Custom Gearboxes

[YCJeon772]

So our team has been thinking about designing custom gearboxes to achieve a fast high gear and strong low gear. How do teams create such fast/strong gearboxes? I tried playing around with the JVN calculator to see what I could get but couldn't get what we wanted.

[cadandcookies]

I'm not really sure what you mean by "we couldn't get what we wanted" out of the JVN calculator. Were you using the single speed or two speed tabs? Were you using all the tooth counts of gears that are available from FIRST vendors?

My typical process for drive train gearboxes is to determine what my design parameters are for the gearbox (shifting or no? max speed/min speed? certain time to distance requirements?), then playing around with JVN until I get a set of gear ratios that work.

I guess the main thing about the JVN calulator is that, like all calculators, it's only as good as what you put into it. It's not magic-- one of the often ignored parts of design is determining what exactly you want out of what you're designing. In my experience there hasn't been a single gearbox I've designed that the design wasn't at least in part simplified by the JVN calculator.

[YCJeon772]

When I said "we couldn't get what we wanted", I meant that we couldn't get a fast speed for high gear and a strong low gear. I was using the two speed tab, and yes, I was using the gears that Vex offered. We were hoping to get at least 13f/s for high gear, and a reduction of at least 10:1 gear ratio.

[Andrew Schreiber]

Originally Posted by YCJeon772

When I said "we couldn't get what we wanted", I meant that we couldn't get a fast speed for high gear and a strong low gear. I was using the two speed tab, and yes, I was using the gears that Vex offered. We were hoping to get at least 13f/s for high gear, and a reduction of at least 10:1 gear ratio.

What's driving these numbers? How do you know you want a 10:1 gear ratio? Wouldn't that depend on the wheel size a little bit? And what you're doing?

[YCJeon772]

Well we just want a general gearbox that would have a fast high gear and a strong low gear, and we use 4 inch wheels.

[Andrew Schreiber]

Originally Posted by YCJeon772

Well we just want a general gearbox that would have a fast high gear and a strong low gear, and we use 4 inch wheels.

So, why build your own? That sounds like a pretty cut and dry use of COTS components? For example http://www.wcproducts.net/wcp-shifter-3cim/ (scroll down to the charts for the speeds) has several options that meet your needs.

I'm not saying don't go custom, just saying that you might want to look at options and see what concepts you can steal.

[YCJeon772]

I think it would be nice to learn making custom gearboxes. If it doesn't work, we could always buy them. And I never knew that site that you gave me existed, so I didn't know if there was something like that.

[cadandcookies]

Originally Posted by Andrew Schreiber

So, why build your own? That sounds like a pretty cut and dry use of COTS components? For example http://www.wcproducts.net/wcp-shifter-3cim/ (scroll down to the charts for the speeds) has several options that meet your needs.

I'm not saying don't go custom, just saying that you might want to look at options and see what concepts you can steal.

As they say, steal from the best, invent the rest. I'd agree that looking at COTS options and borrowing their ratios is probably the best option for you. You might also want to be a bit more flexible with your design-- if you're designing for a certain speed and ratio, you might need to be flexible with your wheel size, for example.

[Oblarg]

Originally Posted by cadandcookies

As they say, steal from the best, invent the rest. I'd agree that looking at COTS options and borrowing their ratios is probably the best option for you.

You could even take it a step further and borrow the entire COTS design, and simply make whatever modifications to the plates and gear setups you deem necessary to get what you want out of it. There's no shame in copy-pasting stuff from a published CAD in FIRST

Originally Posted by PingPongPerson

stoichiometry to get from CIM RPM [5000ish] to feet per second

I don't think that's the word you wanted...

[PingPongPerson]

You are not calculating reactant amounts, but the process is the same

[Tristan Lall]

Originally Posted by PingPongPerson

You are not calculating reactant amounts, but the process is the same

In both situations, the process is called dimensional analysis.

[asid61]

Originally Posted by Tristan Lall

In both situations, the process is called dimensional analysis.

We should probably calm down. Ask yourself: does it matter? Why am I arguing?

Generally, when doing actual speed calculations you should use a good calculator like the JVN one. I can't comment on it's accuracy, but at least it provides a general estimate of what to expect with the tread you are using.

[Oblarg]

Originally Posted by Tristan Lall

In both situations, the process is called dimensional analysis.

Well, I hope you're not calculating your robot speed strictly by dimensional analysis, because on these scales a factor of, say, 2pi is important.

[asid61]

Originally Posted by cadandcookies

I'm not really sure what you mean by "we couldn't get what we wanted" out of the JVN calculator. Were you using the single speed or two speed tabs? Were you using all the tooth counts of gears that are available from FIRST vendors?

My typical process for drive train gearboxes is to determine what my design parameters are for the gearbox (shifting or no? max speed/min speed? certain time to distance requirements?), then playing around with JVN until I get a set of gear ratios that work.

I guess the main thing about the JVN calulator is that, like all calculators, it's only as good as what you put into it. It's not magic-- one of the often ignored parts of design is determining what exactly you want out of what you're designing. In my experience there hasn't been a single gearbox I've designed that the design wasn't at least in part simplified by the JVN calculator.

Actually, I've alwasy been confused about something in the JVN calc: it lists the draw at maximum output load, but is that the normal drive load or pushing match load?

[mman1506]

WCP's drivetrain calculator gives a more in depth analysis than the JVN calculator. http://www.wcproducts.net/how-to-drivetrain/