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This has been quite a project but it is finally done. It is a modified VEX ball shifter with a bevel drive.
Calculations done with a 4in wheel
High: 20fps (Predicted)
Low: 9fps (Predicted)
We know that 20fps is a little fast but it was the best we could figure out without rethinking the whole gearbox. Our idea was to just put a software limit if it is too fast but we will have to see how fast it actually goes. It is going into a custom drive base that we are still working on. We will be manufacturing one as soon as our grant money is put in our account and our mill is up and running!
30-11-2014 01:31
JorgeReyesI think it might be a smart idea to 3D print the side plates, that way you don't have to use all your grant money machining something that might not work
30-11-2014 01:36
Jacob Bendicksen|
I think it might be a smart idea to 3D print the side plates, that way you don't have to use all your grant money machining something that might not work
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30-11-2014 01:49
EricH
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I think it might be a smart idea to 3D print the side plates, that way you don't have to use all your grant money machining something that might not work
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30-11-2014 04:54
asid61|
I think it might be a smart idea to 3D print the side plates, that way you don't have to use all your grant money machining something that might not work
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30-11-2014 12:10
75vs1885I like the idea of 3-D printing the plates. I don't know why everybody is so against it, last year we (1885) used 3D printed parts to join an axle for our intake, it worked very well and only "broke" when we didn't check it and a shaft collar was loose. Then the axle would fall off and we would have tighten the collar up again.
Just use a high quality plastic and use a dense pattern while printing AND MAKE EXTRA'S!!!!! Better to get into 3D printing now while it is still being developed heavily, we all know it will only become more and more common, so this is a great foundation to build off of in the future.
30-11-2014 12:24
EricH
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I like the idea of 3-D printing the plates. I don't know why everybody is so against it, last year we (1885) used 3D printed parts to join an axle for our intake, it worked very well and only "broke" when we didn't check it and a shaft collar was loose.
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30-11-2014 12:30
Jared|
I like the idea of 3-D printing the plates. I don't know why everybody is so against it, last year we (1885) used 3D printed parts to join an axle for our intake, it worked very well and only "broke" when we didn't check it and a shaft collar was loose. Then the axle would fall off and we would have tighten the collar up again.
Just use a high quality plastic and use a dense pattern while printing AND MAKE EXTRA'S!!!!! Better to get into 3D printing now while it is still being developed heavily, we all know it will only become more and more common, so this is a great foundation to build off of in the future. |
30-11-2014 12:43
TungrusUsing 3D printed plates instead of metal is somewhat like using zip tie instead of steel wire. Zip tie is nice, you can quickly fasten most things and reasonably strong, but if some applications will have so much dynamic forces they will just get ripped.
Using 3D parts for lighter loads as in to feed a ball is different than gear box or any structural parts in a drive system.
May be just for prototyping and quick test it may be ok, but for competition robot... its not just worth the risk.
30-11-2014 12:54
cadandcookiesI like the gearbox-- it looks like some nice work. I'll add my voice to the people that would recommend against printing this for actual use on a robot-- I think the others have done a pretty good job of explaining why that's a bad idea. I can say firmly from experience that it isn't nearly as good an idea as it first seems.
That being said, printing certainly has its place in the design of an all-metal gearbox if you want it to. Last year I had a decent amount of success doing a high shell count and drilling/reaming essential holes, and it's always nice to test the geometry in practice as well. With a little bit of adjustment and a small amount of work, you could probably do a manually powered version to print and test before you made a metal version. I'm not entirely sure how beneficial that would be, but it would certainly be cool/interesting to show off.
30-11-2014 12:58
Joe G.
Alternatively, you mention that you're getting an inhouse mill in your first post. Do pre-season testing on a variant without all the fancy lightening and contouring, and then use your external resources and funds to do the full, lightened version for the season.
30-11-2014 13:01
EricH
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I can say firmly from experience that it isn't nearly as good an idea as it first seems.
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30-11-2014 14:23
Cory
This argument shouldn't be about why to 3D print/not 3D print...it should be about why this design is a good use of resources to make at all.
30-11-2014 14:38
Jared|
This argument shouldn't be about why to 3D print/not 3D print...it should be about why this design is a good use of resources to make at all.
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30-11-2014 14:57
Ether
30-11-2014 15:14
asid61|
This argument shouldn't be about why to 3D print/not 3D print...it should be about why this design is a good use of resources to make at all.
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30-11-2014 15:49
Joey MiliaCurious about the questions above.
And,
How you're dealing with the thrust loads from the bevel gear and pinion? If they gear isn't supported with thrust bearings you'll probably destroy the radial bearings you're using.
The cim shafts can move a bit in and out, do you have a way of making sure the pinion is in the correct place?
30-11-2014 15:53
cadandcookies|
That's got me curious--what happened? Got any pictures (or videos)?
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30-11-2014 16:03
Cory
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EDIT: The questions from ym last post: 1. What is the final weight of this gearbox without motors? 2. What is your reasoning for going with a bevel gear setup? 3. What advantages does this design hold over 192's gearbox design from 2014? I still haven't seen a shifting gearbox design that beats theirs in terms of weight or size. |
30-11-2014 16:28
Bryce2471I could vary well be biased, but tend to think that building something unique and ambitious in the off season is almost always a good idea.
Some reasons:
Building something unique tends to get students excited about off season work.
Building something ambitious will force to team to expand their resources.
The experience wI'll improve students' CAD and machining skills.
There is very little risk of failure.
30-11-2014 16:28
magnets|
There are so many better obstacles for most teams to tackle than making custom gearboxes. If 254 were starting a new team right now, I highly doubt we would make custom gearboxes. Maybe custom sideplates to get the right ratio, but that's about it. The stuff that's out there now is so high quality that if you have any question about your ability to solve every other aspect of the game challenge, you really shouldn't be going custom. |
30-11-2014 18:10
asid61|
I'm not trying to denigrate what 192 did last year, because they made a gorgeous, highly functional gearbox, but it should also be asked "what advantage does 192's gearbox design hold over a COTS or modified COTS solution?"
Moving the motors out of the way isn't a good enough reason for most teams, IMO. What is all that extra work and potential compromise of reliability really buying you? An extra 8" in the interior of your robot that you probably don't really need anyways? 192 had the benefit of doing something similar (with worm gears) to OP's design in 2012. They didn't do it again after that. They have at least 4 revs of their 2014 gearbox (as I recall they made 2 prototypes in the 2012 offseason, plus the 2013 gearbox, then the 2014 gearbox). There are so many better obstacles for most teams to tackle than making custom gearboxes. If 254 were starting a new team right now, I highly doubt we would make custom gearboxes. Maybe custom sideplates to get the right ratio, but that's about it. The stuff that's out there now is so high quality that if you have any question about your ability to solve every other aspect of the game challenge, you really shouldn't be going custom. |
30-11-2014 18:36
Joey Milia|
I'm not trying to denigrate what 192 did last year, because they made a gorgeous, highly functional gearbox, but it should also be asked "what advantage does 192's gearbox design hold over a COTS or modified COTS solution?"
Moving the motors out of the way isn't a good enough reason for most teams, IMO. What is all that extra work and potential compromise of reliability really buying you? An extra 8" in the interior of your robot that you probably don't really need anyways? 192 had the benefit of doing something similar (with worm gears) to OP's design in 2012. They didn't do it again after that. They have at least 4 revs of their 2014 gearbox (as I recall they made 2 prototypes in the 2012 offseason, plus the 2013 gearbox, then the 2014 gearbox). |
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While 192 made several revisions, it is relatively easy to copy their design because they've done all the hard work in the basic design. The hardest part of a design IMO is coming up with the overall design first. After that, it all falls into place in CAD.
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30-11-2014 19:26
Dr.GustaWas gone for most of the day today after posting this last night and was very shocked to see how popular this was. I am first going to 3D printing, all of that discussion was all for not because my team does not even have access to 3D printing and would be cheaper to mill one in house then to pay to have one printed. Now to asid61's questions
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1. What is the final weight of this gearbox without motors? 2. What is your reasoning for going with a bevel gear setup? 3. What advantages does this design hold over 192's gearbox design from 2014? I still haven't seen a shifting gearbox design that beats theirs in terms of weight or size. |
R Nicer form factor and it is what the team wants to do
30-11-2014 19:39
asid61|
Was gone for most of the day today after posting this last night and was very shocked to see how popular this was. I am first going to 3D printing, all of that discussion was all for not because my team does not even have access to 3D printing and would be cheaper to mill one in house then to pay to have one printed. Now to asid61's questions
1. I currently do not know how to calculate weight in Inventor but I am sure after a quick google search I will figure it out and get back to you on that one. The plates are 0.25" alum if that helps. 2. We mount our electronics on the belly pan of our robot and constantly ran into issues because the motors were in the way. Also I started this team last year and a vast majority of the team is graduating this year including me. We are working to get a permanent workspace, machinery, etc. so we can establish a program that continues after the founding members leave. We want to create a robot this year that will set a standard for members that follow us that we strive for creativity (bevel drive) and quality custom. I know this can be done in an off season project, too much risk, etc but in the end it is our team and this is what the team wanted to do and that is what it comes down too. I know there are many reasons not to do it but think of what we will learn doing this! In the end it is not about a robot but what has been learned during the process of building the robot. TL R Nicer form factor and it is what the team wants to do3. It does not, that is a BEAUTIFUL gearbox but it is not ours and this is the design fits much nicer in a drive base and works for us. As for our issues with gear ratios what really stopped us from gearing it further down was I thought that 9fps was way to slow already but after being told that is pretty fast and we will have breaker trip issues I will play with the ratios more. I will shoot for 16fps High and 5fps Low. Also here is a link to a better picture of the bevel gear setup should answer some of your questions. The bevel on the CIM is bored and keyed for the CIM then just slides on but a retaining ring will be added but no thrust bearing. The other bevel has a bearing on its 0.75" hub but also has a 3/8" hex shaft that goes through its bore to the rest of the gears. Both don't have thrust bearings. Hope that all makes sense http://i.imgur.com/Vbxs3Sb.jpg There was a lot of questions and comments and I tried to cover them all but what I really want to hit on again is that this is what the team decided as best and we will be making one during the off season using in house CNC equipment. Please let me know if you have any more questions or comments. EDIT: The bevel gears are also lined up exactly to the manufacturer's specifications so they should mesh perfectly and are made of steel. |
30-11-2014 20:15
Joey MiliaThat looks pretty good, with the miter gears being in the first stage I'm not to worried about the thrust loads. However that also means high speed so wear is a big concern.
If you can get your gears from martin sprocket instead of Boston gear, should be the same specs but the former are case hardened (may have been doing this already).
I would also make sure the gear on the cim won't move, it may be fine how you have it but just a possible concern.
Can't wait to see it running 
30-11-2014 20:50
RoboChair|
20fps is too fast. You can limit the top speed in software for the driver, but your acceleration will be very poor with only 4 cims. Seeing as you are running bevel gears, would it be possible to add a 3rd cim sticking stright up?
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30-11-2014 21:11
asid61|
I would not say 20 fps is too fast.
1678 geared our drive for a theoretical 22/8fps high/low. We measured our top speed at about 18fps on our practice field. It was very fast and I will admit we ran a 6 CIM drive train. It should be said that each gear ratio should be tested under load to find it's ACTUAL output speed. But at this gearing and motor to speed ratio you are unlikely to hit the max potential of the CIMs, you will be accelerating for a large portion of if not all of the distance of the field. It takes us about 1/3rd of the field to get moving at full speed with 2 horsepower backing our drive train. |
30-11-2014 22:41
Dr.GustaI just finished re gearing the 3rd stage and it now has a predicted 17.10fps High and 7.54fps Low. I like the idea of adding some reduction in the bevel gear but the whole box was designed around those gears. I would have to pretty much start from scratch in order to do that. Thank you for all the encouraging words.
01-12-2014 07:39
RonnieSFrom this render I can't see but did you in-close the side plate where there was a gap previously to allow access to the bolt for cim? I have been meaning to send you my cad on it, just been super busy.
-Ronnie
01-12-2014 10:44
Dr.Gusta|
From this render I can't see but did you in-close the side plate where there was a gap previously to allow access to the bolt for cim? I have been meaning to send you my cad on it, just been super busy.
-Ronnie |