Blast Gate Design question

[Anthony Whitesell]

I am looking to automate my blast gates. I have seen the automated ones that are available commercially, but I'd like to retrofit the ones I have (plus I think I can do it cheaper).

My design question is this: The 4" gate has to move 4" to open and the really inexpensive actuator I found only moves 3/4". So if I attach the two via a lever arm, how long does the rod need to be (A) and how far from each end (B and C)?

My first thought was (A) 4 3/4" long with the pivot (C) 3/4" from the actuator end. But that seems too simple.

Actuator Sketch2.bmp

[Scott Wigginton]

It passes the paper napkin test, to travel 4" you only need a 4" piece to rotate 45deg. Just make sure to add however thick your pivot is to the width of the piece.

You need to use full self-cleaning gates. Otherwise when it closes it will 1) jam with chips/dust and 2) rack & lockup if it doesn't have enough edge tracking to keep it vertical

Grab some scraps and see how it works.

Also, whats your inexpensive source of actuators?

[Anthony Whitesell]

Door lock actuators for car doors from All Electronics Corp. $5.50 each! That's about the same as some of the smaller compressed air (Bimba) cyclinders I found over at Surplus center. I figure it would be easier to run cheap two conductor zip wire to each gate than to run compressed air tubing.

The only thing I don't know yet, is if the actuator will have enough ummph to move the gate when it is at a mechanical disadvantage of 3/4:4 (or 1:5 1/3). I had to order some other stuff so I snapped one up to see if it will work after the arm measurements are determined.

If everything works out, my concept is to build a control center, when one button is pushed to open a gate, that gate opens and all the others close. It seems like a good idea any way.

[Scott Wigginton]

Anthony, ran across another design similar to what you were proposing, hope it helps!



Auto Blast Gate (.doc)

Blast Gate Drawings (.doc)

Thanks for the source, I'll check into it based on your results. For the control mechanism I might be able to bust out some of my college field programmable gate arrays (assuming I can relearn that stuff )

[Anthony Whitesell]

If it all works (and it might be a while before I can test it) I'll be able to provide the ABEL FPGA program. The current design layout is as follows:

1. Lighted pushbuttons each driving a S/R latch and a multi-input OR gate.
2. The selected push button-S/R latch is set when the corresponding button is pressed, while at the same time resetting all other latches.
3. The S/R latch will drive a relay driver I have used in the past (ULN2003). Because the door latches use reversing polarity to extend or retract, the relay will provide the connections for reversing the polarity.
3. The output of the relay will drive both the light on the push button and the polarity relay.
4. The FPGA will also provide a single output that OR's all the push buttons to provide "a push button pushed signal" that will some 555-timer circuitry to pulse a relay to move all the blast gates.

This should come out pretty cool in the end. In addition, I'm hoping to design the actuator to be able to retrofit the black plastic gates as well as to be used for custom homemade PVC gates down the line.

[Tom Veatch]

... how long does the rod need to be (A) and how far from each end (B and C)?...

You can use any convenient length as long as C = .1875*B or B = 5.333 * C

C = 3/4, B= 4, A = 4 3/4
C = 1, B= 5.333, A = 6.333
C = 1 1/4, B = 6.666, A = 7.916

etc.

As already mentioned, your actuator is going to be working against a 3:16 mechanical advantage so your gates will have to be very smooth and easy operating. Your actuator will need to produce 5.333 times as much force as that needed to directly open/close the gate plus enough more to overcome frictional drag in the joints.