RS775 In Drivetrain?

[baldenb]

Has anyone ever used RS775s in a drivetrain before? Due to their similarity to a minicim in terms of power, and their lightness, they seem like a viable option for a non-defensive game where stalling in a pushing match is out of the question. including a vexpro CIM-ile gearbox, a RS775 weighs about a pound, which is half what a minicim weighs. If anyone has experience with using 775s in a drivetrain or similar application, I would appreciate your insight.

[cgmv123]

Teams have burned out 775 motors trying to use them in drivetrains before. I don't know if anyone has successfully used them. (The power level is similar, but the MiniCIM has more torque and can handle being run at stall/high power levels longer.)

[baldenb]

Originally Posted by cgmv123

Teams have burned out 775 motors trying to use them in drivetrains before. I don't know if anyone has successfully used them. (The power level is similar, but the MiniCIM has more torque and can handle being run at stall/high power levels longer.)

When teams have burned out 775s, has it been because they were stalled or just under heavy load for long periods of time? Is a 775 designed for less continuous use than a minicim, or just not designed to be stalled?

[Kyler Hagler]

We used them briefly last year. We had a 3 CIM Ball Shifter with 2 CIMs and an R775 on each side. We didn't see much performance boost and they became hot and didn't really work out well in our setup. This isn't to say they wouldn't work in your application but we just didn't see the need for them. As to the discussion about them burning out we never had that problem but i could see it happening if pushed continuously for very long periods of time.

[sodizzle]

I've heard of them being used in a gearbox that also has a CIM or two in it. Not sure how much benefit you get out of it though.

[baldenb]

Originally Posted by sodizzle

I've heard of them being used in a gearbox that also has a CIM or two in it. Not sure how much benefit you get out of it though.

We are considering using them in place of minicims in our drivetrain, primarily to save weight.

[cgmv123]

Originally Posted by baldenb

We are considering using them in place of minicims in our drivetrain, primarily to save weight.

That is not something I would recommend.

[sodizzle]

Originally Posted by baldenb

We are considering using them in place of minicims in our drivetrain, primarily to save weight.

I specifically meant when paired with two other CIMs. But as others mentioned it does have some benefits that I was unaware of when in that configuration.

[protoserge]

The RS series motors need active cooling to keep the enamel on the commutator shaft from melting. This is achieved in stock form by an internal fan and air ducts at the front and rear of the housing. The RS series motors are intended for power tools and R/C cars where they have plenty of air movement and are typically driven in one direction for a continuous period of time (not fast forward-reverse motion like the FRC robot).

The CIMs and MiniCIMs have a higher thermal mass to dissipate the heat and typically use the gearbox as a heatsink. The large mating surface area helps conductive heat transfer and the overall larger system mass provides more heat capacity. During extended runs, you will likely notice the housing of both the gearbox and motor are warm, but not necessarily hot, unless there is high friction due to under/over-greasing of the transmission or improper assembly or other motor failure mode.

I do not recommend using an RS motor for a critical, high load (high current) application such as the drivetrain.

[geomapguy]

Remember FP motors? Some teams used them in their drivetrains.

[gpetilli]

Originally Posted by stinglikeabee

The RS series motors need active cooling to keep the enamel on the commutator shaft from melting. This is achieved in stock form by an internal fan and air ducts at the front and rear of the housing. The RS series motors are intended for power tools and R/C cars where they have plenty of air movement and are typically driven in one direction for a continuous period of time (not fast forward-reverse motion like the FRC robot).

I do not recommend using an RS motor for a critical, high load (high current) application such as the drivetrain.

I believe the 775 has a bad reputation because many teams block the air input vents. This is largely because many of the gearboxes (banebots and AndyMark CIM-Sim) cover the input air vents and the motors overheat. One year we used the banebots gearbox and ultimately machined channels in the gearbox mounting face (look at the VersaPlanetary mounting plates) and that made a HUGE difference in the temperature of the 775 motors.

If you do use the 775 in your drivetrain (or anywhere else) absolutely make sure it is well ventilated. If you use the CIM-Sim at least drill some holes in the plate where the motor mounts to allow air to enter the input vents.

That said, the drivetrain is arguably the most important subsystem on your robot. Do a risk/reward analysis before moving from the miniCIM to the 775. Is there anyplace else you can save a few pounds?

[JamesCH95]

Originally Posted by gpetilli

I believe the 775 has a bad reputation because many teams block the air input vents. This is largely because many of the gearboxes (banebots and AndyMark CIM-Sim) cover the input air vents and the motors overheat. One year we used the banebots gearbox and ultimately machined channels in the gearbox mounting face (look at the VersaPlanetary mounting plates) and that made a HUGE difference in the temperature of the 775 motors.

If you do use the 775 in your drivetrain (or anywhere else) absolutely make sure it is well ventilated. If you use the CIM-Sim at least drill some holes in the plate where the motor mounts to allow air to enter the input vents.

That said, the drivetrain is arguably the most important subsystem on your robot. Do a risk/reward analysis before moving from the miniCIM to the 775. Is there anyplace else you can save a few pounds?

Winner winner, chicken dinner.

As a team that has successfully used the 775 in numerous applications with no failures (arm motors in 2011, stalled to hold arm position; shooter motors in 2012; climbing motor in 2013; intake motors in 2014) ventilation in continuous-use applications is strongly recommended. Make sure you're operating in the higher-half of the RPM range too, they tend to heat up otherwise.

IMO 775s would do fine in a drive-train that was driven at high speeds and would not do well in a drive-train that was mostly driven at low-throttle values. This is entirely based on the heating/efficiency of the motor - look at the motor curve and seriously consider where on that curve the motor will generally be operating. For this game, with lots of low-speeds and fine-positioning moves, it might not be a well-suited motor.

Also bear in mind that drive-train weight is generally low in the robot. Removing mass from components higher off of the ground than the drive-train will have a larger positive impact on the robots overall dynamic performance.

[Tom Line]

Originally Posted by gpetilli

I believe the 775 has a bad reputation because many teams block the air input vents. This is largely because many of the gearboxes (banebots and AndyMark CIM-Sim) cover the input air vents and the motors overheat. One year we used the banebots gearbox and ultimately machined channels in the gearbox mounting face (look at the VersaPlanetary mounting plates) and that made a HUGE difference in the temperature of the 775 motors.

If you do use the 775 in your drivetrain (or anywhere else) absolutely make sure it is well ventilated. If you use the CIM-Sim at least drill some holes in the plate where the motor mounts to allow air to enter the input vents.

That said, the drivetrain is arguably the most important subsystem on your robot. Do a risk/reward analysis before moving from the miniCIM to the 775. Is there anyplace else you can save a few pounds?

775's have another black mark against them - that's the shorting issue teams had when they were first released. There's nothing more frustrating than having to repeatedly change out 775 motors during inspection because of internal debris causing shorts that ground your PD board.

We haven't used them since that year. Fool me once, etc. Many other teams have used them since then.

We used 550's very successfully on our drivetrain in 2008. That year, however, you were generally trying to drive at full speed. This year, there is a lot of slower-motion movement aligning, adjusting, and setting things down. That means that any low mass air-cooled motor is not going to be terribly happy. Active cooling on the motor (a fan) will help tremendously.

[protoserge]

Originally Posted by Tom Line

775's have another black mark against them - that's the shorting issue teams had when they were first released. There's nothing more frustrating than having to repeatedly change out 775 motors during inspection because of internal debris causing shorts that ground your PD board.

We haven't used them since that year. Fool me once, etc. Many other teams have used them since then.

We used 550's very successfully on our drivetrain in 2008. That year, however, you were generally trying to drive at full speed. This year, there is a lot of slower-motion movement aligning, adjusting, and setting things down. That means that any low mass air-cooled motor is not going to be terribly happy. Active cooling on the motor (a fan) will help tremendously.

This is absolutely a huge issue. Case shorting is directly attributed to overheating the enamel on the commutator shaft. The BaneBot transmissions that blocked the air intake vent were the leading cause of failure when this issue was present in 2010-2012. Many of the newer transmissions I've seen have this air intake slot already machined into the transmission.

If you have a transmission without an air intake slot, it would be best to mill a slot for air intake.

[Thad House]

Originally Posted by baldenb

Has anyone ever used RS775s in a drivetrain before? Due to their similarity to a minicim in terms of power, and their lightness, they seem like a viable option for a non-defensive game where stalling in a pushing match is out of the question. including a vexpro CIM-ile gearbox, a RS775 weighs about a pound, which is half what a minicim weighs. If anyone has experience with using 775s in a drivetrain or similar application, I would appreciate your insight.

I think I remember hearing stories from you guys either in 2011 or 2012 about burning out the 775's on your drives those years.

Also, even with no defense I would not recommend using 775's on drive. Even though they are not going to be stalled pushing, it still takes alot of torque to accelerate a robot. During acceleration, it is sitting at a higher current load generating more heat. Especially if you have a robot that weighs close to 200 lbs loaded. With high traction wheels and a heavy robot, I think it would burn out even trying to accelerate, unless you also had CIMs on the same gearbox to help with the acceleration.