pic: Finally Done!

[asid61]

Originally Posted by 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.

+1000. We are getting sidetracked. Any discussions about 3D printing might be kept to another thread. OP should do the research and decide that way if the teams wants to print.
Anyway, my post above asked a few questions about this gearbox.

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.

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?
Your final gear reduction looks like it can be reduced to a much smaller/better ratio. Top speed for a 4 cim drive shouldn't hit above 17-18fps if you want to optimize distance/time. OC it depends on the game, but it would be a very rare game that requires 20fps on four cims.

[Joey Milia]

Curious 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?

[cadandcookies]

Originally Posted by EricH

That's got me curious--what happened? Got any pictures (or videos)?

I'll see if I can find some pictures.

I wouldn't say it was anything specific more than the combination of many smaller issues compounded. We had a couple of Replicator 2's that we were just starting to get familiar with, and there wasn't a ton of experience designing for printing on the team then. We printed in the wrong orientation, broke a couple of plates trying to fit in gears, and once we had it all together it made sounds I hadn't heard come out of a gearbox before or since. I think it probably could have worked with some more effort (and experience), but when there's so many nice COTS options out there it just didn't seem to be worth the effort. In retrospect, I wouldn't necessarily say it was a bad idea, just that it wasn't nearly as good of an idea as we thought it was at the time.

We learned a ton about designing for printing from that gearbox though.

[Cory]

Originally Posted by asid61

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.

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.

[Bryce2471]

I 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.

[magnets]

Originally Posted by Cory

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.

A custom gearbox can be cheaper than an off the shelf gearbox, especially for a shifting one. Aluminum to make side plates and bearing blocks isn't that expensive.

[asid61]

Originally Posted by Cory

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.

Advantages:
-2.5lbs less total
-Extra bellypan space (especially with the smaller size this last year)
-Easy motor/gearbox removal (no need to pocket the bellypan as much to pull out the gearbox)
-Money. For a WCP gearbox it's $300 without cims. A non-COTS option with shifter shaft might be half that.
Maybe 254 doesn't need the space, but 115 would have absolutely adored a few extra square inches last year.

Disadvantages:
-Manufacturing time. If designed properly, this can be reduced to a couple hours on a mill early in the season. For our team, it's not a problem to quickly churn out a couple custom gearbox plates on our mill and machine 2x1 sides in a few days while the drivetrain is deisgned. Plus, we would have to wait a couple days for COTS gearboxes anyway, so instead we can just wait for shifter parts.

I open-source all of my designs, so it doesn't need to be redesigned each year. I'm remaking my 192 gearbox clone to be easier to machine and use COTS shifter parts right now.

However, any custom gearbox should be deisgned and tested pre-season. It's too dangerous for many teams to do otherwise.

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.

[Joey Milia]

Originally Posted by Cory

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).

For 192 I don't think the performance and space saving benefit of custom dt gearboxes is of much importance (it's mostly motivation and gives direction). The main benefit is the experience the students get when designing it. I think you learn a lot more from designing something like the DT than you do a lot of the other mechanisms of the robot. You have a lot more time to go through every detail and really think about how it's going to work and make every improvement possible. The skills our drive train team gain are also used in the rest of the robot resulting in a overall better robot.

I think the OP should, at the very least, make one gearbox as a prototype to test the design. He'll learn a lot more from seeing how his design performs.

Originally Posted by asid61

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.

IDK I think the hard bit is making it all work and figuring out all the tiny details

[Dr.Gusta]

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. 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.

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.
TLR Nicer form factor and it is what the team wants to do
3. 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.

[asid61]

Originally Posted by Dr.Gusta

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.
TLR Nicer form factor and it is what the team wants to do
3. 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.

Ah, that explains a lot. Thank you. You could move to 3/16" plate, but for bevel gears I'm not sure you can get a good fit on the side plates.

THAT BEVEL GEAR MOUNTING IS AMAZING!!! Tons of potential here. If you change the ratio of the bevel gears to 1:3 or 1:4 rather than 1:1, then you can eliminate the final stage of gearing. Then, because of the size of a 4:1 bevel gear, you can put the first set of shifting gears right next to the face of the big bevel gear and only require two plates. That would slim down the gearbox a ton and make the weight much lower. The width would increase though, but not by much. The output shaft could be a vex shifter shaft then too.

EDIT: sorry for being pushy, but I'm used to trying to optimize gearboxes. Many times when I see a team's bevel gear setup, they use 1:1 in favor of 1:3 or 1:4. Generally this is because the Vex bevel gears are 1:1, but in this case I don't see why not go for a larger ratio, as it would optimize many things.

[Joey Milia]

That 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

[RoboChair]

Originally Posted by asid61

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?

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.

[asid61]

Originally Posted by RoboChair

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.

4 cim versus 6 cim is a noticable difference at those speeds. 20fps is not too fast (I think 22fps is a good speed, but some swerves can move faster) but for 4 cims it is. The question is not only top speed, but acceleration too. 20fps will simply not move you to a spot faster than, say, 17fps with 4 cims, mostly for short distances. It would be nice to see a graph of different top speeds versus time for a given distance.

[Dr.Gusta]

I 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.

[RonnieS]

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