[DFTF] Motors... ...Drive Motors...

[Billfred]

Originally Posted by Joe Johnson

This is part of a series of posts called Drinking From The Firehose on getting Dr Joe back up to speed on All Things FIRST.

Today's topic:
Motors... ...Drive Motors...

Okay, so I am reading the rules minding my own business and BAM! I am hit with more Watts that any robot chassis has a right to expect.

In my day, there were two drills in the kit with about 200W of peak power apiece. After that, the motor power fell like a rock to the sub 30W range (window and seat adjusters motors mostly the Globes would come later...).

There was literally no reasonable option but to drive with the drill motors.

Fast forward to last year.

• 4 "Coke Cans" from CIM @ 340W each
• 2 550's from FP @ 290W each
• 4 775's from BB @ 270W each (the 18V version scaled to 12V)

That's a lot of Watts.


Sooo... ...I suppose that the most common drive system is still 2 CIM's per side (4 CIM total). Because they are awesome motors in so many ways, not the least of which is that their size allows them to get rid of a lot of heat fast (and we all know that we pour a lot of heat into them -- FYI a curling iron is typically about 20W!)


But it seems that there are enough high power motors in the kit that other options may make sense as well.


Are there folks that used the FP's for driving (either as a 3rd motor per side or to use a CIM somewhere else or to save weight or because your team just felt like it)? How'd that work out?



On thing that worries me about the FP is that they have a circuit breakers in them now a days (at least they did 2 years ago when I was helping a team in MD. That fuse caused my winch to wig out -- not a happy event when you are trying to hang). Did people who drove with the FP's have breakers trip (not the Power Distribution Breaker but the one in the motor itself).



Same questions about the 18V 775's from BB.

One thing I always say is if you don't move, you don't play after lunch on Saturday. To that end, I am very cautious about drive train failures. So... if the FP and BB motors are not up to the task, I want to know about it before we design our robot drive train around them.



Tell me what traps to avoid.


On a closely related topic, let me know if the CIMple Box trannies from AndyMark are as awesome as they look on paper (I love the name, I love the compactness, I love that they do exactly what they need to and no more -- looks pretty sweet to me... ...but if it turned out to be a trap it won't be the first time FIRST has shipped a rookie killer in every kit ;-)


The only thing that I get a little worried about is that output shaft and how it's supported. Can it really stand up to a 2 CIM motor stall with a #35 12T sprocket hanging out their on the end of the shaft? Andy and Mark are clever guys so I suppose it can, but I would like some testimonials if you have "FIRST hand" experience.



Before I go, I want to caution folks to be nice. Drive systems are a touchy subject. Let's not start unnecessary battles (for example the shifters vs non shifters - we can discuss it yes, but let's just agree that we are never going to reach total agreement. In any case, let's keep the flame wars to a minimum).


Joe J.

From our experiences:

-We used the Fisher-Price motors through an AM Planetary on drive in 2010 in a six-motor two-speed setup. It was probably overkill for the game, but our design didn't call for their use anywhere else and they caused us no problems across five robot-events (1398 and 2815 collaborated; both attended two regionals and the former attended Championship).

-Call it lingering memories of 2007's kit gearboxes, but I have been leery of using any of BaneBots' products in mission-critical applications. Indeed, a case short on one of those 775s sidelined 781 in the worst possible place: Einstein finals. We used their smaller motors (540s? 550s? Been so long...) on our roller claw without a problem...but that's something where we could've come up with a Plan B if they were bad. Doing that on drive is a little tougher.

-For all our faults this year, the CIMple Boxes never gave us a lick of trouble. I wasn't sure about the math without that second stage of reduction in the gearbox, but it works out fine once you crunch the numbers (cue Mark Leon...)

-A four-CIM kitbot built properly with the tweaks obvious to you (grippier wheels*, 6WD, sprocket-based gearing choices to match the speed of the game) will usually be an 80th-to-90th-percentile performer on drivetrain at most events. For us, that's enough that we'll stop there and start focusing on manipulator; for one of the pioneers of swerve, well...

*And for that, I really can't beat the bargain of skinning the gray rubber off the kit wheels and riveting your own tread onto them. Especially if you're on a budget: http://twitpic.com/4afp59