MULTIPLE HB-25`s one BS2p poor performance

kennet

Hello everybody,
·I`ve been working on a project which requires the use of nine HB-25`s. Everytime I try to hook up more than four HB-25`s, I get strange behavior, or no reaction at all from #5·thru #9. I think the problem is that the stamp can`t handle the current draw from the HB-25`s. Currently , I am thinking of using multiple BS2p`s in a Master/Slave type of configuration to lighten the load. It would be nice to control all 9· HB-25`s with a single BS2p , but if I can`t , the second option seems like it may give me more flexibility down the road. My plan is to add many types of sensors. I was wondering if anyone out there has any ideas on this problem.

Thanks
Ken

Franklin

You need to power the HB25s from their own power. The only thing the stamp should be supplying is the signal line (and ground)

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- Stephen

LilDi

Seperate power supply for the HB25's, YES. The ducumentation for the HB25 also mentions controlling just two HB25s from a single I/O line. You will need to use 5 I/O line for nine HB25s. (two HB25s per I/O line)

kennet

Thanks Stephen for the reply. The Stamp and the HB25`s share the same 5V regulated power supply ( two LM338K in parallel·on heat sinks).The stamp itself, does not supply power to the HB25`s.

Ken

kennet

Thanks LilDi, the mode of operation you mention is an option if I/O is in short supply. I believe normal operation is still simply to assign each HB25 it`s own pin. Please correct me if I`m wrong.

Ken

Franklin

Ken, what are you powering the motors with and what is your total power draw?

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- Stephen

Mike Green

Sounds like an acute power shortage. Once you get beyond 4 HB-25s, the pair of LM338Ks shut down, thus depriving the Stamp of adequate power and it resets or just doesn't work.

An idle HB-25 draws 50-80ma. Four of these only draw 200-240ma and the BS2p draws around 40ma for a total under 300ma. That's not much. What are your motors drawing? The LM338Ks will handle about 10A. Will your unregulated supply provide that much?

kennet

Thanks your time , you guys are on the money ! I have a LED indicator light on the regulator which I built myself. I did notice that it started blinking whenever I hook up the extra HB25`s. However, I assumed the problem was with a possible faulty ground connection. I should mention that the regulator has its own power battery. But, that battery is activated by a relay which draws it`s power from the HB25 power supply. So we`re talking about two seperate systems. Please forgive me for not providing a more detailed discription of my project and it`s componants.

I am building a "JOHNNY 5" type of robot. Most of the parts are from an automotive junk yard. Each of the robots arms has a SPAL 12V actuator for shoulder operation. I measured the current draw at about 75mA no load for each one. The bicepts have windshield wiper motors. Each one draws 3.3 amps, no load. The elbow motors are from Buehler. They draw 170mA, no load. The forearms also use Buehlers The final HB25 powers the waist pivot. Each arm also has 4 powerful hitec HSR-5995-TG for the wrists and " fingers ". They are on a different system ( parallax servo controller ). I am trying to keep the entire project as compact as possible. I know that eventurally, I will have to use " slave " stamps , but for now it would simplify everything to put all 9 HB25`s on one Stamp.

So , what do you think I should do ?

Ken

Mike Green

Clearly the 12V motors (and the HB-25s) should run directly off the battery which I assume is 12V. The Hitec servos seem to work best at 6-7.2V and need their own regulator for that voltage. I assume an LM338K would work fine for this. I don't know about this servo, but most of them will draw up to 1.5A or so on a stall. The Stamp and any other logic would have a 5V regulator which could also be an LM338K if you want. You need a good common ground for all of this, laid out so the noisy (the high current motor) grounds come separately to a central point apart from the logic grounds.

Post Edited (Mike Green) : 9/22/2007 6:32:33 AM GMT

kennet

You are correct. All motors run straight from their various batteries. All logic circuits operate from a separate 12V, 9amp lead-acid power source. Here is a list of my various power sources.

Two totally separate 24V battery systems , one primary , and one back up,( 2 ,12V,18amp and 4, 6V,4.5amp ). These systems power 2 wheel chair motors and their separate Victor 883 speed controllers.

Two 12V systems, for the HB25`s , primary (one 12V, 38amp battery), and a back up ( 2, 6V, 12amp batteries)

Servos are powered by a separate 7.2V NiMH battery pack.

I failed to mention this earlier, but when I tried to hook up HB25 # 5, the battery almost shorted out, and the motor got really hot.
As I mentioned above all logic is powered from a separate power source. Their is no common ground. All systems are totally isolated. so if I
am reading you right , your saying that I should connect all systems to a common ground , yes ?

Mike Green

Unless they're specifically designed for isolated grounds, most systems assume that there's a common ground. A circuit after all is a circle with the electrons going round and round. Any voltage has to be in reference to some point in the circuit and that, by convention, is considered ground.

The HB-25 takes care of this by providing a logic ground (Vss) terminal on the "servo" cable. This is (has to be) connected to the logic ground. The Victor controller's PWM cable also has a logic ground. If you've connected these properly (with the black or Vss wire connected to the BS2p's Vss terminal), you'll have a common logic ground. Similarly, the black lead for the servos has to be connected to the BS2p's Vss terminal as well as the NiMH battery ground.

There must be something about how you've got things hooked up that's causing the problem and there's not enough detail in your description to sort that out. You'll have to post a schematic. If you don't have a schematic, make one, then post it. Often the process of writing everything down in detail will help you find out what's connected wrong.

kennet

Mike your absolutely correct. Everything you mentioned above, I understand completely. The only reason I isolated the various systems is so that the robot can easily be taken apart for transport and then reassembled quickly for shows (about 5 min). All HB-25 servo cables go directly to a BS2p motherboard. The Victors have their own BS2p motherboard which is connected to a SSC-II . I have a third BS2 attached to a PSC for all of the servos. I might add that I built my own motherboards. I love to build my own boards.

The Victors and their SSC-II ,can be programed or operated remotely with the futaba 9CAP. The PSC and it`s BS2p control the servos flawlessly, but I digress. What I`m trying to convey to you is that I`ve had plenty of experiance with these systems but always through an interface which was purchased. I was doing great until I tried to connect that fifth HB-25.

I will take your advice and back track through the whole system.It may take a few days but maybe there is a bad ground connection some where.

PS. You seem to know about victors. Their controllers are also known to draw alot of current. They solve this problem with booster cables
which can be purchased from IFI. Since I have extra cables I was going to try it on the HB-25. But again, I digress I will take the system apart.

Ken

StampNut2

Sounds like a neat project Bunkleybot, Keep us posted.

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Never give up when things go wrong.

robosapienv2-4mem8.page.tl/

kennet

I will keep everyone posted and in a couple of weeks provide photos.