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...... Radar Ears ......

Got some very nice radar ears from Bill K, and aluminium posts from Jerry C. The radar dishes just needed painting, but the aluminium i'm leaving as bare metal. The tricky part is fitting the motors in.

First tried the expensive metal motors, but they seemed to resonate with the aluminium posts and make a lot of noise.

Found these smaller (6mm diameter) motors at Precision Microdrives in the UK, but they also available from Gizmodo and elsewhere.

The model 206-108 has an ~700:1 gear ratio, giving about 28rpm at 3v unloaded, and the radar ears are so light it is almost no load. They can be slowed by simply dropping the voltage and will still operate at 1.5v, though with reduced torque. Although the torque is obviously small, it's enough for this tiny load at low speed. Since you would want to adjust the speed anyway to get the exact look you're after, i went a bit overboard, keeping the voltage at 3v and adjusting the PWM to get slower speed while maintaining the torque. But the PWM controller was only $3 from ebay anyway.

The plastic gearbox makes it quieter than the metal one but the drawback is the tiny plastic shaft is difficult to attach anything to. The trick is to not rely on the motor for supporting the radial load, but on 3x8x3mm bearings, so it's all housed securely even without the motors attached, then all the motor has to do is turn it. i poked around in the hobby shop until found a piece of aluminium tube with about 3mm OD and an ID that just slipped over the "D" shaft of the motor, added a bit of epoxy cement and pushed them together. Have also seen a rather ingenious design using heat shrink to make a flexible coupling - remember the ears are supported so this connection doesn't have to be very strong at all.

The radar posts came with 2 different tops to suit different different motor sizes. Could have used either but decided to use the one with the larger hole because there was less material to drill out and they already had a surface for the flange of the bearings to butt up against, above and below.

The hole in the ears was 7mm to match the metal motors, i very carefully drilled them out to 8mm for the bearings (originnal hole shown on the right, 8mm hole on the left). i used 3x8x3 flange bearings but you could use standard ones if you were worried about the lip, but it really doesn't show when all assembled.

There are 2 bearings, one on the top and one on the inside. Added a bit of Threadlock to keep the bearings in place, being careful not to get any in the workings of the bearing.

Found i piece of silicone tubing in the junk pile that neatly fitted the inside of the radar post and held the motor in place.


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