RAIL GUN: linear slide ram shooter
 

Team 3135 has nearly completed our prototype linear ram shooter --- just a trigger cylinder needed, and removing excess length wherever possible. It is structured with slotted framing and uses a unique and largely unknown 80/20 nylon bearing slide element pictured below.

The backbone is a 2" x 1" 80/20 segment, that will end up 24-28" long once we remove the excess length. It is a high force, hybrid pneumatic & surgical tubing system that has two slider blocks on the top. To one block is mounted the ram, and to the other is mounted the retractor/latch/trigger assembly.
Needed force required at least dual surgical tubing elements for ram power, and we needed minimum torque applied onto the slider, so we went with a bilaterally powered scheme of surgical tubing and high tech cord wrapped on pulleys to limit length.

Once we realized that it was primarily just hitting peak ram/ball speed during stroke engagement (not launch force or ram momentum) that gave best shots, we minimized the ram weight (dropping down to 20x20mm frame) and shortened the stroke (10" now and headed for 8" we expect). The ball starts right up against the ram tip too.

Surgical tubing is 1/8" ID by 5/8" OD with ~8* of stretch zone and is prestretched by ~6" at the full stroke extended point, with the retracted & ready to shoot position taking the surgical tubing near to 22" stretched, close to the 3X max. recommended extension. Tubing ends are 1/4" H/W, and tricky to keep from pulling out at near 3X stretch levels.

We were planning to do a variable power gearmotor winder scheme, but opted for initially trying a single power pneumatic ram retractor instead. After shots, the gate latch trigger's slider block reengages the ram end by tension from some thin surgical tubing, that also keeps the cylinder's retractor cord taught during reload cycle.

The 4" omniwheel ram tip seems to give a uniformly good enough force distribution on the face of the ball without adding much weight.

We still need to improve the path of retractor cords to be closer to parallel to the latch slide path.

http://www.fastenal.com/web/products...endingMachine=








-Dick Ledford

Re: RAIL GUN: linear slide ram shooter
 

I'd be curious to see the robot that this is going on top of... it looks a bit large for any standard chassis.

Re: RAIL GUN: linear slide ram shooter
 

Its going onto the long version of the AM14U.

Re: RAIL GUN: linear slide ram shooter
 

Currently under 30" when excess backbone frame is removed (camera exaggerates lengh), and removal of other excess component length will further shorten down to as low as 24" OAL.

If stroke is only 8-10" and ball sits high on robot with much of its size protruding beyond 60" elevation we have about 55+" diagonal lengh inside frame to work with for setting our shot angle.

Too few catapult shooting teams are realizing how easily their shots can be defended and blocked by a basic speedy & maneuverable opposinng bot just sitting right in their face. We plan for our shots to clear any possible defending scheme.

-Dick Ledford

Re: RAIL GUN: linear slide ram shooter
 

Bravo! I think I could entertain myself for hours with that thing. :D

Re: RAIL GUN: linear slide ram shooter
 

We have a linear shooter as well, but it doesn't ram the ball, but instead pulls the ball along a tray to shoot it. We thought this type of shooter would be best because its easier to shoot a projectile that launches linearly rather than one that shoots at a parabolic arch.

Re: RAIL GUN: linear slide ram shooter
 

Not sure what you meant by the last sentence above. Once the ball leaves the linear shooter, it's going to follow "a parabolic arch" anyway.

Re: RAIL GUN: linear slide ram shooter
 

Ya I know I was trying to explain how it shoots. A linear shooter shoots the ball out at an angle close to the horizontal axis whereas a catapult shoots at an angle more towards the vertical axis. That's mainly what I meant. Basically a linear shooter gives the ball an angle that's a lot less steep.

Re: RAIL GUN: linear slide ram shooter
 

One thing I'm going to forewarn here, from experience those 80-20 sliders will wear, and once they do nothing will want to slide at all. Also if that 80-20 ends to the slightest bit bent sliding will be difficult if not impossible Having the ability to quickly replace those sliders would be a design consideration you may want to look at.

Other than that design looks awesome, can't wait to see more of it

Re: RAIL GUN: linear slide ram shooter
 

Either type can be designed for a wide variety of exit angles.

Many teams are designing for an exit angle that gives a large "sweet spot" at the goal height (see the JVN Ri3D blog for more info).

What exit angle is your team designing for?

Re: RAIL GUN: linear slide ram shooter
 

We basically have two. One is to shoot from the white line which is at about a 30* angle for our shooter. Another is for a shot from a spot on the field I'm not sure our team wants to reveal yet. That angle will be slightly steeper. Even so, we designed for low angles so finding that 'sweet spot' on the field isn't as critical to get an accurate shot.

Re: RAIL GUN: linear slide ram shooter
 

Yeah, thanks for the heads up, we already have spares made to cover that issue. This was one reason we are being careful to keep all net forces on the sliders as near to axial as possible, with minimum torque being carried by nylon contact area. Still some improvements needed in that regard.

-Dick Ledford

Re: RAIL GUN: linear slide ram shooter
 

I think maybe you misunderstand the concept of "sweet spot" as that term was used by the JVN Ri3D team. Take a look at this blog post:

http://www.buildblitz.com/team-jvn-arens-sweet-spot/

Re: RAIL GUN: linear slide ram shooter
 

Ya I understand that the 'sweet spot' is pretty large and may not be as important to reach that spot every time. I'm just saying the 'sweet spot' will be even less necessary if the ball is shot from a small angle and followed an arch that's close to being linear. Sorry if I'm causing any confusion. I'm not always the best at explaining things.

Re: RAIL GUN: linear slide ram shooter
 

How does a linear shooter solve this problem over a catapult? If you're trying not to get blocked, it seems to me either to have a higher trajectory or get away from the defender.

Re: RAIL GUN: linear slide ram shooter
 

He may not necessarily mean the linear shooter is being used to accomplish this. They may be using another mechanism *hint hint*

Re: RAIL GUN: linear slide ram shooter
 

if you have this problem for 4 or more hours see a doctor immediately

Re: RAIL GUN: linear slide ram shooter
 

What do you mean by this?

Re: RAIL GUN: linear slide ram shooter
 

I mean another mechanism on their robot is being used to make sure their shot is undefended. Did I make it unclear?:confused:

Re: RAIL GUN: linear slide ram shooter
 

Yes. Yes you did.

Re: RAIL GUN: linear slide ram shooter
 

You'll have to wait for the reveal. ;)

Re: RAIL GUN: linear slide ram shooter
 

Correction - the black surgical tubing is actually 3/4" OD and has a 5/16" wall thickness.

-Dick Ledford

Re: RAIL GUN: linear slide ram shooter
 

Here is an update PIC on our rail gun ball puncher, which has been shrunk to a total of 29" length with a stroke that is now 8" in length. We have opted to go with a pneumatic retractor-loader & surgical tubing ram power hybrid design for greater simplicity.

The pictured setup retains the 2"x1" slotted framing backbone and uses dual slider blocks - one for the retractor/trigger assembly and one for carrying the ram.

A 2" diameter by 8" stroke cylinder pneumatically retracts the rear slider block carrying the gate latch trigger mechanism, pulling the ram with at as it further stretches the surgical tubing. Then, when fired, only the mass of the ram and ram slider block are being accelerated by the tubing.

Weaker surgical tubing, after shot is fired, pulls the retractor/trigger slider block forward to reengage the back end of the ram slider into to the gate latch. Then the cylinder initiates a reload sequence to prepare for the next shot.

The bilateral symmetry keeps forces on both slide blocks well balanced for minimum drag.





We were intending to mount the shooter high in the robot, but with all the tip overs in the week one competitions, we may need to rethink this.

-Dick Ledford