Sorry for the repost, I was trying to see if I could change the thread title but accidentally deleted the thread instead.
We were testing our cimulators earlier on our shooter axels and felt that they were getting uncomforably hot and after a few minutes there was smoke coming from the rs550’s! http://www.chiefdelphi.com/forums/images/smilies/eek.gif
So we decided to modify the cimulator to allow for airflow into the front vent holes on the rs550s to help keep them cool. We milled some .1 deep slots into the cimulator around where the rs550s are mounted to uncover the front holes so they could get some airflow.
Here is the unmodified part:
Here is the modified part:
The result is that the rs550s and the transmissions now stay much cooler then before and we can now run them at full speed and not worry about them getting too hot (at least for the length of a match). These wern’t that hard to add and i’m not really sure why they don’t come from banebots like this.
Here is a video of one of the modified cimulator’s spinning up one of our shooter axels: http://www.youtube.com/watch?v=YtiK87pE_9U
We are also mounting a fan above the cooling slots to help with airflow.
Small motors need to breathe, if only a little bit. They have fans on the electrical connection end that force air out, which causes air to be drawn in at the mechanical mounting end. That’s why there is a pattern of “breathing slots” just outside of the mounting pilot.
By letting the motors breathe a little, you extend the time they take to heat up. Without through-ventilation, hot air is trapped inside. Trapped air is a pretty good thermal insulator, so the windings on the motor’s armature heat up much faster than the motor’s case – that means that by the time the case gets too hot to touch, the windings are probably hot enough to burn insulation, releasing the familiar magic smoke.
Conclusion – by letting the motor breathe, you are relieving thermal stress on the windings MUCH more than can be detected just by sensing the case temperature. If you plan to run a small motor continuously, it is essential to let it breathe.
To see another example of breathing holes in a face-mounting plate for small motors, look closely at the twin-FP gearbox in this picture.
We found out today that the motor that smoked before we modified the cimulators had developed a case short and so we are no longer using it. Hopefully that will not happen to anymore rs550’s with these cooling slots added.
We also had an ir thermometer with us today and although we don’t have non modified temps to compare to, after 2:30 flatout the motors were at 105F and 115F, and the transmission was at 95F.
All the slots let air in the front of the motors, the motors suck it through and the small fan in the back lets it out the un-obstructed holes. Tomorrow I can get a picture of it with the motors mounted.
We learned this the hard way last year with our custom fisher price gearbox. Over the course of the season we bought 14 fisher prices, at 11 dollars apiece that is 151 dollars wasted. Anyone who has gearboxes with motors that will experience sustained current draw above ~5 amps should definitely be sure the cooling vents are not blocked.
Direct driving that wheel with the RS-550’s through the Cimulator… Looks like you could be getting 6,000 - 7,000 RPM. With that kind of speed, on what looks to be 8" diameter wheels… SCARY! At that speed, the molded on urethane could be thrown off at speeds approaching 250 feet per second:ahh: . That could be lethal. Be careful around that thing!
We did some modifications to our CIM-U-Lator plates this evening to aid with ventilation. I’ve uploaded the Working Drawing and part files (Both in Inventor 2012) to illustrate the changes we made.
The Working Drawing has the necessary coordinates for the tool path if using a mill capable of moving along multiple axes simultaneously. If using a purely X-Y mill, the 45-degree angles on the slots allow for the plate to be machined by turning the vice on a 45 and then machining straight through
On the face of the plate, you can open the blind mounting hole with an eighth-inch bit. You can then tap through and use 3/4" Bolts to connect the plates, allowing for greater engagement and avoiding the possibility of bottoming out the threads.
EDIT: Thanks to Andy Baker for the inspiration. The modification is similar to that done on the AndyMark Planetary gearboxes.
EDIT 2: Sure enough - the .ipt of the CIM-U-Lator plate that I used for this print had holes in the wrong location. Everything should be resolved now. The idw is attached.
EDIT 3: I’ve uploaded a .pdf of the working drawing for anyone who’d like the drawing without having to use Inventor 2012 to open it.
That’s very nice of you to go to all that work. But could you please upload them as an STP or older-version Inventor file? We’re running Solidworks for CAD, and it can’t handle Inventor 2012 stuff.
To add to the discussion, there are several motors that contain these small fans to assist with motor cooling, the FP for one. It is also important to run the motor at a minimum RPM range to allow the fan to do it’s job.
If the case of the motor is running at 115 degrees, you can bet the internal temperature is much higher.
Thanks all for the work done to improve the cimulator cooling. I am certain that this will save us all a lot of grief!
I also appreciate Martin’s comments concerning the safety of the 8 inch wheels spinning at high speed. Has anyone tested the burst speed of these wheels?
I really dont know if this is true(haven’t taken any physics yet), but i would gesstumate it being about 7500-9000 rpm.
(10TENSILE STRENGTH)^(1/2))= BURST SPEED IN FEET PER SECOND
BURST SPEED IN FEET PER SECOND(60)(12)=SPEED IN INCHES PER MINUTE
3.141592653589793(WHEEL DIAMETER IN INCHES)=CIRCUMFERENCE IN INCHES
SPEED IN INCHES PER MINUTE/CIRCUMFERENCE IN INCHES=ROTATIONS PER MINUTE
(APPROXIMATION)
(108000)^.5=283
283(60)(12)=203760
PI(8)=25
203760/25=8950
