I recently noticed something about skyrise. A team will generally have to make a trade off between strength with scoring cubes and strength with building skyrises when designing their lift, as a lift capable of lifting several cubes will have to be geared for torque, while a lift designed for building sky rises would optimally be geared for speed. This would make it seemingly impossible to create a robot that can master both elements. However, after looking at some models of 2 speed transmission drivetrains, I came up with an idea of taking that concept and using it within a lift, allowing for quick skyrise building, followed by scoring multiple cubes at once. Could this be a viable idea in practice for a lift such as a reverse double four bar or an eight bar lift?
Our team did that last year for Toss Up.
It can be worth it as long as your Driver knows what he’s doing, it’s programmed to where the Driver is comfortable, and if it doesn’t way too much.
Yep, a lift transmission is totally doable this year. If you’re doing an 8 bar, than it will be fairly easy. With a RD4B, it’s a little harder. You have to power it either from the tower or from the middle section where the two 4 bars meet, and each way has its own problems. If you power it from the towers, you run into width issues if you want to have any cubes pass between the towers, and can’t run a common axle. If you power it from the middle section, you have to lift the entire weight of the transmission, and could possibly run into space issues there also. Also, a lot of RD4B’s seem to need active lift stability code to stay straight, especially with four cubes. In order to have active stability control, the motors for the two sides can’t be connected, so you have to build two mirrored transmissions, similar to transmissions on drive bases.
I think a transmission would be worth it if you were able to get it all worked out and get the rest of the bot to a point where it actually has an advantage over simpler bots that have had more time to tune and practice. It just takes a lot of time to do that. Team 44 in Toss Up is the only robot I can think of off the top of my head that got a transmission to the point that it was better in matches than direct-drive type efficiency robots like 21 and 2915A. That’s just my opinion though, 44 got beat.
transmissions are always tricky, especially on an arm where weight is a huge factor. in my opinion the piece about building the skyrises that takes the most amount of time is centering it on the base and other skyrises. not the lifting. if you find the right gear ratio that can lift what you need , you are going to have less problems and spend less time on shifting, replacing bent axles, and you will be lighter. simplicity is huge when you have limited dimensions and limited power.
Power is enough for me and I would not attempt a lift transmission.
I have 1:7 4 motor double reverse six bar, and it is able to lift 2 cubes effortlessly with UTRB. The lift is too fast for skyrise building and the driver is still learning to control it. We lowered the speed for the lift when building skyrise.
With proper elastic assist, a 1:7 reverse double is able to handle 3 cubes while maintaining nice speed.
I attempted a transmission for chaining a linear lift. It would switch between a 1-1 and 1-19 gear ratio. I almost got it working, but decided that it was too heavy, too space consuming and provided too much torque for the rest of the lift to handle.
It is a good idea though, and could let a team truly do everything well, even without a partner.
if anyone is truly wanting to do a transmission for arm or base, cad model, prototype and test the heck out of it! too much friction and weight is the biggest problem most have. if you solve that, then shifting is a problem (normally will not shift if motors aren’t moving). you then also have to make it compact enough that you can fit it and then a large arm and manipulator on top and around it all in a 18x18x18in box.
I do sometimes wish vex made a couple sizes of the outer gears on a planetary gear set like the one in this
so that an automatic transmission could be possible without using chain like this
this would allow much smoother shifting even though vex will never make such product.
I have rarely seen this type of mechanism work in vex.
great job to the few who have successfully designed an efficient transmission and done well in worlds!