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.
YMMV, but yes. The two plates are there to keep the gears in the same position relative to one another. If you can do that without 2 plates, you’re accomplishing the same task.
2 standoffs are enough if they make the gearbox stiff enough. If the plates are bigger, thinner, or further apart, you may need more. If the standoffs are smaller, further apart, or longer, you may need more.
I see the examples here are based on ‘Chain-in-tube’ chassis, and using 1x2 rails. That seems crazy tight to fit inside. Not that I doubt the CD community has this solved, but do you have links to examples or illustrations of how CIT can fit in such a narrow rail?
I’ve never done it but from what I hear, you would use a 17tooth double sprocket for #25 chain. Apparently it’s a perfect match for chain in tube for 2x1 tube
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2363 Triple Helix has some really good videos on how to build the CIT on the 1x2 rails. We did it last year and we were very pleased. We actually used 18 tooth sprockets inside the rails. Good luck.
Here’s our 2019 CAD that features 2x1, chain in tube, and 17t sprockets: FRC 319 - Public CAD 2019
Here’s our 2018 CAD featuring 2x1.5, chain in tube, and 16t sprockets: FRC 319 - Public CAD 2018
Here is a pretty good thread on the pros and cons of chain in tube: chain in tube experiences
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Ours is actually built from 1.5x2.
Here is the videos series.
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YES! I totally endorse the Triple Helix series; all of them. Thank you 2363!
After watching their CIT video, I couldn’t imagine making it work in less than the 2x2.
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But… Their videos use 2x1.5 and I just linked 2 more examples using less than 2x2?
Sorry, I didn’t mean it that way. It seems like a lot to accomplish in a small space. Looking at your links make it look simple now.
The whole robot makes excellent use of space for power transfer.
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My mistake. We used your video and went ahead with 1x2. Your videos are super.
(this might be a dumb question). I am seeing current draw in the 80 Amps range which looks kinda sketch. I know that you do not need to worry about current draw too much for drivetrains because you will not drive at the max speed for a significant chunk of the match (or maybe never). But this still seems too high for me to be able to comfortably design something with such a high current draw without losing speed. Is it normal and safe to design something in the 80 amps range without having your breakers pop during any match, ever?
I’d highly recommend adding some sort of current limiting to reduce high current spikes. Yes, this does affect acceleration. Our drivetrain simulator can help you estimate how much.
Additionally, keep in mind that the breakers are thermal based, so you can draw more than the rated amount for short durations of time. The data sheet will let you estimate how long a given load needs to be sustained for the breaker to trip.
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Thanks a lot
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