# Linear Actuator

3132 here,

We’re doing some research for our kicker and I’d like to know which linear thruster we should order from Bimba. Also, would this be enough to loft the ball, along with an angled plate? :o

Also, would a rotary actuator be a better choice based on our size constraints?

What are you looking for in the kicker? Speed, power, minimal air use, or something else entirely?

Tip: Generally, smaller-diameter cylinders fire faster than larger-diameter ones.

I think a linear actuator would be easier to implement than a rotary one for the situation I think your talking about. As for the lofting the ball, I think your team just needs to do a little experimentation and some calculations to find the optimal conditions, much like most of the teams will be doing.

-Scott

We’re hoping to do just that, but my partner isn’t here today so I hope we’ll make a start tomorrow. We’re in Australia though and ordering parts is a long process for us and this is why a rotary actuator would be suitable for prototyping here as we have one.

I think a rotary actuator may not have enough “oomph” for you. Try it anyway instead of doing nothing. A linear piston can fire a ball pretty far, but there are some trade-offs to consider.

Small diameter pistons tend to fire faster, because the limiting factor is how much air you can pass through those hoses and valves, and smaller pistons use less air.

But they also push with less force. In the extending direction, for example, a 3/4" bore piston can generate about 26 pounds of force using 60 PSI. (More details are in the pneumatics manual)

Large pistons are slower (more air) but stronger (look up the force for a 2" bore piston!).

One technique is to use a lever with a pivot to multiply the speed at the expense of force. Using a 10 inch bar as an example, push at one end at 20 Feet per second, have a pivot at 2", the far end moves at ((8/2)*20)=80 FPS, with 2/8 (1/4) the force. The challenge is here is to manage the size, strength and friction.

Another technique is to pre-charge the piston: Imagine a 10 inch long piston, held in place somehow with 5 inches extended. Charge the backside of the piston with 60 PSI. Then, release the rod so it can extend the full 10 inches - it’ll come out fast and strong. The design challenge here is reliably and safely releasing the rod that is under a great deal of force (obviously some kind of mechanism is necessary)

These challenges have been solved in may ways by others. There are also other ways of “skinning that cat” - but telling you everything would take out the fun, wouldn’t it?

Good luck, we’re all wishing you the best.

Would the rotary piston have enough “oomph” if we added a counter weight (and some elastics)?

My best advice is to try it. Adding a “spring” (even of elastic) can help - I am thinking of using the rotart piston to “pull” the elastic tight, then the force of the piston AND the elastic is used to whack the kicker.

As a first year team, you really need to build a Pneumatics Board. Mount the compressor, gauges, regulators and all the safety pieces onto a piece of wood. Use a circuit breaker (20A) in the power supply. That way, you have a ready source of air to experiment with until you nail down your design.

One more alternative to consider is using the piston to stretch the elastics (use the latex surgical tubing that came in the kit). The elastic then provides the “oomph” - very fast and very repeatable. (A piston force will vary with air pressure. That’s a mighty small compressor there…)

We just found out that we have to order the actuators as we didn’t get any in our KOP so we’ll try and order a linear actuator. Can you recommend a good one for us?

Also, there’s a Bimba distributor in Sydney.

You have to order the pistons from the bimba website, you get three free ones.

There are specific pneumatic cylinders (“Linear Actuators” isn’t their correct name) that you are permitted to use. Look for the FRC link at www.bimba.com

Basically, you can choose whatever you want from the list of permitted cylinders. These come in varying lengths, and in diameters of 3/4", 1.5" and 2". Look in a previous year’s pneumatics manual if necessary, but remember to follow THIS year’s rules. YOU need to decide what amount of force is necessary, and how long it needs to be.

Think about the problems and compromises:
Large cylinders are more powerful, but use more air.
(You have an air budget, just like an power budget. That’s not a big compressor…)
Small cylinders move faster, but are not as powerful.
Long cylinders need more than twice their ‘throw’ in distance to fit. A 24" cylinder ends up something like 50" long when extended.

I was thinking: Since you’re down under, your robot won’t have any trouble flipping back up if it turns over, right? (Or will it run upside down here in the 'states?)

You can also order 1 1/16 cylinders from the Bimba site.

As far as a size goes, we are using an old 1.5 bore that has been in previous kits and it is kicking the ball just fine with a lever. We are going to order different sizes, but this could help you guys have a place to start.

I’m thinking using a compass sensors (reliably) might be out for us.