Spent about 30 minutes today trying to figure out how to trigger my 3 small strobes. I've got a bit of a mix of lights and triggers - 3 pocket wizards, two canon speedlites (a 580EX and a 420EX slave only/ TTL unit) and a cheap, second-hand Nikon SB28. I've also got a set of radio poppers (thanks to the guys at Tricoast) and a Canon ST-ET2 transmitter. A bit of a mess really. The problem is, I can't easily trigger all 3 lights at the same time. I can easily trigger pairs of them, using the pocket wizards, to control the 580EX and one of the SB28 or the 420EX. I can use the ST-ET2 to trigger both the 580EX and the 420EX, with or without the radio poppers in the mix to remove the need for line of sight. But I couldn't get all three to trigger at the same time. Eventually today I worked it out - but it is still a bit of a mess.
I was able to use the pocket wizards to trigger the 580EX, in master mode, that then triggers the 420EX. That works fine. Then if I add in the SB28, also triggered by the pocket wizard, all three only trigger, if the SB28 is out of sight of the other units. The 580EX seems to communicate/ trigger the 420EX within the white light flash output - I thought it might have been IR, but it doesn't seem to be. So the SB28 firing at the same time confused the 420EX in to not firing. The solution was to use the radio poppers to trigger the 420EX, covering up its control window with some duct tape, so that it only sees the control pulse from the radio popper. Not really ideal, but it seems to work at least for now. Next step is working out how to control the output power levels, but mostly I was interested in using the 420EX and SB28 as background/ edge lights in this arrangement, so the power levels aren't too much of an issue.
The alternative is just to buy some more controllable Canon flash units. Tempting!