User:Pranav Rathi/Notebook/OT/2012/01/12/Extend your Opto-mechanical controls with Lego for out of box control

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Due to some airborne noise in our lab we had to put our optical tweezers in a plastic enclosure. This means that either I had to make huge doors or openings in the box to reach the optomechanical controls or control them from outside. And I chose the second one. There are two ways to control them from outside; first by manual- mechanical control and second is by electro-mechanical control. I choose the first one because it was easier and a step stone to electro-control/servo control. Now to mechanical control the optics from outside was not easy because there was no system built on the device itself to tweak the control knob ( I call it knob A) from outside as we can see from slide 2. All I had was two knobs (A knobs). So to control the device from outside I had to build the system around this knob A in a way to extend and transform this knob to the outside of the box. Once this system is in place I can control the knob A with knob B (the one I put). I call the system (structure) Gear Box, because that is what it is. Once the gear box is in place knob A can be controlled with knob B (manual-mechanical) OR servo control (electro-mechanical).

Design and construction


  1. ST1XY-S - XY Translator with Micrometer Drives (thorlabs) or any other optomechanical device
  2. Lego (2x) 40-Tooth Gears
  3. Lego (4X) 24-Tooth Gears
  4. Lego (5x) 8-Tooth Spur Gears
  5. Lego (2X) Worm Gear
  6. Lego Universal Joint
  7. Lego Axles
  8. Lego Bushings and stoppers
  9. 8-32,#8,4-40 and #4 screws and nuts
  10. Gorilla Epoxy
  11. 1/16” thick aluminum plate
  12. Round Dowel of 1/2” and 3/16”
  13. Knobs
  14. and tools like metal cutter, screwdriver, power drill with bits and dremel set.


I am planning to control 2 devices; QPD and steering lens with this. Both the devices are attached to two different Thorlab’s ST1XY-S - XY Translator with Micrometer Drives. This drive is not designed to handle Lego or any kind of attachments like shown in slide 2, 3 and 4. So to attach gears I had to first create my own attachments. So this is what I did: I first create attachments like shown in slide 2,3 and 4 by Epoxy gluing 8-32 nuts directly on the face of the driver in slide 2. But on other side (X-axis) I did not glue the 4-40 nuts on the face but glue on the platform of the knob A, slide 4, because on X-axis the Knob A moves in the vertical Y-direction. So the gearbox has to move with the knob which is not the case on Y-axis. Once I glued the nuts I waited for 24hrs for the glue to set. Now I can bolt the gearboxes directly on the nuts. Next step is to prepare the gear box. I prepared the gearbox such that it can provide me following: Enough precision and speed, constant directionality (both the knobs are in the same direction), some degree of freedom in alignment with aperture-openings on the box, which is provide my Lego universal joints (with these joints the knob does not have to align the opening on the box slide 16) and possibility to servo control. So that’s why I choose Lego because it has all the gears and axels but not the chassis, so I had to design my own chassis. Third part is knobs B. I bought the round dowel from Home Depot and maneuver them to fit with Lego universal joint on one side and knob on other.


I can breakdown the construction in the following steps:

Step 1; choose the right gears and screw them directly on the knobs. I choose 24 tooth gear for Y-axis and 40 tooth gear for X-axis. 40 tooth gear is maneuvered by 8 tooth gear which gives 5X precision. 24 tooth gear is maneuvered by worm gear which provides 2X precision. Worm gear also provides same directionality and great maneuverability for the whole range for the Y-axis knob even though this knob moves in vertical direction as it rotates.

Step 2; prepare the chassis. I measured all the distances between the screws and the gears and the height and diameter of the gears. Using these distances I prepared the frame by cutting it out of an aluminum sheet, slide 8. I prepared two frames one for each axis. Then I folded the frames such their legs fit directly on the nuts.

Step 3; fit the gears. Once I have folded frames I took the gear measurements again to make the axel holes on the frame. I had to be very careful in doing this because the holes had to align very-well. Then in the end put the gear box together, slide 9 and 10. Once the gear box is ready it can be bolted on the driver, slide 11, 12 and 13.

Step 4; prepare the knobs. I used two different size wood sticks (round dowel) to prepare the knobs with handles. I bought the knobs from an astronomy website and sticks from Home Depot. I maneuvered the 1/2" diameter stick in the knob then a 3/16” diameter into the 1/2’’ to prepare the handle. I milled the other end of the stick to fit it into the Lego universal joint slide 14 and 15. Once the knobs are ready they are attached directly to the gearbox with Lego universal joint. Due to Lego universal joint the gearbox does not have to align with the aperture-opening (inputs) of the box, this gives the driver some degree of freedom in 3D, slide 16 and 17. The steering lens has to move in all 3 directions to perform its task so without Lego universal joint the whole setup is useless if the lens cannot move properly. And things change time to time with in/an optical setup so some degree of freedom in maneuverability is absolutely required for out of box control. This system provides more than an inch of freedom in all 3 directions without sacrificing out of box control maneuverability.


The slide-show and video presents the make and the performance.

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{{#widget:YouTube|id=gWHnJh6mEDg}} Slide 18, 19 and 20 shows the out of box control setup for the system. The rubber washers are used at the inputs to provide isolation to the box from the handle bars and keep the inside-setup somewhat isolated from the airborne noise. I prepared two systems one for QPD and for steering lens, both the devices are needed to be controlled during the experiments. Now with this system both the devices can be controlled easily form outside slide 21, 22, 23 and 24.

There is one more device, used heavily during the experiments and needed to be controlled from outside. That is microscope. I made a small arrangement shown in slide 26 and 26 to control the microscope focus from outside. The scheme is similar; I glued a 1/4 inch nut to the microscope knob A. Then use a 1/4 to 8-32 screw attachment to attach a 8-32 screw. Now use Lego universal joint to attach 8-32 screw to control cable of knob B. I used the whole system recently to take the data and performance is promising so far. So I am going to use this as a part of optical tweezers setup and hopefully this will help in enclosing and isolating the tweezers from airborne noise. Now I can easily control most of the opto-mechanical controls from outside the enclosure during experiments.

In future I if get the time I would like to attach control the gearbox with servo motor, so the opto-mechanical controls can be maneuvered electromechanically.