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Here is V.2 ... Made the pocket bigger for the dog shifter to fit better. Took some weights out (Gears and plates). Also made it thinner (modified the gears hubs, shorten the shafts). V.2 is 6.25" by 5.5" by 2" and weighs 4.5 pounds.
Discussion
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16-08-2005 15:51
Billfred
Re: pic: 2 Speed V.2
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Originally Posted by Tytus Gerrish
arefin, what did i tell you about square holes?
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(sorry, couldn't resist)
16-08-2005 15:52
Arefin Bari
Re: pic: 2 Speed V.2
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Originally Posted by Tytus Gerrish
arefin, what did i tell you about square holes?
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Anywho... I made the pocket bigger for the dog shifter to fit better. Took some weights out (Gears and plates). Also made it thinner (modified the gears hubs, shorten the shafts). V.2 is 6.25" by 5.5" by 2" and weighs 4.5 pounds.
16-08-2005 16:03
sanddrag
Re: pic: 2 Speed V.2
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Originally Posted by Tytus Gerrish
arefin, what did i tell you about square holes?
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Of course the easiest thing to do would be to just draw in a fillet and live with a filleted rectangular hole.
As for the lightening, I would recommend a pocketing pattern over a hole/cutout pattern. Even just .063-.090 of material left in the bottom of the pockets will add a lot of strength. Then you leave ribs of the full thickness. Sort of like this: http://www.chiefdelphi.com/forums/sh...ad.php?t=34384
This keeps a uniform plate with no holes (which I think looks nice) that will be stronger than one with holes, but a very close if not the same weight.
Of course, it is all up to you and while it will be stronger without through holes, in this application it probably makes very little difference, when I see transmissions like the AndyMark running .090 plate with no problems.
I'm still curious as to how those dog gears spin on their turned down (to round) portions of the hex shaft.
16-08-2005 16:10
Arefin Bari
Re: pic: 2 Speed V.2
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Originally Posted by sanddrag
I'm still curious as to how those dog gears spin on their turned down (to round) portions of the hex shaft.
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16-08-2005 16:13
JVN
Re: pic: 2 Speed V.2
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Originally Posted by Arefin Bari
If I am understanding what exactly you are curious about... those two dog gears (30, 60 tooth) are always spinning... When you engage the shifter in one of those gears... the hex shaft starts turning. (ofcourse the dog is always engaged either with the 30 tooth or the 60 tooth gear).
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Do you have something like that?
(I believe this is the question sanddrag has been asking...)
16-08-2005 16:16
Arefin Bari
Re: pic: 2 Speed V.2
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Originally Posted by JVN
Typically teams will put a bushing, or bearing inside those gears, to reduce friction. 229 used a bronze bushing.
Do you have something like that? (I believe this is the question sanddrag has been asking...) |
16-08-2005 18:47
Gdeaver
Re: pic: 2 Speed V.2
Looks good. Maybe while your in design mode you could add a take off on the output for an encoder or hall sensor. The output RPM is a little high. Might need a reduction for both. Could be done with plastic gears to keep the cost and weight down.
16-08-2005 18:57
Arefin Bari
Re: pic: 2 Speed V.2
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Originally Posted by Gdeaver
Looks good. Maybe while your in design mode you could add a take off on the output for an encoder or hall sensor. The output RPM is a little high. Might need a reduction for both. Could be done with plastic gears to keep the cost and weight down.
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Please read posts 6, 7, 8, 9, 10, 12, 14, 15 in this thread to get more specific specs on the transmission.
16-08-2005 21:34
Gdeaver
Re: pic: 2 Speed V.2
I was referring to a second output shaft to drive an encoder for autonomous mode. If only low gear was used for autonomous the 1 to 1 on the output shaft for the encoder would be OK. If high speed was used for autonomous, the interrupts per second could be a little high. If you do design in an encoder shaft there is some planning as to how fast the robot will go, the precision that is desired and the interrupt load that can be placed on the controller. If additional reduction is needed for the encoder shaft, then plastic gears could be used.
As for the high speed gearing, 13 fps is fast. It takes a very good driver to control the bot at that speed and may be unusable in a crowded obstructed playing field. It's main use is a mad dash to the end zone at the end of the game. The high gearing also affects the acceleration and responsiveness at the lower speeds most of the game is run at. They are all design choices. I personally go for about 10-11 max. This years kop gear box I believe was 8.3 fps and was very usable. Of course if the next game was all about mad dashes from one end to the other you would have that covered.
16-08-2005 21:45
Arefin Bari
Re: pic: 2 Speed V.2
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Originally Posted by Gdeaver
I was referring to a second output shaft to drive an encoder for autonomous mode. If only low gear was used for autonomous the 1 to 1 on the output shaft for the encoder would be OK. If high speed was used for autonomous, the interrupts per second could be a little high. If you do design in an encoder shaft there is some planning as to how fast the robot will go, the precision that is desired and the interrupt load that can be placed on the controller. If additional reduction is needed for the encoder shaft, then plastic gears could be used.
As for the high speed gearing, 13 fps is fast. It takes a very good driver to control the bot at that speed and may be unusable in a crowded obstructed playing field. It's main use is a mad dash to the end zone at the end of the game. The high gearing also affects the acceleration and responsiveness at the lower speeds most of the game is run at. They are all design choices. I personally go for about 10-11 max. This years kop gear box I believe was 8.3 fps and was very usable. Of course if the next game was all about mad dashes from one end to the other you would have that covered. |
17-08-2005 00:27
sanddrag
Re: pic: 2 Speed V.2
Edit, don't put too much analysis into this post. I forgot about crucial center to center distances. See my "fixed" recommendations on the next page of this thread in my next post
I'm thinking you could drop that 60T gear down to something like a 45T. This would keep your high gear ratio the same but increase your low gear rpm (decreas the ratio) and decrease the ratio between them making for a 3:1 difference.
I'm fairly confident that you could even fit a 40T in between the CIMs if you wanted to as long as you keep the axes of rotation of the CIMs and the 40T gear all in the same plane. (my rough calculation shows you should still be left with about .080 between the CIMs).
This would give you a 2.67:1 difference between high and low which I think is pretty much optimal. This would bring your low speed up to around 4.5-4.8 fps which I think is much more useful.
Have you determined that you must be geared for a low 3fps before you can slip the tires without tripping breakers? I'm thinking you can gear a little higher than that and not trip breakers and still slip the wheels.
17-08-2005 00:38
JVN
Re: pic: 2 Speed V.2
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Originally Posted by sanddrag
Have you determined that you must be geared for a low 3fps before you can slip the tires without tripping breakers? I'm thinking you can gear a little higher than that and not trip breakers and still slip the wheels.
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With 4 CIM motors, a 130lb robot and a coefficient of friction of 1.5...
I'd say you can be at around 6 ft/sec.
(I have run these numbers, once of twice before.)
17-08-2005 00:51
sanddrag
Re: pic: 2 Speed V.2
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Originally Posted by sanddrag
I'm thinking you could drop that 60T gear down to something like a 45T. This would keep your high gear ratio the same but increase your low gear rpm (decreas the ratio) and decrease the ratio between them making for a 3:1 difference.
I'm fairly confident that you could even fit a 40T in between the CIMs if you wanted to as long as you keep the axes of rotation of the CIMs and the 40T gear all in the same plane. (my rough calculation shows you should still be left with about .080 between the CIMs). This would give you a 2.67:1 difference between high and low which I think is pretty much optimal. This would bring your low speed up to around 4.5-4.8 fps which I think is much more useful. Have you determined that you must be geared for a low 3fps before you can slip the tires without tripping breakers? I'm thinking you can gear a little higher than that and not trip breakers and still slip the wheels. |
EDIT: Okay, some of the things in my above post are largely inaccurate due to you need the same center to center distances for high gear.
BUT, I have gotten it all worked out. I think you should do this.
Keep the 12T gears on the CIMs
Those are both in mesh with a 45T gear
The 45 tooth gear meshes with the existing 30T gear
This concludes the high gear lineup and you now have a 3.75" c-c distance between the shafts provided these are 20DP gears. Now for low gear:
On the same shaft as the 45 tooth gear is 25 tooth gear (replaces the 30T non-dog gear you currently have).
In mesh with the 25T gear is a 50t gear (replacing the 60T dog gear)
and you still have a c-c of 3.75 so everything is in mesh.
And that concludes the gearbox. If it isn't clear, I can draw it.
This will get you a smaller lighter setup with the same high speed and a better (faster) low speed. You will have a 3:1 ratio between high and low.
Another option would be to run a 40T gear initially (instead of the 45T I mentioned above) mating with the 12T gears and instead of the 25T gear mentioned above, drop that to a 20T. This will give you a 3.5" c-c distance and a 3.33:1 ratio between high and low.
Or with the 40T gear initially you can go 25:45 for low which will give you a 2.4:1 difference between high and low.
It is all up to you. But the three options I listed are lighter and smaller than what you currently have. Also a bit cheaper money wise.
In any case, I think 4:1 difference between high and low is too much.
17-08-2005 01:02
Andy Baker
Re: pic: 2 Speed V.2
Arefin,
You have come very far. This is stellar. You need to make a "portfolio", like an artist. Keep this up, and you will find yourself with a job of a designer for any number of companies. Someone should dig up the first design you posted on here and compare it with this. Talk about night and day.
Your gears look good. We've talked about the dogs over AIM. (I told him about allowing for some "play" between the dog and the pocket. Also, his pockets are overly deep at 0.3". They don't need to be more than 0.2" deep. Also, I would NOT use a chamfer - that would force the dog out of the pocket under load.)
At this point, there are plenty tweaks you can do. I prefer fastening screws into nuts as opposed to threading into aluminum, but that is just a preference. Put more creativity into your lightening holes, as your buddy Tytus does.
The point here is that Arefin has done a great job. This design could have detailed prints and could be made now. It may not be perfect, but it would be a working gearbox within 2 weeks.
I propose a toast, to Arefin Bari, a FIRST-rate gearbox designer.
Andy B.
17-08-2005 01:11
Cory
Re: pic: 2 Speed V.2
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Originally Posted by Gdeaver
As for the high speed gearing, 13 fps is fast. It takes a very good driver to control the bot at that speed and may be unusable in a crowded obstructed playing field. It's main use is a mad dash to the end zone at the end of the game.
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17-08-2005 01:20
sanddrag
Re: pic: 2 Speed V.2
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Originally Posted by Cory
robots have gone up to 18 or so before.
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Going this fast is a good idea though, especially in Triple Play when the far row can be stolen in a matter of seconds, and your home row can be stolen a few seconds later. If you have someone who can drive it (lots of practice and maybe some programming), I'd say definitely shoot for 14-15 fps. If you want to keep the whole field you're color, you need to be fast like the Cheesy Poofs. Just make sure the robot can still turn when you gear for these high speeds because it wouldn't make sense to race to the other side of the field and have to wast time downshifting because you cannot turn in high gear (turning in high gear - that's the part where the 5th and 6th motors come in
) or a well balance 6wd or omni wheels I guess.
17-08-2005 01:29
Arefin Bari
Re: pic: 2 Speed V.2
There will be a lot of tweaking on this transmission and in the next few days V.3 will be up. V.3 has been always been my lucky version. I am taking a few things into consideration. The dog shifter pin needs to be changed. The depth for the pockets for the gears on the output shaft needs to be .2" depth instead of .3". I am going to also check if I can take more weights out (on the side plates). Mounting holes for the chassis (which can be added when a chassis design is complete). I am going to run a long bolt through the hex stands and use a locknut to attach both plates (easy to do). I am going to also bring up my low speed (will try to achieve 6 fps). For the pneumatics, it would be just fine with 2 bolts instead of 4, so I am going to change that too.
I would like to thank Andy for discussing this design with me to make it better, Also John, for being there whenever I had a question. Thank you David (Sanddrag) for posting about how I can make this transmission better. Thank you everyone else for posting here and keep on inspiring me.
There will be a time when you will finally realize why do you crave for more and more from FIRST.
Stay tuned... V.3 is yet to come....
17-08-2005 01:58
sanddrag
Re: pic: 2 Speed V.2
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Originally Posted by Arefin Bari
Thank you Sanddrag for posting about how I can make this transmission better.
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Plus, transmission designing is a wonderful excuse to procrastinate on HW.
17-08-2005 02:26
NoodleKnight
Re: pic: 2 Speed V.2
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Originally Posted by sanddrag
Not at all a problem. We may have our differences but when it comes to transmissions, the world is united.
Plus, transmission designing is a wonderful excuse to procrastinate on HW. |
17-08-2005 09:45
tiffany34990
Re: pic: 2 Speed V.2
I agree w/ Andy now.. Arefin make sure you do keep everything organized. You need to have all your work in order...it'll help in the long run.. (lemme guess i should help you do that..b/c of yeah... )
keep on dreaming them up..like i've said the past few days...you keep dreaming and designing..i'll help you get into college..lol...
great job.. always proud of your achievements and work
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