I reviewed the power distribution of the robot and the system of 2 batteries… and finally, I’m not satisfied… Having 2 batteries inside take more space, it’s not good for the weight balance and it’s more complicated for the electronic because I would have have to design a board with 2 chargers (LTC4008 and MCP73861) and 2 power monitors (LTC2945). It’s not that complicated but designing a charger board is not obvious and the Electromagnetic compatibility (EMC) would be a nightmare…
So I searched on the Internet for a new battery, and I found this one : Tenergy Li-Ion 18650 11.1V 7800mAh. I could have assembled the battery by myself by buying each element separately which is much more cheaper, but I have enough work to do… 😉
There are many benefits :
- Battery’s weight better balanced,
- Space better distributed,
- One charger and one power monitor,
- More capacity than with the 2 others,
- The battery case is reinforcing the rigidity of the body.
It looks like this once integrated :
New battery integrated
I logically changed the charger and chosen a LTC4006 which fit perfectly to my application. Indeed, the LTC4008 doesn’t have a integrated termination charge like the 4006 and the use case of the robot (charging point of view) will be the same as a laptop, so I needed a charger compatible for this utilization.On the datasheet you can find a good application schema, which I have to modify to fit my expectations in order to handle the average 5-6A consumed by the robot…
However, I’m still keeping my
precious switching regulators :
- 1 PTN78060WAH : 5V power supply of the RasPi, the STM32 and the speaker’s amplifier.
- 1 PTN78060WAH : 3V night vision LED (+ mini fan).
- 3 PTN78020WAH : 7.4V legs power supply : 1 for each pair of leg (front +head, middle, rear).
I replaced the PTN04050C by the PTN78060WAH (boost converter), as I won’t use the 3.7V Li-Po battery anymore.
Here is the new electrical architecture :
Electrical Architecture Rev2
Hi there !
I finished the coxa articulation, this was a bit more complicated than expected, mostly for the shape design… I created a hole inside the part to be able to pass the cable inside, like this it will not be visible 😉 I didn’t had the time for running some stress tests on this part, so I will do it this week and update this post ^^
I still have to finish the leg. As you can see on the global view of Animabot, the legs are not fitting right on the femur : it is normal, and I will correct that this weekend !
Global view, body closed
Looks pretty good, no ?
This weekend I have been working on my Media Center with another Pi.
First I installed OpenElec, which is after some tests, much faster than Raspbmc. You can find here how to install it. Then I overclocked it a little to get Xbmc smoother (tutorial here). I choose the Medium overclocking configuration which runs perfectly well and is very stable on my Pi.
Concerning the integration, I wanted it hidden behind the Tv, but it had to look good (no cables everywhere…). I have looked for a long time for a proper case in aluminium but without success… So I finally decided to use an external hard drive case 3,5″‘. The internal dimensions are sufficient for installing the Pi and the cables. The case is also ventilated by may holes on the side panels, so the Pi will not get too hot inside.You can find it on amazon for 22 euros.
For powering all this I used a switch Mausberry Circuits to be able to power ON/OFF the Pi correctly. But the inconvenient is that you have to do it manually 😦
On others occasions, I noticed that the USB port on the Tv is ON when the Tv is ON and OFF when the Tv is in Standby (I have a Samsung UE55F6400). So I came up with the idea of replacing the original interrupter by a relay commanded by the USB port. I simply connected the coil to the 5V of the USB and put a diode (1N4007) to protect the USB Port. On the interrupter circuit I only added a small capacitor (4,7µF) for the relay bounces.
When I power ON the Tv, the Pi starts automatically and when I put the Tv in Standby, the relay goes OFF with the USB port and the script installed on the Pi send the shutdown request.
This works perfectly !!
Power supply with relay
Inside the box
Box installed uncovered
Box installed covered
On the last few days I have been finishing the fixation of the servos in the body. I changed the fixing studs for stronger ones. I still have a lot of work to do inside, but first I want to finish the legs.
I have advanced in the femur part, I still don’t know if I will keep this design because the upper part is flat and I’m not sure it combines with the body shape… But however, the servos are fixed inside, the part is relatively compact, and the cables should fit… so it’s not so bad 😉
Femur case outside
Femur case inside
Femur lateral cut
I also have temporally integrated this to the body, to see how it looks like and this gives also an idea of the size : Cool isn’t it ?
I think I will have to make the corners of the femur and the body a little bit rounder for the articulations movements… But I will see that with the articulations
The next step is to create the fixations between the body and the femur with a cable passage inside (tricky part…)