Single Speed 2 NEO Gearbox Feedback

I took a stab at creating a standard single speed drive train gearbox design. I will preface by saying that neither myself nor my team has much experience with custom gearbox or drivetrain designs, so any feedback is welcome. For the past few years our team has opted for the Vex ball shifter boxes with two CIMs and one Mini CIM. This gearbox is a first iteration of what I think could be a much smaller and lightweight alternative if we find we need it.

I know there are many different opinions on the subject, but is 13.08 ft/s free speed adequate, to high, or to low for the average frc game?

I’ve seen a few posts about stripped aluminum gears, especially the 20 tooth 20 dp gears from VEX. I wondered if this was worth upgrading to steel for this specific gear, and would that require upgrading the meshing 50 tooth as well?

Recently there has been some discussion regarding the cooling of NEO motors, and how they dissipate heat through the front face. Does this warrant filling in the area of contact between the gearbox plate and motor face to increase heat transfer?

Any critiques are appreciated!

Logan Femling
3674 Team Captain

SingleSpeedNEODrive_3674.step (7.9 MB)


13 ft/s is actually right around the speed spot for this year’s game. In 2010, 2012, 2015 and 2018 it was about right as well. 2018 could have been a bit higher, 2015 a bit lower, but that’s just being picky really.

One thing though. Why use multiple gear reductions instead of just one?

Filling the face in front of the neo is not going to appreciably help cooling.

I’m not sure this is necessary, but wouldn’t thermal paste do the job better?

The heat is transferred most effectively by direct metal-to-metal contact. Increasing the contact area and improving the surface finish of the surfaces in contact will decrease the thermal resistance. Thermal grease is used to fill in the microscopic irregularities in the surfaces to further reduce the thermal resistance.

How many bearings support the output shaft?

Is there a way to add more support between the two grey plates near the bottom end?

If I understand your question correctly, the largest 20dp Vex gear I see is an 84 tooth. A single reduction would be 12:84, which would result in a free speed of 19.46ft/s., which I’m going to assume is way to fast. The 84 tooth gear is also quite large, and would stick out below the robot quite significantly.

If you’re going to use the versablock to attach to the rail, make sure you drill out those garbage #8 holes and retap them to use at least #10s for mounting bolts. It might mean having to add a bit more space between the plate and the chain, but it’s worth it. #8s are for toys, and I’ve seen more than one versachassis gearbox fall off because they break / strip.

There are two bearings supporting the lower shaft, one in the back plate, and one in the front face of the VersaBlock. There is absolutely space to add one or two more bearings on the bottom shaft. I was under the impression that as a general rule you should only use bearings in sets of two, so that small variations in tolerances do not cause bearings to become slightly misaligned, possibly creating a shaft that doesn’t run as smoothly.

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Vex now makes a 9t 20dp CIM pinion. A single 9:84 reduction with NEOs and a 6" wheel gives a free speed of 14.6 ft/s, which is right in the range of single-speed drivetrains.

If you go down to a 4" wheel, you have a lot more options across basically the whole range of drivetrain speeds.

We’ll definitely consider doing that. We’ve used the VersaBlocks for the past two years on the Vex Ball Shifter boxes, and our main stuggle with them has been making sure the screws don’t back out over time. In 2018 we had to retighten them after every match. For 2019, we made sure to generously apply blue loctite, and only had to tighten them up a few times throughout the season

I wasn’t sure if there was also a bearing in the other VersaBlock for a total of 3. The shaft would then be over-constrained, a highly undesirable situation.

By support, I meant more standoff’s between the two grey plates to maintain the spacing between them.

Thank you! I was not aware of the 9 tooth option. Our team has only used 6in wheels in a West Coast configuration, as we wanted to make sure we were able to go over the ramps of both 2018 and 2019. I know teams have gotten away with 4in setups in both of these games, and we may build a 4in wheel drive for our off season competition in December so that we have experience in case we think a 4in setup would be good for 2020 .

Ah. Yep there’s definitely space to add another standoff underneath the lower 50 tooth gear. We’ll add that in.

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