Gio and I were in lab on Monday and Friday.
On monday we created a mold for the dry powder inhaler out of silicon and we let it solidify over night.
On Friday we observed the mold and removed the few imperfections it had. Some of the silicon had hardened inside the nozzle area. This was easily and neatly peeled off. We also looked at some of the previous motor code and tired think of anything more efficient but we could not come up with a way to change the layout and design of the code since the code is already in the most simplest of terms.
We also needed some guidance on what to do next. We really need parameters for the motor code since we are now in the phase of implementing the equipment (Motor & Vacuum) into a testing model for dry powder inhalers.
Sorry for forgetting to post about Monday’s lab. It was pretty uneventful in the fact that we just set up the big easy driver with the same set up as the EasyDriver. Friday lab is where we accomplished the most. As stated by both, Gio and Tyler. We altered the code to get rid of the MS1 and MS2 pins. We decided to do this because we were following a tutorial set up by the created of the BIgEasyDriver. Brain Schmalz. What we noticed was the MS1 and MS2 pins were used for the precision of step, while a full step gives the most torque microstep (1/16th) step gives the motor a smoother flow. We decided to use the smoother flow and surprisingly the torque was better than what we expected. the 1/16th step was default for the BigEasyDriver making it easier on us since we did not have to regard the MS pins. We copied down the code from Brian’s tutorial ( http://www.schmalzhaus.com/EasyDriver/Examples/EasyDriverExamples.html ) and used pins 8 and 9 as direction and stepper pins respectively. After tweaking the code a little be to meet our specification of rotating count clock wise first since the vacuum nozzle required that. We attached the motor to the vacuum to check if the torque requirement was reached and thankfully everything went according to plan. The motor was able to open the valve in an effective manner. The next step is to adjusted the code so it accounts for acceleration to mimic tidal breathing. We did have an issue with the BigEasyDriver heating up from time to time depending on the amount of delays we put in between each step. I e-mailed Brian Schmalz to address this problem and he stated,
” No worries at all.
So you have a 6 wire and have wired it in bi-polar mode. Excellent.
First thing to do is reduce the current limit. Put a DVM on the TP1 testpoint and measure the voltage there as you adjust the current adjustment pot. Turn the pot for minimum voltage on TP1 while the motor still runs. That will significantly limit heating. If your motor doesn’t run well at anything but the highest TP1 voltage then you may want to reduce the BED input voltage. That will reduce heat too.
You can always use a small stick on heatsink like sparkfun sells. Or a small fan.
The driver chip will shut itself down if it overheats (165 C) so you can’t damage it by overheating it.
Hope that helps!
This is awesome news because now we know that the BigEasyDriver will shut off if it does get too hot. We can also implement some of the suggestions Brian gave.
Overall, I think it was a really productive day and we are getting even closer than ever in constructing this breathing simulator.
Gio and I were in the lab on Monday and we were trying to come up with a solution to generate enough torque to open the valve. We finally had a small understanding of how much torque we would need since Andy showed us the valve that we would need to be open and closing to control the vacuum. We knew that the current Wantai Stepper motor that we have would not be able to generate enough torque to open that valve. We came up with multiple solution that Andy helped us out with as well.
1) We can ditch the Wantai Stepper Motor and use the unknown Bergerlahr motor. The problem with this potential solution is that we have no idea how the motor function since it have 10 wires instead of the 2 or 4 wire configuration that we are used to. We found someone selling the motor on ebay and messaged him or her to supply us with a spec sheet. If not we are still looking around the internet to find a spec sheet so we can finally understand how to set up the motor.
2) Another solution is to use gears with the Wantai stepper motor. Andy summarized to us how the gears work and there effects on the torque, basically the bigger the gear the more torque is generates since the motor has to make more revolutions to spin the larger gear compared to a smaller one. Andy also purchase a set of gears that we could use for any motor and hopefully amp up the torque on it.
3) Lastly we decided that by using the Big Easy driver to control and power our Wantai stepper motor would help a lot since the smaller easy driver was really easy to figure but was not able to withstand the optimal current we need. With the Big Easy diver we will be able to use a 2 amp source. This is different then before because the Motor Shield is a bit unfamiliar to us.
Hopefully we will have one or more of these solutions set up Friday or Monday so we can start using the motor with the valve.
This past Monday I set up an account at a Robotic Stack Exchange website which has multiple topics in which you can ask a question or read up about electronics. I was shuffling around a few threads to get a feel for how questions were asked and what type of responses were received. Over all the community was really helpful and pointed one in the right direction. I decided to ask a question about the Wantai stepper motor that we are using in Lab. (The post can be seen here.)
I addressed the problem of trying to decrease voltage to the desirable 3V while maintaining the 2A current we need.
The solution was simple, it was a concept called a chopper driver. I looked this what a chopper driver was on wiki to get a general idea and it stated:
“Chopper drive circuits are referred to as constant current drives because they generate a somewhat constant current in each winding rather than applying a constant voltage. On each new step, a very high voltage is applied to the winding initially. This causes the current in the winding to rise quickly since dI/dt = V/L where V is very large. The current in each winding is monitored by the controller, usually by measuring the voltage across a small sense resistor in series with each winding. When the current exceeds a specified current limit, the voltage is turned off or “chopped”, typically using power transistors. When the winding current drops below the specified limit, the voltage is turned on again. In this way, the current is held relatively constant for a particular step position. This requires additional electronics to sense winding currents, and control the switching, but it allows stepper motors to be driven with higher torque at higher speeds than L/R drives. Integrated electronics for this purpose are widely available.”
I think (correct me if I am wrong) that implementing a chopper driver will help over come the initial torque issues that we are having with valve.
As for the voltage, I believe we will need a high voltage just for the motor to overcome the torque even though the spec sheet for the Wantai motor states its max voltage is 3 volts.
We also have an option of using a more powerful stepper motor that will open the desired valves with ease.
Last Friday, Gio and I got into the lab and started to experiment with the Arduino and the motor. Gio previously made some adjustments on the Arduino by adding in the motor shield causing us to skip the SSR requirement, We messed with a few parameters within the sample code that rotated the motor. We soon realized that 1A was not enough for the motor since it would not run smoothly. Looking for a 2A power supply with a voltage no higher than 12V should do the trick.
I was not able to come to lab this Monday, but from reading Gio’s post, I can see that we have found an alternative power supply. I will be most likely testing the 2A supply to check if it works better. If it reaches the required specifications of torque, we can move on to applying a valve to the motor and experimenting from there.
Hopefully we will be able to get a feel of how much torque we need to open and close the valve efficiently as well as precisely. Then we can move on to calibrating multiple motors,
Today Gio and I were in the lab trying to figure how to exactly implement a Solid State Relay to the motor. A Solid State Relay (SSR) is a simple device that controls the flow of current in a circuit. The SSR is almost like a switch, but instead of pressing a physical button you can send a HIGH signal to the SSR for it allow current to flow.
The following diagram simplifies the understanding of an SSR:
We were able to get the SSR and the Ardiuno to work with each other. At the end of my research time, Gio and I were getting the motor to work for some odd reason. Maybe a loose wire or software, We will check out the problem on Friday and hopefully get the motor up and running again.
Gio, Tyler, and I were in the lab today testing out the DC motor schematic. The initial problem of a 12V power source was solved when I had handed in a spare 9V 300mA adapter which plugs into an outlet. the problem with this adapter was that it was only 9v and 300mA when our max potential on the motor was 12V and 2A.
We tested out other power sources and found out that the motor seemed to stutter a little before it started rotating. We solved this problem by editing some of the sample code we had received from the internet. Gio had the updated code on his computer and I am sure it will post it on his journal.
I ended the day with a successful running motor that can be altered. We need to take the next time into determining if the motor can actually close to valve used for the vacuum pump. To do this we need Andy’s input on the specifications of the motor. I will be in lab again on Friday and hopefully we can take the next step in creating a systematically controlled valves that will reduce the error within our experiment soon to come.