I was thinking about how you would recreate some of the mythical items of legend if the mana levels in the sixth world were higher. I thought of Baba Yaga's magical moving house supported by dancing chicken legs and I realized it could probably be done by turning it into a homunculus vessels. You could just have a spirit just run it from place to place. The book does not list maximums that a spirit of any force can animate, it only lists minimums. A homunculus must be at least 10 kg per point of force.

Anyway What would you stat the house as, or what would you animate yourself?

I found out from a sight advising foundation depth based on size of the cabin that-
Small cabin / playhouse 600-1,000kg
Grill house / mid-size cabin 1,000- 1,600kg
Big multi-room cabin 2,000-5,000kg

The house I put at 1200kg, so the small side of medium.
So it would take about 24 radicals of presumably wood, slate, and bones.

as i recall, frank had a rough idea when he wrote up the rules what the rough sizes should be. i think it was something like force squared liters, or some such thing...

Your average force 2 spirit vessel:

http://www.office365.co.uk/im/pim/568323.jpg

Force 9 spirit. 9*9= 81 liters. Wood usually weighs slightly less than water. But measured as water, 81 liters = 81 kg. 9kg less than the minimum. It only works exactly at force 10.

1200kg of wood would be close to the minimum volume of a force 34 spirit. But be under the rules the minimum size for a 120 force spirit.

Sounds to me like a quickened Animate spell is the way to go. See SR4A, p. 198 for the Quickening metamagic, and Street Magic, p. 172, for the Animate spell.

well, whatever it was, i seem to recall it working out to a force 5 spirit being about metahuman sized.

I'm a little dubious about force² liters as the proper limit. As a thought experiment, let's consider a spirit possessing a fairly average human.

According to the table on p72 of SR4A, the average human weighs around 78kg (~172 pounds). Humans have an average density very close to water, which is why we have roughly neutral buoyancy. Since 1kg of water is 1 liter of water, we can extrapolate that the average human has a volume of roughly 78 liters.

The square root of 78 is approximately 8.83. Since we can only summon integer-Force spirits, we round that up to 9. So, using the limit you describe, it would require a Force 9 spirit to animate the average human body. That doesn't pass the sniff test, since nothing in the possession rules suggests that it requires such a powerful spirit to possess and control a human body. For example, the Corps Cadavre optional rule on p95 of Street Magic says that a possession-tradition watcher spirit can possess a corpse and animate it with a move of 10/25 (typical human speed, so it's not even a slow zombie). So, the rules specifically contemplate the very weakest Force 1 spirit animating an object with a typical volume of 78 liters and a mass of 78kg.

I've played around with various formulas (Force x 200kg, Force x 300kg, Force²*200kg, among others), and haven't come up with anything that seems reliably consistent with both RAW and fluff. They tend to break at either high or low masses.

Maybe it would be better to base it on object resistance. The Animate spell Tanegar mentioned indicates that the object resistance threshold should be increased for objects over 200kg, but (frustratingly) doesn't suggest by how much. The spirit possessing the prepared Harley Scorpion in the example on p12 of Digital Grimoire doesn't face any penalty, even though the bike is probably over 200kg. I also found in my noodling with formulas that linear increases tend to break down. How about adding 1 to the threshold every time the mass of the object to be animated doubles (beyond 200kg)? So, at 400kg, we add +1, then another +1 at 800, and so on?

The house the OP is considering is made of natural materials, so I'd give it a base object resistance of 2. Its extra mass adds another +2, so a possession spirit needs 4 hits on a success test to animate it. It's going to be a prepared vessel, so the spirit will get a dice pool of Fx2+6. A Force 2 spirit would average 3.3 hits on that test, so while it could animate the house if it makes it, it can't possess it very reliably (about a 44% chance). If you want to get up to ~75% reliability, you need a pool of at least 14 dice (which actually gives you about 74%). That takes a Force 4 spirit. F5 gives you 83%, and F6 gets you close to 90%.

A van, on the other hand, would start with a threshold of 5. With a mass of around 2000kg, we'd add +3 to the threshold, for a total of 8. To have an even chance of making it work, you're going to need 24 dice. Since it's probably not a prepared vessel, the spirit has to manage it on Force alone, so you'd need a Force 12 spirit. Even if it is prepared, you'd need a Force 9. That seems a little excessive to me, given that a Force 12 spirit with the right spell could levitate the van almost as reliably.

I begin to see why Frank didn't actually specify this stuff when he was writing. It's a royal pain. Personally, if I were GMing, I'd just set resistance thresholds arbitrarily. I'd give the hutmunculous a threshold of about 4, and the van about 6. The corpse of a (non-great) dragon, I'd set at about 12.

I like this rule.

Homunculus move with joints but with out the need of an engine (though I think they can make use of them). Possessing an object like a toaster that has not been made homunculus is different. Possessing a toaster lets you just make the toaster do things a toaster can do not hop around.

But I don't know if there is any real distinction. It may just be separate entries because the homunculus paragraph has guidelines for the weight of the body but for objects is does not seems to matter how small the object is.

I suppose the same threshold would hold true in both cases. I suppose the way to prevent 2000kg (heavy for an empty delivery van) from being to much is to use a larger multiple than 2. Three four, five, or even ten might work better.

I can see the problem with adding this rule as something hard and fast is that it would require a lot of weight guessing, or looking things up and calculating. This is starting to remind me of Gurps formulas for things.