6 CIM Drivetrains... What's Your Experience?

[SoftwareBug2.0]

Originally Posted by JamesTerm

Ah ok, thats what I thought you did (or something along these lines)... did you make some trapezoidal motion profiling on the anguar velocity to do this? Or was it a fixed angular velocity?

Either of those sound like good ideas, but here's the whole of how it worked:

twist = -( twist - m_gyro->GetRate() / 200. );

[Ether]

Originally Posted by SoftwareBug2.0

...here's the whole of how it worked:

twist = -( twist - m_gyro->GetRate() / 200. );

What is "twist"?

[SoftwareBug2.0]

Originally Posted by Ether

What is "twist"?

The value of the joystick axis that controls rotation.

[wireties]

Originally Posted by SoftwareBug2.0

The value of the joystick axis that controls rotation.

You can read "twist" directly from some joysticks, they report X, Y and twist.

[JimBowey]

Team 955 used a pair of VexPro 3 CIM gear boxes for Ultimate Ascent. We were dashing about at near 18 fps which helped a lot with scoring cycles.

Since then, we designed and built much better quality 3 CIM gearboxes. Neither the VexPro or our own design depleted well cared for batteries, so not to worry.

[JamesTerm]

Originally Posted by JimBowey

We were dashing about at near 18 fps which helped a lot with scoring cycles.

That is amazing! I wonder if there is any video we can see of that, please send me a link if there is. Thanks.

[Bryce2471]

Yes, it was amazing. They were the captains of our alliance for the Portland regional. Watching them run circles around us was one of the reasons I decided that I don't like mecanums, and started pursuing swerve drives. I think they were the fastest robot I saw last year.

[JamesTerm]

Originally Posted by Bryce2471

Yes, it was amazing. They were the captains of our alliance for the Portland regional. Watching them run circles around us was one of the reasons I decided that I don't like mecanums, and started pursuing swerve drives. I think they were the fastest robot I saw last year.

Ah, I think this is the match you are referring to: https://www.youtube.com/watch?v=bIGNlT0VVTk
That was a cool match and the video speaks for itself. I am also a big fan of swerve drives (and a fan of the rare breed of teams that actually can pull off using them in competition).

[andypanda6796]

Hi guys,

I was just wondering if any teams who have had experience using a 6 CIM drive train could post about their experience. My team is considering going this route this year, specifically using the new Vex Pro 3 CIM Ball Shifters with a tank drive setup.

One of the specific questions we have is whether you've had any problems with drastic voltage drops when going from a standstill to full throttle? Or going from full speed to a forced stop i.e. hitting another bot/entering pushing match? Has it effected anything else i.e. radio power?

Any feedback would be great, thanks everyone!

[magnets]

Originally Posted by andypanda6796

Hi guys,

I was just wondering if any teams who have had experience using a 6 CIM drive train could post about their experience. My team is considering going this route this year, specifically using the new Vex Pro 3 CIM Ball Shifters with a tank drive setup.

One of the specific questions we have is whether you've had any problems with drastic voltage drops when going from a standstill to full throttle? Or going from full speed to a forced stop i.e. hitting another bot/entering pushing match? Has it effected anything else i.e. radio power?

Any feedback would be great, thanks everyone!

A person on my team played around with one on the off season, and he said it was a pretty good experience. He said that if you geared the robot for a moderate top speed, acceleration was very quick, and was very maneuverable. He also had some power draw issues. Full forward to full reverse caused the main robot breaker to trip, and that one doesn't reset, so the robot would be dead until somebody hit the switch again.

They solved this by ramping the motors (see here), and when they switched to 2 CIMs plus a miniCIM on each side, they couldn't get the breaker to trip.

[Canon reeves]

My Team is using 6 CIMS this season with a 5.95:1 ratio. it was relatively cheap and we figured we could go faster than most and push the basic bot and hit hard. When it come to a pushing battle, we have enough experience with tank to know that no matter what gear ratio or amount of CIMs, No robot can ever push us sideways, so if we can assist and get across the field quickly, and effectively stop anyone because we can go back and forth extremely quickly, so anyone faster than us, we can push, slower than us, we can block. Thats just what we choose to do from what our experiences are. I like the idea of a fast robot because you can cover more, if you're a rookie team or newer team, and you build the six motor drivetrain, and something to pick up the ball, and drove well and fed well, than you would be a great alliance pick. 6 CIMs with a good driver is a great way to set yourself apart and a great back up if something fails on your robot.

[cadandcookies]

Originally Posted by Canon reeves

No robot can ever push us sideways

Famous last words.

[Canon reeves]

Originally Posted by cadandcookies

Famous last words.

Actually, mine would probably be "hey yall, watch this!". I could never imagine an FRC robot being able to push a robot with tank drive that could only go forwards and back sideways? If one exists I hope I'm on their alliance, not the other way around!

[jman4747]

Has anyone adapted one of the gearbox/drive train calculators to account for a combination of different motors in a gearbox? With the miniCIM and Vex/Andymak having gearboxes for other motors with outputs made to mount where a CIM would, I'm wondering how to enter that. Or do I just write "2 2/3" for the number of motors if I have 2 CIMs & a miniCIM in one box?

[Richard Wallace]

Originally Posted by jman4747

Has anyone adapted one of the gearbox/drive train calculators to account for a combination of different motors in a gearbox? With the miniCIM and Vex/Andymak having gearboxes for other motors with outputs made to mount where a CIM would, I'm wondering how to enter that. Or do I just write "2 2/3" for the number of motors if I have 2 CIMs & a miniCIM in one box?

I don't recall seeing any of the calculators adapted; however, I do recall two things on this topic (1) Paul Copioli designed the mini-CIM to be used in combination at 1:1 gearing with a CIM in a drivetrain, and selected its free-speed and stall torque with that in mind, and (2) Ether did some analysis last year aimed at answering your question above. Maybe he or Paul will see this thread.

Mini-CIMs have a higher peak efficiency than CIMs because their commutators are the same size, while the mini-CIM has a shorter armature. This difference allows the mini-CIM to operate in combination with a CIM without overheating, unless the loading is very high and prolonged.