edit: related to this topic.
Hi guys
What about cooling in cases where the motors are inside f a housing?
Also i have seen a servo where the servo housing was perforated. Any thoughts?
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Hi @JasonLatour!
Welcome to the RobotShop community!
Well, depending on what the case is made of you may get an overheating system pretty quickly (ex: plastic case with no air flow).
Even with passive cooling, a typical hobbyist-grade RC servomotor will probably be near or overheating within 15-20 minutes under a light load. This is just due to how they are designed and what they are meant to be used for.
You may have already noticed, but many of the higher grade RC servomotors actually use a metal (typically aluminium) case with “fins” on the design directly. This can greatly help the motor cool down while still providing large amounts of torque over long durations. Also, being metal, it will react really well to active cooling (ex: a fan pointed towards it / any other active airflow).
While doing some high torque tests (25-30% of stall torque) with a servomotor with an aluminum case I had overheating/shutdown within an hour. By adding a small USB-powered cooling fan I extended my tests to 8-12 hours without overheating at all! Active airflow on metal cases can make a big difference.
The best to do in such a case (inside a housing) would be to either:
- Provide proper active airflow to help cool the parts inside; think of people inside large costumes on Summer days: they always have active airflow to help cooling them down.
- Place all component that can overheat adjacent to a heat sink that is touched both the object and the outside of the housing. Then active/passive airflow can cool that heatsink therefore drawing the heat out from the internal components (ex: what is done with most laptops since the warmers parts (CPU, RAM, GPU) are typically nowhere near the edges of the system and their heat is carried by heatsinks / heat pipes instead towards the fins/outside cooling).
Well, if some of the servo is open to the outside you can force cooler airflow (i.e.: active airflow) into it to help with cooling. Often when testing components that start overheating instead of waiting for it to cool down I use compressed air to help cool the device faster through some of the openings. Similarly, this can be done with active airflow in an assembly where the (over)heating component have holes or other perforations.
The main components to cool down would be the DC motor and the H-Bridge, typically.
Sincerely,
Thanks for the advise.
In my case the motor must be inside the housing and it will run for an hour or more at moderate to heavy torque load.
I will design it with forced airflow into the motor’s housing and then back out of the device. So I will perforate the motor housing (a 25 kg hobby servo) and blow air from a fan directly into the motor.
I will let you know how I made out.
-Jason-
No problem! Glad to help.
Since you expect both the heat to be difficult to remove and the motor to be running for long durations (about an hour or more), I’d recommend choosing a motor that has a high stall torque, so that the require dynamic torque is about 10% of the stall torque. This should help keep the motor cooler.
This would also help the motor stay cool. That being said, it may not be enough to keep the inside coils from getting damaged by heat if running for long (as in the casing will be cooler due to forced airflow but the rate or heat removal may still be too low if the torque is too high for the selected motor & ends up producing too much heat). See note above concerning this.
Looking forward to know how it all turns out. Experimentation is the best option here!
Sincerely,
You can get an overheating system based on the case.