340 Offseason Drive BaseCAD

While helping teach @JOEL340 how to use Onshape, we designed a 3 motor flipped gearbox with a dual output shaft. The gearbox is designed interchangeably, just needing to swap the motors, the output the two gears for the last stage and the spacers to completely witch from falcon to neos or vice versa.

The NEO gearbox is 9.29:1 with an estimated speed of 13.72 feet per second. The gearboxes use 13 teeth to 42 teeth, then a 16 to 46 on the second stage.

The Falcon Gearbox is 11:08 with an estimated speed of 12.93 feet per second. The gearboxes use 13 teeth to 42 teeth, then a 14 to 48 on the second stage.

Onshape Link to the drivebase and gearboxes.

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Interesting gearbox design… Is there a benefit to having 2 output shafts?

Not 340 (used to be), but 340 has taken a liking to 8wd, so I imagine 2 output shafts allows them to skip the middle chain/belt run.

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If this is the case, wouldn’t this be potentially heavier?

Curious to hear what the OP has to say as well.

For sure, but you can also avoid extra chain or belt runs, and garauntee quick turns and speed if you have a belt/chain failure.

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It’s almost certainly heavier as there are more gear stages and larger gearbox plate. I feel like just doing the normal chain run between the two wheels would be easier and lighter, although I am intrigued by a triple flipped gearbox design.

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Maybe, but there’s benefits to redundancy imo.

Plus, 340 isogrids every ounce out of the drivetrain anyway, it will probably weigh less than most teams non-lightened DT :slight_smile:

Looks good Joel & Dom. Excited to hear if 340 swaps to OnShape. Very promising tech for FRC. Gearbox looks right out of 340s shop. Love it

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Thanks Justin. I’m trying to switch 340 to onshape for ease of working together, so before that I wanted to learn it myself.

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The weight isn’t as bad as you think. @Dominick_Ferone can get you the exact weight.

This is for an 8 wheel west coast drive train. The dual output gives us the ability to eliminate two belts and gives us the ability to still have 3 driven wheels on each side if a belt breaks (which has happened to us).

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That makes sense. Clever.

So the Falcon Gearbox weighs 7.5 pounds with the Neo Gearbox coming in at 6.9 ( and you add .75lbs for the 3 Spark Max controllers.) bringing it to 7.65 pounds.

With the dual output shafts you just need to run 1 belt to the outsides (the omnis in this case) which can be hidden in the tube.

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The gearboxes aren’t too bad as I mentioned in another comment about the weight.
Just by using the brushes motors, a custom gearbox will wind up being lighter than and Cot one running 2 cims. So the excess weight which is counted from previous years in drive trains can be moved around.
This year on 5030 we wound up doing 4 individual gearboxes directly on each wheel and in the end it wound up under 10 pounds for all of them.

I like this concept, 2848 did a dual output gearbox in 2017 and had a great experience with it. If you are committed to either 8wd for a butterfly, this simplified a number if things.

I do have a couple questions/ comments.

  • Using a 13t gear as your pinion means you would need to remove it before you could change the motor (unless you use Aren holes). Why did you do 13 instead of 12?
  • related to above, if change to 12, you might be able to keep the gears within the plates and not have the exposed teeth below the tube
  • Steel vs aluminum gears, from a serviceability standpoint I think you should consider doing steel for all or atleast your last stage, a 3 NEO gearbox that is especially not decoupled though belt or chain will nom those Gears, where you will either have to replace or rebuild during the season. If though testing they seem to last though atleast one event, no bag makes this less of an issue. I like the pocketed steel gears so they are worry free for the whole season.
  • The 3 bearings on the output shaft is less than ideal and may cause you issues as you are over constraining the center to center distance of the gearbox. If your c2c on your rail and gearbox plate are not exactly having 3 bearings will lead to added system load and higher current. Given that the output shaft only has a single gear on it, it shouldn’t be that bad to assemble with on the back bearing and one in the tube.
  • It feels like you could shave a 1/4in of width from the gearbox stack-up, by removing unnecessary spacers, as all the VP gears have shoulders that will ride fine directly on the bearings.

Overall, really nice job. Thanks for sharing.

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The 13 teeth geears have an OD of .805 and the hole for the motor shaft and pinion is .875 so there wouldn’t be an issue on needing to take the pinion off first.

I can look back at the math we did, I believe the reason we wound up doing 13 instead of 12 was initially we were calculating the falcons and this gave us around 13 fps which is where we were looking to hit.

This was just me assuming the aluminum is fine to use and @JOEL340 thought we were good, we may need to look over it again.

We weren’t fully sure if we needed the 3’rd or not, I thought we might not but then also left it for overkill. that’s now a lesson learned for the future. So would you just make that a 1/2 hex groove or is it fine to leave it as the empty bearing hole, since the shaft will be supported on the other side? (just wondering if we need to now make this plate different than the other plate, as it currently stands both plates are the same to have less specific parts and make spares more universal.)

I can definitely look into that, in the past, I always put at least a small spacer, as I was trying to avoid the metal on metal. I didn’t know just having the shoulder on the bearing is fine.

Thanks for all the tips to help us improve the gearbox.

You may want to be careful here - my understanding is that the hole for the motor pilot (in the gearbox plate) should be close in diameter to the motor’s output pilot diameter to assist with maintaining correct spacing, as well as locating the motor. I’ve personally been using (and have heard from others as well) .753” for this gearbox hole.

I have no real statistics or anecdotal evidence to say that this might be an issue, but I just assumed this is why 971 and TTB use the Aren hole style when using larger pinions.

Anyone who knows more about this, please correct me if I’m wrong!

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This looks a lot like a combination of our 2019 and 2020 drive bases - we, too are finding the 8wd layout to be quite versatile and robust for FRC. Ours was not as “pretty” but worked like a champ and we only had one issue with a stripped belt by the end of the season - but we hardly noticed it since 3 wheels were still powered (yay for redundancy!).

The NEOs and now Falcons really allow for more creative and compact packaging overall and It’s exciting to see teams creating cool designs around them.

Nice job!

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What exactly is an Aren hole?

Here’s an example from TTB:

These plates feature the Aren Hill 14t pinion holes, allowing easy installation & removal of motors.

I don’t remember what year, but it’s in 971’s publicly available CAD as well.

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  • You are correct that you could make the hole big enough for the gear, but loosing the motor pilot and relying on the screws for a good center to center distance is not a good design practice. This has potential to be extremely bad, especially when you are transmitting torque back through the pinions on the motors from both sides.

  • When I made the suggestion about changing the gear sizes I assumed you would move to an 11 or 12 tooth pinion, which would allow for a smaller reduction on the last stage, having the added benefit of a smaller output gear.

  • Aluminum and Steel will both functionally work, it is just a question of how long it will work for.

  • To remove the 3rd bearing I think you don’t need any design changes, you just don’t put that bearing there and replace it with a hex spacer. You might consider adding a collar or snap ring there as you no longer have the bearing as a shaft retention method.

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