The TacTip is a 3d-printed optical tactile sensor developed at Bristol Robotics Laboratory (Chorley et al, 2009). It aims to fulfil the need for a cheap, robust, versatile tactile sensor, mountable on industrial robot arms and aimed at eventual integration into robot hands for manipulation. The TacTip is available to order from us by email, or can be fabricated following online instructions.

The sensor contacts objects with a compliant tip made from a moulded silicone rubber (Smooth-on Vytaflex 60) filled with a clear silicone gel (RTV27905). The inside of the tip comprises of a series of geometrically arranged white-tipped pins.

TacTip sensor

Pins deform when an object is contacted, and are tracked using an off-the-shelf Microsoft Lifecam Cinema webcam. Different patterns of pin displacement  can provide information on object shape, object localization, contact force, torque and shear.

Experimental stimuli

Pin positions are detected using OpenCV image processing algorithms and their x- and y-deflections are treated as independent taxels. The figure below displays an example dataset obtained by rolling a cylinder along a horizontal surface. Each color in panels A and B corresponds to a pin from the TacTip, as shown on the right-most panel.  


TacTip data

By training the TacTip over given stimuli, we can then apply Bayesian algorithms to classify these stimuli.  Using this approach allows us to apply the TacTip to a number of tasks, such as localization, object identification, contour following .... (see Testing section).


Biomimetic inspiration

Figure 1: Intermediate ridges in the human skin (left), and the corresponding pins in the TacTip (right)

The sense of touch is one of the key human modalities. Tactile sensory input should also be provided to robots to allow them to perform complex manipulation, grasping and exploration tasks. The TacTip sensor is a biomimetic, dome-shaped device based on the human fingertip.

Chorley et al. (2009) were inspired to consider the behaviour of the human glabrous (hairless) skin, as can be found on the palms of our hands and the soles of our feet. They built on previous research showing that Meissner’s Corpuscles work in tandem with the intermediate ridges (Fig. 1), to provide edge encoding of a contacted surface. When the human finger makes contact with an object or surface, deformation occurs in the epidermal layers of the skin and the change is detected and relayed by its mechanoreceptors. The TacTip device seeks to replicate this response by substituting intermediate ridges with internal pins on the inside of its skin. The pins deflect when the TacTip contacts an object and the resulting deformation is optically tracked by a camera.

Technical Design

The four main characteristics of the TacTip's design are listed below:

1. Modular philosophy The latest generation of the TacTip sensor is designed to allow its tip to be quickly replaced. This allows different designs of the dome-shaped part of the sensor, which is in contact with the external environment. Different versions of the tips can be manufactured and tested without changing or re-fabricating the overall structure. The bayonet mount permits the tip and the base structure of TacTip to be connected and disconnected in a fast and user-friendly manner.

Sectional view of tactip

Figure 2: Tip of the TacTip sensor. Left: view from the top, Right: side view

2. Materials The tip of the TacTip is created in two stages: the rigid white plastic (VeroWhite) is 3D printed in a Stratasys Objet series printer, and the black rubber skin (Smooth-on Vytaflex 60) is created through a moulding process. The mould could be adapted to investigate the effect of morphological changes of the skin (shape, layout and number of pins) on performance and sensitivity. The physical properties of the two materials used in the latest version of TacTip are reported in the following table:



Vytaflex 60

Tensile Strength

58 MPa

6 MPa

Elongation at break

10% – 25%


Hardness Shore A




The soft material used to fill the tip of the TacTip is Techsil RTV27905, which has a penetration (mm) [19.5g cone] of 3 to 7 and is completely clear, in order to allow accurate images to be collected by the camera.

3. Pin Layout The hexagonal layout of the pins in the TacTip’s soft tip is designed so that pins are equidistant from each other in the camera image. Since there are 6 LEDs in the TacTIp, this arrangement also keeps the pins as far as possible from the LEDs that illuminate the tip. This avoids the white LED lights being erroneously identified as pins by image processing algorithms.

Figure 3 view of the internal part of the TacTip

4. Sensor safety The TacTip has been purposely designed so that there is no physical contact between the fragile optical elements (camera, LED circuit) and the TacTip's external surface. This significantly contributes to the robustness of the sensor. In case of a strong collision between the sensor and an object, the soft tip dilutes the effect of the impact, and the crucial components of the sensor (LED circuit, camera) are well protected.

In summary, The TacTip possesses enough similitudes with its biological counterpart to make it an ideal platform for biomimetic research and, at the same time, is a low-cost, open-source, robust and easily customable structure. The STL and CAD files for the TacTip parts described above can be found in the Downloads section.



Fabrication of the TacTip is straightforward and consists of 5 steps, outlined below. If you are interested instead in buying a ready-made TacTip, contact us by email for a quote.

3D printed Assembling components     Flesh



1) 3d-printing  2) Skin 3) Flesh 4) LEDs 5) Camera


Laser cutter Soldering iron Microscope
Laser cutter
Soldering iron
Tweezers Wire stripper Screwdriver set Heat gun
Wire Stripper
Screwdriver set
Heat gun

Bill of materials

Image Description Qty Units  Unit Price Link
   Acrylic sheet Acrylic sheet (50 mm x50mm) 1 each £2.50 The Plastic People
Loctite 406 Loctite 406 glue 1 each £11.82 Loctite
770 primer Loctite 770 primer 1 each £17.37 Loctite
Mould release agent 1 each £13.28 Smooth-on
White paint 1 each £1.89 Humbrol
Syringe Syringe (20ml) 1 pack £7.20



Needle  Blunt-tipped needle 1 pack $9.90


RTV27905 Silicon gel RTV27905 Silicone gel 1 pack £130.51 Techsil
LED circuit LED ring 1 each 12 Eur PCB-Pool
LED Surface mount LEDs 6 each £0.161 RS
Surface mount Resistors 6 each £0.052 Farnell
Red and black cables Cable reels (red and black) 2 each £9.43 Farnell
M3 x 8mm Screws  M3x8mm Screws 3 each £0.04 AccuGroup
Camera Camera 1 each £69.99 Microsoft
Insulating black tape Black insulating tape 1 each £1.08 RS
heat_shrink Heat shrink 10m reel  1 each £8.36 RS
USB extension cable USB extension cable 1 each £0.91 Kenable

1) 3D-Printing

STL files for the 3d-printed parts can be found in the Downloads section for printing, along with Solidworks CAD files for easy modifications.

Note that these parts (specifically the tip, ring and body) need to be printed in a high precision (resolution below 0.1 mm) printer such as the Stratasys Fortus 450mc. All parts are printed in VeroWhite material.







Ring + Plug    




Camera mount


Once the parts have been printed, check all holes to ensure they are clear of support material. If necessary use a thin screwdriver to clear them. Then screw the base and mount parts together using the M3 screws as shown.

Body being screwed to mount

2) Skin

Painting pins

Order a tactip skin from us by contacting us via email. We will send you the skin for a small fee.

Spread a layer of white paint on a piece of acrylic. Insert your thumb in the skin and press on the white paint. Make sure all the pin tips are painted white.

Attaching skin

Thoroughly clean the 3d-printed tip and ring, to remove all traces of support material. This improves glue adhesion and ensures all parts fit together.Distribute a layer of Loctite 770 primer on the internal rim of the skin and the 3D printed tip to make the surfaces suitable for bonding with an adhesive.
3D printed tip and ringPutting primer on the tipPriming the skin
Wear gloves. Distribute a fine layer of Loctite 406 glue on the upper rim of the tip. Use a thin strip of a material that will not bond with the glue to do this (e.g.: polypropolene).Press the rim of the skin over the tip. The bond will form very quickly so ensure the  skin is placed in the correct position., flush with the first ledge on the tip. Make sure that no glue is present on the outside of the skin as this would locally reduce the compliance of the sensor.Make a hole in the skin aligned with the hole in the tip. This hole will be used to inject the gel in the tip. Let the glue dry for at least 10 minutes.
Apply Loctite 770 primer on the internal diameter of the 3D printed ring and the bottom part of the skin. Spread a thin layer of Loctite 406 glue on the bottom part of the skin.Slide the 3D printed ring past the rubber dome until it rests on top of the 3D printed tip and apply pressure.Make sure the hole in the ring aligns with the holes in the tip and skin. Leave the glue to dry for half an hour.

3) Flesh


Laser cutter

Download the lens.dxf file and laser cut the lens from a 3mm thick acrylic sheet, without removing the acrylic's protective film. The edge of the lens will be tapered slightly from the laser cutting process, with one side having a slightly smaller diameter than the other. This side will be pressed into the tip first , and is considered to be the bottom part of the lens. 

Lens cover removal Remove the protective film from the bottom part of the lens, and begin removing the top layer, leaving a flap for easy removal later.

Apply Loctite glue around the inside lip of the  tip.Spread the glue thinly to avoid it contaminating the lens.

Press the lens into the tip with its small diameter downwards, ensuring it has been pushed all the way down to the lip, and hold until the glue dries.

Apply a small amount of glue around the edge of the lens to complete the seal. Finish removing the top layer of protective film (tweezers can help for this step).

Silicone gel

Measure out 15g of RTV27905 part A in a plastic cup. Pour 15g of RTV27905 part B in the same cup. Mix the 2 components together vigorously.
Silicon gel part A Silicon gel part B Mix silicon gel components
Vacuum chamber

Place the mixture in a vacuum chamber for 5-10 min to eliminate bubbles. 

Note that if you are able to mix the 2 components of the gel within the vacuum chamber, this will result in less air being trapped in the gel. 

Insert the needle into the hole in the side of the tip. Have some kitchen roll ready in case the gel leaks. Fill the syringe with gel, and wipe it down with kitchen roll to avoid gel coating the outside of the tip.

Push the syringe into the needle and fill the tip with gel, angling it so that bubbles can escape through the air hole in the tip.

Fill syringe with silicon gel Filling gel with a syringe

 Once the tip is filled with gel, remove the syringe and plug the hole with the 3d-printed plug.

Finally, leave to cure for a minimum of 48 hours (if available in an oven at 40 degrees celsius.

Oven curing

4) LEDs

Surface mount resistors and LEDs

LED circuit

Order the PCB circuits online at PCB-Pool, using the Eagle file provided. 

Soldering station


Prepare the soldering station with a microscope, soldering iron with a thin tip, and solder. Ensure you are using an extractor, and have white-tack to hand for fixing the circuit while soldering.

Apply flux to the circuit (side with the mounting pads). Choose one of the 6 series of 4 pads, and deposit a small amount of solder on the left-most of the 4 pads as shown.
Applying flux
Using a pair of tweezers, hold the resistor on the solder and apply heat using the soldering iron to attach it. Apply solder to the unattached side of the resistor.  
Solder Resistor part 2 Solder Resistor part 2
Soldered resistor The soldered resistor should now look like this. 
Next, we will solder the LED, which has directionality. On the top of the LED, a small circle indicates the cathode (negative side). Thus for our circuit, the circle should be on the pad furthest from the resistor. 
Heat the solder on the pad nearest the resistor, and using tweezers as before, solder the LED to the circuit on its anode.  Solder the cathode to the pad furthest away from the resistor to finish the job. 
Solder LED part 1

Check that the LED and resistors are connected as shown. If the solder appears grainy, reapply flux and apply heat with the soldering iron.Then repeat the above steps for the other 5 resistors and LEDs.


Strip cables Strip both ends off 25cm length power and ground cables. 
Solder power cable to the through hole which connects to the inside ring on the circuit. Solder power cable to the through hole which connects to the inside ring on the circuit.
Solder power cable Solder ground cable
Cut the ends off both wires. Place the LED circuit on the 3d-printed body as shown.
Cut cable ends LED circuit in place
Cut the end of the USB extension cable and the protruding green and white cables. Leave the red and black cables, these corresponding to power and ground, respectively, and will power the LED circuit.  Strip the power and ground wires from the USB cable.
USB cable cut Strip USB cable wires
 Cut a small length of heat shrink for each cable, and feed the LED circuit wires through it. Solder the LED circuit wires to the corresponding power and ground wires from the USB cable.  To solder the wires together, first apply some solder to each wire individually.
Apply solder to first wire
 Then fix one cable, bring the other cable next to it and apply heat briefly with the soldering iron to solder the wires together. Using the heat gun, cover the connections with heat shrink.
Solder wires together Heat gun on heat shrink
Completed LED circuit The LED circuit is now completed. Plug in the USB cable to a computer and ensure that all 6 LEDs light up. 

5) Camera

Remove the webcam's clip using a phillips precision screxdriver. Keep hold of the small screw.

Cover the blue light on the front of the webcam with black tape.  Slide the camera into the top of the TacTip mount as shown, and use the small screw to secure it to the mount.
Camera clip Light cover Camera mount

Attach the tip with its bayonet mount. The TacTip is now fully assembled! 


Note that the 3 extra vertical holes in the design are to enable the TacTip to be attached to robot arms through custom designed mounts. The following part is included as an example, and allows for attachment on an ABB IRB120 industrial robot arm: ABB Mount.



The TacTip has been shown to achieve superresolved tactile sensing when tasked with estimating its location over a 40mm diameter cylinder (Lepora et al, 2015).

TacTip cylinder experiment

Superresolution encompasses a class of techniques that enhance the resolution of an image, notably hyperacuity where the resolution of a sensor is finer than the separation between its receptors. This is observed naturally both in human vision and touch as a consequence of sophisticated post processing in the brain.  


In this experiment the TacTip used in combination with Bayesian Sequential Analysis algorithms was shown to achieve a 40-fold degree of superresolution, with 0.1mm acuity compared with a 4mm spacing between tactile elements. This is comparable with tactile hyperacuity in humans, known to be of one order of magnitude. 


The TacTip has also been proven capable at identification tasks. It was tested in identifying gaps of varying widths (range 0.25–5 mm) under depth uncertainty (Lepora et al, 2016).

TacTip Identification Experiment

Using a similar sequential analysis approach to localisation tests, gap width is estimated to 0.35 mm, which is again comparable to human discrimination performance. Gap width identification has particular applications in quality control measurements during manufacture. 

Contour Following

Applying these principles of localization and identification, the TacTip has been tested in a simple contour following task. This has practical implications for autonomous shape recognition. Here we tested the TacTip's capacity for contour following on 2D shapes. (Lepora et al, 2017).

Following a tap, the edge location and orientation relative to the TacTip is perceived using the same biomimetic approach as in the above examples. An exploratory move is then performed along the direction of the perceived edge using a 6-DOF robotic arm (IRB 120, ABB Robotics). The process is repeated until the TacTip has successfully followed the contour, as demonstrated in the following video. 



3D printing - Tip.stl55 KB
LED Circuit.eagle30 KB
3D printing - Ring+plug.stl184 KB
3D printing - Solidworks files1.17 MB
3D printing - Body.stl96 KB
3D printing - Camera Mount.stl115 KB
Lens.dxf3 KB

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