V5 motors overheating

Our V5 motors are overheating. We have 4 teams using V5 and they have some issue with V 5 motors used in their drive systems.
We are using C++ for VEX and the brains have been updated to v1.02. This update fixed the battery issue we had but not the motor problem. The motors are reaching temperatures in excess of 55C and shutting down. Also, before the recent update the motors would not drive at full power, despite the gear ratios being set to a speed ratio and code also written to get a speed output.

If they are overheating than you are putting too much load on the motors.

How do you read motor temperature? We tried to do it and we got about 1.5 billion so I think we did something wrong.

There is a menu on the Brain that you can select a particular motor and get its statistics. I agree that the motors are taking a heavy load but with the new motors we felt this would not be an issue. Upon further inspection of the setup, the team has a simple speed gear train attached to the motor before the drive axle. This should not place any extra load on the system but we will remove it and try direct drive.

What gears are used?

In addition to listing the gear ratio, can you post a picture or two?

The team removed the external gears, changed the ports and now it seems to work. Direct drive is more than sufficient to move the robot efficiently around the field. 60/36 gear ratio was the original external gear set up after the motor, it has been disassembled.

Gear ratios in drives usually won’t work out. You had a 60/36 gear ratio (~1:1.67), meaning your motors are working 67% harder in order to operate the drive compared to just having a direct drive.

The only thing that matters is the final gear ratio. It doesn’t matter whether you use internal or external gears (and friction, and wheel size, and the number of drive motors, and the weight of the robot, and etc.). A lot of the best robots in VEX history used non-direct gearing. If the OP was gearing up a 2-motor drive 5:3, yeah, that’s probably more than the motors can handle with a 200 RPM gear box.


(But in all seriousness @Rick TYler is right.)
1 Like

Looks like 4 motors to me…
A 13lbs bot stresses a 2 motor 200rpm drive and you won’t be winning many pushing matches.

Of course when it was just a chassis the team was drifting it on the field around the platform. After seeing this video, I think they would have preferred a gym.

I was looking for a motor power curve for the V5 motors and couldn’t find one, so I’ll link to this thread discussing the 393. https://vexforum.com/t/motor-torque-speed-curves/21602/1

Never mind! Found it here… a few pages in https://www.vexrobotics.com/v5-architecture.html

For all the smart controls in the V5, it is still a brushed DC motor that is subject to the same physics as any other DC motor. This means that your maximum torque occurs at stall (0 RPM) as does your maximum current draw AND your lowest efficiency. In fact, at 0 RPM, all of the electrical energy you put into the motor goes into heat… you’re not doing any mechanical work (work being F*D, you might have lots of F, but if D is zero then work is zero) and your motor is essentially a heater rather than a motor. Thankfully, as you’ll see in the V5-Architecture document, the smart controller is pretty smart and keeps you from burning out your motor… but you can still overheat it by pushing it hard at low RPM.

You won’t actually get your peak power output until the motor is spinning at a little over 1/2 of its free speed (the speed it spins at when there is no load on it). For the V5 with the output gear pack used in the linked document, that is somewhere around 60RPM. If you’re asking for full throttle and getting less than 60RPM – pushing a heavy object for instance – then you’re putting a lot of electrical power into the motor, but not getting much mechanical power out… and the rest all goes into heat.

Planning to give up a bit of top end speed by switching to a lower gear ratio (or a smaller diameter wheel) will not only improve the efficiency of your motor (more power going to mechanical work rather than heat) but may also improve your acceleration and maneuverability. This might actually get you where you’re going more quickly than gearing for top-end speed… and keep your motors from overheating in the process.


P.S. If you haven’t read the system architecture document… it’s a good read. I wasn’t actually interested in the V5 until I read it… and am still kind of meh about having a more powerful processing unit. Few teams were able to use the power of the original PIC units, let alone the Cortex so the V5 CPU seemed like serious overkill. (Yeah, yeah… I know… but playing Doom isn’t what I mean.) It’s the rest of the system that goes around the new brain that really impresses me. I know that the roll out will make a case study for a business school class one day, but a year from now when the parts are in stock and the firmware stabilized, this is really going to be a killer control system. Heck, it is now from a technical standpoint.

I understand the overheating issue a lot better now from reading this threat.

However, I still have a few questions:

My team is running our six wheel drive base off of 4 200RPM V5 smart motors with no external gear changes. Regardless of this, we have been overheating our motors. At first I thought it was because we had been working for 4 hours straight. However, it happened after 40 minutes of coding and testing–which is fairly moderate conditions. If our motors are overheating from just regular use, is this a VEX issue?