Offseason 2012 chassis

[Nick Lawrence]

Originally Posted by MattC9

Really? Witch team used them?

Yeah, they powered our drivetrain.

We had a secondary sprocket reduction from the gearbox to the wheels though, to make our drivetrain have a theoretical top speed of 11.14 fps.

-Nick

[akoscielski3]

We used CIMple boxes this year for Maccanums ... but they dont have enough torque to turn the wheels for straifing (spelled that wrong). And i believe it would be alot better if you had more torque over speed, because if a team gets in your way it would be easy to push through them, unlike if you only have speed, then you can't.

And Nick did you use 1 transmission per side or 1 per wheel??

I dont beleive we will use CIMple boxes for drive again, but instead use 2-speed Gen 2's, then we have speed or torque depending on what we need

[Chris is me]

It's not a matter of what gearbox you use. It's a matter of what gear ratio you use and what kind of drivetrain you use. You can't just say "CIMple Boxes are bad" when one of you is talking about an 8 inch mecanum drive and another person is talking about a chain-reduced 4" 6WD.

The CIMple Box is a good gearbox for people not interested in direct driving wheels. It packs a lot of reduction into a single gear stage so that you can "finish the job" with your chain reduction.

[akoscielski3]

Originally Posted by Chris is me

It's not a matter of what gearbox you use. It's a matter of what gear ratio you use and what kind of drivetrain you use. You can't just say "CIMple Boxes are bad" when one of you is talking about an 8 inch mecanum drive and another person is talking about a chain-reduced 4" 6WD.

Im not saying that CIMple boxes are bad, i'm just saying that they weren't good enough for maccanum drive. They need more torque for what we were using them for (it was just our fault for picking the transmissions)

[Andrew Schreiber]

Originally Posted by akoscielski3

Im not saying that CIMple boxes are bad, i'm just saying that they weren't good enough for maccanum drive. They need more torque for what we were using them for (it was just our fault for picking the transmissions)

Did you have an additional reduction after the Cimple Box? Were you using 6" or 8" Mecanums?

[akoscielski3]

Originally Posted by Andrew Schreiber

Did you have an additional reduction after the Cimple Box? Were you using 6" or 8" Mecanums?

unfortunatly we were direct driving them. this was the first year we tried maccanums, we never even tested with them before. And we were using 6". Another team in Pittsburgh was using 8" Maccanums and they could do everythign fine :$

[Andrew Schreiber]

Originally Posted by akoscielski3

unfortunatly we were direct driving them. this was the first year we tried maccanums, we never even tested with them before. And we were using 6". Another team in Pittsburgh was using 8" Maccanums and they could do everythign fine :$

This... is why we do the math.

[Thad House]

Does anyone know a good gear ratio for speed and 6 inch wheels. i would like to know what kind of reduction i would need in the chain, or if i should just move to toughbox mini's and reduce the ration inside of them to get more speed.

[thefro526]

Originally Posted by sst.thad

Does anyone know a good gear ratio for speed and 6 inch wheels. i would like to know what kind of reduction i would need in the chain, or if i should just move to toughbox mini's and reduce the ration inside of them to get more speed.

What's speed are you aiming for?

816 ran TB's (Tough Boxes) with 6" wheels from '08-'10 with a 25:22 reduction (25 tooth sprocket on trans, 22 tooth on wheel) and it worked well for us. Floor speed was somewhere around 11/12 fps.

[BrendanB]

Originally Posted by thefro526

What's speed are you aiming for?

816 ran TB's with 6" wheels from '08-'10 with a 25:22 reduction (25 tooth sprocket on trans, 22 tooth on wheel) and it worked well for us. Floor speed was somewhere around 11/12 fps.

What type of trans were you using in these years?

[Brandon Holley]

When you are reflecting on a failed design it is important to not get caught up in incorrect interpretations of that design.

For instance, the fact that one team was using 8" mechanums successfully vs. your 6" mechanums is really irrelevant. I think you understand this already but I just want to drive the point home. The size of your wheels is irrelevant to other teams designs. Your wheels must fit with your design like everything else does.

It appears you are looking to use off the shelf components for much of the geartrain of your drive system. That is a great start, many teams find success using tried and true off the shelf components. It does limit some of your choices however. Make sure you are analyzing what kind of speeds and torques your drivetrain will put out when you design your system. Instead of thinking in terms of "I want 6" wheels, directly driven off of toughboxes", think in terms of "I want a DT that can move at XX feet/second". Pick a starting point and start to design towards that.

For instance, assume your target is 10 feet/second. You can start your feasibility analysis at a very broad level and begin to focus it down to what fits for your team. I suggest doing this:

-The first would be to forget what exists already and determine what theoretical gear/sprocket/belt ratios can get you to your speed. A quick rule of thumb is not exceeding a 4:1 reduction in a gear set (this is due to the torque increase over that reduction and the yielding of gear teeth in that application). Don't worry about part numbers or specifics just yet, just determine what combinations would work to get you there.
-Next, start to look at if using an off the shelf gearbox can help save you design and manufacturing resources (if this is important to your team, which it should be.) See if with that rule of thumb an off the shelf gearbox can get you to where you need to be. It's important to note that you need to constantly be evaluating your design criteria. In your findings you may discover that using an off the shelf gearbox you can get to 11 ft/s very easily. You have to ask yourself in that situation is 10 ft/s an absolute must have? What if you purchase/make different wheels? What if you add an intermediate reduction? There are so many variables you can play with, you just need to keep working towards what works best for your team.
An example: Our team is fortunate enough to have a great deal of manufacturing resources at our disposal. We’ve made many custom gearboxes and fully custom drive trains so we are comfortable doing so. However, one Achilles heel for us is wheels. We’ve made our own wheels many times and they were successful but they ate up a great deal of our resources. A lesson we have learned is to design around off the shelf wheels. We can tailor the gearbox and other components to make certain wheels work, so we use that as a design constraint to start nailing down the overall drive design.

I think you are off to a great start. Just thinking about your future designs is more than most teams do so you are doing a good job! If you have any other issues or questions feel free to ask them here. Just about everyone provides some form of constructive criticism so keep firing away!


-Brando
(sorry for the long winded response, I guess I'm just passionate about the design process)

[Madison]

Originally Posted by Brandon Holley

-Brando
(sorry for the long winded response, I guess I'm just passionate about the design process)

Half a page is hardly long-winded and entirely what these forums are missing. Nearly everything else in this thread is pointless.

What we have here -- and what we often see on CD -- are pretty pictures with nothing substantive to offer. This thread is, so far, much of the same.

We see a bit of the criteria used in driving this design -- a desire to minimize machining time and to use COTS components. That's a great start. What's missing, though, are other goals and constraints -- speed, weight, cost, etc. Without first establishing those constraints, there's very little "process" going on and so, in my mind, there's not too much to discuss.

The next step is to fill in some of the broadly sketched strokes that take you from ideation to design. The wheels use purchased pillow blocks -- from what supplier? What do they look like? How are they fixed to the chassis?
How is the chain tensioned? How do you run chain to the outer wheelsets?

These things don't happen magically. This is where real design happens most of the time, it's the most interesting thing to discuss and it's the thing we see least here on CD these days.

Sorry to be Ms. Cranky Pants, but I've been waiting for awhile to see someone take the next step and offer real information describing how their pretty pictures came to be.

[Aren_Hill]

Originally Posted by akoscielski3

Im not saying that CIMple boxes are bad, i'm just saying that they weren't good enough for maccanum drive. They need more torque for what we were using them for (it was just our fault for picking the transmissions)

If you properly designed it they would be part of a geartrain that had plenty of torque for a Mecanum drive, your wording of "weren't good enough" blames the gearboxes, not the person that improperly used them. I apologize if I sound harsh but you need to go some research.

I suggest you go look at JVN's mechanical design calculator and learn how many options there truly are ratio wise between a motor and wheel.

[Nick Lawrence]

Originally Posted by akoscielski3

And Nick did you use 1 transmission per side or 1 per wheel??

We used one per side.

-Nick