I am building a platform with a robotic arm using Lynxmotion brackets and servos and I can use some advice. I think I am having trouble getting enough current to the two HS-5745MG servos I am using for the shoulder and elbow. It is important that I can control this using an RC receiver. It is going to be attached to a mobile RC crawler platform. Normally I use an 7.4V ESC or electronic speed controller to control the vehicles motor, and it sends a 5-6 volts of DC power to the RC Receiver. I normally then just plug in the servos to the receiver. When I plug in any of the HS-5745MG servos, the arm bounces, and does not lift. Perhaps it is to heavy, but It does work when I plug in a 4.5 volt battery directly into the receiver and bypass the ESC… by the way I am using 2 of the HS 485 HB for the pan/tilt assembly. Ultimately I would like to drive 6 or 7 servos with this rig. I think the problem lies with the ESC not having enough output current. I have already burnt out one with a 110 amp output.
Any ideas?
Thanks
Hi,
Using a rock crawler as a robot platform seem to be a great idea, looking good!
Have you considered using an UBEC for powering the servos? I’m using this one:
Those 5745’s can be very hungry for current! The arm you have is very large. I’m very curious to see how it behaves. I think the best way to power these guys is direct to a 6vdc battery if possible. You can still use the ESC, but you should pull the red wire from the connector and let the big 6vdc battery power the servos and receiver.
Robot Dude
Yes the arm is large. I am trying to get the camera up to 24 inches.
I like your idea, about adding a second battery, but I’m not sure what you mean "pull the red wire from the connector. What connector? pull it from where to where?
Can you draw me a diagram?
Thanks for your help
Chris
The ESC has a regulator that it uses to send back 5-6 vdc to power the receiver. This is not desirable as you will be connecting the big battery to the receiver to power it and the attached servos. This happens by way of the red wire on the cable that goes to the receiver. To disable it you pull the red wire. Check the diagram.
Ahh So
I think I get it.
Since my platform is small, and instead of using a big lead-acid 6 Volt battery, I’d like to use a 7.4V Lipo battery with lot of mAh to power the receiver. I guess I’d have to put in a BEC between it and the RX to regulate the output to the Receiver. I’m thinking I probably need 5 amps to run those 5745’s. What do you think?
I am already using one 7.4 V Lipo to power the ESC.
I’m not suggesting you use a lead acid battery. There are several chemistries available that provide 6vdc not 7.4vdc. Using 7.4vdc makes it necessary to use a regulator for the 5745 servos. When the servos need current they will need a lot and they need it like NOW. So I’m recommending NiHM or some of the variants of that chemistry.
Sounds good. I’ll give it a try.
Thanks
Chris
Do you have any idea of how many amps those 5745’s will pull under load?
The 5745 with no load, running should see around 840mA, at stall, which would be maximum current draw is 4.8A.
If the weight of the arm gets to be an operating issue, there are probably ways to modify the arm design to reduce weight and keep the functions generally the same.
I’m all ears. Although I haven’t hooked it up. I’d like to hear any ideas. My goal is to keep the camera height at a minimum of 24 inches off the ground. right now its at 26"
just a quick idea to save on the load would be to move the “pan” servo further down the “forearm” and use push rods to move the camera using a ball baring.
this way you dont have the extra weight of the servo toward the end of the arm?
using this system, kinda.
http://i531.photobucket.com/albums/dd355/innerbreed/dfghwerhgr.jpg
if you dont get what i mean i could prob build it so you can see what i mean?
or…and even:
viewtopic.php?f=6&t=6300
just an idea.
NIce, I get it. I like this idea. you don’t have to build it , unless you want to…
happy to inspire. 
OK, so I hooked up a 2000mah 6 Volt NiMh battery to my futaba reciever which, by the way, can handle 8 Amps continuous and 10 Amps peak, and pulled the red wire on my ESC so all the servos can now get 6 V direct from the RX. and the arm worked! for a while… about 5 minutes then the shoulder servo started smoking, so I quickly unplugged everything… I am going to have to reduce the load to the shoulder/ elbow… perhaps try a 10 Amp BEC…on a 7.4V Lipo
Does that mean my shoulder servo is toast?
Best guess for what just happened?..
Smoke comming from a servo is usually bad news, but if it still works, then it may still be good. I’d recomend using a very small servo on the end of the arm, or put it at the elbow and move the cam by linkages. Linkages/cables are often used to keep weight off of the ends of arms.
What smoked? The wiring, or one of the servos?
Accurately measure the voltage being sent to the servos!
Alan KM6VV