First time ever I attempted to design a gearbox just by myself. A mesh shifting two speed transmission. Still there are a few modifications to be made like move the motor inside the gearbox. Feel free to give any suggestions. thanks…
First time ever I attempted to design a gearbox just by myself. A mesh shifting two speed transmission. Still there are a few modifications to be made like move the motor inside the gearbox. Feel free to give any suggestions. thanks…
Looks good Arefin.
Now keep improving and between you and Greg Perkins, I believe we will have 2 great new transmission innovators in FIRST 
Hey Arefin,
It looks very good, I can tell you have worked hard in it and it would be interisting to see every modification that you make to improve it.
Good Luck 
Arefin nice job on the gear box. now how is inventor? just so proud of you. first you could not get inventor now you can, good job.
okay. awesome arefin. great job working with inventor.
now for the Critiquing…
i question the sheer size of this gearbox and the long skinny standoffs holding the plates together. the CIM is a 300 watt motor Perfectly capable of bending, breaking and shearing aluminum with its torque. secondly i suggest some machining to remove material from those gears, i say this not from a weight standpoint but rather from an inertial standpoint. a robot traveling in one direction at full throttle having to slam it into reverse or turn would benefit from less inerta in its gear train simply because its easier, more efficient and takes less time and energy to reverse the direction of a 4oz gear then an 16oz gear. the mass of your gears along with the skimpiness of your standoffs is a deadly combination. also removing the hubs making speed holes and using key ways, or if you don’t have a broach witch is most of us try using one of the various locktite products for binding rotational parts together. the stuff works great and it doesn’t take much work to use it. i would also suggest that instead of using the clevis’s for mounting the cylender i would suggest you drill a hole in your plate and use the threads of the cylender as a bolt and lock it on with some 5/8-18 nuts that would also then act like an extra standoff for you. On the happy side, i like how simple your shifting is. just slide the gear easy right? well, make shure you chamfer the edges of the gears that are meshing into each other to keep them from grinding when you shift. Well, thats my twoCents.
thanks everyone…
thanks tytus for your input… i will consider all of your suggestions. i did think about the sheering problem. but seems to be i solved it (Thanks to JVN). Also thanks to greg for giving me his inputs for this transmission… this is only version 1.1, this transmission will be modified a lot of times.
and tom… greg is way smarter than i am. i have to learn a lot to get there… 
Hey man, it looks great!
Arefin,
Have you considered the problem of the center gear grinding against the bottom gear? It seems to me that if you’re sliding two moving gears along each other, you could potentially have a problem with grinding of the teeth.
EDIT: I saw you referred to the “sheering problem”. Is this what you meant?
Yes jeff… thats exactly what i meant… thanks for your input…
So what did you do to solve said problem? I’m just curious.
Using 20 dp gears and space each shafts out with the pitch diameter also added another space of .003…
There is probably room in the gearbox to shift ratios so that the shifting gears are spinning faster with less torque. Specifically, increase the size of the CIM pinion, then increase the final stage ratio.
I assume this is all 20 pitch? As I’m sure you know, make sure to buy the strongest material that you can find the shifting gears in.
A good question that I can’t answer is wether extra backlash is a good idea for the shifting gears. More backlash means they will be able to shift faster (less friction, more time to do so), but more backlash also means they are slightly weaker. I’d guess a few thousandths extra is a good idea, but this is definitley a question to ask someone who has built a sliding gear shifting gear box.
Also, where are you purchasing that long gear in the final stage?
Spur gear stock… available from SDP-SI, McMaster, etc
Max, Thanks for your input… yes those are all 20 dp gears… but i am thinking about switching them to 16 dp gears. the shifter works fine. and thanks cory for answering the last question.
Edit - Also there will be holes in each gear just not to reduce weight but for what tytus pointed out (look at his post above). Each gear will be anodized.
EDIT- didnt want to post again… so here i go replying to alex from 469. yes i am considering what tytus has said. Also (if you see in the description of the picture) i am planning on moving the motor between the two plates. if i leave it like that i will sure mount it on the chassis somehow to make it stronger. thanks for your inputs.
Structurally, the position of the CIM motor just sticking out on a sheet of (I’m guessing) about 1/4 aluminum just seems like a hazard to me… but then again I have little engineering knowledge to judge this by. Also, as Tytus mentioned, I think the extra material from the gears needs to be removed and the pieces holding the plates together should be a little bit thicker.
Arefin, Great job on the drawing; it looks great!
_Alex
If your gears are steel, I don’t believe they can be anodized. And if they were aluminum, why would you anodize gears? It would add extra “thickness” on every anodized suface (not much but enough) which could cause a problem with teeth meshing. The only anodized gears I’ve ever seen are made from stock that is already anodized, then the gears are cut leaving a fresh precision surface for the teeth.
Perhaps you meant hardened?
yup … sorry for the confusion… i meant to say harden the aluminum gears…
If I’m looking at this right, it seems that in the transition period between high gear and low gear the motor shaft is locked, because both gears are engaged at the same time. Is this actually what is desired? It seems needlessly cruel to the motor, and I would think actually makes slipping into the new mesh more difficult.
By all means lighten the gears if it is easy for you to do, but I suspect that the inertia of those disks is negligable in comparison to the momentum of the 130 pound robot, or even just the wheel attatched to this gearbox.
Why aluminum and not steel? I’m always a fan of saving weight (aren’t we all) but I like to keep a bit of “beef” in areas prone to failure, or where I have seen failure before.
I don’t know enough to do the calculations, but if someone can mathematically convince me that aluminum 20P gears are suitable in a FIRST robot gearbox application (even say non-shifting), then I’ll run right out and by some.
But, because I can’t mathematically prove or disprove the success of aluminum gears, I always just opt for the safer side and go with steel, as do most teams I assume.
If someone has done an aluminum geartrain and it worked, I’d love to hear about it and see some pictures. If anyone thinks it will work, I’d love to see some calculations. I’m not by any means saying it does or will not work, I am saying I have no clue and would really like to find out.
You need to adjust the spacing on the shifting shaft. By the picture you posted, I can see that there needs to be more lateral play on the shaft. The current setup allows for both gears to be engaged at the same time. You need to have space so that one gear is fully disengaged before the other is engaged.