You don't say what kind of servos you have attached to the IoTinys. The servos I'm using in my robot pull 7 amps each when working hard or starting up. When many are running or starting up this will quickly overwhelm an IoTiny or the amps that a battery can provide when using the wrong one for an application.

Current is lazy. It will go the easiest rout. If your Mega's load is not as demanding as the Iotinys or there is an easier path to the load through it then that's the way most of your current will go.  Maybe that's why the Mega keep running? Are the Iotinys on one circuit from the battery and the Mega on a different one?

Eliminate as many connections and bottlenecks as possible (connections, plugs, and other devices sharing the load). and provide a big unobstructed roadway (wire) for your current to get to the load. To keep your wiring limited consider using wiring blocks near your load or a central location for the motors to connect to. Then run large main branch lines to each block.

I'm not a battery expert but I wonder if the lead acid battery your are using will provide the startup amps needed for your servos. I've read that Lipo batteries are much better at providing the super fast and much higher amp draw that motors take when starting up then when normally  running.

@Jeremie referred to @smiller29 power devices. After reviewing I'm impressed by his choices! One thing that stands out is his use of a 110acv input to 6dcv, 60 amp Regulated Switching Power Supply for his main power source in his Inmoov. The key feature here is the 60 amp rating.

Thanks guys. I reset the Tiny and set it back to AP (master mode). It is now working perfectly. Very strange. However, I did this before and the problem returned so I assume the problem will come back. Seems to be an issue with the Tiny.

Some answers:

• Each tiny is connect to 6 x JX PDI-6221MG (smaller) and 1x  PDI-HV2060MG  ( larger)
• I haven't measured the current draw. But I disconnected all but one of the smaller servos on one of the Tinys but the problem persists even with just one. I also programmed in delays so that they are not all firing at once
• The Mega is powering 7 of the larger servos and works perfectly. I have the KEYESTUDIO Mega Sensor Shield on the mega which is externally powered by the battery.
• The Mega and the Tinys are on the same circuit. I have run tests with only one of the Tinys running to reduce total current draw but the problem persists.
• Due to the fact that the Mega is running 7 larger servos no problem, I would assume that the battery is sufficient
• I tried powering the servos on the Tiny externally from the battery instead of coming through the Tiny but it did not help.

Thanks for the link to @smiller29's build. Very well done.

@elektrophunktronic Yeah sounds like the battery is good if it's working with the Mega, as I suspected the servos are connected to the power externally to the Mega so it makes sense that it's not browning out.

To me it sounds like something in your IoTiny circuit is getting hot and opening up with the current draw gets too high (temperature gets too hot).

I've never come across an issue on the IoTiny that wasn't power related in some way. I would double-check to see if the wiring gauge is suitable for the amount of current draw you are running. As I mentioned before 2.1mm Barrel plugs (CCTV style) are likely to cause issues with high current as they have a 22 gauge wire connecting the positive barrel to the terminal block. For high current applications with long wire runs, I'd recommend 16-20AWG wire. For the 2.1mm barrel plug I'd recommend the style that you can solder directly to.

The only other idea I had is that if these are IoTinys from the original batch, they had an input capacitor that was ceramic instead of electrolytic and it did cause some issues with some servos when they switched directions quickly. Could you check? It's located at the bottom left corner of the WiFi module. If you're unclear please attach a photo to your response.

They are brand new so I assume they are later models. I have attached a photo. I need to take the inmoov to a festival this weekend so I cant risk risk them not functioning. For now I will just run multiple servo wires from the MEGA

Yep, those IoTinys are the newest revision v1.1. The 2.1mm CCTV style barrel plug that’s in the photo is the exact type that I was referring to that can’t handle high current. I would advise switching it out if you are running high current through the IoTiny.

OK thanks good to know. I will order plugs with a larger gauge.

So I swapped out the plugs for ones with a larger gauge connections. I am pleased to report that it has been functioning perfectly since. Fingers crossed this is the final solution. Thanks Jeremie!