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03/31/2013
My first custom-made robot design
The idea to design & construct my own robot started in my teenage years & finally came into existence a few years ago when I finally started collecting various robot parts & kits since they are now more affordable as well as affordable in size.
After looking at various systems for a number of years, I finally decided on the type of robot that I would design & build.
My idea for this project is to build a robot that utilizes a dual-propulsion system which will be four-wheeled & quadrapedal or hexapedal motion-capable. The purpose of this dual-propulsion system is to give the robot the capability to travel along smooth & semi-smooth surfaces via wheeled propulsion & to also travel on rougher surfaces as necessary by automatically switching over to a quadrapedal or hexapedal propulsion system.
It will have two controllable "arms" front & rear, each with a gripping capability that has an up/down motion, but for now will not rotate 360 degrees at the "wrist" joint. This feature will be implemented in the future.
The power supply will consist of a high-amperage capacity rechargeable type battery & possibly have a series of solar cells integrated into the design to use natural & artificial as a constant source of recharging energy.
I'm going to use the CrustCrawler S3 Panning Sensor System bracket kit with servos that I won from a written article contest that I had entered into but had forgotten about it after submitting my entry, that was sponsored by ROBOT magazine. This bracket may have some type of electronic detection system installed on it at some point, such as an IR or Active-Sonar type of ranging device for obstacle avoidance & navigation purposes.
Getting this robot to move will be the most challenging task of the entire project since I have to mount the quadraped or hexaped frame to the wheeled frame of the robot. Hopefully I’ll have enough clearance between the wheels & the legs. Next, I’ll have to mount the servos on the quadraped/hexaped legs, wire them up then test each one for proper operation. I’ll also have to install a microcontroller & write the code that will operate the robot in a hopefully autonomous mode.
There’s much work to be done before this robot is completely finished.
Logan Mitchell Sr
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04/14/2013
Okay, so now I have my second chassis for my custom-designed robot. This one is Black in body color which is an all-metal chassis & has 4 smaller wheels with yellow-colored hubs and an electric motor for each wheel which basically makes this a 4-wheel drive chassis, unlike the first chassis which is made of plastic with large rubber wheels which was originally part of a radio-controlled (R/C) car with only one electric motor for the rear wheels and also contained a left/right front wheel steering servo. This all-metal chassis is the SainSmart 4WD Drive Aluminum Mobile Robot Platform For Robot Arduino Raspberry Pi *Black*http://www.sainsmart.com/sainsmart-4wd-drive-aluminum-mobile-robot-platform-for-robot-arduino-uno-mega2560-r3-duemilanove-black.html. The chassis comes un-assembled & with the screws to put the pieces together which is very easy to do in about 15 - 20 minutes. It has some pre-drilled & pre-cut holes and slots for mounting various things, but my challenge is to make it waterproof, if possible, which means finding waterproof motors for the wheels & a light-weight metal container for the batteries that can be waterproofed since they along with the motors will sit inside the metal wheeled-chassis. Such is life as an engineer.
After conferring with Evan of Hobbytown USA in Parkville MD who is into robotics, he explained to me that the plastic-body rear-wheel drive chassis would not be as effective at steering & turning as the metal-body chassis since the metal-body chassis can use its 4-wheel drive capability to turn left, right & circularly just like a tank does, since it can use its front-left/rear-right or right-front/left-rear wheels to make those turns.
The metal-body chassis also allows me to add more options to its frame compared to the plastic-body frame, and by it being of all-metal construction, this will allow the robot to take a little more punishment.
Logan Mitchell Sr
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04/20/2013
Finally, the two walking robot kits that I ordered on 04/07/2013 from ThanksBuyer.com, http://www.thanksbuyer.com/product/search?&filter_name=robot, came in the mail today from ShenZhen China (13 days).
I ordered the following kits -
1. Aluminum Hexapod "Spider" Six 3DOF (Degrees Of Freedom) Legs Robot Frame Kit Fully Compatible with Arduino, Item #18249 $76.89, http://www.thanksbuyer.com/aluminium-hexapod-spider-six-3dof-legs-robot-frame-kit-fully-compatible-with-arduino-18249?page=1
2. Tortoise-shaped Robotic 9DOF (Degrees Of Freedom) Aluminum Robot Frame Set, Item #19848 $51.99, http://www.thanksbuyer.com/tortoise-shaped-robtic-9dof-aluminium-robot-frame-set-black-19848?page=2
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03/23/2014
After just over 1 year since I first started constructing my robot, I'm now working on getting the robot ready for display at an annual robot festival in Linthicum MD called RobotFest, www.robotfest.com at the National Electronics Museum that will be held on 04/12/2014.
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04/01/2014
I started constructing servo pulse circuit generator circuit using a schematic diagram from an online source that incorporated the Signetics 555 IC Timer chip, but the circuit didn't work because of construction errors on my part which resulted in a blown out 555 IC Timer chip. I drew the schematic for a similar circuit that I had built before for other applications that I knew would work.
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04/13/2014
After seeing that the robot's supplied motors are not strong enough & the wheels are not large enough to allow the robot to make left & right turns, I decided that I had to upgrade those items to be able to carry out this function since it would only go forward & backward. I started the process on 04/12/2014 & stayed up until 4:45am this morning to replace the wheels & motors that I purchased from Pololu Robotics & Electronics, so now the new motors and larger wheels allow the robot to go forward, backward, turn left & turn right. This has been part of the learning process for me in understanding the importance of having the right size wheels and the motors that have the correct torque capability for a robot's propulsion system to be effective.
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04/28/2014
Received two robotic arms with gripper claws that have 4 Degrees Of Freedom (4DOF) of movement per arm in the mail from China that I purchased through eBay. Each robotic arm comes with all necessary hardware including four MG995 digital servos for each arm but no assembly instructions.
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05/18/2014
Assembled 1 of the 2 robot gripper claw arms after 3 weekends of trying to figure out how to put this together since they came with no assembly instructions.
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05/25/2014
I started working on the servo pulse circuit generator circuit again & was finally able to get it working at 3:00am this morning. It puts out enough voltage to operate the analog & digital servos that I have for the robot. Now I have to select heavy duty servos that are appropriate to provide the right amount of torque for each section of the robotic arms & their gripper claws.
Installed a 2-position switch with a Center Off position to allow the manual selection of two operational speeds to allow the servos to go from slow-pulsed to fast-continuous. Added new electrolytic capacitors to give a slower timing factor to the circuit for one of the speed selections. The pulse generator circuit also has a variable speed control that works in connection with the setting of the 2-position speed selector switch to achieve the above listed operational speed settings.
Replaced the previously blown out 555 IC Timer chip & the servo pulse circuit generator circuit now works. Tested the pulse generator circuit on the previously installed front & rear robotic arms that have the Torobot TR205 analog servos installed on them and they work. Also tested the assembled 4DOF robotic arm that has the four Tower Pro MG995 digital servos installed on it & they work as well.
Since this is a dual circuit board, I'll construct a duplicate servo pulse generator circuit on the adjacent empty circuit board next to the finished circuit in a few weeks. One circuit will provide controlling pulse voltages to the gripper claw arms on each end of the robot.
The whole project is getting closer to completion as time goes on.
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03/19/2015 - I started working on my self-designed servo pulse generator circuit again on 02/22/2015. I was able to add some passive components that now allow me to get the servos to move in a forward & a backward direction. I also attempted to use an op-amp based amplifier circuit to do the same thing for the reverse movement action but the circuit did not work, so I will stick with the passive components that cause the forward & backward movements to work
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04/16/2015 - I started working on the housing box that will contain the dual servo motor pulse driver circuits for my robot. After some experimentation I found out that my digital Traxxas 2075 waterproof servos will not respond to the pulser's signals & the MG995 digital servos significantly load down the pulser circuit to the point that it stops functioning within seconds of operation. The Hi-Tec 422 servos which are analog, work just fine, so even though they have only 46 oz in. of torque, they at least function properly.
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03/13/2016 - Finally, after around 1 yr since I last worked on designing a working servo motor pulse driver circuit to get the servo motors to go forward/backward/left/right/up/down, I now have two working circuit designs. I incorrectly built the first one for a PNP transistor without knowing it until after I tested the design which to my surprise worked. So after that triumphant milestone in the entire 3 yr-long process since I first started this project, I'm finally coming to the end for my basic robot design.
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03/20/2016 - I had to redesign one of the servo pulse driver circuits that I initially designed on 03/13/2016 using a PNP transistor & thought that it would work only to find out again when testing it the 2nd time around that circuit did not work. After about 2 hrs I decided to try an NPN transistor & switch some of the parts around. Lo & behold the circuit redesign worked, so now I have successfully designed one servo pulse driver circuit that moves the servo motor in one direction & another servo pulse driver circuit that moves the servo motor in the opposite direction. One more hurdle has been overcome, so now it's time to see if these circuits produce enough voltage & current for the servo motors on the robot's aluminum gripper claws & linkage arms to be able to move with no problem. Product development is no easy task & can take a very long time to get right.
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03/24/2016 - SUCCESS. I connected one of the servo motor pulse driver circuits on the prototype board to the robot's gripper claw servo motor & the gripper claw's metal angle arm servo motor. The pulse driver circuit operates all four servo motors successfully. Maybe I'll attach the CrustCrawler S3 Panning Sensor System bracket kit with servo motors to the top of the robot.
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03/25/2016 - FAILURE. The servo operational success of yesterday from the prototype board is not the same today since now the servo pulse driver circuits that I assembled on the pc boards is only working partially, as in one side of the driver circuit rotates the servo motor in one direction, but the other half of the servo pulse driver does not make the servo motor rotate in the opposite direction.
I may have to replace the Hi-Tec HS-422 analog servos with some digital servos since the analog units don't seem to lock in place after the power is removed. That presents a problem as the gripper claws tend to drop down sometimes when the system is powered on or off at the robot's front & rear which prevents the chassis from moving forward or backward.
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04/14/2016 - The partial servo motor failure that I experienced on 03/25/2016 has now disappeared after I connected the servo motor control wiring in the robots motorized chassis to the servo motor control wiring inside of the metal case that sits on top of the chassis where the gripper claw arms are attached. I can't explain what happened other than that now that all wiring is connected, there is no more servo signal discrepancies to overcome, hopefully.
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04/16/2016 - I've been working on my robot steadily since 03/13/2016 which I took to yesterday's USA Science & Engineering Festival in DC & am getting ready to display it at the annual RobotFest event at the National Electronics Museum in Linthicum MD on 04/30, so I've been focused on that.
Finally after starting this project on 03/31/2013, it's finished to the point where it moves forward, backward, turns left & right & has two opening/closing gripper claws w/servo motors on a front & rear moveable arm w/servos that goes up & down. The robot is controlled entirely by switches & a dual pulse servo motor controller circuit that I designed using a 555 IC Timer chip, 4 transistors, resistors, capacitors & LED's for status indicators.
Eventually I'll design my own logic board to autonomously control it as I'm not a fan of just sticking an Arduino module in it as others think that I should do because someone else already put in the hardwork to design & get the Arduino to do what it does. I want to design my own circuits so that I'll have a better understanding of circuit design & it has been tough with many a late night until 2:00 or 5:00am working on things & just getting those things to work correctly. My thought process is that designing & building it myself completely by hand has taught me what it's like to take on a project of this magnitude and to appreciate what others before me have endured when they've done something similar to this.
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09/30/2017 - After much time & thought, I decided to experiment with by powering the robot's servo motors by temporarily connecting 4 alkaline D-cell 1.5 volt batteries in series to get 6 volts since each servo's minimum & maximum operating voltage ranges are from 4.8 to 6.0 volts DC.
As I'm slowly learning, the more operating voltage that the servo receives, the better it operates. Previously, the entire robot's drive wheel motors & servo motors were powered from 4 AA 1.2volts DC per cell NiMH (Nickel Metal Hydride) batteries, so that's 4.8 volts DC total. When I connected the 4 alkaline D-cell 1.5 volt batteries in series to get 6 volts, the servos seemed to operate much better than before.So now I'll have to connect 5 NiMH cells in series to get the 6.0 volts DC necessary. These cells each put out a current of 2500mAh so that's about 10000 mAh of current.
The robot's drive motors work well when powered at 4.8 volts DC. Due to space limitations in the drive motor compartment that also houses the current 4 AA NiMH batteries, I'll have to use C cells instead of D cells. If space allows, I may leave the current 4-cell AA size battery holder in place in the drive motor compartment & hopefully will be able to install a 4-cell C size battery holder next to it. Connecting the two cell holders in parallel will increase the output current to the drive motors which should add a little more punch to the drive motors operating efficiency..
Currently, the gripper arms housing has no separate battery power supply, so the current AA battery pack located in the drive motor compartment has the heavy load of providing simultaneous power to the 4 drive motors & the 4 servo motors of the 2 gripper arms. To isolate the two motor sets so that one power source is not under unnecessary strain to operate everything, I am considering installing a separate C-cell battery holder in that housing, & if room permits, a AA 4-cell battery holder connected to it in parallel to solely power the servo motors of the gripper arms.
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10/14/2017 - I ordered & received a Traxxas 2075X waterproof digital metal geared ball bearing servo, https://traxxas.com/products/parts/servos/2075x, which is part of the Traxxas 2075 Waterproof Digital Servo series - https://traxxas.com/products/parts/servos/2075.
The Traxxas 2075 & 2075X servo both have a torque range of 125 oz-in of torque with a servo movement transit time of 0.17 sec/60°.
Since the Traxxas 2075X is waterproof & has a 125 oz in torque capacity, I will eventually replace all of the current HiTec HS-422 servos on the RoverBot's gripper claws that have plastic gears & only a 46 oz in torque capability.
The Traxxas 2075X's may have enough torque in them for me to install them on four separate walker leg assemblies that will be used to raise the RoverBot off the ground when it encounters rough terrain that it cannot roll over easily & use the walker legs to traverse the rough terrain until it reaches smoother & more easily negotiable terrain at which point it will lower itself down then retract the metal legs to resume using its wheels to move about.
Traxxas 2072/2075 servo series technical specifications sheet.
https://traxxas.com/sites/default/files/KC2398-R01_2072X_ServoGearINST-ML-PRESS.pdf
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03/05/2018
So several months ago after talking with an engineer at Hi-Tec about the maximum operating voltage that their HS-422 servo can safely use & I was told that it's 6 volts DC, I started thinking that maybe the operating stability issues of those servos on the RoverBot 2013 could in fact be that 6 volts is not enough, so I wondered if they would in fact work better at 7.2 volts DC.
After being a first-time judge for a High School robotics competition in Sept 2017, I noticed that the contestants used 7.2 volt battery packs with great success. I added a 5th battery cell to increase the robot's gripper arm servos operating voltage from 4.8 volts DC up to 6.0 volts DC & noticed a slight improvement.
After much delay, I was finally able to temporarily add a 6th C-cell battery around 1:10am this morning & noticed an improvement in the servos operating speed. I still have unwanted cross-talk between the servos which creates jittering movements amongst them because I have them hooked up with only servos Y-cables but no active components such as transistors & IC's which could help to electrically isolate them from each for smoother individual operations, so after removing the 5th single C-cell battery holder & replacing it with a double C-cell battery holder, I'll start working on an electrical isolation buffer/amplifier circuit to connect the servos to.
Experimentation & Innovation is a touchy thing that can take a long long long long long time before an acceptable end-result is achieved.
I will eventually achieve the success that I want.
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02/09/2021
As of a few weeks ago, I have decided to start working on my RoverBot 2013 as I will be 63 yrs of age in August 2021 & am not getting younger, so I need to make the most of my remaining days as productive as I can for my years of dreams that can truly become my living reality & hopefully my legacy at some point.
Today I received 4 Dagu # RS002B Sensor Pan/Tilt Kits (www.dagurobot.com) http://www.dagurobot.com/rs002b?search=RS002B&description=true&limit=100 from Jameco Electronics (Jameco part # 2214601), each containing 3 metal servo motor mounting brackets & 2 DG9g micro servo motors from Jameco's eBay posting, so if you purchase the micro servos by themselves, then their manufacturer's part nbr is RS001B, but if you purchase them through Jameco's eBay listing or directly from DaguRobot that also includes the 3 metal pan/tilt kit motor mounting brackets & 2 micro servo motors, then the entire kit's part number is RS002B.
The micro servos are rated at 9 grams of weight, Torque rating of 1.5kg/cm (20.83 oz. in.) at 4.8vdc & 2.0 kg/cm (27.77 oz. in.) at 6 vdc for up to <500mA pwr consumption, plastic gear type, coreless motor, so they not strong enough in my opinion for what I need to do, so I'll have to invest in stronger servo motors..
At this point in time I am looking at adding additional pan & tilt brackets plus a good gripper claw & metal arm extension on the left & right sides of the RoverBot 2013 for picking up objects, etc. & to eventually include an alternate locomotion system for the robot.
I'm hoping that after making some much needed improvements, that my robot may catch the attention of NASA & other companies involved in future space exploration ventures. Wouldn't that be something !?
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02/10/2021
These are the servos that I have for my robot -
4 Dagu DGServo 9g RS001B micro servos - https://robosavvy.com/store/dagu-9g-2-kg-cm-micro-servo-motor.html
2 Hitec HS-311 servos - http://www.hitecrcd.com/products/servos/analog/sport-2/hs-311/product
6 Hitec HS-422 servos - http://www.hitecrcd.com/products/servos/analog/sport-2/hs-422/product
8 TowerPro MG995 servos - https://servodatabase.com/servo/towerpro/mg995
4 TowerPro MG996R servos - https://servodatabase.com/servo/towerpro/mg996r
4 Traxxas 2075 waterproof servos - https://traxxas.com/products/parts/servos/2075?t=overview
4 Traxxas 2075X waterproof servos - https://traxxas.com/products/parts/servos/2075X?t=overview
DS3218 Waterproof 180 270 Degree Digital Servo Metal Gear Motor 20kg for Arduino -
https://www.ebay.com/itm/DS3218-Waterproof-180-270-Degree-Digital-Servo-Metal-Gear-Motor-20kg-for-Arduino-/173859633299 **** not in possession yet
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02/13/2021
Today I worked on re-attaching the forward facing primary servo gripper claw mounting bracket to the secondary mounting bracket with some additional washers & some longer screws to make the assembly more sturdy to keep the various screws & nuts from coming loose in the future because of vibrations & movements that come from the gripper arm's two servo motors. I still need to add some more longer screws & washers and this whole process takes about 3 to 4 hours for disassembly, hardware retrieval, placement then re-assembly & that's just for one gripper claw assembly partially finished with one more to go.
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This website was created on 04/10/2013 & was last updated on 01/04/2022 by Logan Mitchell Sr. © All Rights Reserved 2011 - 2022
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