Simple Single Stage 2x Falcon 500 Gearbox

So if I remember right, I was the first one to publish a NEO gearbox last year. With the excitement of the new brushless motors coming out, I decided to make a specialty Falcon gearbox. With the free speed of the Falcon being nearly 6400 RPM, it isn’t as ideal as the NEO was for fitting into a CIM gearbox. It’s still possible, just have to play with gearing a little more.

It’s currently geared 8:54 for a free speed of 16.5 Ft/s, or adjusted at 13.36 Ft/s on 4" wheels. I’m a little worried how the 8 tooth pinions are going to hold up with that much torque. I put another gear on partially for that reason, giving more contact area on the pinion to prevent stripping.

Besides having to mill the hub off one gearbox, and possibly add holes to bolt the gears together, there are only 3 parts that need to be manufactured, the two plates and the output shaft. Everything else is COTs. It is currently weighing in at 2.8 lbs according to SW, but I didn’t double check everything had the proper weight assigned.

Final SS1.zip (37.6 MB)

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My biggest concern here is your lack of standoffs between the inner and outer plate.

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$.02…

I would recommend clocking your motor mounting holes by 90*.

This would allow you to keep the gearbox assembled at all times with the standoffs in their current place, using flatheads on the Motor mounting plate. Then, since the motor mounting holes are clocked 90*, you can replace a motor with no interference from the gear, and without having to disassemble the entire box.

Edit: Also… It appears to me that your holes are not in a true bolt circle? Is this just an illusion?

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The plate the motors mount to should be in a true circle. The one that will attach to a tube, is not in reference to the output shaft of the motors. This is to allow for the plates to be tapped in those locations and add more mounting holes to the frame. They have to be farther away from the output shaft of the gearbox to make sure the heads don’t interfere with the hex bearing that would be on the rail. If that makes sense.

Or alternately, rotate the motors 90 degrees and have four standoffs, also addressing @Connor_McBride’s concern .

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Correct me if I’m wrong, but isn’t the primary concern not the speed of the drivetrain but where along the motor curve it operates, and how much torque we have as a result? The Falcon has a higher free speed, but also a higher stall torque (it just puts out more power). Doesn’t this mean that a similar gear ratio would allow for enough torque to run the drivetrain safely, even at the higher speed?

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It does for sure, but there gets to a point where you can’t control at that speed well. I can’t remember what the speed was, but at some point it just gets too fast, and you just look messy. I know for my former team, they currently have newer drivers. Just from what I’ve seen, I think they could handle driving with the speed set on this gearbox.

Even though you can safely run at a higher speed and have the torque you need, if you don’t run at those speeds often, or at all, you may appreciate the higher acceleration and more torque.

Darn. 2 hours too late. I went 8:66 for my ratio and skipped the second plate.

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0.3" ground clearance on a fresh 4" wheel… that’s a bigger gear then I would be comfortable running. I was thinking more in the range of:

8:60 14.85fps free speed
9:60 16.70fps free speed

This would give you two different speed options with the same output gear/C-C spacing, and would have 0.45" ground clearance (for us something like 0.35" ground clearance if we enclose it like we like to do).

EDIT: Could also do it with the following below for a little faster speeds and a little more ground clearance:

8:58 15.36fps free speed
9:58 17.28fps free speed

This would have 0.5" ground clearance (~0.4" in our enclosed gearbox setup).

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.3" is a fine ground clearance unless we have a ramp like 2018 and 2019. We ran less than that in 2017.

Your gear ratios seem fine depending on the game. So do mine.

A gear is just a wheel with extra grip.

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#science

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Threw together something similar to @Ty_Tremblay real quick but for 6" wheels:

JVN Calc gives approximately the same current draw for this when compared to a 2 CIM/3 Mini CIM drivetrain geared for 13 fps free.

The 84T gear is 4.3" OD, so we get just under an inch of ground clearance for the gear.

I posted this here because I have no idea if this would actually be a good idea. I think it would work, but I don’t know if I should be considering something other than the “Pushing” current draw on the JVN calculator.

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I don’t want to derail the thread but I wanted to ask this here since I’ve seen 2 example of it already. I posted a thread earlier of a west coast drive my team is building in the offseason. Most of the responses I received stated how there should be more standoffs and a couple said to delete the outer plate.

I see in your gearbox and plusparth’s gearbox, there is no outer plate. There doesn’t appear to be a bearing block either from what I can see. So given this, I’m assuming it would be fine to put bearings inside tube without a bearing block? Along with press fit bearings, I’m assuming 2 standoffs on the gearbox motor plate is fine?

We aren’t doing chain-in-tube like the above gearbox designs.

We have used bearings in tubes without bearing blocks and haven’t had any problems. But we used 1/8 tubes for our drivetrain. With 1/16 tubing, it’s probably a good idea to use bearing blocks.

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Not an expert on what would be safe here, but usually we do use bearing blocks with our 1/16" tube and the only reason I skipped out here was because I was being lazy and this specific thing will never built.

More Standoffs
The purpose of standoffs is to make the relationships between the gears rigid. The efficiency of a gearbox is greatly affected by the spacing between meshing gears, and we can’t have that changing as the gearbox is used. In the case of the gearbox posted here, the standoffs are very large (.75" diameter) and the shaft in the middle also helps to stiffen the relationship between the cluster gear and the pinion gears. The plate is also quite close to the tube, reducing standoff length and further increasing stiffness. If you’re not doing chain-in-tube, your inner plate will be further from the tube, and you may need more standoffs to increase stiffness. Finally, my standoffs go through the inner wall of the tube and are attached to the outer wall (again for stiffness).

Outer Plate
In the case of these gearboxes, the inner face of the tube serves as the outer plate.

Bearing Blocks
We use .125" wall tubing so we don’t need bearing blocks and can put the bearings directly in the wall of the tube. If the walls were thinner, we’d use bearing blocks.

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This is very interesting and similar to what I was thinking. Did you enter the data for the Falcon, or is there a JVN Calculator out there with it already available?

So an outer plate is not necessary if the gearbox is a simple single stage gearbox. And 2 standoffs are enough given they are large?

I entered data for the Falcon (data from https://motors.vex.com/vexpro-motors/falcon) into the DATA sheet in JVN’s calculator.