pic: 2 speed dogshifter

[Arefin Bari]

loading photo ...

[Alex Cormier]

nice work fin!
now give us the juicy details, ft/ps, torque...

are you going to try to get a little less weight out of it too? ya can shave a little off those plates and make some cheese in the same process. looks like you can also take down some of the sprocket for weight and less movement of the dog shifter. other then that it looks great and i hope to see it on a robot near you in the future.

[Arefin Bari]

High Speed - 12 feet per sec.
Low Speed - 3 feet per sec.

This transmission needs a bit of work. The gears are shaved off. Yes I can still take weights out of the plates, and I will. The sprocket is a 10 tooth sprocket. Yes the dog movement can be less which makes the transmission skinnier, better. Thanks for your input Alex.

[tiffany34990]

after 4 hours and being on the phone w/ me.. u did a pretty good job..

of course anything arefin did wrong now..he'll probably blame me since it's my fault for everything

great job.. keep up the good work as per usual...in some theory it works..now you can go make it

oh yeah i still have .625 memorized ha... i forget the other number u told me...

[sanddrag]

What are the output RPMs at the sprocket on the box? I see that you are gearing down quite a bit initially, but then gearing back up some in high gear. If your goal is to have a fast gearbox with a larger external sprocket and chain reduction, that is just fine. Many gearboxes are done this way. Personally, I like doing all the reduction in the box and going direct drive to the wheels.

As for weight in the plates, you might want to evaluate how much you will get out of them and how much work it will be. I know every last ounce helps, but since they are aluminum, you might not get much out of them at all. If you've got the machines and the time though, some nice CNC pockets could always make it look nice. I'm confident you can still get some weight out of those gear hubs, and instead of holes in the gears, you may want to look into facing them thinner in the center section (between the hubs and the teeth). You should be able to go down to 1/8" thickness safely. I'm guessing the weight savings will be comparable so it is more of a fabrication/style preference.

The shifting dog looks somewhat non-traditional. Is there a reason the "fingers" one one side are in line with the pockets on the other side? I can't support this with any calculations but to me it seems like it would be stronger if the fingers were inline.

Also, I'm curious as to how the dog gears are riding on the shaft. Are you using bearings? If so, what size? If not, are you using bushings or just riding them plain and greased?

Last, what are the tooth counts on all the gears?

[Arefin Bari]

High Gear max output RPM – 742.50
Low Gear max output RPM – 185.63

108’s 2003 transmission had all the reduction done inside and output was the wheel. We had a lot of problem with that transmission. It broke quite a few times, bent a lot of shafts. Let’s put it this way… we took apart and put together that transmission 16 times at Florida regional. Personally I don’t like to do inside reductions, because it gives me an option to put the transmission wherever I want on the chassis.

I am not worried about the weight. It’s 5 pounds, and I think I can kill 10 pounds on transmission out of 120 pounds. Yes, every ounce helps. Maybe I will shave the gears more, maybe will do some CNC on the plate. But that is after I know the transmission works perfectly.

I didn’t understand your question about the dog. If you were asking why it is not inline all the way, its because I left it out in the drawing so everyone could see what the dog looks like. In reality the dog will be engaged with the gear at all time while running.

No I am not using any bearings. I am doing it just like any other dog shifter where you have a pin that is moving the dog back and forth with the pneumatics.

Tooth counts:

Cim Motor – 12 tooth… meshes with 60 tooth gear… on the same shaft there is a 30 tooth…. Next shaft over (shifting) another 30 and a 60 tooth. output of the transmission there is a 10 tooth sprocket. Easy and simple.

[sanddrag]

Originally Posted by Arefin Bari

High Gear max output RPM – 742.50
Low Gear max output RPM – 185.63

108’s 2003 transmission had all the reduction done inside and output was the wheel. We had a lot of problem with that transmission. It broke quite a few times, bent a lot of shafts. Let’s put it this way… we took apart and put together that transmission 16 times at Florida regional. Personally I don’t like to do inside reductions, because it gives me an option to put the transmission wherever I want on the chassis.

I am not worried about the weights. It’s 5 pounds, and I think I can kill 10 pounds on transmission out of 120 pounds. Yes, every ounce helps. Maybe I shave the gears more, maybe will do some CNC on the plate. But that is after I know the transmission works perfectly.

I didn’t understand your question about the dog. If you were asking why it is not inline all the way, its because I left it out in the drawing so everyone could see what the dog looks like. In reality the dog will be engaged with the gear at all time while running.

No I am not using any bearings. I am doing it just like any other dog shifter where you have a pin that is moving the dog back and forth with the pneumatics.

Tooth counts:

Cim Motor – 12 tooth… meshes with 60 tooth gear… on the same shaft there is a 30 tooth…. Next shaft over (shifting) another 30 and a 60 tooth. output of the transmission there is a 10 tooth sprocket. Easy and simple.

First, I'm not quite sure I'm understanding your ratios. In high gear, is this the sequence 12T meshes with 60T that meshes with 30T and dog engages 30T to output shaft? If so, you are looking at a much higher output rpm than 742. More like 2120. If how I understand the setup is the way it actually is, the 60 tooth gear is merely a means of transferring power in high gear. It provides no reduction. To me, it looks like your high gear reduction is 30:12. If what I have said is true (and it might not be, I could just be really missing something, but I think it is) then I get 530 rpm for your low gear. Were the rpms you quoted after your external chain reduction?

That aside, I'd like to know a little bit more about the 2003 transmission. Do you have a picture of it? As far as direct drive goes, that is a very good point that without it you can put the transmission in many more places. Personally, I like to avoid the extra chain to tension, but it is all a matter of preference. There are benefits and detriments to both ways.

For weight, does the 5lb include motors? If so, that is excellent. Even if not, you are still doing okay. Our HexaMax gearbox was a beast 13lbs each (including the three motors).

For the shape of the dog (the shape of the actual green dog, not the position of it on the hex shaft), I'm curious as to why it is not something like in this picture http://www.team696.org/hexamax_ratios.jpg where the dog fingers/protrusions are timed to be inline. Back to back fingers and back to back pockets instead of finger back to pocket like you currently have.

Finally, I know how the actual dog shifting works (I designed/built one -- that was fun ) but my question was with regard to the gears with the dog pockets. They cannot be rigidly fixed to the shaft. They must have some provision to spin freely. In your design, what is that provision?

Looks good. Keep making progress and one day soon, hopefully you'll have a bunch of shiny new parts fresh out of the machine.

[JVN]

It is exciting to see someone post something that looks like it could actually be built.
Excellent job Arefin, you've come a loooong way!
It is apparent you've put some serious time in on this design.

Of course... now you know my advice for the next step.
Keep tweaking/tuning!

The shifter may need a little bit more work. As others have said, you may be able to get some more weight out of it; but making up a quick lightening pattern for a gear is something that can be done later.

Props, for making both gearbox plates identical (and also for accomplishing the entire design with only 3 different gear sizes!). Two plates, 2 shafts... simple and elegant. It shows you've put some thought into the design. (As opposed to some transmissions, which contain 20 different plates, some of which cannot be made outside of the magical world of "inventor").

If you tell me you've got a print-package made up, I may just wet myself.

Kudos,
Can't wait to see the next revision. (No, you're not done yet. You still have 4 months.)
-John

[Arefin Bari]

Originally Posted by sanddrag

First, I'm not quite sure I'm understanding your ratios. In high gear, is this the sequence 12T meshes with 60T that meshes with 30T and dog engages 30T to output shaft? If so, you are looking at a much higher output rpm than 742. More like 2120. If how I understand the setup is the way it actually is, the 60 tooth gear is merely a means of transferring power in high gear. It provides no reduction. To me, it looks like your high gear reduction is 30:12. If what I have said is true (and it might not be, I could just be really missing something, but I think it is) then I get 530 rpm for your low gear. Were the rpms you quoted after your external chain reduction?

That aside, I'd like to know a little bit more about the 2003 transmission. Do you have a picture of it? As far as direct drive goes, that is a very good point that without it you can put the transmission in many more places. Personally, I like to avoid the extra chain to tension, but it is all a matter of preference. There are benefits and detriments to both ways.

For weight, does the 5lb include motors? If so, that is excellent. Even if not, you are still doing okay. Our HexaMax gearbox was a beast 13lbs each (including the three motors).

For the shape of the dog (the shape of the actual green dog, not the position of it on the hex shaft), I'm curious as to why it is not something like in this picture http://www.team696.org/hexamax_ratios.jpg where the dog fingers/protrusions are timed to be inline. Back to back fingers and back to back pockets instead of finger back to pocket like you currently have.

Finally, I know how the actual dog shifting works (I designed/built one -- that was fun ) but my question was with regard to the gears with the dog pockets. They cannot be rigidly fixed to the shaft. They must have some provision to spin freely. In your design, what is that provision?

Looks good. Keep making progress and one day soon, hopefully you'll have a bunch of shiny new parts fresh out of the machine.

Let me give it a try one more time. On the cim motor output I put 12 tooth gear on. which meshes wtih the 60 tooth gear, as the same shaft as the 60 tooth gear there is a 30 tooth gear (1st shaft). Next shaft over (2nd shaft) I have another 30 and 60 tooth gear. the 60 meshes with 30 and the 30 meshes with the 60. The configuration shown in the picture is for a robot with 4" wheels (wheels would have a 24 tooth sprocket on it).

I don't remember the whole configuration of 2003 transmission by heart (its been a while). I don't even have any pictures either to share wtih you.

The transmission (without the motors) weighs 5 pounds.

I wanted to try something new. If you look at different transmission, every single dog doesn't look like team 696's dog shifter. There are a lot of other options and other way you can design it and still accomplish the same thing.

On the last shaft (where the shifting is taking place), the gears has pockets (yes it needs to be done with a CNC), the dog sits perfectly inside the pockets of the gears. The gear pockets and the dog is also a bit champfered so it engages better.

Thank you for you comments and suggestions.

Originally Posted by John V. Neun

It is exciting to see someone post something that looks like it could actually be built.
Excellent job Arefin, you've come a loooong way!
It is apparent you've put some serious time in on this design.

Of course... now you know my advice for the next step.
Keep tweaking/tuning!

The shifter may need a little bit more work. As others have said, you may be able to get some more weight out of it; but making up a quick lightening pattern for a gear is something that can be done later.

Props, for making both gearbox plates identical (and also for accomplishing the entire design with only 3 different gear sizes!). Two plates, 2 shafts... simple and elegant. It shows you've put some thought into the design. (As opposed to some transmissions, which contain 20 different plates, some of which cannot be made outside of the magical world of "inventor").

If you tell me you've got a print-package made up, I may just wet myself.

Kudos,
Can't wait to see the next revision. (No, you're not done yet. You still have 4 months.)
-John

I didn't want to make another post... so just editing this one.

The credits for this transmission goes to John V. Neun and Andy Baker, the two who taught me how to design a gearbox.

Yes John, the transmission needs a lot of work. But I had something to show to the community. I wanted input from everyone, so I could use them while modifying this.

I am not happy with this transmission just yet... V.2 is yet to come...

[JVN]

See attached spreadsheet.

I used the numbers Arefin gave, and just plugged them in quick for some speed estimates. Using a 4" dia wheel, with a 24 tooth sprocket (the 229-2005 layout - fairly average final gearing) I have this guy moving at ~13 fps & ~3 fps

You can plug in similar numbers, and see what you come up with.
Ary is dead on.

[Karthik]

Originally Posted by JVN

See attached spreadsheet.

I used the numbers Arefin gave, and just plugged them in quick for some speed estimates. Using a 4" dia wheel, with a 24 tooth sprocket (the 229-2005 layout - fairly average final gearing) I have this guy moving at ~13 fps & ~3 fps

You can plug in similar numbers, and see what you come up with.
Ary is dead on.

Isn't it great when the math works out?

I've seen the tendency among many young designers to just throw things together in Inventor, without doing any real calculations to see if they'll actually work. From this design, it's clear that Arefin has taken the time to do some calculations to ensure his design solution actually satisfied the constraints of his initial design requirements. I urge all of you designers who are learning the ropes to play around with John's spreadsheet and become familiar with it. It's an amazing tool that will help ensure a certain level of feasibility in your design. Plus, you'll see that math can actually be fun!

Arefin, congratulation on a well thought out and simple design. I can't wait to see what you come up with next.

[sanddrag]

I am 99% confident that I understand what is meshing with what in your transmission. What I'm not confident in is that you have calculated your ratios correctly.

As I see it, in high gear you have a 12:30 reduction with a 60 tooth gear that just so happens to be idling in the middle connecting the 12 and the 30. If this is not the case, please let me know as I'm curious to find out exactly what I'm not "getting." I think I know what I'm saying, but sometimes I get locked onto an idea only to look at it later and go "oh yeah, huh, I was wrong"

So for now, forget about the low speed side of the transmission. All I want to know is if high gear goes 12:60:30 (: represents mesh)

If this is true than your maximum free speed (no load, theoretical) will be somewhere around 2120 RPM in high gear (at the box, not after sprockets) depending on what free speed number you use for the Chia. With a 10:24 sprocket setup and a 4 inch wheel I calculate this will give you a 15.4 fps theoretical top speed, which might amount to something like 14.5 fps in real life which is good for a top speed. I just wanted to make sure we are both on the same page when it comes to the reduction/rpm calcs.

EDIT: I'd prefer not to work with any fancy spreadsheets for the purposes of my questions to you. I'd just like to see how you came up with the 742 rpm. Thanks.

[Bharat Nain]

First off Arefin, great job with the shifter.

You spend hours after hours on things like this and we all know positively that you are one of the great future engineers this world will have. Even though I am not great with transmissions - It is pretty obvious that this is not something ordinary and there is a lot of thought and effort put into this. Great job buddy and keep up the good work.

Originally Posted by sanddrag

EDIT: I'd prefer not to work with any fancy spreadsheets for the purposes of my questions to you. I'd just like to see how you came up with the 742 rpm. Thanks.

Even though I am not one of those students who understands the calculations and such of a gearbox fully, JVNs spreadsheet has helped me learn and understand how the mathematics of all this works. This spreadsheet has not only helped me but many other students on ChiefDelphi and outside. It's no "fancy" spreadsheet. Infact, it's a very efficient and effective spreadsheet. It would be greatly appreciated if you give second thoughts to what you say, to who and about who you say. Have some respect.

[JVN]

Originally Posted by sanddrag

I am 99% confident that I understand what is meshing with what in your transmission. What I'm not confident in is that you have calculated your ratios correctly.

As I see it, in high gear you have a 12:30 reduction with a 60 tooth gear that just so happens to be idling in the middle connecting the 12 and the 30. If this is not the case, please let me know as I'm curious to find out exactly what I'm not "getting." I think I know what I'm saying, but sometimes I get locked onto an idea only to look at it later and go "oh yeah, huh, I was wrong"

So for now, forget about the low speed side of the transmission. All I want to know is if high gear goes 12:60:30 (: represents mesh)

If this is true than your maximum free speed (no load, theoretical) will be somewhere around 2120 RPM in high gear (at the box, not after sprockets) depending on what free speed number you use for the Chia. With a 10:24 sprocket setup and a 4 inch wheel I calculate this will give you a 15.4 fps theoretical top speed, which might amount to something like 14.5 fps in real life which is good for a top speed. I just wanted to make sure we are both on the same page when it comes to the reduction/rpm calcs.

EDIT: I'd prefer not to work with any fancy spreadsheets for the purposes of my questions to you. I'd just like to see how you came up with the 742 rpm. Thanks.

Yes,
12:60:30
is the same as:
12:60
60:30
which is the same as:
12:30

Everyone is using the same math. Though for some reason, there seems to be an inordinate amount of communication confusion going on.
Your numbers are correct for the last gearbox shaft RPM...

Now multiply by 10/24 to account for one last chain reduction (not shown), then add an 81% speed constant (to approximate the speed losses of the real world) and you'll reach Arefin's numbers. He was citing the final output wheel RPM.

Everyone was right.
John

[Karthik]

Originally Posted by sanddrag

EDIT: I'd prefer not to work with any fancy spreadsheets for the purposes of my questions to you. I'd just like to see how you came up with the 742 rpm. Thanks.

From what I gather, here's how the 742 rpm was achieved.

Initial Reduction: 12:60 -- 0.2
Second Reduction: 60:30 -- 2.0
Sprocket Stage: 10:24 -- 0.083
Total Reduction = 0.2 x 2.0 x 0.083 = 0.167 (1/6)

Wheel RPM = Motor Free Speed * Reduction * Drivetrain Efficiency
= 5500 * (1/6) * 0.81
= 742.5 RPM

EDIT: Hognabbit, John beat me too it...