8 MINI-CIM SWERVE

[Kevin Ainsworth]

Would any one else like to see (8) MINI-CIM motors allowed so the swerves can be on par with the (6) CIM tank drives?

Looks like an 8 MINI-CIM motor swerve drive would be very close to power and weight of 6 CIM motor 6WD/8WD.

POWER
CIM 6 x 337 watts = 2022 watts total power
MINI-CIM 8 x 230 watts = 1840 watts total power
Within 10% instead of down 50%.

WEIGHT
CIM 6 x 2.80 lbs = 16.8 lbs
MINI-CIM 8 x 2.16 lbs = 17.28 lbs

Seems like the current rules favor a 6 CIM tank over a 4 CIM swerve for acceleration and top speed. I personally would like to see this somehow corrected. Maybe separating BAG motors from the MINI-CIM motors and a allowing 8 MINI-CIM motors?

This could be calculated by adding the watts of all motors used with a not to exceed. Or even more simply a CIM=1 and a MINI-CIM=.66 or .75 and a maximum of 6 when added up.

What's your thoughts?

[nuclearnerd]

I'm not averse to the rule change, especially if limiting total power is the aim of the rules. 8 mini cims ~= 6 cims.

The performance gain might not meet your expectations though. A tank drive will be better at putting that power to the ground (in a straight line anyway). When accelerating or pushing, the bot will "squat" toward the back wheels. As the weight comes off the front wheels, the force they can apply may become traction-limited, rather than power-limited. In a tank drive the front wheels and back wheels are chained together, so the weight distribution doesn't matter, but in a swerve drive, those front motors may spin uselessly.

The math on how big an effect this is is left as an exercise for the reader

[nuclearnerd]

Originally Posted by Kevin Ainsworth

This could be calculated by adding the watts of all motors used with a not to exceed. Or even more simply a CIM=1 and a MINI-CIM=.66 or .75 and a maximum of 6 when added up.

This kind of formula would even allow the GDC to dial back the maximum total power equivalent (TPE) if they wanted to (as some commenters propose). Hypothetically backing down the limit from 6, to say, 5, would result in *less powerful bots*, but still allow teams to use the following combinations (for example):

4-Cim (divisible by 2 and 4, TPE = 4)
6-Mini-Cim (divisible by 2, 3 and 6, TPE = 4.5)
2-Cim + 4 Mini-Cim (divisible evenly by 2 only, TPE=5)
8-9015 motors (divisible by 2, 4, and 8, TPE=~4.8)

[Electronica1]

Originally Posted by Kevin Ainsworth

Would any one else like to see (8) MINI-CIM motors allowed so the swerves can be on par with the (6) CIM tank drives?

Looks like an 8 MINI-CIM motor swerve drive would be very close to power and weight of 6 CIM motor 6WD/8WD.

How would you fit two motors inside a wheel?

[EricH]

Originally Posted by Electronica1

How would you fit two motors inside a wheel?

You'd use one to drive the wheel and one to turn the module.

[Electronica1]

Originally Posted by EricH

You'd use one to drive the wheel and one to turn the module.

But that would not allow you to have similar power to a 6 cim tank drive, which is the point of the 8 mini-cim argument right? (I might be missing something) You could have more than 4 modules in order to match the 6 cim power I guess.

[AdamHeard]

Originally Posted by Electronica1

But that would not allow you to have similar power to a 6 cim tank drive, which is the point of the 8 mini-cim argument right? (I might be missing something) You could have more than 4 modules in order to match the 6 cim power I guess.

You could do a swerve using those fancy mercury free mechanical slip rings and put the motors where they belong (external to the module), and easily do 2 per wheel.

[Max Boord]

Originally Posted by Electronica1

How would you fit two motors inside a wheel?

6 inch wheels. Baxter Bomb Squad already uses them and it would give you 1/2 inch of clearance on ether side. How the gearing would work is a totally different story.

Originally Posted by AdamHeard

You could do a swerve using those fancy mercury free mechanical slip rings and put the motors where they belong (external to the module), and easily do 2 per wheel.

But THIS

[EricH]

Originally Posted by Max Boord

But THIS

But this nuttin'. Try one of THESE! (Just swap the FPs for more CIMs.)

It's not about more/less points of contact with the ground, or about how much power you can put into the drivetrain, or how much traction a given wheel has. It's the balance of all of the above. I don't think that adding two more motors will do all that much--just make ya more likely to be traction-limited instead of torque-limited.

[Tyler2517]

Originally Posted by EricH

But this nuttin'. Try one of THESE! (Just swap the FPs for more CIMs.)

It's not about more/less points of contact with the ground, or about how much power you can put into the drivetrain, or how much traction a given wheel has. It's the balance of all of the above. I don't think that adding two more motors will do all that much--just make ya more likely to be traction-limited instead of torque-limited.

Look at what happen with the change from 4 cim drives to 6 cim drives. They are classes of there own.

[Max Boord]

Originally Posted by EricH

But this nuttin'. Try one of THESE!

Upgraded.

[JesseK]

2 extra motor controllers, 2 fewer available 40A ports on the PDB - 8 Mini CIMs vs 6 CIMs is a lose IMO.

[nuclearnerd]

Originally Posted by JesseK

2 extra motor controllers, 2 fewer available 40A ports on the PDB - 8 Mini CIMs vs 6 CIMs is a lose IMO.

For me too, but If another team decides they would rather have all 40A circuits going to the drive, and only use lower power circuits for the rest of the bot, why should the rules keep them from making that trade-off on their own?

[JesseK]

Originally Posted by nuclearnerd

For me too, but If another team decides they would rather have all 40A circuits going to the drive, and only use lower power circuits for the rest of the bot, why should the rules keep them from making that trade-off on their own?

Drive trains are easy to build. Without understanding the fundamentals, drive trains are very hard to perfect as part of a greater robot with other mechanisms. I feel that increasing the amount of power through to the drive trains is a cop-out low & mid-tier teams who don't bother to try to perfect their drive train. I'd much rather the GDC limit total electric power through the drive train if there were any rule changes in that respect. It would force the trade-offs to be actual engineering decisions rather than "BIGGER IS BETTER RAWR!1".

On top of that, I feel that anyone who mentions 6 CIMs as what led to success in an anecdote should have a gigantic caveat stickied across their post. I don't know about the exact wording, but perhaps it could say something like

Dear FRC participant, 6 CIM drive trains (or 8 MiniCIMs) may lead to some nice zippy acceleration if you "like to go fast". Yet here are some side effects you should consult your robot engineers about:

• Your drivers keep getting penalties for high-speed ramming
• Your robot "passes out" for about 30 seconds after getting into a pushing match
• Your batteries from last year's competition no longer hold a charge for the entire match
• Your other motor-driven subsystems are noticeably slower towards the end of a match
• The tread constantly strips off of your wheels when merely grazing another robot
• Your aluminum output shaft shears
• The chains snap apart at the master link or eat the teeth off of the sprockets after a quick reverse

These were witnessed, BTW.

Full disclosure, 1885 took a beating by powerful drivetrains at champs this past year. Getting double-teamed as a single-speed 11ft/s drive train got very aggravating very quickly. We endured, had some great matches and I know what to do for next year. We even had our very first actual zero-maintenance and very agile drive train this year across 4 competitions. Hopefully I've presented this in such as way that shows more thought has gone into it based upon several years of drive train design experience, rather than a single competition's worth of bias.

[Oblarg]

Originally Posted by JesseK

On top of that, I feel that anyone who mentions 6 CIMs as what led to success in an anecdote should have a gigantic caveat stickied across their post.

4464 used a 6-CIM drive last year, and I'd be the first to add caveats when we talk about the success it brought us (I've detailed the problems we encountered several times on these boards), but it is important to recognize that every single problem you've mentioned is something that can be either mitigated or avoided completely with proper diligence.

Yes, a young, inexperienced team naively going "MORE IS BETTER!" and mindlessly adding motors to their drive can easily do more harm than good, and designing a 6 CIM drive in a way that doesn't run into the mentioned problems is nontrivial (we had to swap our gearing before champs last year, and it wasn't because we hadn't put a lot thought into the gearing we originally had), but I don't think that every 6 CIM success story is necessarily ignoring or downplaying the negatives, or overstating the positives.