I've been looking through the R3R and have been wondering how to do stationary drones, or drones that don't have their own motive power.

They are included somewhat with trailers but the smallest is body 2. I'm interested in man-portable or semi-man-portable body 0 and body 1 stationary drones.

Here's an example:

A lookout tripod drone used to temporary provide surveillance coverage for an area. These might be placed around a military encampment or used in the city for construction and crowd control. Such a device might have a Beacon(spotlight), sensors, intercom, and loudspeakers. Also included might be retransmission units or electronic warfare equipment.

While you could jury-rig the R3 rules with a new chassis and make small stationary drones I recommend you design the item and assign the stats yourself. R3's design rules stifle innovation.
The idea of intelligent gear is interesting and an underdeveloped area of the game.

Controversy!
Take Gerzel's concept, how do trailers encompass man portable sentry guns? How many innovative designs have turned up in the decade since R2 introduced design rules? If there's no chassis available people tend to either assume a vehicle can't exist or try and pigeon hole their design into an existing chassis which mangles the idea.
The design rules, both vehicle and gun, are open to exploitation which means the GM may as well spell out the stats if he's not giving the players carte blanche.
Further, I guess I probably dislike R3 and take any chance to disparage it ;)

So, small walker, battery plant, drone pilot, autosofts, and a single weapon mount is somehow unnacceptable?

Body 1, so it's fairly small and light. While it can technically move around on its own, that wasn't part of the design goal, so it has bad speed and acceleration (the mobility is mainly so it can adjust it's position if it calculates that there is an obstruction preventing it from getting a favorable firing solution).

If you skimp on armor, engine tweaks, and miscelaneous toys, the whole thing won't be much heavier than the gun, ammo, and a tripod. The only major difference from your stated intent is that it can control it's own legs if programming or a rigger demand it.

Toss in a design factor or two, and that .25 markup can drop a bit more and almost make it a viable, inexpensive defense component.

That would be misinterpreting "stationary drone". Much.

just build the damn thing and BOLT IT DOWN ? *g*

If you want it on the ceiling you put hooks into the ceiling, which hold the drone by rubber bands? I think he´ll want to spend the weight and space for motor controls and gear on something useful?

Battery life would strongly depend on sensor rating. With grid access power is unlimited. You need to decide on your own, but I would say if the sensor fits on the vehicle, battery life is unlimited for gaming purposes.