Dual servo lifters?

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Team Orr
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Dual servo lifters?

Post by Team Orr » Thu Aug 01, 2013 9:40 pm

Forgive me if this is a silly question, bit rusty so thought I should ask.

In my newest robot "China Drum" I intend to use 2 metal gear servos for the lifting arm. I'm just about to place the order but its suddenly occurred to me that there may be a flaw with this idea. If the servos are running slightly out of faze/time as i suspect they will naturally, could having 2 servos actually be detrimental to the overall performance? I.E one servo is slightly faster and drags the other behind?

Would this have any noticeable effect? Should I just stick to 1 servo?
Cheers.
"if it wasn't for Edison we'd be watching TV by candlelight"
Jack Orr
Team Orr Robotics

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peterwaller
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Re: Dual servo lifters?

Post by peterwaller » Fri Aug 02, 2013 8:32 am

First of all it nice to see you back again.
There are some things to watch out for when using two servos together.
If you put them in so both arms are to the middle or outside then one servo has to be reversed.
Also if they are not quite in the exact positions they may fight each other when they should be at rest using more power.
In flippant I dont join the servos together just allow the arms to push the lifter independently.
Normally you will find the faster servo will tend to do slightly more of the work but it doesn't seem to be a problem.
With the new more powerful servo's capable of running at higher voltages you might find it easier to use one.

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Re: Dual servo lifters?

Post by haz » Fri Aug 02, 2013 9:51 am

Hehe, everyone seems to be wanting to do dual servos atm

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Re: Dual servo lifters?

Post by Team Orr » Fri Aug 02, 2013 11:46 am

It's more for symmetry than anything else :roll:

Thanks for the reply Pete. The servos I was thinking about using were these: http://www.graysonhobby.com/catalog/red ... -2029.html

In a robot similar to this
image.jpg
image.jpg (51.53 KiB) Viewed 3389 times
As I can't really see a way of having the arms not attached to the plow my only two options are to either try and see how it works with 2 or use one more powerful servo (which are the ones of choice nowadays? I still use sd200's for most things...) and use the other side as a pivot. That does seem like the more sensible option now that I think about it.

Thanks for the help.
"if it wasn't for Edison we'd be watching TV by candlelight"
Jack Orr
Team Orr Robotics

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Re: Dual servo lifters?

Post by peterwaller » Fri Aug 02, 2013 3:15 pm

I would never recomend mouting the flipper / scoop directly onto the servo arms there is to much chance of any impacts stripping the servo gears.
I would recommend mounting the flipper / scoop arms on to the chassis and connecting the servo to it using a linkage system.
It is a bit old now but here is a shot of one of my run all day demo bots that you may remember.
Image
You can just see the left mounting / hinge screw through the spokes in the wheel.
With the resurgence of the low flipper I am considering an updated version of this for my team. :wink:
As you can see this uses the Park HPX F servo but I know the are many more powerful ones arond now.

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Re: Dual servo lifters?

Post by Team Orr » Fri Aug 02, 2013 3:48 pm

I agree that your method does much to prolong the life of a servo. However, as my scoop hangs out way in front of the chassis I'm not entirely sure how I could implement such a linkage. Perhaps some sort of rotating axel connected to both arms? Maintaining full 360 degree rotation of the scoop is another matter entirely. I was rather hoping the metal gears and some clever shockmounting may solve that issue. May be time to redesign already :roll:

I've also decided to stick to one servo for the time being. Saves further issues and allows more room for battery's
"if it wasn't for Edison we'd be watching TV by candlelight"
Jack Orr
Team Orr Robotics

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