OpenServo.com

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

Andy was generous to send me a HiTec HS-645MG servo to examine for upgrade to an OpenServo controller. This is a high-torque (133oz in) servo with metal gears and a powerful motor. In examining the existing controller board, I'm hoping someone can help me identify the FETs used in the H-Bridge to control this servo. Below is a picture.

As far as I can tell, the identification labels are ""D N 5A"" and ""B M 4L"". I'm wondering if these FETs are proprietary to HiTec or if they are standard off the shelf FETs that can be obtained from a components supplier such as DigiKey. I found this site to help identify SMD devices, but I haven't had any luck yet. I believe the package is a SOT89 or SOT223, but I could be wrong.

-Mike

prolinuxfan · Joined: 17 Feb 2006 Posts: 21

When you are able, can you clean off some more of the silicone around the far edge of the chips to verify the number of pins there just to limit the package down to either the SOT89 or SOT223? (Make sure how many tabs are on the other side)

Also, I have noticed from reading through some Panasonic data sheets that they don't seem to be using standard package notation, so theirs have completely different names too Sad

We can either find these, or some that are suitable, no matter what. To that end, do you know what the motor characteristics and specs are? Like what is the max stall current, etc.
_________________
Allen
(My R2 *WILL* climb stairs when I'm done)

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

I have no further information on the specs of the HiTec HS-645MG with regards to the motor characteristics. Perhaps someone knows where to find this information or determine it.

I'll try to post a better picture when I get a chance as I would really like to figure out what MOSFETs these are.

-Mike

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

I tried to peel away the hot glue on the Hs-645MG PCB and put together a better set of photographs at the link below:

http://www.openservo.com/moin.cgi/Servo_HiTec_HS-645MG

Hopefully this will make it a little easier to identify the MOSFETs used in this servo.

-Mike

prolinuxfan · Joined: 17 Feb 2006 Posts: 21

It occurs to me that I need to buy at least one servo for some software development anyway, maybe I should just get one of that model and put it under a microscope?

I like the new pics, but they just don't quite answer my questions, so I will change my open order to swap out one of the ones in my shopping cart for that model, and go from there. In the meantime, I will keep looking for those FETs, and also work toward converting the existing pcb design into an Eagle format.
_________________
Allen
(My R2 *WILL* climb stairs when I'm done)

ginge · Posted: Sun Feb 19, 2006 10:21 pm Post subject:

I have already created the schematic in Eagle, and I am just putting the finishing touches on it.
I have created a new Eagle library with all of the non stamdard components, to make development for other people easier.

I Will let post when I have finished.

Barry

prolinuxfan · Joined: 17 Feb 2006 Posts: 21

You're probably further along than I am, then... I haven't yet started. I'm patient, and I will await your posting for that, although I will probably play around with the TQFP design a bit.
_________________
Allen
(My R2 *WILL* climb stairs when I'm done)

andylippitt · Posted: Mon Feb 20, 2006 4:51 pm Post subject:

I noticed in the spec sheet for the 645MG that it uses a 3 pole motor. I don't know much about them, but that suggests to me that this is not your run of the mill h-bridge setup.

prolinuxfan · Joined: 17 Feb 2006 Posts: 21

If it has only 2 brushes, that is all that will matter. It has only 2 wires connecting it, so it is probably going to be much like any other.

All PMDC motors with brushes that are supposed to be self-starting will have an odd number of poles so that they never have them perfectly aligned with the brushes in a position such that they'd need a 'push' to get turning.
_________________
Allen
(My R2 *WILL* climb stairs when I'm done)

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

Hmm. I don't know anything about 3 pole motors. More stuff to learn I guess Sad

.

In the photographs of the HS-645MG it's not really clear, but there are three wires coming from the motor -- orange connected to the positive tab (red marker), brown connected to the other tab, and a black wire soldered to the motor case.

http://www.openservo.com/moin.cgi/Servo_HiTec_HS-645MG

Hopefully this won't complicate the H-bridge to any significant degree. I kinda assumed that the black wire was connected to ground, but perhaps not. Even if we can't identify the exact MOSFETs the H-bridge circuit shouldn't be too hard to reverse engineer.

-Mike

ginge · Posted: Tue Feb 21, 2006 4:52 pm Post subject:

Looking at the pictures you have taken, it look a lot like the Black wire goes from the motor chassis to the GND on the driver board. If this is so, then it will be a case of replicating that on the Openservo.

I quick +5v On the orange and brown wires should confirm my suspicions that this is just a ground wire. I have seen the grounding of motors before on larger chassis products.

Prolinuxfan seems to have hit the nail on the head with the 2 brush answer.

Enjoy the hols!

Barry