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Dagu 2dof Robot arm question

I bought this dagu 2dof arm recently

http://robosavvy.com/store/product_info.php/products_id/1594?osCsid=7ed23d473b22d4db12b8d1ecca353a39

I've wired everything up and it seems to work ok, however the servo that controls the gripper seems to get very hot, even when the gripper is open. I've been switching it off after a minute or so as i don't want to damage it.

Has anyone else here used one of these? Is it normal that the gripper servo gets so hot?

I found an instruction manual for the 6dof arm on the dagu support site  which seems to use the same gripper

https://sites.google.com/site/daguproducts/home/instruction-manuals

The manual seems to indicate that if the pwm pulse high time is outside of the range 660-1300 then the servo will get very hot.

On my gripper if i use a pulse high time of around 900, the gripper seems to be fully open, but the servo still gets really hot.

A pulse of around 2100 seems to almost fully close the gripper, but the servo gets even hotter.

Does this sound right ?

Any help or advice would be greatly appreciated

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If you're using the small dagu miniature servos, then I have noticed this also...but not to extremes.....I can adjust the pulse and it seems ok, but the problem I'm having is a constant chatter. I'm driving the servo from a 555 timer with a great square wave...about 80 to 90 hz and standard pwm settings (1.5 ms center)...the same circuit works well on my GWS servos, but continue to chatter on the Dagu.....any info?

 

I also have the same gripper. To check the servo position I connected a couple of potentiometers to an Arduino and read the servo position on the serial monitor. I also found out that the gripper servo gets hot when it is "stalled", it pulls 1A when stalled so I it's not surprising it gets hot. Here is a video of me testing the gripper :)

https://vimeo.com/41647626

Thanks for the quick reply :)

Do you have any idea roughly what range of pwm pulse values i should be using? If i have a rough idea then i can experiment from there.

It seems that no matter what values i try the servo heats up really fast. For example if i set the pulse high time to around 1100, the gripper is not quite fully open, but the servo still gets really hot. Likewise if it's fully open or closed.

Check that the gripper can open and close easily. If the screws are too tight then friction could be the problem.

Thanks.

I'll have another look at it tonight.

You are trying to drive the servo beyond it's range of travel. Like most servos the gripper servo can rotate aproximately 180° but the gripper mechanism only allows it to rotate about 60°.

As the servo horn will not always be mounted at exactly the same angle during assembly you must test for yourself to see what pulsewidth range is suitable otherwise the servo motor stalls trying to drive the servo to a position it cannot acheive. When the motor stalls it draws a lot of current and becomes hot.