Hi guys & gals.
Anyone out there that have modified one of these puppies to spin 360* instead of only 60*? I have tried to modify it but dont want to continue because I might ruin it :/...
Im hoping to use it to lift an arm on a 6 kg fighting robot but with only 60* lift its not gonna work...
Thanks in advance,
Markus, Team Bad Teeth, Sweden
Typically, in robotics, servos are also modified and used as the motive force in wheeled vehicles. To modify servos for 360 degree (continuous) rotation, the potentiometer is decoupled from the output shaft (the electrical connections are left intact) and the two internal physical end-stops (or mechanism) are removed (previously used to prevent damage to the potentiometer.)
Now when an input is given to the servo, the potentiometer is no longer providing feedback. So the error signal can never be reduced. So the DC motor continuously turns. In this arrangement, (known as an open-loop scheme) the input now controls the speed of the motor. The larger the input, the faster the motor turns.
Well...thanks for the info Woody, very nice. However though after removing the two visually physical end-stops (1 inside the pot and 1 on the biggest gear, the servo still only turns 60* :sad:.
So...Im a bit baffled. Any input highly appreciated.
Remove the pot .....take it out... or.....disconnect it mechanically .......but NOT electrically....from the internals.
http://www.seattlerobotics.org/guide/servohack.html
http://dalewheat.com/servos.php
(Message edited by woody on July 09, 2006)
Try replacing your pot with one of these from Maplins.
9.5mm (3/8€Â) Square 22-Turn Cermet Preset Potentiometers ......the 5k is ideal.
A bit of twiddling will be needed to set the centre OFF position.
http://www.maplin.co.uk/Search.aspx?criteria=UH24B&DOY=10m7http://www.maplin.co.uk/Search.aspx?...UH24B&DOY=10m7
(Message edited by woody on July 09, 2006)
Cheers mate. Excellent help and very fast
I did the first part, replacing the pot with 2,2 kohm resistances, and removed the physical stops.
Now it works but the centre off is weird. When I first connect the servo to the receiver (with a failsafe inbetween) its stable and doesnt even jerk a little. But when I switch on the transmitter the servo starts to run. I tried to fix it with the trimmers on the tx but it only slows it down, not fully to a complete stop.
The most worrying though is when I swtich the TX to off. The servo goes nuts and start to continously spinn very fast in one direction. The failsafe lights but doesnt seem to be able to stop the servo.
The failsafe is an Xtra Failsafe (Tehcnobots part no 3402-001). I have tried both of the ones I have but with same result :sad:.
So...do I change the resistances to some higher ones or try to get the Maplin pot in the post above? Or is there an easier solution?
Tnx
The null point of your newly modified servo is going to wander around anyway, due to changes in voltage and temperature
You should have been able to trim this out on the transmitter... ( Ive seen reports of people having to do this EACH time they use their bots ) ...the trim pot I mentioned will help to get a more accurate off position.
Youll need to set up the failsafe with the transmitter ON and the servo at rest / stopped.... or at the moment just creeping
2K2? You need to use something adjustable to set the centre stop. e.g. the maplins pot.
The servo doesnt move when first turned on with the Tx off because there are no pulses received.
When you turn the transmitter on, the centre off isnt correct with the fixed resistance so the servo turns slowly. You could trim this out on the Tx.
Then when you turn the transmitter off again, the failsafes kick in, but are outputting the wrong setting to stop your servo. If you take the failsafes off, you will see the servo stops when the Tx is off.
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