This week the CIM students in my class took the time to rebuild our Lynxmotion Arms, some of which have been running since 2009, without an problems. The screws were starting to come loose, and some of the servos were a little twitchy, so we used some grant money to get some new upgrades from The RobotShop.
The students thoroughly enjoyed the “hands-on” time, especially after programming in Robocell for the last two weeks!
Follow along below to see what upgrades we did to make our robots like new again, and see what it nets us in the long run. The numbers in the picture below of the finished bot coincide with the numbers below.
All servo data came from here: http://hitecrcd.com/files/2013_HRU_ServoMat_2.pdf
1. Medium Weight Wrist Rotate: We upgraded from no wrist rotate, or from the lightweight wrist rotate. The lightweight wrist rotate came with a tiny HS-85BB micro servo that would strip rather easily and only had 42 oz-in of torque. The medium duty wrist rotate uses a larger HS225MG with 55 oz-in of torque, and only weighs about 0.4 oz more. This is negligible and the new servo has metal gears. Great bang for your buck.
2 & 3. Shoulder and Elbow Servos: We upgraded from the 2009 “stink so bad the company dicontinued them” servos to the ones that come in the kit now. The shoulder servo is a Mega HS805BB that has 343oz-in of torque, and blows the other one out of the water. It also makes the extra weight of the medium duty wrist rotate a moot point. The elbow got the upgrade to the HS755HB Quarter scale servo with 183 oz-in of torque.
4. Wire protection: Corrugated Loom from NAPA was used to cover the wiring from the bot to the controller. All connections were electrical taped and tested, then put inside it. Cleans it up nice and should prevent it from being pulled apart.
5 & 6. SSC-32U & Bluetooth Adapter: Upgraded from the SSC-32 to the SSC-32U. Main difference are better connection, no more serial converter, or 9v battery, and wireless capability! See the video below.
7. Custom Made Mounting Plate for VEX: Thank you Brady! One of my students spent his free time designing this specialized mounting plate in Inventor, and then cut them out of 1/4″ acrylic on our Brightstar laser. He will post the file here shortly! Notice that the switch (not switches, as the need for the 9V battery went away!) is hidden under the board so it cannot accidentally get hit, but can be used to stop the robot in an emergency. Keeps the wires out of the way as well!
Link to part file coming soon!
8. Heavy Duty Base:Once again, this upgrade was done for the metal gears over the plastic; it should never strip under normal use. Also the squeak of the plastic base is long gone, and is smoothed out by the bearings in the servo and the base.
Conclusion: I get so many emails all the time about how these arms are just “toys”, and “…they are not very robust”. Yes, they are toys compared to a Scorbot, but they also cost about $14,000 less. I have had most of these since 2009, and the students love working with them, and besides, every group of 2 or 3 students get a robot to use; can you do that with scorbots in your classroom? Besides, they play nicely with the VEX stuff too.
I have personally built and/or repaired more than 120 of these arms now, at CTI’s around the nation, as well as at high schools. Everyone that thinks they are junk, and do not have a good experience with them, is usually because of one of two reasons: Either they are built incorrectly, or the students are allowed to abuse them.
I know the directions are not perfect, but honestly, these were made for hobbyists who don’t mind having to figure it out. Once you have built one though, they’re easy. And kids using them to sword fight or “battle” one another? C’mon… what do you expect.
I make sure they are built correctly (I built the first one my self) by grading the kids with a rubric on how well they are put together. This raises my students level of concern quite high, and they do a nice job. I also do not allow my students to misuse them in the classroom as well. Have I burned out a few servos? Yes. Do my students enjoy using them in the classroom? Yes.
To see some examples of how they can be used in your classroom see the Youtube playlist below.
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