In order to save space on our electronics board, we’re hoping to mount our jaguars above our CIMs for the drivetrain. To be more precise, we’d like to mount them on a 1/4" piece of acrylic that’s bolted to the hex shafts that we’ve got as crossbars between our CIMple gearboxes. We’re running four CIMs. The one thing we’re concerned about is the heat. Last year, one of our team members reported the CIMs had a temperature of above 300 degrees F (can’t verify that number personally, it does seem a bit high. We do admittedly drive very hard, though.) We’ll cool them between matches with fans, but during matches, we don’t really have any cooling system on them (last year we were drawing enough power that we’re reluctant to add on more power draw.)
So, questions.
Are the CIMs really going to be radiating that heat much?
How sensitive are the Jaguars to the sorts of temperatures that could be induced in them?
What sort of power draw would a small fan have? Anyone have any experience with active cooling on their robot?
I personally don’t believe that the CIMs would get quite that hot. Even with heavy driving, we’ve only ever gotten the CIMs to barely being warm, and never so hot that you can’t grab onto one without injury (with everything powered off of course)
Over a two-minute match, I wouldnt believe that this could be a problem, but somebody else may have had different experience with overheating CIMs?
In our team’s experience, under continual use CIM Motors can get very hot. Hot enough to practically fry an egg on. This would often happen when were trying out drive team, practicing, or in the final paces of a tournament. The acrylic I would believe would dissipate the radiating heat somewhere else, but as far as I know only the CIMs get hot, they don’t actually radiate heat like a heatsink for a CPU.
Acrylic should not be anywhere on your robot. Acrylic, aka plexiglass, is not impact resistant and is likely to shatter if used in FRC. I recommend using polycarbonate (aka lexan, makrolon, and a bunch of other brand names). This stuff is literally bullet proof.
That being said, Air is your friend, nearly All thermal insulation used on earth (space is another story) is air based. A small gap between your Jaguars and CIMS (0.5-2 inches) should be plenty to allow them to stay cool. leaving the area around them open will further decrease heat by allowing air to pass around the motors and Jags. This should be done regardless of the proximity of the jags to the CIMS whenever possible.
We’d love to use polycarbonate. Unfortunately, our manufacturing capabilities are somewhat limited in regards to plastic. As such, we’re going to laser-cut several parts out of acrylic at a local machine shop, but they don’t allow polycarbonate (pesky toxic fumes.) Hence the acrylic. We’re limiting it to only parts that will experience very little load, and we’ll fasten very, very securely, as well as coming with several spares and reinforcing key points. If anyone’s willing to run polycarb or aluminum routing for us, let me know, but we really just don’t have the resources. We’re also using acrylic plus, which is considerably more impact resistant.
Awesome, thanks. One of our design goals this year was to keep the CIMs clear. We’ve got plenty of free space in front and behind them, and we’re venting the space below them, too. I’ll lobby to throw in fans, and we should be in business.
That’s pretty lucky. Ours, and many other teams, have gotten very hot. You could burn yourselves on them. Watch out for it.
Shouldn’t be too hard to keep them within that range. Thanks!
Sounds like our experience. We mounted fans on our cart in order to cool down between matches. Glad to hear that they shouldn’t radiate too much.
If you have table saw, band saw, or scroll saw, you can cut polycarb. You can even do it with a hacksaw if you prefer not using power tools. A floor mounted belt or disk sander cleans up the edges nice, for a clean cut look.
We just got a major (more than 400 pounds of large scrap) polycarb donation, so we are building most of our robot out of it. It’s easy to use, easy to cut, and strong in a planar dimension. To build the mount that our shooter is attaching to, all we have constructed so far is to make a 7 inch gusset for two sides, and an 1/8 inch aluminum tube going up, and you can push the robot around easily without it bending (yes, we are reinforcing it with more…)
Fenix,
A couple of things to think about.
300 degrees on the outside of a CIM indicates that the internal temperature exceeds that by quite a bit. I am confidant that the failure point of the insulation on the internal wiring of the motor is being reached by those temps. Please double check that figure. The high temps indicate excessive electrical usage as well indicating that the motors are being operated outside recommended practice.
There is a condition called ‘thermal runaway’ in electronics. This is a condition where the temperature reaches a point where the electronics have a mind of their own and cease operating with any control. Since the Jag internals (or any other electronic device) suffers from this effect, catastrophic failure of the device is likely should these temperatures be reached.
Acrylic is considered a hazard on FRC robots and therefore fits under that category in the rules as being a banned material under R08.
Per [R08] and the blue box, the MSDS is what determines if a material is hazardous. Per the MSDS, Acrylic is non-hazardous. Pulmonary Wellness
[R08] also allows for something to be disallowed if it is “unsafe”. However, I find it hard to believe that you would say that every use of acrylic is unsafe, sight unseen. I do agree that many (or even most) uses in an FRC robot could be unsafe, but I would be hesitant to make the blanket statement. It’s been a very long time since the manual explicitly banned acrylic.
Joe,
The MSDS sheet is not a deciding factor.
“Teams should provide MSD Sheets for any materials they use that might be considered questionable during Robot Inspection.”
The ‘safe’ materials are those that are not only safe for the students on the teams but also for those on the field, i.e. refs, field resetters, judges, VIPs, etc. While acrylic is not specifically banned, an unsafe part of a robot can be questioned.