# Overheating Servo



## asterix0 (Nov 5, 2008)

Hi,

We have a heat problem with a servo motor I'm using in a prop and wondered if anyone had suggested solutions. We're building an animated dragon and using the ST-200 servo controller from Cowalicious to drive a Hitec HB635 servo. Both the servo and the power rectifier on the ST-200 generate too much heat. We've already replaced the heat sync on the ST-200 with a larger one but it's still too hot. However, the real problem is the servo which eventually overheats and stops working. Has anyone had similar problems and come up with a solution?

Thanks,
Asterix0


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## asterix0 (Nov 5, 2008)

Obviously, when I typed "heat sync" I meant "heat sink."


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## Otaku (Dec 3, 2004)

Interesting. How many volts is your power supply? That may be part of the voltage regulator heating problem.


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## asterix0 (Nov 5, 2008)

It's the 9V 500 mA from Cowalicious.


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## Otaku (Dec 3, 2004)

I see that the HS-635HB draws between 400mA and 500mA (4.8VDC and 6.0VDC respectively). This is the operating current draw with no load on the motor. It's likely to draw more current when it's actually moving something. You're pretty much at the limit with your power supply. Try a higher amperage supply and see if that doesn't help - you really should have at least a 1A supply for that servo. Are you sure you're not exceeding the capacity of the servo?


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## asterix0 (Nov 5, 2008)

Thanks. I'll try a higher amperage supply. 

The servo is operating a jaw which fits inside a commercial latex head. A smaller servo almost worked but just didn't give us the movement we were looking for.

Asterix0


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## Otaku (Dec 3, 2004)

asterix0 said:


> Thanks. I'll try a higher amperage supply.
> 
> The servo is operating a jaw which fits inside a commercial latex head. A smaller servo almost worked but just didn't give us the movement we were looking for.
> 
> Asterix0


It sounds like that servo is working pretty hard and maxing out the supply. Check the head and see if you can't relieve the load a bit and make it easier for the servo to move.


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## asterix0 (Nov 5, 2008)

Otaku,

Thanks. We'll take a look and see what we can do.

Asterix0


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## fritz42_male (May 5, 2009)

Don't know if you solved your problem but I mentioned this to my brother-in-law who is a model aircraft freak and he suggested reducing the load on the servo by 'counterbalancing' the jaw with a spring or elastic bands. Anything that reduces the workload of the servo.


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## spinman1949 (Jun 29, 2009)

*Exactly*

My design for a 3 axis skull will use some counterbalance for the nod and jaw. In the jaw I will counterbalance to bring the jaw closed lightly. Likely the Latex mask is providing resistance to the jaw opening, so in your case it might help to add some spring assist to open the jaw. Basically, whatever position the jaw tends to remain at, you want to lightly counter. If you can get the jaw to hover in mid stoke with an appropriate spring, then that is the ideal.


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## hpropman (Jul 27, 2008)

If the servo is shutting down then it is overheating so I agree with what everyone said a larger power supply and making it easier for the servo to move. If you can post some pictures of the mouth it might be helpful.


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## dscrimager (Jun 6, 2008)

*Heatsink on the Servo*

Did someone mention this? You might use some thermal paste and/or bond a heat sink to the servo and have a small muffin fan blowing on it to more quickly exhaust the heat. Also since it's enclosed do you have any place on the prop head to set up cross ventilation like in a PC case? All my current character cases, where all the electronics reside, have ventilation holes and small fans to keep the air circulating.

If you know how to disassemble servos and get them back together you might ventilate the case carefully to help heat dissipate. Although anything like this obviously voids warranties and makes it more susceptible to environmental incursions ( i.e. water damage, insects).

The counterbalance idea should certainly reduce the servo load.

Freshly Doug


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