I’ve lurked these forums for quite a while and have slowly been in the process of gathering the parts I need to build my very own hexapod. I love the look of Phoenix so I decided to go with that style.
My Phoenix is using all HS-645MG’s and it only is using a SSC-32 because I do not want to commit to a single processor at the moment but I defiantly want to start programming for it. I just finished building it and have yet to even re-route wiring so it looks like a mess and it has not been properly calibrated at all. I’ve just been trying to do a very rough test to see if things are good so far. Well they’re not of course
At the moment since I’m already tethered to the computer with a serial cable I figured I’d just use a wall adapter for power. I purchased the 6.0vdc 2A regulator that can be found here at lynxmotion along with the accompanying harness and switch. After applying power to the ssc-32 with all servos connected I get the solid green led on the ssc-32 which tells me I’m good so far but when I send the ALL=1500 signal through lynxterm I get strange results. Servos will twitch and then go limp. The LED will sometimes go off, sometimes go off and then back to solid which tells me its resetting.
If I send the ALL=1500 signal many times while suspending it in air i might get all the servos to hold in the correct position and I can tell because I can hear them all struggling to maintain the position. But if any kind of force is applied to them such as setting it down on the ground or the nudge of a leg the whole hexapod immediately goes limp.
I’m just wondering if anyone has tried this setup with the wall adapter before and gotten similar or even successful results? I double checked all my jumper settings so those should be fine. I’m wondering if its the screw on clamps that the harness goes into. They don’t look like a super solid connection…
Any ideas? and thank you for all the help and the wonderful forum and product
the short answer is the power supply can’t handle the sudden surge of all the servos going active at the same time and this causes the input voltage on VS to drop low enough that the controller on the ssc-32 gets reset.
the solution is you need to seperately power the VL input, that is remove the VL=VS jumper and use a 9V battery on the VL input (using the 9V battery clip supplied with the ssc-32).
It seems like using a 9 volt battery to power supply just prevents the SSC-32 from resetting. Do I have this right? If so how while the servos behave when the power supply fails to supply the power needed to drive the servos? Will they still go limp? Or would they just be sluggish and/or lacking in torque?
servos are actualy fairly tolerant of noise on the supply rails and depending on how badly the power supply is being overloaded you may or may not even notice.
the controller on the ssc-32 pretty much looses the (all=1500ms) command once a severe power drop resets it… which if you tried to move all the servos at once with VL=VS on a power supply rated 2A output is pretty quickly. 2A is probably adequate once everything is initialized unless you put a lot of weight on the servos or have more than one or two binding up on something. each hs-645 servo can probably pull nearly 2A if you torment it badly enough (data sheet probably has stall current listed if you really want to know). normally though they pull somewhere between 50 and a couple hundred ma depending on load.
I’m not sure too many people are trying to run full hexapods on the 2a supply but you are probably pushing the limits of what you can get away with rather than using even a 6v 1600mah battery pack.
I didn’t realize the servos required so little current. Is that the case when they are supporting the weight of the bot? Or just the appendage to which they are attached?
Um, this is why they make data sheets with specifications on them. Note the stall current isn’t indicated, they don’t encourage operating them at stall, so you will have to determine the value empirically at the risk of your own servos if you really want to know.
huh, I don’t know what I was thinking buying that power supply now… It seems obvious that the robot would sink more than 2A under stress… hmm maybe it might be a good time to invest in a real variable power supply. I guess I figured since it was sold here it was the preferred power supply for something like the phoenix.
Are their any other good, somewhat cheap power supply’s you could recommend that deliver something more like 18-20A? or would I just be better going for a battery or a nice variable power supply.
So theoretically a Phoenix could draw almost 32-33 amps? holy crap that’s a lot.
servos draw large currents in short bursts typically and then the holding current depends on the amount of load. the 6 servos at the body don’t draw a lot but the ones on the legs can at times.
an alternative to a large power supply, which is more often than not a couple of hundred usd or a hacked PC supply (which presents it’s own challenges), might be to use a small battery pack in float service using the 2A supply to keep it charged up. basically the battery handles the bursts of current and the 2a supply handles the idle current and keeps the battery charged.
the preferred power supply for the phoenix is batteries from what I can tell. a couple folks have gone so far as to use 3s2p lipo packs and 10A BEC regulators to get the most bang for the buck possible in run time.
Yes I understand that. Please bear in mind that some of us are new to this and don’t always fully understand the spec. In fact I thought the running current was the stall current. Since that is not the case does running current mean that each servo draws 450mA@6V on average under normal load? If so doesn’t that mean that 18 servos would draw a little over 8A and subsequently overwhelm a 2A power supply? What am I overlooking?
it really depends on how much torque each servo is subjected to since the current required is roughly proportional to its output torque when operating within the servos design range. stall current is what happens when you lock the rotor of the motor and it becomes like a resistor with fairly low ohms. remember though that geometry plays a major part in how much torque is applied to any given servo at any time. As I suggested earlier the 6 servos at the body don’t draw much current at all when idle because all of the load on them is in an axis other than that of the servo output shaft. probably the worst case is when the hex has only 3 legs supporting the body in an alternating tripod gait. that is 6 servos pretty actively loaded, 9 of them are relatively unloaded as the legs are off the floor, and the remaining 3 are pushing the body forward. in your case there is no battery in the body so what are you really moving for weight… not a whole lot. you might get away with it but I would venture to say that a 2A supply is about the absolute minimum you would want to use.
“float service” is sort of an old term used primarily with lead acid batteries where they are maintained with a trickle charge on them that primarily replaces the self leakage current. this keeps the batteries at a fully charged state of readiness. My suggestion was an analogy to this where you keep a voltage across the pack where you are not really charging the batteries so much as keeping them in a charged state so that they can supply the heavy current moments when the servos are asking for more current than your power supply can deliver. realistically this isn’t the way you want to store your bot if you are using nicd, nimh, or god forbid li-ion cells, however when using it for programming and demonstrations it should be fine (except for li-ion cells which should not be used in this manner unless they have an active protection electronics module built in.)
It’s a pretty good supply for a robot arm. Good for about 5 or 6 servos. The Phoenix does indeed require around 8 amps when running. Running the bot from batteries is a good idea for several reasons. Betteries can deliver the required current to operate the bot. Depending on what the robot is doing the servos may need some cool down time after a run. Most people have about 2800mAh of capacity on the bot. So after about 20 minutes it’s probably time to let the beast rest.
Since that is not the case does running current mean that each servo draws 450mA@6V on average under normal load? If so doesn’t that mean that 18 servos would draw a little over 8A and subsequently overwhelm a 2A power supply? What am I overlooking?