Power supply for my hexapod

Lynxmotion Legged Robots
1

Hello Guys!

I am doing a hexapod using arduino mega, SainSmart mega sensor shield V2 (amzn.com/B00C4QVTNU) and 18 Tower Pro SG90 micro servos. My code is correct and the legs are moving properly when I hold it in the air, but when I put it in the ground. The legs just stall and not moving. I can feel all the six legs’ torques aren’t enough compared to powering a single leg at one time. It should be the power issue but I use LiPo battery to power the servos and a 9v battery to power the arduino so the power for legs should be enough (please let me know which type of battery I should use if the one I am using right now is not correct). I can tell the load of my robot is heavy but the legs’ torque are definitely not enough. If the leg can supply enough torque it should be able to support this kind of load.I measured the voltage output from the servo shield. It is varying from around 2V to 5V when all six legs are moving.

I have tried another plan for my hexapod. I bought 4 NIMH batteries (2700 mAh rechargeable POWEREX 1.2V. link: amazon.com/Powerex-MHRAA4-2 … +batteries). I connected them to the servo shield using the external power mode with two wires. When I tried the first servo, it is working fine, but the arduino mega board underneath the servo shield burns when I connect the second servo. But the second servo is not broken (I tried that servo after this thing happened). I am really confused about this. The reason why I tries 4 NIMH batteries is because I saw a project called Hexy that it uses the same power supply for 18 micro servos and it works perfect. So I decided to try them on my project. From calculation, 4 NIMH batteries are 4.8V, it should not be able to burn anything. I am so confused. I really need help with this thing. My questions:

1: According to my descriptions, where is the problem with my hexapod, do I need to use another power supply? which brand and type of battery should I use? Feel free to provide another plan of different electronics to fulfill the hexapod!
2: why 4 NIMH rated at 4.8V in total will burn the arduino mega when connecting the second servo (servos are not broken.)
3: Is the Tower Pro SG90 a good servo? Is it possible that the servo is bad and not designed for the hexapod?

Thanks so much for everyone who is trying to help. I really need a pro to help me to troubleshoot this thing. I am struggling by my own for a long time. Thx!

Update: I’v tried to measure the current flowing through the servo for two situations: 1: I measured it when connecting only one servo, I put my hand against the servo and it draws current up to about 0.5A, and it draws 0.1A in normal situation (no barrier against to it). 2: I connect all 18 servos and then measure the single servo, it is vary like from 0.02A to 0.07 or from 0.02A to 0.1A even when I put my hand against to it. (I don’t quite remember the exact value of current draw but it is definitely less than the first situation!!).
From the above, it looks like it is a battery issue but the battery should be enough with no doubt. This is why I am so confused about the power supply.

2

Tower Pro likely take 6V max. Your voltage regulator should output 6V ideally. However, with a 7.4V LiPo, it’s likely just at the limit of providing 6V - check the dropout voltage.

A 4.8V battery likely won’t burn the MEGA, but it’s not enough to power it. Note too that AA batteries tend not to be able to discharge at a higher current.

Can you provide a photo of the hexapod? Normally these consume high current. It’s not at all designed for a robot - this still still RC servo tech adapted for robotics.

The issue is likely that the servo simply does not have enough torque, and a side issue is that they are power hungry.

3

My reply:

  1. I just noticed that I used voltage regulator to regulate 7.4V from LiPo battery to 5V, which could be the issue because you mentioned that the servos run at 6V and I just forgot this fact

  2. I do see a hexapod project using 4AA NiMH batteries called “Hexy” and it works robust enough. Because this battery is rechargeable and has 2700mAh capacity. Here is the link to that project : arcbotics.com/lessons/powering-hexy/

  3. Here are pictures:
    https://mail.google.com/mail/u/0/?ui=2&ik=daf6b00ad1&view=fimg&th=15cd6a7863dd1add&attid=0.1&disp=emb&realattid=15cd6a72c59a55f89331&attbid=ANGjdJ_pE29WSQDOOLmZB6cRotNOdMT313YjF5XL7JIrM0H_iyzUpssxOQioxi49NS0-KvnNcW4wmRtiE3jZVRUiSx9F_RRsq1vZAaAkYe-xapHLGpTqqtevv6Bd6j4&sz=s0-l75-ft&ats=1498250716826&rm=15cd6a7863dd1add&zw&atsh=1

https://mail.google.com/mail/u/0/?ui=2&ik=daf6b00ad1&view=fimg&th=15cd6a7863dd1add&attid=0.2&disp=emb&realattid=15cd6a774bcdcd361312&attbid=ANGjdJ9umdm0eDWnVaP3awh8zfpDRge-XOcsZhyk9APzYFCBrCmhjJWHV0g3NXGrR35wPxtk1uw3P-E90vhqOo14axvBBPc8vDt_82LrNJn0mv-g0fN4vnmdxwgU-9s&sz=s0-l75-ft&ats=1498250716826&rm=15cd6a7863dd1add&zw&atsh=1

4

Servos can run at 4.8V to 6V (and a bit above), but 6V for most servos tends to be best and lower current.
Can you provide a photo of your project? Hexy has fairly short legs and mechanical advantage to limit torque.
Photos don’t seem to have loaded properly.