Servos Modified with External Pots Info and Advice please.

B

Borneoben

Member
Hi Guys

I am still plugging away at my camera mount system and need some information on modifying servos for use with external pots.

I see all the High end camera mounts use modified servos. Photohigher and teh AV130-200 and the new cinestar mount plus a few others.

Please can you point me in the right direction so i can find info about how to do this mod and where to find the correct Pots.

Just to make sur eim not missing anything, the main reason to modify the servo and place teh Pot in teh axis of teh actual part of the mount to be moved is so that the sercos travel is no longer limited?

Correct?

We are basically fooling the servo to into thinking its only moved 90 degrees (or what ever) when in actual fact, due to teh gear ratios used its moved maybe 180 degrees.

If this is the case cant we simply relocate the original pot from inside the servo to the new axis??

My new camera gimbal would require about 120-150 degrees rotation on the pitch axis and with a gear ratio of 50:1 i would need to get upto 300 degrees of rotation from the servo correct?

Im planning on using my Hyperion DS20FMD's that I have on the shelf.

Cheers

Ben
 

Bartman

Bartman

Welcome to MultiRotorForums.com!!
the potentiometer in the servo is providing position information to the controller inside the servo so it can position the arm where the receiver is telling it to. when you use an external "pot" you are giving the controller the same position information but now it's being measured at the camera plate and the servo is going through more turns to get it there. the servo doesn't know the difference between one turn or two turns to get to the commanded position, it just wants to get to that position.
you'll have to remove any mechanical stops that would keep the servo gears from turning beyond their design range
with the the servos i've modified so far i've left the pot in the servo and just clipped the wires and used an aftermarket pot.
hope that helps.
bart
 


Bartman

Bartman

Welcome to MultiRotorForums.com!!
right now i'm just using the pot from my MKTR which has a "B5K" on the back of the case.
 

B

Borneoben

Member
Do you think it a good idea to try and re use the original Pot from the servo?

Im not sure how easy it is to do that with teh hyperion servos but it would save allot of guess work and save a little bit of money!!

Cheers

Ben
 

Bartman

Bartman

Welcome to MultiRotorForums.com!!
it depends on whether the pot shaft is part of the gear train and whether it has threads for mounting outside of the servo. I'm experimenting with an old Hitec and I had to break the stops in the original pot so they wouldn't hinder the rotation of the servo. i also had to grind off a post on one of the gears that would have kept the servo from rotating beyond it's design range.
 


R

RTRyder

Merlin of Multirotors
Borneoben said:
Do you think it a good idea to try and re use the original Pot from the servo?

Im not sure how easy it is to do that with teh hyperion servos but it would save allot of guess work and save a little bit of money!!

Cheers

Ben
Click to expand...

No, the pot is too fragile and the shaft is too small to reliably attach it to an axle on the camera mount. I recently replaced one of the Hyperions on my old AV130 and from experience I know reusing the internal pot externally would be more trouble than its worth. Much easier to go to the local electronics supply house and get a larger pot that is easier to work with unless of course there are no electronics supply shops locally.

Ken
 

B

Borneoben

Member
Ha!

Thanks Ken!

You just saved me some trouble!

Do you have any specs i can use for these external pots? or will any old Potentiometer do?

Can you send a picture of the Pot you use with your Hyperions?

Would be most appreciated

Thanks

Ben
 

R

RTRyder

Merlin of Multirotors
Borneoben said:
Ha!

Thanks Ken!

You just saved me some trouble!

Do you have any specs i can use for these external pots? or will any old Potentiometer do?

Can you send a picture of the Pot you use with your Hyperions?

Would be most appreciated

Thanks

Ben
Click to expand...

The ones I have came already installed on the AV130 mount. The tilt axis pot is much smaller than the roll in part because it doesn't need to be able to rotate more than 1 turn and not even that much in practice. The roll axis is a 10 turn pot because the servo needs to do many revolutions to travel from one extreme of the roll axis to the other end on the AV130 with its gear drive. As I recall they are usually 10K ohm pots though I would need to put a meter on one to check it out.

Ken
 

Bartman

Bartman

Welcome to MultiRotorForums.com!!
Ben,
How do you intend to use the pot in your mount? Some use it as a pivot point in which case you need enough threaded shaft to put through your frame and secure in place with a nut and lock washer. You also need enough of the inner shaft to clamp onto with your camera tray. It sounds like Ken's AV mount uses the potentiometer somewhere else where it's rotating more than the camera tray is so multiple turns are necessary.
If you search using the B5K identifier from my MKTR pot, you'll be in the ballpark of what you actually need. Then it's just a matter of wiring it up and experimenting with it to see how you'll have to go about getting it to work. If you pull apart the hyperion servo, there may be identifying marks on the pot that you can match up to a more stout example with the same electrical specs.
Bart
 

B

Borneoben

Member
Hi Bart

I planned on mounting the Pot on the end of each shaft of each axis.

They will be 6mm diameter shafts so just need to figure out how to connect the 2.

Will take a look inside the Hypeions and see if i can find a spec to search for alterntives. I didnt get chance last night as got home late.

I will not be using the Pot as a pivot point, I highly doubt they were designed this way and wont have the correct bearings etc built in.


Thanks for all your help guys, I love this forum!

Ben
 

J

jes1111

Active Member
If you have a multimeter you can measure the resistance range of the existing pot. Remember, too, that apart from facilitating multiple turns, the other reason to replace the original pot is quality: a high-spec wire-wound multiturn pot will give the servo's feedback circuitry a cleaner, more accurate "signal". Every little helps, as they say ;)
 

B

Borneoben

Member
Jes

Where did you learn all this stuff???

You seem to have very good understanding of all things multirotor that covers both mechanical engineering and eletricalengineering?

Were you a Nasa rocket scientist in a previous life before your Portugese photography adventure?

Thanks

Ben
 


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