pic: 2012 frc971 transmission

[roystur44]

loading photo ...

[MattC9]

Are those custom gear's or are they ones from andymark?
Also, Where do you get these special pneumatic pistons, bimba? and how are they different from the standard ones?

[Akash Rastogi]

I loved your simple solution to saving space this year, along with the pancake cylinders for shifting. Are there any tips or tricks you might have when making an "inverted" gearbox? Were there any issues you encountered that were unique to this type of setup? What would you do differently?

Thanks!

[Jared Russell]

Is there any measurable benefit to the fan above the CIMs?

[Cory]

Originally Posted by MattC9

Are those custom gear's or are they ones from andymark?
Also, Where do you get these special pneumatic pistons, bimba? and how are they different from the standard ones?

The pistons are from Bimba. They are shorter than a standard piston (albeit wider). They also generally ouput less force, as the rod is smaller than the commonly used shifter pistons.

[SteveGarward]

Do you have a part number for the pistons? I was looking at a couple of different ones a couple of weeks back. Just curious which ones people are using.

[R.C.]

Originally Posted by Jared341

Is there any measurable benefit to the fan above the CIMs?

Jared,

They really helped on the practice bot. I was talking to Austin at Davis this year and was unsure about trying out fans. After Davis we put fans on the practice bot, it really helped us get longer practice time.

On the comp bot in 2 minute matches, totally unsure 971 would have to answer that one.

-RC

[cbale2000]

Originally Posted by Jared341

Is there any measurable benefit to the fan above the CIMs?

I don't have any experience with them on CIMs, but I added one to the KOP air compressor on our demo bot and it dropped the running temperature and idle cooling time significantly. We had been having issues where the compressor would get so hot from running constantly it would melt the hose coming out of it (causing an "explosive" loss of pressure). Since adding the fan we have yet to see such a problem occur again, even after a 5+ hour demo that was outside on a hot day and in direct sunlight.


Somewhat related, on this years robot we used two FisherPrice (I think) motors to run our shooter system. We had been having an issue where after moderate use, the motors would heat up and then, the lower one in particular, would stall when trying to shoot a ball. The motor had been mounted to the robot using an aluminum collar we made for it (which covered about 60% of the motors surface area and was roughly 3/4" thick). To fix the problem, I took the collar off and cut small groves around it (like a computer heat-sync, and since putting it back on the robot we have yet to have the launcher stall on us again.


I could see a fan on a CIM being useful particularly in elimination rounds where you have a lot of matches close together with very short breaks between them. In years past our motors have gotten very hot (one year we even used a can of compressed air upside-down to cool down our drive motors) during finals, so an active cooling system could be a good way to alieviate such problems and maybe squeak out that little extra bit of performance during the most important matches.



TL/DR version: Temperature matters, cooler running motors will perform better.

[AdamHeard]

I'm not seeing how this is single reduction. I can't get the numbers even close to those speeds, and in the picture it looks like the gearshaft is above the wheelshaft (or the wheels would hit the CIMs).

Is there another gear reduction external to this gearbox that directly drives the center wheel?

[James Kuszmaul]

Originally Posted by AdamHeard

I'm not seeing how this is single reduction. I can't get the numbers even close to those speeds, and in the picture it looks like the gearshaft is above the wheelshaft (or the wheels would hit the CIMs).

Is there another gear reduction external to this gearbox that directly drives the center wheel?

You are correct; A 15 tooth gear coming from he transmission drives a 50 tooth gear which is on the same axle as the wheel.

[kevincrispie]

In the back of the picture, you might be able to see that some of the wheels had gears on them. These were the center wheels that interfaced with the transmissions.

[roystur44]

The use of the final gear allows us to make the transmission removable while the belts and wheels can stay on the chassis all tight. Let's see a WCD do that.

We need to make the inside side plates a little stiffer by insert some bends into the plate. This will give us a flange to mount the plastic grease guards.

We need to insert alignment pins from the transmission to the chassis to ease the assembly and get the optimum gear spacing. We had to manually tune the alignment and if the screws became loose the transmission would have power loss.

[roystur44]

Originally Posted by Jared341

Is there any measurable benefit to the fan above the CIMs?

Yes,

Fans help out on other motors too. Try running a pair of Fisher Price motors at high load and run them intermittently in forward and reverse. They don't like that and you will see how smoking hot they get. Attach a pair of small fans to direct continuous air flow over the motor cooling slots and casing and you will see a tremendous improvement of the power output over a time frame.

[Nate Laverdure]

I love the space savings with this "inverted" setup, but in order to place the CIMs outboard of the gearbox, you risk a higher moment of inertia. This will have the effect of making the robot harder to turn.

Some quick calculations tells me that moving the CIMS outboard will increase the total moment of inertia by about 5% (for a "long" chassis) to 8% (for a "wide" chassis) for an otherwise equally-distributed robot. For a constant turning torque, this results in a similar percentage less angular acceleration.

Takeaway: for a snappy turning response, mount your heaviest items as close to the center of rotation as possible.

[Nuttyman54]

Originally Posted by Nate Laverdure

I love the space savings with this "inverted" setup, but in order to place the CIMs outboard of the gearbox, you risk a higher moment of inertia.
...

Takeaway: for a snappy turning response, mount your heaviest items as close to the center of rotation as possible.

This is a good point, and 5% is something that will be noticeable to most drivers. There are a few other factors as well that go into the decision for us:

1) With most 6wd dropped center setups, turning is usually really really snappy already, sometimes too much. Especially with a robot geared above 15fps, turning response can be almost uncontrollable without a lot of practice.

2) The drive code that 971 uses (along with 254 and maybe some other teams) is set up to do controlled radius turns in normal operation, rather than controlled turn rate, which mitigates the "snap" turn response characteristic of 6wd. This makes the robot much more controllable at high speeds (the 971 2012 robot was geared to 17fps no load). Further discussion on this style found here. Because of this, we try to avoid needing to turn in place when we drive, so the moment of inertia aspect isn't really an issue for us.