360 Servo pendulum mount. Part 1: bodgerneering

I have been using Tower Pro MMG 995 servos for pan motion for one reason: they have an M3 thread on the output spindle. This means I can fix a Picavet cross directly to it for lightweight cameras and have no fear of the fixing working loose: it’s metal to metal and I can use a nylock nut too. The Picavet mounting has worked well, up to the point where I can use a folding cross without risk of the fixing working loose.

For the last of the L rig batch I want to use my preferred suspension, a pendulum. I like its simplicity and robustness,  they are reliable and can be fitted to the line with one hand.

The MMG 995s are on the web pre-hacked for 360 operation for robotics applications and this saves time for little expense. The last one I ordered arrived unmodified and I found it quite easy to do this, there are good tutorials out there (search for ‘360 servo hack’) and the parts ( 2x 2.4kOhm resistors are 35p each at Maplin) are cheap. Rather than solder to the board I cut the potentiometer off leaving long tails to fit the resistors to.

The next problem is the tricky bit: how to fit the pendulum to the servo. This must be securely fixed and shock proof. The pivot of the pendulum will be at the kite line so this joint will have to take both the turning force of the servo and whip of the swing at its maxima but will not need to handle any pivot movement.

CRW_1581I have used the same method on 3 previous rigs so the fixings are proven if a little over sized.

For all the robustness of the pendulum the mounting pin looks fragile to me. Especially so when the single M3 Jesus nut carries the entire weight of the camera.

CRW_1582This is what you might call ‘bodge-er-neering’: the fitting is based on what I can lash together with what I have in the shed. It strikes me I could reduce the size of the post and its fittings and still have a working pendulum. As it is all my pendulums are based on a 5mm ID tube which fits over the post- this has proved practical and just about within my metal working skills to produce. You can see what fun I had cutting the thread on the post- it slipped in the vice as I turned the die. A neater power supply would be good – the UBEC is to turn down a PP3 9v cell to 5 v to keep the controller in safe voltage limits. A smaller post would be nicer too but for now the last of the L rig set is done.


About billboyheritagesurvey

Heritage worker
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One Response to 360 Servo pendulum mount. Part 1: bodgerneering

  1. Pingback: Around the Archaeology Blog-o-sphere Digest #5 | Doug's Archaeology

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