SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Jan 23, 2010, 08:15 AM
It's a spiderweb of knit lines
Souderton Pa. USA
Joined Mar 2002
2,639 Posts
Discussion
DIY servo amp board

Hi,
Anyone know of a DIY servo amp board? The board inside a servo, not a servo driver.

I'm looking into building a micro servo. I have some ideas for the mechanicals and can design/build boards. I'd like to use a very small micro controller, but have no programming experience.

If I can't find code I could use the chip out of an existing servo but they are pretty big and heavy. I'd like the servo to weight around 1 gram so using an existing board isn't an option.
mcross is offline Find More Posts by mcross
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 23, 2010, 11:15 AM
Registered User
ITALY
Joined Sep 2004
928 Posts
info

I have that.I have it on another pc,i enclose all the as soon as i can.It use a pic 12f683 and only 2 n&p channel mosfet,i am not able to change the software,the only problem is that the servo with this driver have long travel,we need to reduce it,and we have to convert this software from pic 12f683 to a pic 10f series if possible.Are you able to make this change?
With this software we can use or potentiometer or hall effect sensor,i have tested it and work.
Ivan2280 is offline Find More Posts by Ivan2280
Reply With Quote
Old Jan 23, 2010, 12:02 PM
Registered User
mudville
Joined Nov 2002
952 Posts
mcross,

maybe you could scavenge parts, etc from an existing servo and use them in your mechanics,

This thread describes a servo than can be dissected..
It has a servo amp board that might you might be able get the chip off of, and has the chip data sheet.. showing the chips application circuit..
No S/W involved... just surface mount desoldering/soldering..
on a new board you can design..

SteveH



http://www.rcgroups.com/forums/showthread.php?t=1173308
shoutchen is offline Find More Posts by shoutchen
Last edited by shoutchen; Jan 23, 2010 at 12:25 PM. Reason: spellin
Reply With Quote
Old Jan 23, 2010, 12:27 PM
Registered User
AleG's Avatar
Bangkok
Joined Oct 2007
1,633 Posts
Quote:
Originally Posted by Ivan2280 View Post
I have that.I have it on another pc,i enclose all the as soon as i can.It use a pic 12f683 and only 2 n&p channel mosfet,i am not able to change the software,the only problem is that the servo with this driver have long travel,we need to reduce it,and we have to convert this software from pic 12f683 to a pic 10f series if possible.Are you able to make this change?
With this software we can use or potentiometer or hall effect sensor,i have tested it and work.
Ivan, I'd be interested in the schematic of the H drive you use with that. I've been wanting to make a servo driver using and AVR microcontroller for some time.
AleG is offline Find More Posts by AleG
Reply With Quote
Old Jan 23, 2010, 02:54 PM
It's a spiderweb of knit lines
Souderton Pa. USA
Joined Mar 2002
2,639 Posts
Ivan, I'm interested in looking over your control board. The 12f683 should be small enough.
mcross is offline Find More Posts by mcross
Reply With Quote
Old Jan 23, 2010, 03:15 PM
Registered User
mudville
Joined Nov 2002
952 Posts
Ivan2280

It might not be posible to use the 10f series.
the 12f683 has a built in H/W pwm channel,
and none of the 10f series parts has one.
the 10f series has a couple less I/O pins,
so there might not be enough..


the 12f683 comes in several packages.
You can get it in an 8 pin dfn package, which
is a surface mount chip that is 4 mm x 4mm x .9mm
,small enough for sure..


Do you have the schematic available with the 12f683?


mcross,

Even if the 12f683 is small, that will need possibly 2 to 4
fets for the hbridge, along with the resistors asociated with driving them.

You could change the hbridge out to something like an a3901
hbridge for a one chip hbridge , but that would most likely
require changing the S/W, and apparently the source code
is not availabe

... The servo contoller chip
does not use any xtra transistors for small servo motors,
and only some resistors, ,capacitors, and the feedback potientiometer.

Way less trouble...in my opinion

SteveH
shoutchen is offline Find More Posts by shoutchen
Last edited by shoutchen; Jan 23, 2010 at 03:24 PM. Reason: spellin
Reply With Quote
Old Jan 23, 2010, 03:53 PM
Registered User
ITALY
Joined Sep 2004
928 Posts
driver

I have used this driver in my small servo:
http://www.rcgroups.com/forums/showthread.php?t=948988
We have only to mod the software for have less travel.
I can enclose all the info and pcb file for build this type of servo if you are interested.
Ivan2280 is offline Find More Posts by Ivan2280
Reply With Quote
Old Jan 23, 2010, 03:59 PM
Registered User
ITALY
Joined Sep 2004
928 Posts
driver board

This is the driver photo.I can make it more small without problem.This driver work with only 1,8v.
Ivan2280 is offline Find More Posts by Ivan2280
Reply With Quote
Old Jan 23, 2010, 05:00 PM
Registered User
mudville
Joined Nov 2002
952 Posts
waht are the FETs?

I know there were several servos that use
12f675/12f683 and the FDC6327C fets from fairchild.
one is the falcon servos and the other a JMP servo.
I have got both of them in my servo pile..

SteveH
shoutchen is offline Find More Posts by shoutchen
Last edited by shoutchen; Jan 23, 2010 at 10:39 PM.
Reply With Quote
Old Jan 23, 2010, 05:12 PM
Registered User
ITALY
Joined Sep 2004
928 Posts
fet

I use fdg6322c

www.fairchildsemi.com/ds/FD/FDG6322C.pdf
Ivan2280 is offline Find More Posts by Ivan2280
Last edited by Ivan2280; Jan 23, 2010 at 05:14 PM. Reason: update
Reply With Quote
Old Jan 23, 2010, 05:24 PM
Registered User
mudville
Joined Nov 2002
952 Posts
ivna2280,

Those are newer ones. and they come as small as sc-70,
which are really tiny..

also what is cool about them is that
they need no biasing or gate drive resistors...
that is even better than the servo hbrieges on
similar things like a blade msr brick..


it looks like your board onlyneeds the cpu, the 2 fets,
and maybe a couple
of bypass capacitors... Is that all?


can you change the code in the hex file?
Did you write the source code?



mcross,

the parts count is pretty low after all.. it will definitlet weigh
less than the dedicated servo chip and its support parts.

if the S/W is somewhat supportable/changeable, then
this may be a good way to go.

it only costs about 30 bucks for a usb pic
programmer that will program these parts..
they work with a windows program..

SteveH
shoutchen is offline Find More Posts by shoutchen
Last edited by shoutchen; Jan 23, 2010 at 05:46 PM. Reason: spellin
Reply With Quote
Old Jan 23, 2010, 06:29 PM
Registered User
ITALY
Joined Sep 2004
928 Posts
servo

The servo in photo work well,we have only to reduce the travel but i don't know how to make this mod.I enclose asap also hex and asm file.The software is not mine.I have only designed the schematic and the complete servo.It need only the pic and 2 fet.
Ivan2280 is offline Find More Posts by Ivan2280
Reply With Quote
Old Jan 23, 2010, 06:46 PM
Registered User
mudville
Joined Nov 2002
952 Posts
ivan2280

If the owner of the S/W does not mind,
can take a look at the asm file if you wish..

You can use the microchip assembler built into MPLab that they
give out for free on their website to change the asm file it and
rebuild the hex file with changes in it.

The CPU has to continously measure the servo pulse width, and read the
voltage on the resistive wiper and decide how hard to drive the motor , in one direction
or another. The code should have also some logic in it to
see that the servo it at or beyond the limits of the servo travel
and stop the motor...



SteveH
shoutchen is offline Find More Posts by shoutchen
Last edited by shoutchen; Jan 23, 2010 at 06:55 PM. Reason: spellin
Reply With Quote
Old Jan 23, 2010, 06:47 PM
It's a spiderweb of knit lines
Souderton Pa. USA
Joined Mar 2002
2,639 Posts
Ivan,
I don't think any s/w change would be required. I intend to make a rotary servo very similar to the new Falcon servo but with a pot instead of the hall. The circuit board will be part of the structure and have the surface mount pot soldered onto it, so I'll have to change the board.

I have a Baseline Flash programmer but it won't do the 12f638 so I'll have to order a new one.
mcross is offline Find More Posts by mcross
Reply With Quote
Old Jan 23, 2010, 07:14 PM
Registered User
mudville
Joined Nov 2002
952 Posts
mcross.

a pickit2 will program those parts.

the servo should not try to keep driving the motor if
it is at the end of its travel. There may be a mechanical stop,
but it is still bad to have the CPU drive the motor when it is
mechanically binding. that makes the motor draw the "stall current",
and if that is higher than the rated value of the FETS, then they
will burn out and smoke.. if not then the battery will drain really fast..and if
the discharge rate of the battery is not that good, then the battery
lifespan will be shorter


SteveH
shoutchen is offline Find More Posts by shoutchen
Last edited by shoutchen; Jan 23, 2010 at 07:20 PM. Reason: spellin
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion IDEA: DIY Brushless ESC w/ I2C & PWM support (for quadrocopter) asifjahmed Multirotor Talk 8 Feb 11, 2010 11:36 PM
Help! hobbylobby rec/servo board draza1 Scratchbuilt Indoor and Micro Models 1 Jan 25, 2010 08:45 AM
Discussion CPU board + Servo board to control servos for Bicycle Deraillur project Z06kal UAV - Unmanned Aerial Vehicles 1 Nov 17, 2009 05:25 PM
Sold 375W 12VDC 15 AMP Power Supply - DIY darkfa8 Aircraft - Electric - Batteries & Chargers (FS/W) 2 Nov 05, 2009 11:55 AM
Discussion Corona 2.4Ghz DIY Module & 8ch RX (DSSS) only $34 !!! Gyroguru Radios 2 Oct 06, 2009 07:07 AM