okidey
Hello everyone, I have a question.
I am continueing my work on Hank, and I am back to needing a seperate power source for the high torque servo's. Allthough Hank is no longer a hexapod but a quadruped instead, I still have 12 high torque servo's to power. Ofcourse I do not want to exceed the 6v power limit and have been looking for a LiPo battery to power them. Unfortunaty there is no 6v LiPo battery but with 12 high torque servo's i will be needing quite some amps if i want it to work for some time without having to charge every 15 minutes, or so.
I have a hard time understanding the options that I have. Hank isnt al that big and it wont be able to carry a huge lead acid battery on its back. Im not farmiliar with the functioning of a bec or esc and i want to avoid using nimh or alkaline batteries. There is this idea that keeps popping up in my mind and I just have to ask..
A diode will generally cause a loss of power by approximatly 0.7v, right? So if i were to place 2 diodes in series on a 7.2v plus lead, would that not come to about 5.8v? Its seems so simple to me and im wondering if maybe it is a bit too simple and may not work as I hope it would.
What do you guys think? Will using 2 diodes in series reduce the voltage of a 7.2v battery, to properly power the hightorque servo's?
Kristian.
Yes in principle that would work. You just need to make sure that the diodes are capable of the current load. I would get a cheap multimeter just to measue the volts to see if you get what you expect. Calculate the maximum current load by looking at the spec of the servos then choose an appropriate diode then you will be good to go
Awesome! I am using 12 times towerpro (or towardpro) mg996r. I cant really find a datasheet on these servo's but according to someone's comment on some webpage they draw about 937 mah - 4.1w under load. So I would need diodes that handle at least 12 amps right?
This is great, now I have an idea how to tackle this, thanks!
937ma seems high maybe max load I suppose. So if they were all on max load you would need 12amp diodes. They could get hot so be careful
Yes, I believe that was under pretty much a Max load. Im going to assume that all of them are likely to be running at the same time at some point. And most of them may also be likely to get near of reach a max load and draw about 1 amp each. The 12 servo's alone do weigh quite a bit, including 2 or more batteries and the rest of Hank, it all adds up quickly and it'll be power hungry. So the diodes are likely to get very hot and I will keep that in mind, thanks.
I have just one more question. To have a decent run time I will probably end up using 2 batteries in parrallel. But 3 batteries would be too much and was thinking that maybe I could add 2 or more solar panel(s) on its back to give it that litte extra bit of juice. What kind of a voltage would I need to actually charge a 7.2v LiPo battery? Anykind of charge I'll be more then happy with as litte as it may be, assuming ofcourse that it is even possible to charge a LiPo battery in such a manner.
I have little experience with both components, so any information woud be very helpful.
Most Solar Panels are for charging lead acid cells (Car and Boat batteries). I have a charger that takes mains or a 12 volt car battery as an input that is designed for LiPo batteries so you can charge RC models in the field. So 12 volts and a special charger would be needed but I think the size of panel you would need to produce enough amps to make it worthwhile would be prohibitive. Is it that sunny in the Netherlands? take a look on RC model sites and see if there is anything there. Found this on You Tube should give you some sort of idea on the size of everything
Haha alright, you dont need to say any more. That pretty much rules that idea out and I have a clear answer to my question, thanks.
Alright, so I've bought a couple of 7.4v LiPo batteries. Ive charged them and soldered the wires together with the diodes to bring down the voltage to just below 6v. I measured the voltage and to my surprise the batteries are actually 8.33 v. this is not a problem as i will simply add more diodes to bring it where i want it to be.
Still though, is this normal? I was sort of counting on it to be around 7.4 volts lol
The diodes only drops voltage under load, if you have no load connected that's your problem, 2S lipo charged to full 8.4v, 4.20v per cell.
The better and more efficient way would be using a BEC as commonly used in R/C car/heli applications. This is a very popular and powerful BEC: http://www.aprohobbies.com/castle-creations-switching-regulator-lipo-input-p-104.html
Use two of them in parallel will provide 14amp of continuous current, 20amp peak. The default output is 5.1v, output voltage can even be custom set (4.8v-9v) using a PC software if you also purchase the Castle Link device.