In an effort to create a design that my team would actually make, I tried to use all COT’s parts with the obvious exceptions of the standoffs I used and the front and back plates.
All questions and comments are very welcome!
Standoffs or spacers can also be COTS. Check out mcmaster.
What does the output shaft go to? It’s too short for a WCD.
Edit: also, you need a way to mount it
Edit2: oh this is your first gearbox. This is really good then. Good job!
Congratulations on a terrific first gearbox design. It’s oders of magnitude better than my first attempt at a gearbox.
Here’s a few notes/questions:
How do you plan to get power from the output shaft of the gearbox to the wheels?
Do you have access to both of the mounting bolts on the 775s without removing the center gear?
If this is your team’s first custom gearbox, I might recommend using CIMs over 775s, just because they are more of a known quantity in the drivetrain, and there is more margin for error.
I agree, it looks great, especially for a first try!
Here’s a general question this render raises for me: The 775pro requires vents in the mounting plate (or standoffs between the motor and the plate, which leads to mechanical problems). Is it a problem that half of those vents are mostly blocked by the large cluster gear? Is there a recommended clearance distance between this gear and the motor plate?
I’m guessing – guessing – that it isn’t critical, because most of the heat in a motor is generated at the armature, which will rotate past the one open vent every rotation, so the whole motor will be cooled by airflow in any case.
This isn’t a problem at all. Those holes provide more than enough ventilation for the motors especially when you compare the airflow to things like the versaplanetary mounting plates for them.
Simple question for everyone. Where do you get the gears to fit the 775 pro shaft? Are they press fit on? i found some on servo sites and amazon but was not sure if anyone has a go to source. Actually the larger steel gears seemed harder to locate.
Available here:
http://www.wcproducts.net/32-dp-gears
We are getting more inventory in about 2 months. Sometime around October - November we’ll have steel versions of the 60/80/100T so teams can use those sizes in drivetrain. Would not recommend the aluminum versions in drivetrain.
I recommend these gears. Thanks, R.C., for letting us know when you expect to have them back in stock.
It is also possible to make pinions from pinion rod – which is hard to find in stock now as well. As R.C. noted, carbon steel is the way to go.
I’ll agree this is a nice gearbox, especially for your first time designing a gearbox. I’ll echo a some suggestions and add a few of my own.
Other than those few things, it looks good. If you release your CAD (GrabCAD is a good resource for this), we can take a closer look and give you even more tips.
The backs of the motors don’t need to be supported.
Fair enough. You have more experience with them than I do.
Would you agree about the extra support by the air vents, or am I being overly-conservative? It wouldn’t be the first time.
First off, thank you all for your suggestions. I’ve been roaming around on this forum for 4 years and I was still surprised to come back to so many comments so quickly.
In response to Chak: I didn’t think to go look at McMaster Carr for standoffs. The team personally has a lathe which can be used and is used for most of our standoff and spacer needs. When I said I was trying to design by using COTs parts, I was more doing that so this doesn’t take up any extra time on our mills because those are always running slower than drawings are generated.
And to everybody else: In my excitement of actually creating a gearbox that looked like it might be feasible, I may have forgotten about needing to mount or get power from the thing:p It’s hard to see in the render, but there are bolt holes towards the bottom that currently would work to bolt the gearbox to a 2x1. I’ll move the holes an inch lower and it’ll work even better.
And yes, I do need to make the output shaft longer. It’s not very useful so short. I’m currently using the “ShortBallShifter” so I can switch to the long one and see if that fixes the problem.
Why would you run the motors at only 80% the available voltage? Am I missing something?
1.Yup, I’m going to move the mounting holes I have currently, down a bit so they work better.
2.See above.
3.This is one that I saw myself. I’m not positive on if we have anything smaller than 0.25 mill bits if we were to make the plates inhouse then it’d be a pain to cut slots smaller than that. If we send these plates out to a machine shop, then I’ll definitely make the slots(arc?) fit closer to the holes in the motors.
4.I’m not familiar with that term, but I’m assuming that you are referring to the middle shaft. It’s a hex shaft with the ends rounded and stuck through round bearings so that it’s trapped without the need for fasteners.
And I’ll see about sharing the CAD. I’m using fusion 360 so I’ll figure out how to share.
I’m not very well versed in how the electrical side of the robot works, but isn’t it true that if less voltage is applied to a motor, it can last longer being stalled out without burning up? Am I right in this or have I confused myself?
Assuming that the above is true, I wanted to run the motors are a lower power so that if we were to be in high-gear and stall out the motors, there’d be more than the 4-5 seconds before we toasted the drive motors. Something a little longer so the driver would have time to notice what’s going on and either shift into low (which is traction limited) or just generally fix the problem.
Here is the link the view the updated CAD for anybody that is interested:
Again, any and all comments are welcome.
It looks great! I’m really not seeing anything else that needs attention. I do have a couple remaining questions of you and the rest of the people reading this thread though.
For you:
How do you plan to transfer power from the output shaft of the gearbox to the non direct driven wheels?
For everyone:
Would you trust the two piece output shaft of the Vex ball shifter to support a direct driven wheel? What about a cantilevered wheel? I’m curious to hear what people think about this, because it is one of the main reasons I have avoided designing the Vex output shaft into WCD gearboxes.
What our team has done in the past is either put pulleys on the output shaft and run belts to the wheels, or direct drive one wheel with that shaft and just belt the remaining wheels together. That was my current plan for how to use this but it really depends on what next year’s design calls for.
