Minotaur Drive Gearbox - 4915 Off-Season CAD

This is the first of the 2020 Infinite Off-Season projects that has been finished here on Spartronics.
This is a gearbox for a dual Falcon 500 Drivetrain. This season, we ended up filling our and that got me thinking, is a dual motor drivetrain viable? The answer turns out to be yes if you use Falcon 500s due to the fact that they have roughly double the torque of a CIM.
The upsides to this drivetrain model:
-Lightweight: This gearbox with the motor weighs a hair under 2.7lbs
-Compact: When you have fewer motors, you take up less room. Furthermore, this gearbox is designed to have the chain run inside one of the chassis tubes and the motor is flipped over top.
-Fewer PDP Slots

Less Power: I would imagine most teams will be using quad Falcon 500 or sextuplet NEO drivetrains
-No redundancy: If one of your drivetrain motors fails in a match, you can spin and do pretty much nothing else.


Sweet render! Clever design thinking.

Do you have space for a wheel underneath that Falcon?

What current draw are you assuming the battery supporting? The datasheet for the Falcon extends into a range that’s not always accessible.

1 Like

It sure looks like any wheel big enough to keep the gears out of the carpet will have to pass through the motor.

This version of the gearbox does not support the wheel going under the motor, however I will design one that does (just have to make a minor change to the middle plate).
I did not look at the current draw, however the viability of this gearbox does not depend on the motor being able to run at full power,

This version of the gearbox does not support a wheel on the output shaft, I will make a change to the middle plate to make that possible once I finish my Swerve Drive

Can you expand on this a little bit more? Are you matching the stall torque to an existing 4915 gearbox?

Any chance you could share a CAD link?

The primary point of this gearbox was to make a light, functional gearbox that saved on PDP slots, it is not in any way focused on being able to push other robots out of the way (maybe if they have an H-drive). I am not comparing this gearbox to any others that we’ve used, I am purely looking at the torque capability of the Falcon 500 compared to a CIM.

Yeah, sorry, I forgot to add it into my post and now it won’t let me.

1 Like

What’s that thin back plate for? All I see it doing is over constraining one of your gear shafts

The 1/8" thick backplate goes on the outside of the 1x2 chassis tube

Looks great! One recommendation I would make - when doing renders, instead of using the darkest black to represent black anodized or powdercoated parts, try using the second darkest (usually a grey). It’ll appear closer to the actual part color in real life, and will show more definition and detail of the part in the render (I find the darkest black colors usually cause the details to all blend together and be hard to see).

Keep up the great work!


In that case, would it be possible to not have the “leftmost” plate be supporting the second stage driven gear, and just have that be canted off the chassis tube? Essentially, remove the part highlighted in red and find a different way to support that plate.

It might save a bit of weight depending on how you do it.

Probably, that’s a good point. I could also push that down to .125 rather than .1875

Having cant in a gearbox, especially that much, is not a good idea. You would probably see gears skipping under high load. It might be a better idea to remove the bearing from the center plate so that the shaft is only supported on the outmost bearings.
And having 3 bearings on a shaft isn’t the end of the world.

I’m a little bit confused about how this will get put together. Does the small plate go on the outside of the drive rail, or does it stay on the inside and the shaft has to be extended through the 2x1 to reach the wheel, or does the wheel go inside the 3rd plate? A picture of this assembled might help.

1 Like

I would double check to make sure you actually want to run a drivetrain at this power. Falcons at 40A do not quite have twice the power of a CIM (I believe it’s about 400W compared to a CIM’s 270W). I have not heard of any teams using a dual falcon drive this year and I do not think that just two will be able to deliver the power that you want.

Yeah, you would definitely be down on power, this is just me having fun with CAD and thinking about a potentially usable solution to a couple of issues. It certainly isn’t ideal.

1 Like

The thin plate goes on the outside of the drive rail. This current design would have the gearbox sitting between two wheels and wouldn’t have a wheel on that output shaft. It is designed so that it CAN have 3 bearings but it’s not supposed to. The gearbox would be oriented in such a way that the cant is only pulling the teeth away when going backwards, if I were to build this and if that issue were to come up, I would look into using nicer bearings than the standard AM or VEX ones and I would look into making that shaft out of steel to decrease play and flex.