We recently got a new BBQ, a Weber Q. Its only been used a few times but is pretty fantastic. The only thing I was nervous about before getting it is the ability to use a rotisserie in it. I used that a fair bit on the old 4 burner BBQ, especially when friends are over, to save oven space.
The Weber information is lacking quite a lot with regard to the rotisserie, I guess its not a main focus of theirs. Most of the info videos they put out are great, but none focus on using the rotisserie or answering any of the questions I had.
The main thing I wasn't sure about before buying the BBQ itself, was if the rotisserie is even a product anymore, as it is not mentioned or stocked at a lot of stores. So I would suggest going to a proper Weber stockist ... luckily we have one nearby. Walking in there allayed those fears, as they had absolutely everything that Weber produce.
The rotisserie motor that comes with the kit is pretty much the same as the generic ones you buy for normal BBQ's. I already had one of those, and all the spears and hooks to hold everything in place, but its the shield from the Weber rotisserie kit that you really need. You might be able to make one yourself but that is beyond my ability or care factor. The heat shield raises the Weber BBQ lid up enough to put the rotisserie in and to put a roast in. The heat shield also holds the mount for the roisserie motor.
To set up the BBQ to use with the rotisserie, you set it up similar as you would for roasting (apparently ... I haven't tried that yet). Set a deflector on the grill, but rather than putting a roasting rack on top of the deflector shield, use a (heat resistant) container with some water in it to help keep things moist. You can buy a roasting kit from Weber, but I just used some doubled up aluminium foil with a meat tray with some water in it.
The main thing I was unsure about is whether the generic rotisserie motors you can get (from Bunnings etc) would work. The one I have certainly does work, the mounting slots on the Weber for the rotisserie motor are close enough to the standard ones that you can use them. There is a little slop in the motor, but it is big enough that it sits in place. I teseted this out using a 2xD cell battery powered motor that worked well. The motor doesn't quite fit exactly, but its close enough. You can see in the picture below with the battery powered motor that the slot for the spear is sitting a little higher that with the Weber motor. Its close enough to work though, the good thing about this is that it means I can take it camping!
If you haven't set up a rotisserie before, there are plenty of other resources for that, doing it for the Weber Q is not much different, you just have to make sure the pointy end of the spear goes in the motor (to line up the rounded parts of the spear with the shield), and try to balance the meat and center it.
The size of the Weber provided spear works with the generic spikes, so you can use your old spikes if you like. I like the four sided ones that came with my old generic kit. The Weber ones are only 2 pronged ... thats fine for some things, but for chickens the four prongs are handy for keeping legs and wings in place without having to tie things up with string.
The other thing that was a little difficult to find out information for was what to set the gas to for a starting point. In the end I found the line in the rotisserie manual that suggests to refer to the roasting instructions. Following those, I set the gas to just over half way, which had the temperature sitting around 180 deg C - keeping in mind it was a little windy where the BBQ was sitting, so some adjustment would be needed.
After an hour the temperature had moved up to closer to 200 deg C but still at a comfortable cooking temperature.
I'm something of a bucket cook, ie I do things a bit by feel, so I am not exactly sure how long I cooked it for, but it was only a little over an hour. The result was great!
So I can confirm the Weber rotisserie definitely exists, and defintely works. You might be able to use your old battery powered motor depending on size, but the mounting slots are close to the same. I think the Weber Q rotisserie setup is better than my old 4 burner BBQ rotisserie due to the smaller cooking space, the 4 burner BBQ had a much larger 'oven' size. I used the normal method I use for roast rotisserie chook (onion and lemon chunks in the cavity, and salt and pepper outside) and it came up great ... I'm not sure if its the rose coloured glasses of a new BBQ, but I think its better than the old one.
If you don't have a local Weber stockist, you can order the rotisserie from quite a few places online, this was going to be my backup option if I coudln't get the rotisserie locally. Catch, dealoftheday and similar online stores seemed to stock Weber parts when I looked ... ymmv.