Many parts of the robot this year, like the launcher, will only require the motors connecting to it to spin in one direction. This makes it possible to mimick a transmission like the one team 62 made for skyrise by attaching 2 ratchet and pawl systems to the same axle and facing them in opposite directions. With this device rotating the axle counterclockwise will power one gear and clockwise will power the other. Hopefully I will have a video of this device on Wednesday.
That actually sounds cool.
Is it a planetary transmission type system?
I don’t believe so. It’s just two ratchet and pawl systems facing in opposite directions on a single axle. Whether or not a ratchet and pawl system is classified as planetary I do not know.
I remember that when I was little, I built this lego helicopter with a similar mechanism. Motor spinning one way spun the top rotor, motor spinning the other way, the rear rotor spun. This mechanism did not, however, use a ratchet.
Could you explain how this mechanism worked, the wikia page doesn’t describe it.
My team designed a passive transmission using two homemade differentials. Trust me on this, it’s a road that you do not want to go down! I calculated a all the efficiency losses within the system. It turns out, usually less is more when it comes to gearboxes.
I’m not sure how that lego one works.
For anybody who is interested I got mine to work by two motors driving two differentials. Both outputs of each differentials were mechanically linked together. One side with chain, one side with three gears. Using this type of configuration if the motors turn the same direction the output will go to the gears, and the sprockets if the motors turn opposite of each other. The problem with this mechanism is that the systems were not independent, which caused a lot of problems. In a perfect world this would work, but with a different efficiency for each system (arm and wheels) causes energy to divert to the other system unexpectedly. This was also a nightmare to program. I believe to tackle this we had 6 PID loops, all affecting each other. Needless to say we trashed this idea after wasting most of the year on it.
Hope this helps!
Thank you for the warning. I will test the efficiency of the motor before and after I attach the transmission to it later today and let you all know how it fares.
Here is a video of the single direction dual axle passive transmission (I just came up with the name for it). It is a prototype so it is horribly bulky and I cannot put too much stress on the axle or a part of the rachet and pawl system will fall out of place. This will be easily fixed but until then I cannot test the efficiency (however there doesn’t appear to be any lost efficiency here).
That really clever. What did you use to build the ratchet and pawl?
Well, I probably should have used the one vex makes but my team isn’t very organized so I’m pretty sure we lost it. Instead I used a block bearing (with a large washer on the end to make it thicker and longer) and a sprocket in the same way that you would use the vex parts. I did everything else the way that many YouTube videos and vex forum threads have described.
I’ve done this also during toss up where I had the lift motors assist the drive when the robot was not lifting things.
Unfortunately, this system is fundamentally flawed (no amount of PID/programming could have fixed it) as the maximum torque (or power, for that matter) output of two motors driving a single differential (from two opposing sides) is… equal to that of a single motor. (rather unintuitive)
The only way to get around this is to have some actuating mechanism that locks the two sides in sync, at which point you might as well do something simpler.
Glad to know another person made the same mistake as I did 
I was thinking of a system very similar to this. This was the solution I thought up to a one time motion. Since you don’t have to use anything extra to power it, I like to call it “free motion”. I’d be excited to hear what you plan to do with this free motion. It would be quite interesting if we both had the same idea without ever discussing it!
We are planning to use it to switch between gear ratios. 10:1 and 25:1 are the ratios we are thinking about using, but we will have to do a lot of testing to find the best efficiency for each range of distances.
I thought I would throw another use for this system out there. My robot uses 10 motors and pneumatics so I needed to use the least amount of motors possible. My intake has two powered stages. A bottom stage picks the balls up off the field, and a top stage feeds them into the shooting mechanism. They are independently powered by one motor using a ratchet and pawl system. When the motor spins one direction, the top intakes activate and feed a ball towards/into the shooter. When the motor spins the other direction, the bottom intake spins, picking up balls off the field. This system allows us to always be ready to pick up four balls no matter how many are loaded and regardless of their position in the intake.
Here’s a picture of how I built that system:
I have changed a few things since this picture. In particular, the 12 tooth ratchet gears have been switched to high strength.
I am not quite sure how the one Stanley made in that video works, but it is planetary and the one I made is not. I posted a video of it at the bottom of page 1.