Lessons Learned

A project log for Choose your own adventure bot

Ultra low cost 3D printed Open Educational Resource Walking Robotic Platform

shane.snipeshane.snipe 09/27/2021 at 10:170 Comments

I have a friend that has been telling me that is not what I do that is important but it is what I learn. Well I thought I would explain the three things I learned this weekend in 20 hours of robotting.

It is not always the things that you worry about that bite you.

My boards came in as planned on Friday night and I was ready to assemble. 

I was worried about 3 things. First that the FFC would not be tight enough in the connector and they would fall out as the legs moved. - Absolutely no problem on this point. The connectors were great and I could use the FFC as a handle to pick up the robot. -  No problems here.

I was worried about the 0.5mm pitch FFC not having enough current capacity. I connected the wires and got a toasty FFC. Then I realized that I had designed in the B type connections and the pins were reversed. I changed the FFC to the one with pins up on one side and down on the other and this took care of the heating - No problems here either.

The third thing I was worrying about was that I was regulating 3.3V and 5.0 and putting them both into the ESP as inputs. I usually only put in 5V. It seemed that in the end, it would with both 5V input and 5V and 3.3V inputs so it was wasted cycles thinking about it.

I hooked up the batteries in series, got my 8.2V at the BMS output and I thought I was off to the races. I soldered in the 7805  5V regulator and the output at the BMS dropped to 2.0V.  I thought I burned out the BMS and I took it off the board and it still worked. I put a new one on and got the same thing. I cut off the regulators and everything worked. I tried the regulators separately and they worked. I tried with just the 3.3V, double checking the pins because it is different from the 5.0V regulator but nothing there. It did not work when it was on and worked as soon as I removed the regulator. I finally removed the BMS and ran voltage from a power supply at it was fine.  I put the BMS back on and it was still fine.  I tried with another different type of BMS and it did not work with batteries but did work with external voltage.  My conclusion is the BMS and the voltage regulator do not play well together. I guess I will just have to find some that will. The big take away is I need to breadboard more. 

The second big lesson came from the next step. I decided to go forward with just the power supply and to finish the debugging. I then found this issue that ended my run with the new boards. My pin definitions on side of the header were different from the other. On the brainboard I was using Kicad and on the hip board I was using Easy EDA. On footprint was using alternating pins and the other was running ccw so even though the schematics looked the same, the pin definitions we totally different.  My end pins worked but the ones in the middle did not. Game over, time to order again. The big lesson is a I cannot skip the excel sheet showing the pins on each connection. Also, no more ECAD at one in the morning!

Well I still had some closed loop programming to do and newly printed hips I was dying to try out so I went back to the Flex circuit design. I decided to run with a power supply and I tapped in a 7805 5v regulator to the 5V and  ground line.  I think ran wires down to the flexes from the input and now I had adjust power for the motors only and a stable 5V for the rest of the circuit. I conformal coated all the flex connections with hot glue and got on with the assembly. 

The new prints with deeper pockets worked OK but there are difference between joints that I can not yet explain. I will do a more detailed log with some plots and consider it more. I put a screw through the left legs flex in assembly and lost movement of the left femur but over all I had something to work with. Putting in variable voltage makes it exciting. The joints move fast and with great power. The down side is you can strip the motor shaft/gearbox shaft connection. 

And because some movement is better than none, here are some of the comical wild flails of Cya.