Are all 3 objects (shooting tank, explosion SFX, and exploding tank) activated by a display sequencer or did you just set each one up individually and tell it to activate every 20 seconds?
I ask because one of the highly annoying things in PC is that animatronics (which would be both tanks) spawn in random positions in their animation cycles each time you load the park, UNLESS they are tied to a ride trigger or a display sequencer. Thus, if you have each one set for 20 seconds by itself, they will all still run on a 20-second cycle, but the cycles will be out of phase with each other due to the randomness on spawning.
Also, the shooting tank fires about 8 seconds into its animation (after rotating its turret), while the exploding tank requires about 14 seconds to reset after its animation, and the explosion will repeat about every 8-10 seconds. So even with display sequencer or trigger, you have to use some delay times.
To make this work as you desire, do the following:
1. Place a display sequencer.
2. Edit the display sequence for the display sequencer.
3. Create a display group for the display sequencer.
4. Connect all 3 objects (shooting tank, exploding tank, and explosion SFX) to the display sequencer within this display group.
5. Give both the exploding tank and the explosion SFX an 8 second delay, leaving the shooting tank at 0 seconds. This will make the explosion SFX and the exploding tank's animation both start when the shooting tank fires.
6. Give the overall display group including these 3 objects a 20-second delay (anything over 15 seconds will work). This prevents the explosion SFX from firing by itself before the 2 tanks have reset.
7. Set the display sequencer to run a continuous loop.
So, the display group will start. For the 1st 8 seconds, the shooting tank will rotate its turret towards the exploding tank. At 8 seconds, it fires and the exploding tank and explosion SFX also go off. Over the next 6 seconds, the shooting tank rotates its turret back to its original position while the exploding tank sits there dead, then returns to its pre-exploded state. Nothing happens for 6 seconds (now a total of 20), then the cycle repeats.