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  #46   Spotlight this post!  
Unread 10-01-2017, 12:23
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Re: 2017 Drive Train

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Originally Posted by JediSy View Post
I personally think mechanum or Omni with tread-wheel hybrid. That's just an idea though. Problem is the amperage for mechanum.
How is amperage for the the mecanum wheels an issue? You will not be stalling them and thus you will not draw much current. Instead of stalling mecanums normally break the friction of the carpet and spin (if remember correctly).
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Unread 10-01-2017, 15:06
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Re: 2017 Drive Train

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Originally Posted by dardeshna View Post
On a slightly different note, what motor / gearing / wheel size setup are you all using? Ideal feet per second I would imagine is relatively high. Shifting or no shifting? We are leaning towards 6 cim ~10-12 fps no shifting but I don't have great experience to tell if we got it in the right range or not for this game.
Wheel size: small as you can reasonably get them. I personally see no good reason to have drive wheels larger than 4". Lower ground clearance, less reduction, and less overall torque in the system is always a good thing. The only downside is that your wheels will wear more quickly. I imagine the <4" and 4" hex bore Colson wheels will be very popular this year.

Motors: my go-to combination is 4 CIMs & 2 MiniCIMs.

Gearing: I am usually an advocate for single speed gearboxes, and I still think you can't go wrong with them this year. My issues with shifters is that most teams are not able to fully realize the benefits of their shifting gearbox; whether that's because of poor design, a game that doesn't need two-speeds, insufficient driver practice or just mistakes in the engineering process, they're adding weight, cost and complexity and not getting much in return. However, this year is a good year for shifting gearboxes if you go that route. you have long open stretches of field you need to get across quickly and you have tight spaces where you need to push defenders out of the way. I have not done any of the math yet to really figure out sprint distances and distance to reach full speed, so I'm just guessing on the numbers themselves. But for this game, I'd say:

12 ft/s for a single speed gearbox
8 & 14 ft/s for a two-speed gearbox.
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  #48   Spotlight this post!  
Unread 10-01-2017, 15:35
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Re: 2017 Drive Train

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Originally Posted by TheMagicPenguin View Post
Here on 1640 we plan to use our swerve drive again (big suprise). This year we are also going to introduce our CVT swerve to the field.
Do you have any of the source files for this CVT swerve design anywhere? I'd love to look at them.



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Originally Posted by Darkseer54 View Post
How about 45lbs, with a functioning control system, working pneumatic system, a compressor too big for its own good, a metal tank, and a huge excess of wires and pneumatic tubing? Just because one 8 motor octocanum weighs 90 lbs doesn't mean all of them do.

https://www.youtube.com/watch?v=sf-mNuGsVhQ
That looks great! Mind if I ask what traction wheels you're using?

You're right, 45 lbs. is much more reasonable and your chassis looks both agile and powerful. I expect you'll see a lot of success on that that chassis.
But the reason I always will recommend a simple 6 or 8 wheel drop center chassis over the more complicated drive systems is that a well designed, well built, and well practiced tank drive will perform as well as something more complicated for most cases. Yes, there are situations in which it'd be really convenient to just move 6" to the left in a match. But those scenarios are not worth the time and effort that those more complicated drive systems require. And the robustness of a tank drive cannot be beaten.

In short, I think it's more important for teams to field the best robot and not the best drivetrain. Any time spent on a complicated drive system is time not spent developing other subsystems.
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Unread 10-01-2017, 19:32
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Smile Re: 2017 Drive Train

Speaking of drive train, we finally came up with the drive train we are going to use for this year. We were deciding between skid steer and mechanum and I was for skid steer. However, the main mentor already ordered the parts for mechanum. We're still deciding on our robot design, but at least we have a drive train.
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Unread 10-01-2017, 19:39
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Re: 2017 Drive Train

Quote:
Originally Posted by Cothron Theiss View Post
Wheel size: small as you can reasonably get them. I personally see no good reason to have drive wheels larger than 4". Lower ground clearance, less reduction, and less overall torque in the system is always a good thing. The only downside is that your wheels will wear more quickly. I imagine the <4" and 4" hex bore Colson wheels will be very popular this year.

Motors: my go-to combination is 4 CIMs & 2 MiniCIMs.

Gearing: I am usually an advocate for single speed gearboxes, and I still think you can't go wrong with them this year. My issues with shifters is that most teams are not able to fully realize the benefits of their shifting gearbox; whether that's because of poor design, a game that doesn't need two-speeds, insufficient driver practice or just mistakes in the engineering process, they're adding weight, cost and complexity and not getting much in return. However, this year is a good year for shifting gearboxes if you go that route. you have long open stretches of field you need to get across quickly and you have tight spaces where you need to push defenders out of the way. I have not done any of the math yet to really figure out sprint distances and distance to reach full speed, so I'm just guessing on the numbers themselves. But for this game, I'd say:

12 ft/s for a single speed gearbox
8 & 14 ft/s for a two-speed gearbox.
So I was reading about traction limiting. What advantage does a 6 cim setup provide if your drivetrain is traction limited?
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Unread 10-01-2017, 20:31
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Re: 2017 Drive Train

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Originally Posted by Cothron Theiss View Post
That looks great! Mind if I ask what traction wheels you're using?
That uses 2" Colson wheels which were hex broached. From what I've heard from members of the team, they may be planning to diamond cut them this year. The idea behind using such small wheels is by making the wheels smaller, the overall size of the module is less so you save weight.
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Unread 10-01-2017, 20:40
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Re: 2017 Drive Train

Quote:
Originally Posted by dardeshna View Post
So I was reading about traction limiting. What advantage does a 6 cim setup provide if your drivetrain is traction limited?
Less amperage per motor, which means you're more likely to traction limit before tripping breakers or overloading a speed controller. Less amps also means less voltage drop in your wires to/from the motors, which means you're spending more watt-hours on pushing and less on heating up wires. It's a small thing, but I suspect every little thing you can do to minimize unnecessary battery drain matters, even if you're using a fresh battery for every match.
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  #53   Spotlight this post!  
Unread 10-01-2017, 20:48
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Re: 2017 Drive Train

Quote:
Originally Posted by dardeshna View Post
So I was reading about traction limiting. What advantage does a 6 cim setup provide if your drivetrain is traction limited?
Additionally, having 6 cims would allow the robot to accelerate faster than a setup with fewer cims.
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Unread 10-01-2017, 21:10
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Re: 2017 Drive Train

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Originally Posted by dardeshna View Post
So I was reading about traction limiting. What advantage does a 6 cim setup provide if your drivetrain is traction limited?
Here's a really great paper looking at 4 CIMs vs 6 CIMs. Were you referring to the advantages of 6 CIMs over 4 CIMs or 4 CIMs & 2 Minis?
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Unread 10-01-2017, 22:00
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Re: 2017 Drive Train

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Originally Posted by Cothron Theiss View Post
Here's a really great paper looking at 4 CIMs vs 6 CIMs. Were you referring to the advantages of 6 CIMs over 4 CIMs or 4 CIMs & 2 Minis?
Great, thanks for linking the paper. I was originally referring to the difference between 6 CIMs and 4 CIMs, although I presume the same concept applies.
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Unread 12-01-2017, 16:34
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Re: 2017 Drive Train

Our team is building both an omni and the KOP drivetrain this year and making them the same dimensions with the same opening location for ball retrieval. The plan is to use the omni, but with the backup option of the KOP DT.

Are we allowed to switch out drive trains at the competition if the need arises? If so, would both drivetrains need to be included in our 120 lbs? Do we need to come to the competition with the second drive train un-assembled?
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Unread 17-01-2017, 20:05
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Re: 2017 Drive Train

Bumping the thread to ask, "Our team was driving and finding alignment time issues with the feeder station and gear deployment station, we are using the AM14U2 chassis in the 6 wheel configuration. Is H-drive worth is to overcome the drive practice required to become efficient at loading?" Our team has not built it before, and I am curious as to how difficult it is with the standard chassis.
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Unread 17-01-2017, 20:27
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Re: 2017 Drive Train

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Originally Posted by Southpaw View Post
Bumping the thread to ask, "Our team was driving and finding alignment time issues with the feeder station and gear deployment station, we are using the AM14U2 chassis in the 6 wheel configuration. Is H-drive worth is to overcome the drive practice required to become efficient at loading?" Our team has not built it before, and I am curious as to how difficult it is with the standard chassis.
Your team is driving and prototyping already? Awesome!! You are exactly where you want to be. Switching to a completely different drive system that you don't have experience with and requires MORE driver training than a standard tank drive seems like a fool's errand at this point.
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Unread 17-01-2017, 20:42
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Re: 2017 Drive Train

Quote:
Originally Posted by Southpaw View Post
Bumping the thread to ask, "Our team was driving and finding alignment time issues with the feeder station and gear deployment station, we are using the AM14U2 chassis in the 6 wheel configuration. Is H-drive worth is to overcome the drive practice required to become efficient at loading?" Our team has not built it before, and I am curious as to how difficult it is with the standard chassis.
Definitely stick with your current drivetrain. It's not worth the time to add strafing. Focus on getting good at lining up with your current drivetrain!

On another note: I'm very happy that 4607 built a Butterslide drive with 4" omnis and 2" custom traction wheels. We're essentially duplicating that drivetrain with some useful improvements. Being able to strafe while also having the ability to resist pushing while scoring is going to be so useful. If we hadn't built that drivetrain in the offseason there's no way we could've done it during the build season!
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Unread 18-01-2017, 00:54
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Re: 2017 Drive Train

Our team decided to go with a 6 wheel tank drive this year, with a sort of modified west coast style. We have a frame CAD model attached and would love to hear what you think.https://drive.google.com/file/d/0BzJ...ew?usp=sharing
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