RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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.)

Re: RS775 In Drivetrain?
 

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?

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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

Re: RS775 In Drivetrain?
 

That is not something I would recommend.

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In 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?

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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.

Re: RS775 In Drivetrain?
 

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.