All it will make you do is vomit,this then causes your abdomen to contract and 'may' start labour. I know a few people who have tried it and none went into labour due to the castor oil.
K82, daffy is right, it will only turn your guts and the last thing you need is, to go into labour naturally and fine you are throwing up in bucket as well.
Try to keep on the move round the house or just some gentle exercise. All will come when ready as you've said.
not only will it give you a tummy ache and the squits but also baby.
Its not the best thing for them to poo in waters as they inhale the fluid and the poo. 12 hour observation if there is meconium in the waters usually.
try the other old wives tales but avoid the castor oil if you can.