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.

[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.

[baldenb]

Originally Posted by Thad House

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.

That's a good point, robots this year will be moving around a lot of weight. We might test this on our demonstration/drivebase test robot.

[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.

[Scott Kozutsky]

Honestly, it may work. I wouldn't risk it because any match you don't drive is a match you don't score. At all.

If there's an auto problem and you drive into a wall you could be dead for a match and have to replace drive motors. Even stopping or accelerating abruptly could cause problems.

Stick to CIMs. It will be cheaper and less time consuming to save weight somewhere else then it will be to put 775s in drive then troubleshoot them. Even if it would work properly it's not worth the risk IMHO.

[Jefferson]

Originally Posted by baldenb

We might test this on our demonstration/drivebase test robot.

You gave yourself the best advice in this whole thread. Test it out for yourself in your application. That's really the only way to know.

[cglrcng]

My only personal experience w/ the RS775's is we used them on our shooter head drive wheel to accelerate & shoot those foam basketballs a few years back (one on each side, 1 running forward / 1 reverse on a large wheel in CAN w/ Black Jaguars), and they sometimes made some pretty flames mid- match. YES real fire, not just the magic smoke (we replaced quite a few that season I remember), until we made the mounts huge Alum. heatsinks to bleed off enough heat from the motors (so, in the end there was no real wt. savings in the end result, over using CIMS or mini-Cims).

And they were not constantly reversing direction often as in a drivetrain (or at all), just momentarily stalling of the wheel, as the fed balls made contact, and they were running very hot. Cooling them is very necessary if you do choose that route....Might also want to keep a fire extinguisher really handy while using them to drive weight this year, if that ends up your final choice. Just a suggestion.

They sure made those basketballs fly though, w/ real good backspin too! That Mid-Field Beam Though...Ugggh! Cracked every weld on that 2 sided bot repeatedly.