4 replies to this topic

[rmjlmartin]

What are safe operating temperatures for different types of motors?

I'm trying to integrate keeping tabs on motor temperatures into my setup and performance evaluation, but I don't really have a good point of reference. Plus, different types of motors seem to run at different temperatures, too.

What started this is that when I asked ProSlot last year for advice on gear ratios for the then just-released Speedball, I was told to keep the motor temperature under 180 degrees. The Speedballs that I've monitored seem to push that when geared about where they get the best performance, but several C cans that I've been using to practice motor building (X-12, SuperWasp, and S16C), and a 16D that I just built seem to run significantly cooler. And then I have a cobalt motor wing car that seems to hit about 220 degrees fairly quickly, which makes me a little nervous.

I'd really like to avoid burning up an arm, especially in the middle of a race...

[crazyphysicsteacher]

Gear them so you can still touch the arm. Beyond that, the varnish will begin to start to fail and the winds will change color on you.

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[Dave Crevie]

Keep a log book. Set the car up to get your fastest lap time, and check the temp of the motor after several laps. Write it down in a notebook, along with all the other set-up parameters. Regardless of what anyone else tells you is optimum operating temp, the motor will tell you where it likes to be by giving you your best times running in that temp range. And don't forget to check the motor temp after an extended run. Temperature is cumulative, and as the motor retains more heat, the performance will go down. In the end, though, there is no magic formula that I know of that will let you just slap the car down on the track and win with it. You need to sort things out real world, and above all, keep notes of what you tried. 

 

If you need a fairly cheap way to check the actual temperature of the motor, Tempilsticks work pretty well. These are essentially crayons that are designed to melt at a specific temperature. You can get them at industrial supplies, hardware stores, and even Amazon. You buy the ones listed to check the temp range you want to know. (I.E. if you want to check if the motor is running at 200 degrees, you will need sticks for 190, 195, 200, 205 and 210 degrees. You can fine tune this info by getting the 196, 197, 198, 201, 202, 203 and 204 degree sticks.) You can get sets as well, but you will be buying a lot of sticks you may never use. 

 

  

[rmjlmartin]

Thanks Dave, I hadn't thought of keeping tabs on the motor temperature to evaluate performance, but that's a good idea.

 

But what I'm mostly interested in is not overheating a motor to the point of burning up an arm.

 

Like I said, ProSlot advised me to keep a Speedball under 180 degrees, so I've been using that as a point of reference, but I don't have anything else concrete for a safety margin. Most of the motors I've observed seem to be in their good performance range at well under 180 degrees, but that cobalt motor seems to get a lot hotter than that. That's the first cobalt motor I've owned, so I don't know if they just run hotter, or if there's something wrong, and I'm running a risk to keep running it.

[Dave Crevie]

Here's where keeping a running account of each motor's best running temp is important. If you don't gear it to run over that temp, there is little chance the motor will burn out from overheating. And in the real world, running the motor a bit colder isn't going to hurt your times that much. Say your motor runs consistently at 180 degrees geared 10/30. Going to a 31 tooth spur may only drop the temp to 178 or 179. Now your choice of spur becomes based solely on "on track" lap times. A bigger spur gives better punch out of the corners and better braking. But if the temp drops to, say 170 degrees, you will probably want to stay with the 30 tooth gear to keep bank speeds up. 

 

Cobalt motors just run hotter due to the thicker wire and fewer turns used. But the same practice holds true. If the performance drops off as you get close to that "threshold" temperature, back off on your gearing.