Wednesday, August 12, 2009

The Dummy Has Landed


This was the cheapest doll I could find at Le Target, that was anywhere near the size of a baby. The weight’s not right, so my plan is to stuff the hollow bits with cleaned river sand, gravel, and small stones, in the hopes of getting the weight up closer to 7 pounds or so. The reason for that is that I think the mass will matter for compressing the foam and other substructures of the various seats and devices I plan on G-force testing. Moreover, the mass will matter even more for the bumps and bounces themselves. Too light and it will move differently than a real baby. Well, I mean, it will anyway, because it’s a plastic and fabric doll, but we can get closer to reality by modifying it.


You can see I’m taking the thing apart already. I want to run some baseline tests that will mimic – none too precisely I’m sure – the G-forces sustained under various activities. Obviously, with real babies, you want to support their heads because they have no neck muscles to speak of. This baby’s head was attached far too stoutly, so I took it apart, drilled a few holes, and used zip ties to keep it attached in a looser configuration.

This doll has some creepy habits. I cries if you pinch the right foot. It laughs if you pinch the other. If you feed it, it makes a sucking sound and bucks. Then if falls asleep and snores. See the video if you don’t believe me. Worst of all, when you shake it vigorously – as you should never shake a real baby, of course – it laughs. All in all, it reminds me of a cleaned-up Chuckie.

In fact, I think we go ahead and name her right now: Chuckette.

OK, so Chuckette needed to gain some weight. I want her at least 5 pounds so that she’ll bounce a bit more like a real baby, and compress the foam in various carriers the way a baby will. I think a 1.5 pound doll will probably jump and jerk more quickly than a 5 or 7 pounder, and that, in turn, would bias the results from the accelerometer – to the high side, I think. It seems logical and self-evident to me that it takes more force to reverse the direction of a bigger mass. Since the forces we’ll be dealing with are going to be consistent (assuming constant velocities, bump amplitudes, etc.), I think it follows that a more massive baby (doll or real) is going to fly upward less far than would the nearly weightless one , influencing the G-force readings we’ll get. What’s that, some kind of inertia thing? (I’m no physicist, as the now-giggline physicists can attest. These are just my hypotheses.)

Anyway, here’s how we got Chuckette on a weight-gain diet. We fed her rocks. And sand.


I procured the above gravel from a nearby stream bed. Then I washed it with clean hosewater to get out most of the finer particles and organic matter. Once I put this inside Chuckette, I don’t really want it to start rotting.


There’s Chuckette, unstuffed and ready for a sand and rock infusion.


Here, Chuckette’s Mommy stitches her back up so she won’t leak sand all over our gear and into her clothes. That reminds me, I need to stick a diaper on Chuckette so we have realistic arse padding.


OK, Chuckette weighs close to 5 pounds now. If I get bored, I might add a bit more sand to her arms and legs to get her up closer to 6 or 7, but for now, I think we’re close enough.

1 comment:

  1. I want to thank you so much for performing these experiments. I summarized your results for 5 experiments. I ordered them by the maximum peak of most of the data (the maximum Gforce for most of the time the baby would be exposed to). In order of most stress to least: bouncing on parent's knee, in an ergo with parent jumping around, in a jogging stroller on a gravel path, in an old burley solo with a car seat, car seat in car. THANK YOU so much for conducting these experiments. I now feel confident in riding with my son in his car seat in our bike trailer. Thank you so much.