What mechanism should I use?

VEX Robotics Competition Discussion VRC > Starstruck (16/17)
#1

I’m thinking of what mechanism I should use. I have two ideas:

  1. My first idea is a torque ratio with a slip gear, so it won’t go so fast.

  2. My second idea is a choo-choo mechanism, but when it forces the motor it might ruin the motor.

#2

First of all, a slip gear pretty much needs to have a gear ratio or the motors will not be able to supply enough torque. A radial release (choo-choo) doesn’t have a point that places stress on the motors directly, just on the joints in the mechanism.

Both systems have pros and cons. I believe there is at least one other thread out there about this, and you should take into account what you want your robot to accomplish and base your choice off of that.

#3

I don’t have access to test thing out yet, but it seems like most people think that a slip gear will probably be the best option.

Here are a few other options in this thread:

https://vexforum.com/t/catapult-actuation-poll/34911/1

#4

I will say that one potential benefit of slip gear versus choo-choo is that a slip gear is easier to make in a smaller/tighter space, whereas a choo-choo requires a good amount of room to draw back. However, choo-choo does not usually require as much gearing because you’re essentially designing a lever while you pull back, so if you have the space and time to tune a choo-choo, you might find that it will be faster and more effective launching wise.

To sum up, slip gear = easier, space efficient, light loads; choo-choo = slightly harder, more space, powerful enough for heavy loads.

#5

Having worked with both over an extensive amount of time, I personally prefer the choo choo radial release over a slip gear. The choo choo can work much faster under heavier loads than a slip gear can, however a choo choo must be kept in pristine condition to do so. The joints tend to loosen themselves over time and must be kept at proper tension.

#6

I started developing a prototype of a choo choo mechanism, but it will require a strong stabilizer to counter the shock that it produces after launching, unless the robot is able to sustain the shock, i would not recommend using a choo choo

#7

I think you’ll have the same amount of shock with either mechanism. With a choo-choo, that shock will go through the mechanism, including an axle. With a slip gear, that shock goes through the stops, although a catapult’s rotary motion could send the shock through the geartrain and potentially damage the teeth or motors, depending on the design.

#8

My prediction is that the shock from most of these will cause the robot to tip and land harshly back on it’s wheels, eventually bending shafts.

#9

I could see that happening…
SUSPENSION!

#10

Anti-tip mechanisms?

#11

Must have 4 point pneumatic suspension for each wheel.
MOAR PNEUMATICS

#12

I think all you need is high strength axles and reinforced gears around the central part of the launcher, and then enough foam should be enough to keep the robot from destroying itself. If it’s built well with lots of structural support, then even launching 6 stars shouldn’t break the robot.

As for tipping, there’s been lots of passive anti-tips designed in the past (like Stanley’s from Skyrise), so I think that shouldn’t be a problem. Just build the robot well and include lots of redundancy in key areas I guess.

(Still haven’t finished my robot yet, so if I discover that this is a problem then I might soon be singing a different tune :P)

#13

For suspension, I was thinking more along the lines of passive shocks. Anyway, it’s probably not even going to be necessary, and I think I’d rather prevent the rocking motion than mitigate the damage caused by it.

#14