Bot Building Questions!

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joey_picus
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Re: Bot Building Questions!

Post by joey_picus » Wed Aug 24, 2016 6:02 pm

I'd echo Alex, although servos are a tad more user-friendly for attaching arms to - I think your best bet re: Y-leads would be to splice one together yourself as commercial ones tend to be quite bulky.
Joey McConnell-Farber - Team Picus Telerobotics - http://picus.org.uk/ - @joey_picus
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peterwaller
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Re: Bot Building Questions!

Post by peterwaller » Wed Aug 24, 2016 6:08 pm

Remember if you use two servo's you need to make one run the opposite way to normal which means reversing the motor connections.
If you are not modifying it to 360 operation you also need to swap the outer connections on the pot.

bot_bandit
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Re: Bot Building Questions!

Post by bot_bandit » Thu Sep 08, 2016 2:17 pm

[quote="peterwaller"
If you are not modifying it to 360 operation you also need to swap the outer connections on the pot.[/quote]
Thanks for the advice everyone! Being new to all this I'm not entirely sure what the above quote is referring to however? could you rovide a little more detail Peter? thanks!
Luke H - Team Bandit

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BeligerAnt
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Re: Bot Building Questions!

Post by BeligerAnt » Thu Sep 08, 2016 7:36 pm

If you want to use two servos to drive a flipper they are usually mounted facing each other. This means that for both to lift one needs to turn clockwise and the other counter-clockwise.
In order to reverse the direction of a servo it's necessary to do some surgery...

(Apologies if you know this bit) A servo consists of a controller, motor, gearbox and feedback potentiometer (pot'). The pot' acts as a variable voltage divider, its output voltage is controlled by the position of the output shaft of the servo. The controller compares this voltage with the command signal from the receiver and drives the motor to turn the output to adjust the voltage to match the input.
So, as you push the stick up (say) the input voltage increases and the motor is driven to turn the output clockwise to increase the feedback voltage.

If you want one servo to turn counter-clockwise when you push the stick up you have to reverse the motor and also electrically reverse the operation of the pot'.

The motor is connected to the controller by 2 wires, simply swap them over to reverse the motor.

The pot' has 3 wires, the centre one is the variable voltage fed back to the controller, the ends are positive and negative references. You have to swap these over so that turning the pot' counter-clockwise increases the feedback voltage rather than decreasing it.

Note that you only need to do this if you want 2 servos to run in opposite directions from the same signal. If you want to reverse a single servo just flip the channel reverse switch on the transmitter!
Gary, Team BeligerAnt

bot_bandit
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Re: Bot Building Questions!

Post by bot_bandit » Thu Sep 08, 2016 7:59 pm

Can't thank you enough for taking the time to write such an in depth and eloquent run down on servos. This answers any questions I could've had and more. I'm looking to have two running in opposite directions for a flipper/lifter yes.
Luke H - Team Bandit

bot_bandit
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Re: Bot Building Questions!

Post by bot_bandit » Fri Sep 16, 2016 10:03 am

Thanks to you guys I've successfully reversed a servo! May not be a lot to you guys but an achievement for me. I bought that 5 pack of Tower Pro MG90s off eBay that Peter mentionned at some point and they were orettt easy to take apart and change.
Luke H - Team Bandit

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