%.

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I believe I counted those (25 teams), since the data had a SparkMax PWM column. However if the PWM teams created things differently in code, they’d be missed.

Supposedly the lack of a key is one of the reasons an 8T pinion is offered for this shaft. That 8T pinion allows for a single stage drive gearbox for 6" wheels (if I did the math right) with an 8:84 reduction that pulls about as much current as CIMs do when geared to 13FPS free. I posted the JVN calc results here:

Honestly this may be the differentiator compared to NEOs for us if this is reasonable to run.

In the spirit of Car Nack’s predictions - I’ll very confidently say that every single alliance on Einstein at both post season expos (or as FIRST calls them, championship events) will contain robots that use CIM or MiniCIM motors as the primary motors in their drivetrains.

The winning alliance at both expos will contain CIM driven robots.

These motors are cool, but for the vast majority of teams that extra couple percent efficiency or the lighter weight is not the primary constraint on their robot performance.

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The Mini CIM line is a cop-out (even we prefer Mini CIMs, and nobody would dare declare the Pandamaniacs an elite team). How many are putting the big ones on to cross the endless sands, O great and wise one?

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I can get behind this and hope that it is true!

I don’t see them as substantially different given they can be fairly easily swapped with a minor cost compared to swapping to Falcons or Neos.

(I don’t think this is equivalent but included for completeness)
4 CIM => 4 mCIM : $120
4 mCIM @ 29.99 => $120

4 CIM => 6 mCIM : $280
6 mCIM @ 29.99 => $180
2 VictorSPX @ $49.99 => $100

4 CIM => 4 Neo: $460
4 Neos @ $39.99 => $160
4 Spark Maxes @ $75.00 => $300

4 CIM => 4 Falcon : $560
4 Falcon 500 @ $140 => $560

(I don’t think this is equivalent but included for completeness)
4CIM => 2 Falcon : $280
2 Falcon 500 @ $140 => $280

3452 hasnt used CIMs since 2017, and I dont think has any intentions on going back. 775s have been replacements for us, lighter, and as long designed for properly, can be better than CIMs. The Falcon motors I think are gonna be huge, with more power and most likely better control than NEOs. I dont see any reason to go back to CIMs really.

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Maybe some team just used the normal Spark class in code and never bothered to change it. I wonder what team did that.

Hmmmmmm

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Can CIM’s compete, yes.

Is it worth a team wanting to be competitive to run CIM’s, no.

With all the early adopters of NEO’s last year, proving the functionality, reliability and strength of them, running CIM’s in 2020 isn’t worth it. CIM’s are bigger, heavier and weaker than both the Falcon and NEO. Having driven a whole season on 6 NEO’s, both offense and defense, I can’t think of any times a robot running CIM’s had me beat on a drivetrain scale. There were teams this year though that had success with CIM’s or Mini-CIM’s, 148 and 3538 for example. For low resource teams, CIM’s and Talons/Victors will work just fine. But for most teams wanting to gain a little edge in their drivetrain and save some weight, CIM’s are a thing of the past.

We, like most teams, will test the Falcons before we decide on whether to use them over NEO’s. But seeing CIM’s on our drivetrain would be interesting after our, and others success with NEO’s last year.

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Thanks for posting the Drive Train Simulator. I had a crazy idea of using 3 Falcons per side and keeping the ratio as close to the KOP and wheel size as possible (84 tooth driven, 8 tooth driving, and 6" KOP wheels). Time to goal is less (1.6 vs 1.8), but I’m having trouble understanding the acceleration distance section. Could you explain that a bit more?

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+1. I think I bought the last one. A couple of hours later when I realized I wanted a second one (not a drive train) it was sold out.

^^ So much this. Teams with big budgets will continue to go brushless, but ~$80 for a high-end motor and controller (and free re-use) will continue to appeal to teams on a more limited budget. Assuming CIMs are still legal and the main breaker stays at 120A, I expect there will be captains and first picks powered by CIM winning events after 2020’s freshmen have graduated.

:rofl:

First, a fundamental concept - with DC motors, a robot will lose acceleration as the motor reaches its maximum loaded speed. We can calculate this maximum loaded speed, but then certain designs never reach maximum speed on a FRC field, strictly speaking. Also remember that since we’re estimating friction in the drive train, the maximum loaded speed could be off a bit. Some physical drive train builds are great at reducing friction, and others not so much. So to provide a compromise of strict detection that acceleration = 0ft/s^2 vs designs that are fielded by high-performing teams, I created a threshold for determining when a robot is at max speed.

The acceleration distance is the distance an initially-stopped robot travels before acceleration (ft/s^2) is below a threshold. By default, that threshold is 1% of theoretical 12V free speed. In your example, the robot takes 15.6 feet to accelerate to the point where the total motor output torque generates less than .159 ft/s^2 of acceleration. There is a way to adjust this threshold, but as-is it seems like a good rule of thumb for games 2015-2019.

The flag “Under-Geared” is just a warning to inform a designer that the robot will likely take longer to accelerate to full speed than what the designer desires (in your example, that is the 16 foot Sprint Distance input). For a team who values good throttle response and also tends to gear for specific time periods of a match rather than an overall speed (like mine), keeping acceleration distance well under sprint distance is a good thing.

On the right-hand side, the middle chart shows the impacts that changing a gear ratio has on acceleration distance and cruise distance within a single sprint. This type of math has helped my team understand how to adjust gearing in order to get a more desired outcome for a meta-game we didn’t expect in 2018. So I’m piloting that chart to the public this year, in the hopes that it helps more teams out.

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Ok, that helps a lot on the Acceleration Distance. Basically it tells you the point the acceleration goes to zero because it’s at it’s max speed. And that makes sense why the 6 Falcon (15.6 ft) vs 4 CIM KOP (14.5 ft) is different is because the top speed of the 6 falcon is higher and therefore the distance is going to be longer, even though to get to the same speed, it will be a shorter time or distance. I knew there was something there I didn’t understand, so thank you much for explaining it.

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Thats exactly what we’re thinking and the weight savings is why we’re making the move. I think the “unfairness” comes when all the sudden there’s 12 extra pounds of weight to do something with (or strategically stay light) rather than drivetrain performance itself.

I’ve seen similar comments about poor teams a few times and I know there’s teams out there that have to reuse parts each year. But, I also think a lot of teams buy new motors and controllers fairly frequently. Maybe I’m naive…

For six mini-CIMS ($180) and six Talon SRX controllers ($540) you spend a total of $720. We’re replacing those with four Falcon 500’s for a total of $560 so it’s a savings of $160 per drivetrain.

I know that the output shaft is driving cost up with new pinion gears, spacer kits, etc… but still it’s not an outrageous purchase for teams that are going to buy electronics for their drivetrain anyways.

I guess if the cost argument is about teams that will order 30 of these and use them on every mechanism I can get the concern. But, I also think the teams that afford to do that probably already have superior design, programming and manufacturing abilities that make the difference more than motor selection.

It depends on the role a particular team plays. Every year, we see teams strapping on weights to go play defense. Often, these are teams with lighter, simpler robots that were nowhere near the weight limit to begin with.

Except presumably for six mini-CIMS you would run 2 Talon SRX and 4 Victor SPX, for a total cost of $180 + $180 + $200 = $560, so, equivalent cost to four Falcons. For all new hardware, no cost savings by going with Falcons, other than maybe gears, but no additional cost either.

One interesting thought though is that with six mini-CIMS, you have six 40A of breakers available to the drivetrain. With four Falcons, it’s only four 40A breakers. Has anyone done the further math on this? I’m wondering if the limiting factor becomes the battery, or if there is performance to be gained by the 6 lesser powerful motors over the four more powerful ones.

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