Members and Communities – Page 134

Spiderbot Systems and Interactions

May 6, 2014/in Communites, Members and Communities, Spiderbot, Spiderbot Generation #2/by arxterra

By Matthew Clegg – Computer & Control Systems
and Kristine Abatay – Project Manager

The following figure is a top-level systems diagram for the planned configuration of Spiderbot:

The method for powering Spiderbot from the Fall 2013 semester has been adapted at the moment, since the components used involved a NimH battery pack, as opposed to a LiPO battery, which would allow Spiderbot to meet the level 1 safety requirement.

This next figure was created by Matthew, using the program Fritzing, to show how the servos for Spiderbot will be connected to the microcontroller:

As was stated in a previous blog, Spiderbot will execute code using an Arduino Uno R3, which does not support the amount of servos that will be used. This will involve the use of breakout boards, which are shown in the diagram above. Power will be supplied to the Arduino Uno and the two breakout boards separately. In addition to providing accommodation for all of the servo motors, the breakout boards serve as a sort of “protection barrier” between the servos and Uno, which is an added bonus, considering it would be cheaper to replace a breakout board than it would be to replace an Arduino Uno.

This final figure is a diagram, created by Matthew using the program Eagle CAD, displaying the connection of each individual operational component for Spiderbot:

These connections are described in the following interface matrix.

This diagram shows the allocation of pins of operational components of Spiderbot. Overlap between the components demonstrates interactions that will allow the servo motors to communicate with the microcontroller.

Level 1 Requirements – Final Iteration

May 6, 2014/in Communites, Members and Communities, Spiderbot, Spiderbot Generation #2/by arxterra

By Kristine Abatay – Project Manager
and Matthew Clegg – Computer & Control Systems

The final statement of our mission objective created a new level 1 requirement regarding wireless control of Spiderbot through the Arxterra control panel and Arxterra Android app. The following is the final list of the level 1 requirements for Spiderbot, along with their corresponding verification tests:

1. Completion of the project will be achieved by May 12, 2014.

This is the date of the final assigned specifically for EE400D.

Test: If project Spiderbot is completed by this date, then this requirement will have been achieved.

2. The legs and complete chassis components of Spiderbot will be designed to extend into three spatial dimensions.

Test: This requirement will be verified within the SolidWorks program, which enables our manufacturer to define the three axes of a design. If, at any rotated view of a component design, three separate pieces of the design can be chosen to define a respective x-, y-, and z- plane, then this requirement will have been fulfilled.

3. Match the speed of the track rover project on a flat surface. This value was determined to be 0.2003 m/s.

Test: In order to verify this requirement, a flat surface, straight-lined course will be measured out and Spiderbot will complete the course while being timed. The resulting quotient of the length of the course, with the amount of time it will take Spiderbot to complete the course, will be calculated. If this value is equal to or less than the calculated rover speed, then requirement will have been achieved.

4. Operate in accordance with the CSULB College of Engineering Health and Safety Policy

(found here: http://www.csulb.edu/colleges/coe/views/safety_and_environment/safety_policy.shtml)

Test: The CSULB College of Engineering Health and Safety Policy states that

“Faculty…shall: Implement the university’s Health and Safety Policy and all other university safety programs in work areas under their supervision/control.”

If Professor Hill, a faculty member of the CSULB College of Engineering, approves the operation of Spiderbot in the classroom, then this requirement will have been met.

5. Have a height clearance of 4 in. and width clearance of 2.5 in.

These values were obtained through measurements of the largest obstacles found in the assigned course. The following image is an aerial view of the course that Spiderbot will have to maneuver. The total length of this route was measured to be 41.80m. It is located in the eastern wing of the CSULB campus.

Test: Verification of this requirement will be done by measuring the height clearance, as well as the length of one leg sweep of the fully constructed Spiderbot.

6. Spiderbot will be capable of being wirelessly controlled using the Arxterra Control panel, in conjunction with the Arxterra Android phone application.

Test: If a command sent to Spiderbot through the Arxterra Control panel matches the command that Spiderbot executes during operation from the Arxterra Android phone application, then this requirement will be satisfied.

Final 3D Model

May 6, 2014/in Communites, Members and Communities, Spiderbot, Spiderbot Generation #2/by arxterra

By: Simon Abatay – 3D Modeling and Manufacturing

The final model is here! The following image is the final design that will be manufactured for Spiderbot that was created using SolidWorks:

This final design was done in response to our project requirement that all components of Spiderbot’s body be three-dimensional. The chassis is composed of both 3D and 2D elements, but as a whole, it is three-dimensional. The inner portion of the chassis contains two 2D disks that will serve to hold the operational components of Spiderbot (i.e. microcontroller, breakout boards).

Just for kicks, here is an image of Spiderbot in a real-world setting (not shown to scale, of course):

Frame assembly

May 6, 2014/in 3D Printer, Communites, Members and Communities/by arxterra

By Gregorios Rios – 3D Modeling
and Jessica Salazar – 3D Manufacturing

When I first got Sasha, she was not the prettiest Mendel 3D printer. Sasha’s rods were a bit rusty; wiring was held down good but aesthetically was not pleasing to the eye. I was even concerned that it would not work at all or not print properly. After she was plugged in, she was alive and all that was needed to be done was to do a bit of calibration. Prints were pretty well done. Of course there is always room for improvement, especially since now there are new and better frame designs.

The Mendel printer is more of a triangular structural design weighing about 16 pounds, twenty inches high with and square base of sixteen by fourteen inches. When Jessica and I broke down Sasha, we realized that there were a lot of different components for a Mendel printer. It included printed parts, different rods, types of screws, washers and other miscellaneous part. Since the Mendel version requires so many parts it would require a lot of work in order to replace parts, repair or do any upgrades. Luckily the new P3Steel frame will take care of those issues. Once Sasha was broken down we separated everything that was going to be salvaged and parts that were not compatible with the P3Steel Design. The salvaged parts for the new frame were the Ramps board, most of the wiring, stepper motors, heated bed and 4 smooth rods.

This is the new Sasha. P3Steel design is derived from the Prusa i3 frame. The main difference between Prusa i3 and P3Steel is that the frame is cut steel plate, along with the y-axis frame replaced the y-axis rods. This frame design has a stronger frame due to its construction which will reduce vibration which will increase accuracy. When the new Sasha is complete, the printer will weigh about 23 pounds, which is much heavier than the Mendel version but it is not enough to be considered a bad thing, unless you are planning to transport it frequently.

Since the frame was lasered from steel, it needed to be painted to prevent corrosion. Because the frame was lasered from specific measurement it was supposed to fit with enough clearance. But after being painted that extra layer of paint was enough for parts not to fit properly which caused scraping parts or take off the paint of the frame when assembling. After being built, I had to go back, primer the part that the paint was scratched off during assembly and then repaint it.

Before adding the y-axis rods on the y-frame, rods needed to be cleaned from corrosion. I used a bench grinder with a wire brush disk, which worked very well. All four rods needed to be cut and luckily Jessica knew where to get them to the correct measurements. When adding the y-axis rods on the y-frame, the rods would not fit the opening on the y-frame. For some reason they were too loose when installing the rods, either the rods were slimmer than the opening or the opening were too big. The solution for this was to buy Amazing Goop which is glue that works with metal. This added an extra layer on the openings giving it a really good fit without movement, which will reduces vibrations during printing.

There was another minor problem with the stepper motors. Some motors didn’t seem to take M3 screws; it was a mixture of M3 and M2.5. The only way to solve that issue was trial and error. Try different screws on each spacing and add extra washers because the screws were too long. In the end it was mounted very securely and was no longer loose.

After many hours, of putting together the frame, trial and error, we had a completed frame. All that was needed was to prepare the printed part to be mounted on the frame, pulleys, bearings and belts. This was result of a lot sweat, tears and blood.

Preparing Printed Parts

May 6, 2014/in 3D Printer, Communites, Members and Communities/by arxterra

By Gregorios Rios – 3D Modeling

Our 3D mentor (Mike Pluma) provided the printed parts to be use on the new P3Steel design frame; which is very similar to that of the Prusa i3. All of the printed parts were printed out of ABS plastic because ABS is very sturdy and has a higher melting point compared to PLA plastic. When dealing with printed parts, there is a process that needs to be done on each part so that it can be installed properly into the frame. This can include parts that need to be cut off, sanded, trimmed or be drilled. Support material is part of the printing process that helps support material when being printed. This support material needs to be removed by cutting it off with a sharp blade and pliers for every printed part.

For most of the printed parts, M3 screws would not fit, so a drill was used to make them big enough to fit correctly. The drill was also used when there where opening that were too small and needed to be expanded. A Dremel could have been used but it is usually better for larger openings. When using a Dremel, being precise and cautious is very important. You do not want to ruin the part and have to spend more hours re-printing a replacement.

Both x-axis mount ends took longer than expected to get them prep to install into the frame. Apart from the above procedures done to them, all four opening for the smooth rods were too small and needed to be increased in diameter. This was done with a combination of a drill and the Dremel. The drill was used to make the diameter as big as possible without making it big enough for the rods to be loose, and the Dremel was used to grid off the hole evenly big enough for the rods to go in nicely snugged to avoid vibrations. When installing the rods, you have to be sure that you do not force the rods in too forcefully; this can split open the a-axis mount and ruin the x-axis mounts. The Dremel grinder was used to make enough room for the linear bearing to be put in the mounts. When installing the linear bearing it is very easy to break off the linear bearing walls. Just enough clearance for the bearing to go in is essential.

For both extruder and hotend clamps printed part also needed to be altered in order for bearing and screws. In order for 608 bearings to be installed, a Dremel with a round grinder was used to make sure the bearing fit correctly. E3D dual clamps that are attached to the X-carriage needed a good amount modification. Both the diameter and height of the inner walls of the clamp needed to be cut down in order to adequate installation with the E3D hotends. In the picture below you can see how it originally was and the end product.

There were times that parts needed to be replaced after being prepped and installed, but were replaced by better designed parts that in the long run will benefit Sasha’s reliability. Regardless of the time spent on the discarded parts, it will reach our goal of providing an overall better quality printer.

All these steps were done to several of these parts:

http://reprap.org/wiki/P3Steel_Proteins

Hexapod Coding Preferences

May 6, 2014/in Communites, Hexapod, Hexapod Generation #2, Members and Communities/by arxterra

By Chau To

Introduction:

This blog post will discuss some issues of the servo library (Servo.h) and how coding of the Hexapod was built including functions and subfuctions as well as some tips and troubleshooting.

Note: Hexapod team drives 19 servos directly from the Arduino board (digital I/O pins), and it uses the built-in Servo.h library functions such as “write” and “attach” as the main code to rotate the servo shaft. If your hexapod uses an additional servo controller boards such as the Adafruit etc, some of the materials discussed in the post would not apply in that situation.

How to create object servo in the Servo.h library:

Since the coding will require “for” loops, creating individual servo object such as servo1, servo2, etc.. Similar to the example in the Ardunino websites is impossible. The only way is to create an array of servo object. How can we do it? We can define a number of servo then call the servo library to create and array of servo object:

#define number_of_servos 19
Servo servos[number_of_servos];

So, we will have an array of servos; in this example, we will have array of 20 servos. Each servo will be appearing like this servo[1], servo[2], etc… NOW! We can put these into for loop. For example: servo[i].write(180).

Array:

Array is very important. As mentioned above, when we run “for” loop we need to use array because it will optimize our coding. An array of digital I/O pin is a great example since we need to attach each servo to a specific pin on the Arduino. Here is a sample code:

int pins[] = {30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48};

void set_servos() {

for (int i=0; i<number_of_servos; i++) {

servos[i+1].attach(pins[i]);

}}

The above example is a simple function I wrote to attach the pin to the servo. My digital pins will be from pin 30 to pin 48 of the ADK board.

The same concept applies for the servo’s shaft angle rotation. If user wants a specific servo to rotate at a specific angle, they can make an array of angles and run it in a for loop. More detail about array of C++ can be found at: http://www.cplusplus.com/doc/tutorial/arrays/

Subfunctions:

Subfunctions are smaller functions that will be called in a main or larger function. Breaking a long and complex function into smaller subfunctions is very useful because it’s easier for the user to double-check and debug the code. For example, one of the main function of the hexapod is run which includes 2 stages; first stage is moving the femur, tibia, and shoulder to a new position, and second stage is to bring them back to the initial position. So, we can break these 2 stages into 2 subfunctions. And, even smaller subfunctions for controlling and debugging.

Serial Monitor:

Serial Monitor can be turned on by Ctrl+Shift+M after uploading the code into the Arduino board. The serial monitor is extremely useful when testing the code. It’s used to keep track of the codes and fix all the bugs before uploading to a real model. This is the sample of the serial monitor added in my set_servo function that was discussed in the previous part:

void set_servos() {

for (int i=0; i<number_of_servos; i++) {

servos[i+1].attach(pins[i]);

Serial.println(“attach pin”);

Serial.println(i+1,DEC);

Serial.println(pins[i],DEC);

}}

With these serial function added in, I can monitor for my loop as well as to see which servo had attached to which pins. The serial monitor is available at: http://arduino.cc/en/reference/serial

Note: In order to run the serial monitor, in the setup you have to call the serial.begin

void setup()

{

Serial.begin(9600);

Figure 2

Thermoelectric Peltier Cooler Secondary Testing & Print Bed Installation

May 6, 2014/in Bio-Printer, Communites, Members and Communities/by arxterra

By W. Mevan Fernando

Due to the first set of TECs we purchased being faulty, we decided to purchase a single high quality TEC with a current rating of 10A. This would provide enough cooling by itself to cool the print bed.

The video below shows the print bed setup. A much larger heat sink was used along with the TEC and a fan was used to cool the heat sink. The TEC and fan were connected to our 12V, 30A power supply. Premium Ceramic Polysynthetic Thermal Compound was used on both sides of the TEC to provide better contact with the heat sink on the bottom and the aluminum print bed on top. The infrared thermometer we used before was faulty as well and hence a regular glass thermometer was used to show that the temperature of the print bed did in fact decrease. The temperature of the print bed was clearly colder than what was read on the thermometer due to the fact that all sides of the thermometer were not in contact with the aluminum. This could be seen by the condensation that was forming on the print bed and also just by touching it. Once again thermal compound was used to provide better contact with the thermometer and print bed.

Video at this link:
https://www.youtube.com/watch?v=aijkuX2GWC0

The pictures below show the installation of the whole print bed setup to our printer. 8-32 threaded rods were cut into 12” and used to attach the print bed to the printer. Two pieces of plastic were attached under the fan to ensure that there was space for airflow at the bottom of the fan.

After screwing the print bed on to the printer, an iPhone app was used to check if the print bed was levelled so that there wouldn’t be any complications while printing.

Thermoelectric Peltier Cooler Explained & Initial Testing

May 6, 2014/in Bio-Printer, Communites, Members and Communities/by arxterra

By W. Mevan Fernando

Peltier cooling modules are solid-state active heat pumps that transfer heat from one side to the other based on the Peltier effect. A TEC has two plates, the cold and the hot plate. Between those plates are several thermocouples. All those thermocouples are connected together and two wires, the negative and the positive, come out. If voltage is applied to those wires, the cold plate will be cold and the hot plate hot. In our design, the hot plate will be connected to a heat sink so that the heat gets pumped out. If not, the device will not work properly and may break down. In our design, we will use the peltier cooler to create a cool bed made of aluminum to cool down the agarose gel we use as our printing material so that it will cool down faster and maintain its shape as layers are added to the 3D structure. A schematic of a TEC connected to a heat sink is shown below.

In our design we will use 4 TECs to provide enough cooling for our print bed. The TECs we purchased had a current rating of 6A. We ran the TECs through our 12V, 30A power supply which we use for our printer. The video below shows the tests we ran to see the behavior of the TECs. One of them was connected to a heat sink to observe the difference in temperature readings with and without the heat sink. As expected the temperature of the one connected to the heat sink decreased while the temperature of the rest increased.

Video at this link:
https://www.youtube.com/watch?v=YwmJ70BcB7k

The following picture shows the setup we used to connect the TECs to the aluminum print bed. The placement of the TECs was decided upon the fact that the printing will be done only towards the center of the print bed. Thermal adhesive was used to glue the TECs to the bed.

After connecting the TECs to the print bed, they revealed to be faulty. This maybe because we didn’t use a fan to cool down the heat sink once all of them were connected together or because of the poor quality of the TECs we purchased.

References

Picture of schematic: http://www.tetech.com/FAQ-Technical-Information.html

Resolution And Software Summary

May 6, 2014/in Bio-Printer, Communites, Members and Communities/by arxterra

By: Anh Nguyen

I/ X,Y,Z Resolution

The object of this experiment is to calculate the resolution of the x, y and z axis of the 3D bio printer. First, the theoretical values from the manufacture’s specification sheet are used for the resolution calculation. Then the experimental values are used to calculate resolution. We will use both online RepRap calculator and the formula for the resolution calculation.

1/ Z axis:

The threaded rod is used for the z axis

The following parameters are used for the z axis:

– Motor Step Angle: 1.8 degree/step and 360 degree/rev

step/rev = = 200 steps/rev

– Driver Micro Stepping: 1/16 u step (we use the 1/16 Pololu motor driver)

– Presets: 1/4” 1/16” ACME

a. From the specification sheet, the lead screw pitch is 1.5875 mm/rev

+ Using RepRap calculator, the resolution is 2015.75 step/mm

+ Using the mathematical formula:

Leadscrew ( * * Motor ( =

(( * * 200 ( = 2015.75 step/mm

b. To get the experimental lead screw pitch value, we will need to measure the length of the rod and the number of lead screw within that length. Since we do not want to take the printer apart, we choose a part of the rod to measure the length and count the lead screw. The length of this section of the rod is 75.2 mm and the number of lead screw is 50.

Distance between each lead screw:

= 1.504 mm/rev

+ Using the RepRap calculator, the resolution is 2127.66 step/mm

+ Using the formula, the resolution is 2127.659 step/mm

Percent error between the theoretical and experimental resolution:

*100% = 5.55%

This percentage error is relatively large. This can be a result from human error in calculate the number of lead screw and also the uncertainty from the equipment (caliper).

We decide to use the theoretical value for the software to calibrate the z axis. We will later re-calculate the resolution of the z axis from the calibration’s result.

2/ X and Y axis:

The belt and pulley are used for the x and y axis

The following parameters are used for the x and y axis resolution calculation:

– Motor Step Angle: 1.8 degree/step and 360 degree/rev

step/rev = = 200 steps/rev

– Driver Micro Stepping: 1/16 u step (we use the 1/16 Pololu motor driver)

– Belt presets: 2mm pitch

a. From the specification sheet, the belt pitch is 2mm and the pulley tooth is 30

+ Using RepRap calculator, the resolution is 53.33 step/mm

+ Using mathematical formula:

(motor_steps_per_rev * ) / (belt_pitch * pulley_number_of_teeth)

(200 step/rev * ) / (2mm * 30) = 53.33 step/mm

b. The measured belt pitch using a caliper is 2mm. The number of pulley tooth counted is 29

+ Using the RepRap calculator, the resolution is 55.17 step/mm

+ Using the mathematical formula, the resolution is 55.17 step/mm

Percentage error between theoretical and experimental values:

* 100% = 0.289%

The percentage error is small. We will use the theoretical value for the software to calibrate the x and y axis. We will later re-calculate the x and y resolution from the calibration’s result.

2/ Sofwares:

To control the 3D bio printer, we will use the three following softwares: NETFABB, Slic3r and Pronterface.

NETFABB is a free cloud, which allows us to clean the .STL file so it is ready to be sliced into G-code (machine code which represent the created model).

Slic3r is software that converts the .STL file into G-code. The software can be downloaded online from: http://slic3r.org/. There are 4 tabs in the Slic3r software: Platter, Print Settings, Filament Settings and Printer Setting. We will add the G-code in the Plater tab and set the settings for each requirement.

In the start of the G-code, the printer is told to home all axis and start printing. At the end, only the x-axis is home and all the motors are turned off.

Pronterface: After the G-code is ready, it will be loaded to the Pronterface software.

The baud rate of the Pronterface is set to be 25000, the same as the baud rate of the Marlin Firmware.

The Marlin Firmware is used for the Arduino to set up the movement for the 3D bio printer. The firmware can be downloaded from: https://github.com/ErikZalm/Marlin

In the code, the speed of communication is set to be 25000.

// This determines the communication speed of the printer

#define BAUDRATE 250000

// #define BAUDRATE 115200

We will take out the thermal settings in the code because we will use a Peltier cooler attaching to the bed to cool down the printed gel and a second Arduino to control the temperature of the gel inside the syringe. However, when we comment out the thermal setting of the code, an error is returned in complying because the firmware wants to run the subroutines that control the thermal settings of the bed and the extruder. To solve this problem, we connect 100kohm resistor instead of the thermistor and keep the original code.

// 0 is not used

// 1 is 100k thermistor – best choice for EPCOS 100k (4.7k pullup)

// 2 is 200k thermistor – ATC Semitec 204GT-2 (4.7k pullup)

3/ Wiring:

We use a new linear actuator for the extruder. It has 2 pairs of wire: red/ red white and green/ green white for two phases.

First, we will test the polarity of the connecting wire from the ramp to the actuator. The ramp side has 4 wires: black, brown, red and orange. The actuator side has blue, yellow, green and read wires.

Ramp Actuator

1A Red Green

1B Black Blue

2A Brown Yellow

2B Orange Red

Red / Red White will go to 1A and 1B while Green / GreenWhite will go to 2A and 2B or vice versa. We need both two phases of the actuator for precise movement. The current goes through the actuator should be from 1.75 to 1.2A. Since the actuator does not have any motor in it, its motion depends on the control of the ramps on the Arduino board. We need to check the connection of the ICs on the Arduino board to make sure there is enough current going through the actuator.

Gel Point Test Plan

May 6, 2014/in Bio-Printer, Communites, Members and Communities/by arxterra

By Omair Tariq

Scope

It was determined that agarose gel will be used as the “ink” for the 3-D bioprinter. Agarose gel was chosen primarily because of its low cost and its use as an overlay for cells in tissue culturing.^[1]. The gel point is the temperature at which the gel mixture transitions from a liquid to a gel. The melting point is the temperature at which the mixture melts from a gel into a liquid. Agarose gel is special in that it has a different melting point and gelling point. The purpose of this test is to determine the gel point of agarose gel Type A0169 by Sigma Aldrich.

Equipment needed

Equipment	Quantity
Spatula	1
Measuring balance accurate to a 100^th of a gram	1
900 Watt Hot Plate	1
100 ml beaker	1
50 ml graduated cylinder	1
Glass thermometer (Range: 0^oC-110^oC)	1
Agarose gel Type A0169 by Sigma Aldrich	See Table 2
Distilled water	See Table 2
Safety Goggles	1 per person
Latex Gloves	1 per person

Table 1. Equipment needed for Gel Point Testing

The amount of Agarose gel and Distilled water is to be determined by the desired gel concentration.

Concentration	Agarose Gel Type A0169 (± 0.05g)	Distilled water ( ± 0.1 ml)
1%	0.50 g	50.0 ml
2 %	1 g	50.0 ml
5 %	2.5 g	50.0 ml
And so on…

And so on…

Table 2. Amount of agarose gel powder and water required to produce desired gel concentration for 3D bioprinter

For the purpose of the bio-printer the amount of distilled water is to be limited to 50.0 ml since the extruder is a 60 ml syringe. The maximum amount of water is limited to 50 ml rather than 60 ml to avoid spilling of the gel and consequently, the waste of valuable gel mixture.

Test Plan Instructions

Note: This test plan can be carried out to determine the gelling point of any concentration of gel. 1 % gel concentration was chosen randomly for this test plan.

Put a 100 ml beaker on the weighing balance.
Zero the balance so that the weight of the beaker does not hinder measurements.
Use a clean spatula to put 0.50 grams of Agarose gel Type A0169 powder by Sigma Aldrich into the beaker.
Measure out 50 ml of distilled water using a graduating cylinder.
Pour the 50 ml of distilled water into the beaker containing the 0.50 grams of Agarose powder.
Measure the weight of the solution using a measuring balance. It should weigh about 51 grams.
Mix the solution using a Mercury-in-Glass Thermometer or a spatula.
Put the beaker containing the mixture from Step 4 onto a hot plate.
Bring the solution to a boil and let it boil for 5 minutes.
At the same time, place the graduating cylinder filled with water on the hot plate.
Reweigh the solution after boiling.
Add enough hot water from the graduating cylinder, if necessary, to bring the total weight of the solution to 51 grams.
Allow the mixture to cool. Mix the solution continuously until the solution reaches a temperature of 50^oC. At this point, further mixing might lead to problems in accurately determining the gelling temperature of the solution. Observe the viscosity of the solution every 10^o C until the solution reaches a temperature of 40^oC. Once the solution has reached a temperature of 40^oC, or when the solution starts to gel, the viscosity of the solution must be observed every 1^oC.
The viscosity is to observed using the following steps:
1. Take a small amount of solution on the spatula,
2. Raise the spatula about 12 inches above the beaker.
3. Carefully, drop the solution by tilting the spatula.
4. At the gelling point, the solution will have turned rubbery. If it is attempted to mix the gel at the gelling temperature, it will be observed that the gel will break into smaller pieces. The smaller pieces will not merge after sometime as they would if the gel was still a solution. This would not happen if the mixture were still a solution, thereby proving that the gelling point was reached.

Conclusion

By determining the Gel point, we will be able to determine the temperature that should be maintained in the extruder head. The extruder head should be kept at a temperature of 1-2^oC above the Gel point. If the extruder head is maintained at a temperature equal to or lower than the gelling temperature, extrusion cannot be performed accurately since the gel will only extrude as large chunks rather than flowing smoothly from the extruder head. Therefore, maintaining the temperature of the extruder head 1-2^oC above the gelling point will enable smooth extrusion of the gel. The plate must be at a temperature lower than the gelling temperature so that the gel is able to hold its shape after extrusion.

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