Servo replacement

kimbear

Member

• Jun 27, 2017

• #1

Inexpensive toys usually dont use standard servos, they make their own servo with a standard brushed motor, with 4 leads.
I need to replace the transmitter receiver, and I would like to use a standard 3 wire servo, but I cant because a really complicated steering geared mechanism.
Can I somehow interface a standard servo output to this weird 4wire servo??

 

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Last edited: Jun 27, 2017

alec_t

Well-Known Member

Most Helpful Member

• Jun 27, 2017

• #2

You would need to know the voltage/current/protocol used by the 4-wire system in order to design an interface.
Could you link a standard servo to the steering gear mechanically instead?

 

kimbear

Member

• Jun 27, 2017

• #3

all I can say is that the system was originally 6vdc. the motor that runs this servo is just a small brushed one.
it seems as tho this is actually just a switching arrangement to stop the motor after travel, in either direction, more than a actual servo.
I cant actually add a servo to this, the gear that runs it wont fit on the drive shaft.

 

alec_t

Well-Known Member

Most Helpful Member

• Jun 27, 2017

• #4

I see the output gear has a horn with a push-rod attached. What does the hex shaft on the previous gear drive?

 

kimbear

Member

• Jun 27, 2017

• #5

The hex drives a whole arrangement that animates a character on the top. If it was just the rod, no problem, but the hex is the stumbling point. The huge amount of gears ensures that the figure moves slowly.
I could just drive the existing motor with a esc , but then, I wouldnt have the limit switching to make certain the the figure doesnt twist too far

 

alec_t

Well-Known Member

Most Helpful Member

• Jun 27, 2017

• #6

Do the contacts on the end gear provide a motor reversing function as well as limit-switching?

 

kimbear

Member

• Jun 27, 2017

• #7

I belive they do, but Id be happy with simply limit switching, but to drive it from a standard servo output, is the difficulty

 

kimbear

Member

• Jun 27, 2017

• #8

I understand that the switching arrangement is some sort of H-Bridge...

 

alec_t

Well-Known Member

Most Helpful Member

• Jun 27, 2017

• #9

So how is rotation direction presently commanded/controlled?

 

kimbear

Member

• Jun 27, 2017

• #10

It originally had a remote controlled receiver, that someone was nice enough to remove, so I have no reference.

 

alec_t

Well-Known Member

Most Helpful Member

• Jun 27, 2017

• #11

Can you trace the motor drive/switching/supply circuit and show us?
To use a standard servo signal would likely require converting that to clockwise/anti-clockwise/neutral commands. With limit-switching as well, it's looking like a job for a MCU.

 

kimbear

Member

• Jun 27, 2017

• #12

i shall try