Lynxmotion Tech Support

yes, I know, I just didnt know how you were going to implement the Servo's original pot, I understand now though, sorry for the confusion

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Joe A.
Built in Canada with Lynxmotion Parts!

Hey zoomkat, which web page are you refering too ?

"Hey zoomkat, which web page are you refering too ?"

http://www.webcom.com/sknkwrks/mowers.htm

One other thing to consider is using this setup as a large motor speed controller. Setup somewhat like a continous rotation servo, the speed and direction omotor rotation could be controlled. I'll look at the speed control range of the 12v motor I have. In the BGMicro link I posted, on the front page they have a 60A P MOSFET for $1.49, and some 70-75A N MOSFETs for $1.79. They also have a 28A N for $1.49 and a 23A P for $1.99. In the regular catalog they also have 30A 12v SPDT relays for $1.99. Looks like it might be possible to make fairly high current H-bridges for less than $10.00 each. More tinkering and testing to do.

Thats really good, since I kind of had the idea to recreate that SHB-01. Would it be possible or would you have to program it. I think ifs its possible the only requirements we would need is bigger mosfets to take the amps.

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Joe A.
Built in Canada with Lynxmotion Parts!

No programming involved in a basic h-bridge, just supply it with the desired input. One would control it by sending servo control signals between the range of maybe 1460 to 1540, with 1500 being the center point where the motor is stopped.

ok, so one would need a parts list for the SHB-01 and replace the mosfets and other neccessary components (resistors ect) with more powerful or more desireable kinds. Than a simple .5w pot from radioshack (or Canadian Source CC*).

sounds interesting, I would do it if it wasnt science fair time, have to complete my project.

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Joe A.
Built in Canada with Lynxmotion Parts!

One would only need the parts list/schematic for the SHB-01 if one wanted to duplicate that h-bridge. Otherwise just get a schematic and the parts for the h-bridge that one wants to make. I don't know if any construction details for the SHB-01 are publically available, so duplicting one exactly may not be an option. I'm interested in the h-bridge made by the lawnmower guys as they apparently actually made one and reported that it works using the servo board outputs to the servo motor for control pulses. I guess the task now is to make one and verify that it is good solution for controlling large 12v motors. Probably time for a parts order to BGmicro.

The lawn mower project used an HS-805 but they retained the motor and geartrain, they just added the FET driver to eliminate the losses in the bipolar transistor stage. I posted it here with the asumption that a larger motor could be used instead of the servos motor. I don't really know why an HS-422 motor amp couldn't be used to drive the FET's.

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In my test I am driving my MOSFET switch using the output of the h-bridge in the HS-422, which basically indicates I can drive a much larger h-bridge for larger than servo motors, such as auto windshield wiper and electric window motors. The below picture is the lawn mower guys doing something similar with a large gear head motor. Bottom is a winch that might make a giant servo if an appropriate bracket is carefully welded to the spool. Maybe somebody could be inspired to make a 5 or 6 foot tall Brat.



http://www.harborfreight.com/cpi/ctaf/d ... mber=92860

I've done some tinkering attempting to duplicate the H-bridge in the schematic and have been unsuccessful so far in getting it to work as described by the origional builders. Trying to drive it as described from the servo motor leads generally results in a dead short thru the P and N MOSFETs, letting the magic smoke out of my fingers when I touch them. Definately more tinkering to do.

A while back in Nuts&Volts there were articles on using MOSFETs, including using NPN MOSFET transistors as high side drivers. The below was given as a simple way to impliment this approach to bootstrap gating the transistor when the transistor when is being turned on/off faster than ~1HZ. Just wondering if this would be practical in an h-bridge driven by the power pulses being sent to the servo motor. Apparently this is found in switching power supplys.

Went to the Harbor Freight parking lot sale today and picked up one of the winches (below, shown with a standard servo) to tinker with for $39.99 plus tax. I was hoping the control switches would be easy to push, but they are fairly stiff. The idea being that a single servo could operate the switch buttons (eliminate the need for a large H-bridge). Spring pressure in the buttons would need to be reduced. Current operating thoughts would be to use a servo to control the control switches, a pot mounted on the winch to show the drum position and provide an analog value to a controller/pc (via an ssc-32 for the pc), and the controller/pc to send the servo control info to position the button control servo as needed to position the winch. A strong mounting point would need to attached to the winch spool for leg mounting and such. I could see three of these winches being used on a large scale Kronos robotics three servo hexapod, possibly large enough to ride on. Not as dramatic as the spider car, but possibly cheaper and easier.

http://parkinglot.harborfreightusa.com/ ... e&type=RET

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Well, why not use relays or solid state switches (even a servo driver), instead of trying to push the buttons with R/C servos!

Also, the winch takes a lot of turns, so a typical pot is out. Just use an encoder, and somehow put limits on the cable payout. This could be done with "knots" (little clamps) on the cable, arranged such that they move a "fork" when the two extremes of cable travel (all out, all in) are reached.

Alan KM6VV

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The quick answer is cost. I've priced relays and solid state switches and they can't compare to the possible $5 el cheapo servo price. Idealy the origional heavy duty switch contacts would be used. They have a positive on/off click, which helps prevent a weak switch contact pressure.


I think you missed the point that this would be used like a large servo which rotates ~180 deg max. The cable would be removed from the spool and replaced with attachment hard points.

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http://youtube.com/watch?v=pWjMvrkUqX0
http://youtube.com/watch?v=qfyRA-g1nhI
http://web.comporium.net/~shb/S2000video.htm