pic: Shifting Drivetrain with Transmissions

[Jared]

Originally Posted by Andrew Lawrence

Why are the wheel wells indented so much for just 1" wheels? You're greatly decreasing your available bellypan space.

I can move the wheels out 3/8". The frame was just an example, so I just made the indent an even number.

What's with the double set of sprockets on each wheel? Just lazy to make spacers, or do you have a reason for doing so?

I made the spacer a configuration of the sprocket to save time, but I forgot to make the changes in this assembly.

What is the reasoning behind not having your gearbox plates backed by the frame? The spacers there make me iffy about the strength. If your goal is to save space with the inverted CIMs, ask yourself if it is really necessary that you save that much space. Because I feel as if lessening your wheel wells will save plenty of extra room and you won't require a design more complex than you need.

We used this design with a 3 CIM transmission last year and we saw no problems. Inside those spacers are two 1/4-20" grade 8 bolts that screw into threaded inserts welded into the frame. These same bolts also retain the outer plate too. It lets you take out the transmission by unscrewing two bolts and it just drops straight down out the bottom of the robot. We managed to remove a transmission, disassemble it, replace a dog, put it back together, and install it in under 30 minutes, with no practice doing this repair. This is way faster than any typical transmission, which require that there is room to slide the transmission out (which we usually don't have) in order to do maintenance.

Also, see a size comparison. https://drive.google.com/file/d/0Bzf...s3WFROeTA/view
Moving out the wheel wells saves me .875". Switching to the WCP gearboxes makes me lose over 9".

I would also argue that this design is no more complicated than the WCP gearbox, is significantly cheaper to our team, and lets us use 3.25" wheels because it has more ground clearance.

I'm sure a 2 CIM WCP DS would work perfectly in its place and save you a lot more time and trouble than this custom design is worth.

I don't want to run 3.25" wheel that wears down on the same shaft as a 3.1" OD gear. Also, this design is cheaper, and meets the needs of our team better.

If you have any more questions about drivetrains or transmissions, feel free to hit me up with a pm. This has a lot of potential, but you need to have more focus on what you want to accomplish with it and how it will fit your team's needs and resources.

The goal is for the transmission to be cheap, to have two speeds, and to be maintainable. These two transmissions would cost our team $321.71. Two WCP DS transmissions cost $520, and require that we spend $50 more on wheels. That is a $500 savings on two robots. It is also significantly easier to remove than a WCP transmission, and weighs almost the same.

I like your design, but I'm not a fan of cantilevered gears, especially with questionably fitting hex bearings. Last year, we had cantilevered gears, and we saw accelerated wear and eventually failure. Also, it seems that your design would be slightly thicker, as you do not have the cluster gear over the shifting shaft.

Originally Posted by DampRobot

I wonder if you could get a little more size and efficiency out of your gearboxes by putting both CIMs around one idler gear that went to the cluster shaft, rather than the two idlers both going to the cluster shaft as you have now. I assume you have to use idlers because the cluster gear can't be made big enough for the CIMs to direct drive it.

Yep. If I make the cluster gear bigger, it hits the dog. I've played with the gear ratios a lot, and it just isn't possible with vex gears.