pic: 1296 Mittens
 

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Because of the location of the intake I keep seeing this as Mittens pre-launching itself to go over the defense, ie travelling right to left.

Re: pic: 1296 Mittens
 

It is actually traveling left to right. The arm raises straight up and catapults in the direction of travel. ie: the intake is in the back of the robot, but it shoots forwards.

When crossing the ramparts we only take up half of it, making for a nice jump.

Re: pic: 1296 Mittens
 

Oh I know. But my mind wants me to believe the opposite.

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don't leave us alone in the 775pro drivetrain club :eek:

Re: pic: 1296 Mittens
 

16 Is there too.


1296. Looks VERY familiar.

#teamMiniPult

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Pretty sure 3310 is there too

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You aren't alone! 16, 1625, and 3310 are also running 775pro drivetrains.

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If I may ask, what prompted a switch away from the 775Pro drivetrain? I have been curious as to their performance, seeing a few robots with them on CD, ans would love to hear more about what you liked and didn't like about them.

Re: pic: 1296 Mittens
 

I'm sure they liked the size and power output but disliked when they were on fire.

Re: pic: 1296 Mittens
 

We loved the 775Pro drivetrain! Each side with 2 775s, plate and reinforced VP weighed about the same as a single CIM. But we got something a little bit wrong (single speed, geared a little too high maybe? too much torque required to turn though it was blazing fast? needed better inter-match cooling?) and burned the motors up during semis at 2 different regionals after placing 2nd and 4th in quals.

We think we could figure it out and be OK. But bottom line, we don't want anyone to shy away from picking us (or accepting an invitation) in St Louis because we are sporting the same drivetrain that failed us twice this season.

Re: pic: 1296 Mittens
 

Oh yeah I could see how that could be a problem. It would be an interesting offseason project to see how robust a 775Pro (or other similar motor) based drivetrain could be, and what the full scope of possibility is for them (two-speed? An absurd number of motors? PTO? Other stuff I haven't thought of yet?).

Re: pic: 1296 Mittens
 

Let's just say, all of those are possible!;)

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You guessed our main off season project, honestly the possibilities of running 775pros is just too good for us to ignore.

The biggest disadvantages to a 775 drivetrain that we have noticed is robustness (we still are not 100% sure what happened at Dallas) and not being very good for pushing (can't stay at stall torque for very long). Drivetrain cooling is critical.

Main advantage is that you get the working torque of a CIM in a stupid small and lightweight package. I think our drivebase with no mechanisms attached weighted in under 30 lbs this year, almost half of that being the wheels. The entire robot has varied between sixty and ninety depending on what iteration the mechanisms were on. Want to talk about building an agile robot?:yikes:

On a completely unrelated note, this discussion has clearly attracted a lot of attention from individual team members.

Re: pic: 1296 Mittens
 

Can't quite put my finger on it, but there's something about this robot I just really like... Looking good 1296! See you in STL!



-Brando

Re: pic: 1296 Mittens
 

I know in 2012 the Poofs had a drivetrain that had two CIM's per side and a 775 (I think it was a 775) per side as well (with 2-speeds, no less), per this source, and also from me seeing it at Champs. This seems to me like it could be the best of both worlds, and a CIM/775/775Pro hybrid opens up a ton of possibilities.

Re: pic: 1296 Mittens
 

Quite a few teams have utilised the BB775-18 in conjunction with CIM's in previous seasons.

775's especially the 775pro because of the bearings, are more efficient then CIM's, so this is another advantage. I think that in a shifting gearbox, 775pro’s are highly effective alongside CIM’s or with sufficient cooling could be highly effective alone. 3360’s drivetrain utilises 8 775pro’s that is a lot of power. While the motors may not like being stalled, it is very unlikely they will be stalled in a pushing match (this is more power than 8 CIM’s).

Cooling CIM’s with a fan etc. during a match isn’t very effective, because most of the heat is contained in the rotor, in-fact the outer case of the motor continues to heat up after the match ends, because of the heat conducting from the rotor. But with 775pro’s because of the low thermal mass and the fact that they aren’t sealed means that in-match cooling can be used.

The 775pro is designed so air is drawn in through the front holes, and is then expelled out the back after it has passed around the rotor. The VP mount has special holes for this, but the holes in the the VP motor input stage, could be enlarged to increase airflow.

In the 2014 KOP there was a thing called an “ICE cube” supplied by EBMpapst which allows fan-forced cooling keeping the motor cool, even when the fan is not rotating. It looks ideal for a task like this.

http://first.ebmpapst.us/docs/Instruction_RevC.pdf

There was some discussion about it on this thread http://www.chiefdelphi.com/forums/sh...ght=775+cooler

Re: pic: 1296 Mittens
 

We had problems at Toronto, probably like 1296, because our gear ratio was too fast. The power peaks we had made us brownout. we replaced a 5:1 for a 9:1 in the planetaries at Montreal, and we had twice the torque, and the speed is still decent, about 9ft-sec, now with no brownout problems.

Like you said, with all the power, if we get in a pushing match, the wheels slip instead of stalling the motors. They get warm, maybe hot in elims, but they will not burn

Re: pic: 1296 Mittens
 

We were running around 16ft-second with our 775pro drive. Our problem in Palmetto was stalling the 775pros and not having any software current limiting (which was heavily tested and implemented for Dallas). That happened 3 straight matches (new motors every match) and led to our early exit from the elims. Although we thought the issue had been solved for Dallas and we cooked the motors again in the elims. Since we have plenty of weight we decided to go to a 1 CIM and 1 miniCIM per side drive that will be implemented at champs.

Re: pic: 1296 Mittens
 

my point, exactly. 4 775's at 16ft second has 4 times less torque than our setup, at 8 775's. Having more torque makes sure you don't stall the motors and burn them. We also learned it the hard way :rolleyes:

Re: pic: 1296 Mittens
 

It is probably reasonably quick to change gearboxes/motors over if your using VP's. However because 775pro's are such a precious resource this season, with the supply issues it can't exactly be practical to be going through them at that rate:)

Have you had any issues with the carrier plates of the gearbox or any other issues with them?
The load rating data sheet, says that the big reduction(7,9,10:1) carrier plates says that they can withstand up to 100 N-m, so your not to close to that, but there are a lot of different stresses in a drivetrain. I suppose part of the reasoning for having the sprocket reduction after the planetary reduction stage was to reduce the torque on the gearbox?

Also how often do you grease the gearboxes?

Re: pic: 1296 Mittens
 

How many 775 pros did you buy?!

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we have a special technique for the carrier plates... we punch the gear pins so the expand. they last longer that way. the sprocket reduction after the gearbox does reduce the torque, but the main idea behind it was that it was easier to install that way.

We greased the gearboxes once when we built it, and one more time when we changed the ratios at Montreal. We don't plan on greasing them again

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We got the motor swap down to about 7 minutes per side. On the VPs we weld the pins and bore out the gears putting needle bearings in to spin on the pins and fortunately we did not have any problems. Swapping the VP would have been a much longer task.