Hey everyone! Over the past few days I decided that I missed designing FRC items so I took a stab at making a flipped gearbox!
I have yet to run a weight analysis on it but I will update this part when I do.
This is the first time I’ve done anything like this so I appreciate any kind of feedback.
I’ll do my best to answer any questions.
Are you concerned with the potential for the chain to rub on the lock-nut for the bearing block? You could easily change that into a tapped hole if needed. I don’t know if the cutout around the falcon shaft is big enough to account for the spacers to hold the pinion in place. It looks to be close for fitting. Great looking gearbox!
Question: It looks like the chain that runs on the double sprocket would need to route right where your standoffs are located. Am I missing something?
Overall looks good, but yeah those standoffs need some changing.
I’m not too terribly concerned but I could definitely tap the holes.
I was planning on press fitting the pinion onto the shaft. I assume you can’t do that? I haven’t used Falcons before.
You’re looking at the correctly. I failed to realize that that would potentially be an issue. Thanks for pointing that out.
I don’t believe there’s a way to do this. For the falcons we used on our shooter we used the spacers in the falcon 500 box and an 8-32 bolt on the end. I believe this is how VEX recommends spacing the pinion gear.
Depends on what shafts and what pinions you have (how close to spec they are). Technically there should be a slip fit between the shaft and the pinions, but this year they were out of spec and the shafts have to have the pinions pressed on. My team ran our pinions just pressed, with no spacers or retaining bolts, because our shafts were out of spec and we were satisfied with the press fit (hard to press even with a 10 ton arbor press) but in the future if parts are closer to spec you should use the spacers and 8-32 bolt as recommended.
I would be careful with this and press fitting them, because then it is virtually impossible to get that pinion off that shaft, thus making that motor useless if you can’t use that pinion that’s already on it because your not able to get the motor face plate off. Vex did release a way to sand down the shaft to make the pinions slip on and worked well for my team.
Without a gear puller, yes. You wouldn’t be able to take the front plate off or swap the shaft. However, all it takes is a basic gear puller and your worries no longer apply. We had to do this (and easily did do this) when we had to loctite all of the shaft mounting bolts.
This is a pretty compact gearbox design, I had a few questions that I was hoping you could answer.
Was there a reason you have that front plate that is driving the 40 tooth gear? I know that the WCP flipped gearboxes dont have a plate in front of the gear and so taking out this plate might save you some weight and horizontal space. Also I looked in the CAD and the first stage seems to be a 12:64 reduction and the second stage reduction appears to be a 22:42 which doesnt match the jvn numbers if you could update those that would be amazing. Not trying to detract from the amazingly compact gearbox just thought I should bring that up. Thanks for sharing these designs.
Thank you all for the notes on the falcons and pinions.
Yea so the big thing is that I wanted to give that gear a shield as it will be spinning pretty quickly. Most 166 robots have mechanisms that are VERY close to the drive transmissions so when we have to do maintenance on the robot, we aren’t slicing our hands on gears (2017 was scary).
Excellent catch! I’m working on another project and I guess I uploaded the wrong picture. I will update that now.
This looks good, I would run some simulations on your middle plate because it looks a fair amount overbuilt. With the webs being as wide as they are, you could probably bump the material thickness down to .1875 on the middle plate and maybe even .125 on the outermost plate. Also, rather than using bolts and washers to keep the shafts in, I would recommend retaining rings, they’re lighter and less likely to come out.
166 has always had problems with retaining rings (NCT 2020 Semi 1-1 is a prime example) so thats why I chose this method. The weight difference isn’t that much more with washers and bolts than retaining rings.
Noted!
Did the rings come off? And if so, would heavier duty ones work better? I ask because I use a lot of them in my designs.
A few items to consider.
The driven gear on the second stage hits the spacers.
The heads on the four screws that hold the output plate all interfere with the drive rail. This will require the drive rail to be drilled out in at these four locations. I recommend adding a section of 2x1 rail to visualize this.
The screw retaining the bearing on the output axle is hidden by the driven gear in the first stage. This could be a pain if you needed to access the screw. For example any maintenance on the output axle, sprockets or gear.
I like this gearbox a lot, and I had a few concerns which have already mostly been addressed.
I think this plate is quite unnecessary from every standpoint except the shield aspect, in which case could you just have a 3D printed cover that attaches by the motor mounting holes? You’d definitely want to move the bearing back to the 2nd 1/4” plate, but that’s not too much cantilever. If you don’t want to print it, you could also just add a thin polycarb plate there.
Note that this could also be mitigated by counterboring or chamfering those holes and using bolts to match.
I would get rid of the innermost plate and move the bearing to the middle plate if possible. Big weight savings and less likelihood of misalignment of the inner big gear causing wear problems could be had by reducing the lever arm by moving the bearing in.
EDIT: if you need the shielding, use a passive plexi shield, instead of adding a bearing and increasing complexity.
Is there a need/benefit of using the long spline shafts instead of the short ones?
The short spline shafts for Falcon’s are for VP’s. I don’t think it’s long enough to capture a pinion gear.
