Death of a Crab

Post by **aferguson** » Sat Jul 12, 2008 3:22 pm

well, my worst fears were realized today. I put the chains on the rotor and the rotor is now too heavy for the motor to turn it.

So, at this point i have two choices. I can either finsish it as a static display Crab, or i can make a new rotor and use black string instead of chain. This will be light enough to rotate but look kinda 'meh' on display.

Sadness..

B-29 · Post by **B-29** » Sat Jul 12, 2008 4:54 pm

aferguson wrote:well, my worst fears were realized today. I put the chains on the rotor and the rotor is now too heavy for the motor to turn it.

So, at this point i have two choices. I can either finsish it as a static display Crab, or i can make a new rotor and use black string instead of chain. This will be light enough to rotate but look kinda 'meh' on display.

Sadness..

Well, here's a better option. Go to a hobby shop and get a gearbox for the motor. It won't turn as fast, but it would allow you to keep the scale look.

Post by **aferguson** » Sat Jul 12, 2008 5:00 pm

there's nowhere to put a gear box. The problem is this little hand held fan motor just doesnt have the grunt to overcome the inertia of the rotor with all the chain on it. If i could get it spinning somehow i think the motor would be strong enough to keep it spinning but there's no way to get the rotor up to speed.

I thought of two motors, one on each end of the rotor but this is getting to labour intensive, time consuming and i can see all kinds of other problems, so i've decided to just use it as a static displlay model.

A week's work shot to heck......but oh well, that's life i guess.

Some day i'll get a stronger motor some, 9v batteries and give this another go..

olifant · Post by **olifant** » Sat Jul 12, 2008 5:18 pm

Too bad to hear Aferg. I bet it looks good nonetheless though.

kduck · Post by **kduck** » Sat Jul 12, 2008 8:39 pm

Keep your eyes open for some plastic chain. I can't think of a source but I've seen it as part of a number of toys.

Spudkopf · Post by **Spudkopf** » Sun Jul 13, 2008 4:52 pm

Lego make a plastic chain link, but the actual links are quite large

A quick Google using “plastic chain’ as an image search criteria I found the following:

http://www.zdsicc.com/

http://pionusparrot.com/catalog/index.p ... ex&cPath=6

That’s just two of the many, many sites that came up, a text search would reveal even more hits.

With the above apart from the fact that the chain size may be an issue (oversize) the weight savings using these over metal chains may be negligible, so maybe you could use the roller bead type chains found on vertical and horizontal blinds. It should be quite light and would look better than string alone, the weight of beads should also make the strands hang better when not revolving.

Post by **aferguson** » Sun Jul 13, 2008 5:46 pm

some good ideas there....but i suspect the roller beads would all be too large...and yes, i think the plastic chain would still be too heavy.

The only real solution is a more powerful motor.....or two motors, but i don't have the emotional gas to start over.

So, i'm just going to make this a static Crab and someday, if i stumble across the ideal motor/power combination i may take another shot at it. It's a bit disappointing though. I had some pretty swish ideas for the power set up, battery placement, activation switch etc.

Spudkopf · Post by **Spudkopf** » Sun Jul 13, 2008 6:17 pm

What about super (crazy) gluing the chains in the operating or extended condition, this way the motor only has to rotate the shaft like a propeller this way the motor does not have to use inertia to overcome the gravity effect of the hanging chains to obtain extension, thus reducing the load on the motor.

It does mean however that even when not rotating the chains will look as if frozen in time, but the compromise might be worth it?

I have seen this gluing method used on smaller scale dioramas from time to time and it looks quite nice, especially if posed ripping through the barbed wire defences of a D-Day beach.

VMF115 · Post by **VMF115** » Sun Jul 13, 2008 6:38 pm

How about cheap jewelry chains?

Post by **aferguson** » Sun Jul 13, 2008 7:02 pm

that's what i used. But i needed about 7 feet of it and that gets pretty heavy for a little electric motor.

KAMIKAZE · Post by **KAMIKAZE** » Sun Jul 13, 2008 10:12 pm

That is an excellent suggestion Spudkopf.
I might try a variation of that on another project.

Mark

Post by **aferguson** » Mon Jul 14, 2008 1:41 am

Spud.....i thought of that too but the chains are long enough that they strike the ground, so the rotor will just get stuck....making the chains shorter so they don't hit the ground will look sorta weird.......like a big spinning propeller rather than a flail.

Also, it works well in smaller scales but super gluing lengths of chain of this size doesn't work so well as links tend to keep breaking free of the glue, especially towards the base of the chains, where the load is higher. I've tried that method on other projects and found it to be quite tedious and fairly fragile, as Kamikazw will soon be learning...

STUKA · Post by **STUKA** » Mon Jul 14, 2008 8:26 pm

heavy fishing line?

Panzer_M · Post by **Panzer_M** » Mon Jul 14, 2008 10:21 pm

heres da crab...which is now no longer among the living