[EWCP] Skid Steer Drive Optimization

Ever wondered how top teams design their 6 or 8 wheel drive systems? What factors they consider when choosing top speed? Well, join us tomorrow evening at 9pm Eastern when we ask them. We’ll even be breaking down the mystery of 25’s drive train.

So, join us at the usual place (http://www.talkshoe.com/talkshoe/web/talkCast.jsp?masterId=98466&cmd=tc) and the usual time (9pm Eastern) and let’s talk drive trains.

This week’s cast will cover:

  • How to choose a drivetrain that fits your strategy (how to do WOT for drive type)
  • How to design a drivetrain that fits your resources (why just because the Poofs do it one way doesn’t mean you have to)
  • Analysis of the drivetrains of past FRC Champions (HEAVILY favors 4/6/8WD skid steer setups)
  • How fast do you really need to go? What drives your choice of ratio?
  • To shift or not to shift…that is the question
  • Wheel choices: Omni, Colson, Roughtop/Wedgetop, How many (how many do you need?), How big (the argument to go small)
  • CAN MY DRIVE TURN?!?!. Talk through the Hibner paper, briefly talk about 25’s drive and why it can turn, talk about why people drop center wheels
  • Chains vs. belts vs. gears…pros and cons
  • Jags vs. Victors vs. Talons: Pros and cons in a drive train
  • How to control it in teleop: Arcade vs. Tank vs. Cheesy drive
  • How to control it in autonomous (brief, since a future cast is more controls centric I believe). Talk about the tried and true encoder+gyro combo.
  • Impact of chassis rigidity
  • Impact of CoG

For anyone who isn’t familiar with the significance of 25’s drivetrains, check out the links below of their drives over the past 10 or so seasons. 25’s drive does not have a drop center.

http://www.chiefdelphi.com/media/photos/35347
http://www.chiefdelphi.com/media/photos/28717
http://www.chiefdelphi.com/media/photos/19942
http://www.chiefdelphi.com/media/photos/17116
http://www.chiefdelphi.com/media/photos/14625
http://www.chiefdelphi.com/media/photos/14623

For some one who dose not live on the west coast, can some one explain how cheesy drive is different from arcade or tank?

Arcade drive means having one axis on your controller for forward/backward movement and one axis for turning left/right, either on a single joystick or split across two.

Tank drive is having two joysticks with independent control over each side of the drivetrain. So pushing forward on the left joystick in a tank would make the left side go forward, turning you right and vice versa with the right joystick. Pushing both forward would make you go forward, pulling on both would make you go back, one forward one back would make you spin in place, etc.

… snip …

As mentioned by others, the use of arcade drive using one joystick for turning and one for movement is known as Cheesy Drive.

So all West Coast Drives are ‘Cheesy Drives?’ and all ‘Cheesy Drives’ are West coast drives?

Actually, Cheesy Drive is a control scheme used by teams such as 254, 971, etc. The West Coast Drive is a separate drive system.

In Cheesy Drive, one analog stick is used to control forward/backward motion, and the other one is used to control left and right movement (think driving a car by changing the power on each side). This allows for small adjustments while driving that teams use to line up with the field and maneuver around obstacles. Alongside those “slow turns”, which only allow the robot to turn a little bit, there are buttons that when held down on the controller do “instant turns” by making the two different sides of the tank drive go in opposite directions.

Aside from a game controller, you can use a steering wheel to do the small turns instead of an analog controller, with other buttons for forward/reverse, and instant turns.

First off, my descriptions of these control methods only apply to skid-steer drivetrains like 4wd/6wd/8wd etc. Other drivetrains may call their control method Tank or Arcade, but the control is implemented differently. Skid-steer drivetrains work by using a speed differential between the left and right wheels to cause the robot to turn.

A brief summary:

Tank - 2 joysticks, each being used like a throttle for a drive side. Left stick controls the speed of the left side, right stick controls the speed of the right side. The x-axis on the joysticks are not usually used for anything.

Arcade - 1 joystick, the y axis controls the average speed of the driveline, and the x axis adds/subtracts a constant value from each side to create a differential speed, causing the robot to turn. This is not

“Cheesy Drive” - Usually implemented with a steering wheel, but can also be done with a single joystick. It works like a more advanced version of “Arcade” drive, where the steering wheel/x axis controls the turning radius (like a car), and the y axis controls the throttle/speed. This is a very important distinction, especially for high-speed drivetrains. It lets the driver control turn *radius *and speed, rather than turn *rate * and speed. At high speeds, a small change in turn rate results in a very fast change in robot heading, and with an Arcade setup, changing the throttle setting alone will change the turn rate. With “Cheesy Drive”, as long as the steering wheel position is held the same, the robot turn rate remains the same, regardless of the throttle setting. The steering wheel is not necessary, but it provides a familiar control input, since the radius/speed control is exactly what you get with a car.

A lot of top teams us some implementation of “Cheesy Drive”, including 254 (of course) and 971. I believe 111 and 973 both used it in 2011, meaning the entire winning alliance was using it in some form.

*Here at CD, “skid steer” usually refers to a drivetrain with non-steerable wheels that steers by giving a different speed command to each side (left/right) of the drivetrain.

Tank Drive, Arcade Drive, and “Cheesy Drive” all refer to the Operator Interface (OI).

Those IOs are usually used with a skid steer drivetrain, but if you wanted to, you could implement any of those OIs with a mecanum or omni drivetrain.

If you did that, however, the OI would not give the operator access to the full range of motions that a mec or omni is capable of executing.

We had a spam issue tonight, I think I caught most of them and edited them out if I didn’t PLEASE let me know.

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<SabreBytes772> 1st.
<wing1002> the golden noise
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<Guest 33> WOTs?
<Guest 20> that's hib-ner, btw - not hibe-ner 
<Guest 22> field geometry
<wing1002> Definitely the playing field
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<Guest 33> Reliability!
<AndrewLawrence> Game rules
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<SabreBytes772> sheetmetal vs Tubing vs extrusion
<Guest 33> What machines do you have? Is sponsoring out parts concidered ethical by you?
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<schreiaj> Sabre, whichever resource your team has the most experience with
<wing1002> sponsoring out parts is ethical
<wing1002> because
<wing1002> that's fabrication
<SabreBytes772> Kit bot on Steriods!
<wing1002> also
<wing1002> it doesn't matter in the end if the students get the engineering experience
<Guest 33> Yeah, wing, but it doesn't teach design...
<SabreBytes772> yea I know I'm just saying those could be what you use
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<wing1002> yea it does
<wing1002> in fact
<wing1002> you need to design in a much better way
<wing1002> if you want it to be cut in a waterjet or CNC.
<wing1002> also, this topic is some thing very heated
<schreiaj> and somewhat unrelated 
<Guest 33> Ok, sure, I'll leave it.
<wing1002> 
<SabreBytes772> and theres tons of mounting places
<wing1002> I went to an offseason. My old time decided to use a kitbot on steroids and build a balancing bot only
<wing1002> old team*
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<SabreBytes772> the AndyMark one is now Belts too
<wing1002> they were chosen on the finalist alliance, and part of the reason was the solidity of their kitbot on steroids drivetrain
<SabreBytes772> which I don't like 
<Bryan33> Andymark looks to have really outdone themselves this year with the Kitbot.
<wing1002> in fact, only 2415 had a better drivetrain
<Guest 33> Belts? I know, right!
<wing1002> 2009
<wing1002> 4 wheel
<SabreBytes772> 148 2008!
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<schreiaj> (I added 4 in after the fact)
<wing1002> ahh
<SabreBytes772> yea but they were swerve, aren't you asking who wasn't tank?
<alecmataloni111> and 09
<SabreBytes772> oh nvm :P
<Guest 33> All 6 wheel swerves make it to einstien!
<wing1002> oh man, the 07 finals
<SabreBytes772> on the field...
<Guest 33> How do you calculate acceleration?
<wing1002> first derivative of velocity
<AndrewLawrence> Velocity final - Velocity initial/delta t
<AndrewLawrence> I like equations. :P
<Guest 33> You mean, write a function for torque over time and use newton's second?
<SabreBytes772> 1114 doesn't shift either unless their battery is low.
<wing1002> I honestly think that the toughboxes are good enough
<wing1002> i mean, shifters are nice
<wing1002> but i've never had a reason to go to one
<SabreBytes772> we had shifter... but then fixed them to low gear...
<AndrewLawrence> I like CIMple Boxes. We've gotten great speeds from them, 1 stage, and nice weight.
<wing1002> CIMple boxes are nice
<wing1002> but i do prefer more torque
<Guest 33> Acceration?
<AndrewLawrence> Just gear for torque. Unless more stages = more torque. I don't know that
<Guest 22> more stages can = more torque, depends on the ratio of those stages
<Guest 33> Is weight the only reason to go custom?
<Bryan33> We pretty much only do shifters. However, I think we are one of very few teams that actually uses autonomous shifting.
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<mattc9> where do you get y'alls gears?
<schreiaj> 36, who are you?
<Bryan33> Makes it like driveing one speed.
<Bryan33> *driving
<wing1002> mattc9, what team are you from?
<mattc9> 2158
<mattc9> ausTIN CANs
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<mattc9> why?
<Guest 33> And center drop
<Bryan33> Tortional stiffness!!!
<wing1002> just wondering
<wing1002> the whole y'all thing. It's a southern thing
<Guest 22> 6 corners... hexagonal robot time!
<AndrewLawrence> Steel chassis = strongest chassis.
<wing1002> the rock
<mattc9> ohhh yeah
<Bryan33> False
<Guest 39> then what is/
<AndrewLawrence> Solid steel
<wing1002> I personally see 8 for more flat
<wing1002> and 6 for barriers
<Guest 22> why would one want to use 14 wheels?
<schreiaj> that's why I asked 
<wing1002> there was one robot with 12
<Guest 22> ah
<AndrewLawrence> In all seriousness, we used steel tubing this year (.75 diameter and 1/16 thick), and it was really strong and light.
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<schreiaj> 703 in 2007 had 14
<wing1002> i wonder why
<Guest 39> yeah, we used steel tubing. its great
<Guest 33> Hard to work with, imo
<Bryan33> What was your frame weight?
<Guest 39> that is true
<AndrewLawrence> Guest 39, what team are you from?
<wing1002> Colson ftw
<Guest 39> breakaway
<AndrewLawrence> Our superstructer was below 15 lbs.
<AndrewLawrence> *superstructure
<alecmataloni111> 25's giant skyway wheels
<Guest 33> Roughtop is awesome
<Bryan33> Meaning tower and everything?
<wing1002> Has there been any record of plactions breaking?
<AndrewLawrence> Yeah
<AndrewLawrence> Tower and everything
<alecmataloni111> Nick lawrence has
<Guest 33> Going over the bumo
<Guest 22> we did for our roller claw
<Bryan33> Thats pretty good. We were at 12ish.
<SuperNURDs3255> The tread on our plactions kept coming off 
<SabreBytes772> only on roller's have i seen them
<Guest 33> Bad rubber backing. Even for roller claws
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<wing1002> the performance wheels are expensive
<wing1002> compared to plactions
<Guest 33> But worth it
<AndrewLawrence> Colsons = the answer to all your problems?
<AndrewLawrence> yes
<wing1002> Colson?
<SabreBytes772> team 25.. and 469 has...
<wing1002> Blue Nitrile
<mattc9> Colson= $$$
<schreiaj> colsons are cheap
<schreiaj> $6 a wheel?
<wing1002> robotmarketplace.com
<schreiaj> Just gotta plug em
<AndrewLawrence> Use WCP hubs
<wing1002> I think he's referring to customizing the hubs
<Bryan33> The AM high grip wheels actually really impressed me. I would not be suprised if we used the 4in ones this year.
<wing1002> though WCP has dead axle hubs
<Guest 22> plug is what gets a lot of people i assume
<wing1002> what about Blue Nitrile?
<Guest 33> 4 in or smaller if you do custom
<mattc9> if you cant make you're own hubs it gets pricey, $6 a wheel but then plus $20 for a hub
<Bryan33> Smaller= equals better
<schreiaj> Haven't used it
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<Guest 33> smaller=smaller reduction
<wing1002> 4 for lots of torque i would say
<wing1002> 8 if you want speed
<wing1002> 8" *
<alecmataloni111> smaller frame profile
<Guest 46> 4 or 6
<alecmataloni111> possibly
<alecmataloni111> lower CoM
<Bryan33> 4in wheels also maximize your wheelbase.
<Guest 39> whats CoM?
<wing1002> center of mass
<alecmataloni111> center of mass
<Guest 22> center of mass
<wing1002> Toughboxes
<AndrewLawrence> I prefer to use 6" or smaller wheels, and then make my frame low to the ground.
<Guest 33> 4's easy with live axles
<wing1002> with breakaway i liked large wheels
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<SabreBytes772> i wonder if you can turn faster with smaller or larger wheels?
<wing1002> i'd say it would be on smaller wheels
<Guest 39> it wouldnt matter, its an angle
<wing1002> not realted to wheel size per say
<Bryan33> I shouldn't matter
<wing1002> but weight
<Guest 22> ooh segue fancy words
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<AndrewLawrence> Aaron, smaller as in thinner, or smaller in diameter?
<Guest 33> unobtanium
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<Guest 41> Im pretty new to this EWCPCast. definitely enjoying it! am i the only one who feels like they're giving a lot of pretty general vague answers?
<Guest 22> i think they modify the corner wheels so that they have less cof
<Guest 22> in one direction than the other
<SabreBytes772> Diameter
<schreiaj> We're trying to present concepts.
<MarkKramarczyk> ask for the specifics you want
<AndrewLawrence> Diameter wise, it shouldn't be too much of a difference. Thinner wheels turn easier
<Bryan33> They'll answer your question
<Bryan33> just ask
<Guest 41> Cool thanks
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<Guest 33> And it is awesomely helpful
<Guest 8> downloading is noisy
<Guest 41> what about chain, belts, or gear drives? how do you choose?
<Guest 33> Thats for later, I think
<schreiaj> 41, that's actually coming up shortly
<AndrewLawrence> Guest 41, those are all scheduled for later in the cast
<schreiaj> https://trello.com/c/ujj3AJlK < what we're talking to
<Guest 39> not chains, they are really annoying
<Guest 39> they pop and stretch a lot
<Guest 41> ^thanks guys!
<Guest 33> And cofx vs cofy
<Guest 39> gears is probably best but they weigh a lto
<Guest 39> *lot
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<wing1002> chains are fine
<wing1002> they are annoying
<wing1002> but if you tension properly
<wing1002> it's fine
<Guest 22> whyd it get quiet?
<Guest 39> we had to tension ours
<wing1002> i've had a robot been through 2 competitions without breaking chains
<Bryan33> All three can be used to great effect
<wing1002> because we tensioned it properly
<schreiaj> 22, you may need to refresh, talkshoe has some issues
<Guest 22> ok then
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<Bryan33> We never throw chains
<Guest 33> Us too
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<Guest 33> 3.16"
<Bryan33> Make it adjustable?
<Guest 33> *3/16"
<AndrewLawrence> 1/8
<SabreBytes772> how is drop related to frame?
<wing1002> the bending
<Bryan33> Tortional stiffness
<AndrewLawrence> Steel doesn't bend. 
<schreiaj> 2mm ~ .08 for those of us who use irrational measurement units
<Guest 33> Frame flex could make 6 wheels touch
<SabreBytes772> ohhh............
<Bryan33> If your frame is not stiff the corner wheels dig in when turning
<SabreBytes772> this makes a lot of sence....
<Guest 41> this makes sense. how do you measure "stiffness" of your frame?
<wing1002> 8020 has some good torsional stiffness if gussetted properly
<Bryan33> It makes your wheelbase artificially long
<SabreBytes772> ours wasn't ridged enough
<Guest 51> stiffness of frame is very subjective
<AndrewLawrence> Guest 41, basically through how well you design your frame and what material. Thin aluminum bends easily.
<Bryan33> A good way is the clamp it to a table hanging off and push on it
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<AndrewLawrence> ^
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<Guest 33> Do you actually do this in season?
<AndrewLawrence> yes
<AndrewLawrence> We don't since we use steel.
<Bryan33> We do it in the offseason
<Guest 33> What happens if it flexes too much?
<SabreBytes772> add braces
<Guest 41> ok thanks!
<Bryan33> Add more drop or make it stiffer
<schreiaj> Add an upper structure 
<SabreBytes772> it's harder to turn depending on your drop
<wing1002> since the distance between the wheels is more
<wing1002> it makes sense
<Guest 51> i believe 8wd should have more drop than 6wd
<Bryan33> 8wds also cut your turning scrub almost in half
<Bryan33> t can be the same
<Bryan33> *it
<SabreBytes772> should be around the same...
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<SabreBytes772> we did 1/8 and had to put duct tape on our outside wheels...
<Bryan33> If you drop the middle wheel an 1/8 inch then the outer wheel is 1/4 inch off the ground
<Bryan33> in a 6wd
<Guest 51> i though 8wd required more
<Bryan33> in an 8wd this is not the case
<Guest 33> Belts c-c?
<Guest 53> SPAM!
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<Bryan33> spam
<schreiaj> don't click on 53's link
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<Guest 39> dont be putting that stuff on here, keep it clean
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<Guest 54> SPAM!
<Guest 33> Hopefully the pullies in the kop are hex...
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<Meredith16> "bikini breasts" and "don't click" - wonder which of these things will be noticed most
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<Guest 51> im assuming guest 54s link is bad too
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<Guest 41> what about 25? aren't they known for gears-only drives?
<Guest 33> Wait! Center to center?
<schreiaj> what about center to center?
<SabreBytes772> we did direct drive... but i kinda want to do chain...
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<mattc9> chain tensioning tips?
<Guest 33> Does it work?
<Guest 56> SPAM
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<wing1002> Zipties during competition
<alecmataloni111> oh dear.
<wing1002> so the way i do chain
<Guest 39> acryllic is good for tensioning
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<wing1002> i wrap aroudn the sprocket til the links meet
<wing1002> then cut one extra off
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<wing1002> mcmaster also has some good self tensioners
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<wing1002> use that or idler sprockets
<wing1002> Zipties during competition
<Guest 33> Thanks!
<Guest 57> SPAM!
<Guest 15> Automotive timing chain tensioners!
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<Guest 23> We create acrylic tensioners that are adjustable and haven't had any issues.
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<wing1002> more spam
<mattc9> yeah im hoping to hear idler sprockets vs bearing block
<AndrewLawrence> This is amazing: http://www.use-enco.com/CGI/INSRIT?PMAKA=505-3405&CS_003=5341490&CS_010=505-3405
<SabreBytes772> we used to do a bolt with acrylic on it, that we lower into the chain
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<Meredith16> I actually hope none of my rookies are here for this chains and belts conversation and see these links. :P
<wing1002> I love that chain tensionrer
<wing1002> the one Andrew posted
<schreiaj> I'm sorry, there's not a whole lot I can do short of turning off chat 
<wing1002> that one is so wonderful to use
<SabreBytes772> our chain tensioners are on slided
<Bryan33>  schreiaj, can you do anything about these?
<schreiaj> When I post the cast on notes on CD I'm going to filter these out
<Meredith16> Sorry, John and I are giggling...
<AndrewLawrence> It works so well. Makes what used to be a 4 day job a 4 minute job
<wing1002> yea
<Guest 23> How do you stretch your chains?
<wing1002> use the tool andrew posted in his link
<alecmataloni111> We use these:http://www.team221.com/upload/sl_tension_close.JPG
<wing1002> http://www.use-enco.com/CGI/INSRIT?PMAKA=505-3405&CS_003=5341490&CS_010=505-3405
<wing1002> VICTORS
<alecmataloni111> http://www.team221.com/upload/sl_tension_close.JPG
<Guest 46> how does chain strech
<wing1002> VICTORS FOR DT
<thefro526> dead space all things! 
<SabreBytes772> VICTORS> Jaquars
<AndrewLawrence> Talon@
<Bryan33> victors!
<AndrewLawrence> !
<mattc9> what is dead spacing?
<Guest 59> SPAM!
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<alecmataloni111> -_-
<Guest 33> Linear drive output?
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<thefro526> Also, chain doesn't 'stretch' but it does wear over time and loosen up which makes it seem like it stretches
<Guest 46> thanks
<thefro526> Dead spacing is when you use an exact center to center spacing
<wing1002> Jags dont like metal
<wing1002> or high current
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<Guest 41> ^ nor do victors
<wing1002> victors handle both better from my experience
<wing1002> i've had jags die and victors NEVER die
<Guest 39> me too
<Guest 60> SPAM
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<Guest 46> victors fans dont break going over the bump in 2010
<schreiaj> Guys, again, I apologize for these spammers 
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<wing1002> you may want to put a password or something next time 
<AndrewLawrence> I've had victors die. Although it did have a bunch of metal shavings in it
<SabreBytes772> its okay we understand
<Guest 41> ive burned out many victors.
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<wing1002> has anyone stress tested the talons?
<wing1002> by getting an unknowing freshman to drill over it while running
<SabreBytes772> IFI has Jagaurs now... anything about that?
<thefro526> AM did some testing with the talon
<Guest 23> I have had five jags die in four years and 0 victors
<Guest 23> Footprint is smaller
<BREO> SPAM!
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<thefro526> NOT SPAM: http://www.youtube.com/watch?v=jniX4FrBiWY
<thefro526> talon testing
<SabreBytes772> 33 ran Talon's at IRI!
<mattc9> who is planning on running talons this year?
<wing1002> holu crap
<wing1002> that's a nice fvideo
<SabreBytes772> i want to but idk if team wants to
<SabreBytes772> yea they do put metal on it. but they say dont try it at home lol
<schreiaj> can I try it at my robot shop?
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<Guest 41> theyre tiny.
<SabreBytes772> you will probably do it without even knowing lol
<SuperNURDs3255> I'll test talons if someone is willing to fund them for my team. 
<AndrewLawrence> Anyone know if CTR has tried to get them FRC legal?
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<wing1002> Halo drive on xbhox 360
<Guest 41> and when you dump metal shavings on it, they come out easily.
<SabreBytes772> yea they're trying currently
<wing1002> with exponential outputs
<schreiaj> Guys, just a heads up, to contest some of this spam I'm gonna try muting people talking when they first join in for a minute. If they stick around I u
<AndrewLawrence> Guitar Hero Controller + Wiimote nunchuck
<wing1002> sounds like a plan
<wing1002> Andrew. Wut.
<AndrewLawrence> Look up Wildstang 2009
<alecmataloni111> the entire 2011 championship alliance used 254's drive code
<schreiaj> Obviously, if you have an account with a name that I recognize (i recognize most of the users in here) you're good.
<SabreBytes772> we used xbox using front back on one stick, left right on other at Tennessee, used Hoystick arcade on other regionals.
<Guest 33> I saw some team try to use it in 2010
<Guest 33> A guitarhero controler
<wing1002> There's this one joystick
<wing1002> that I love
<SabreBytes772> I prefer Tank, over arcade... but i dont drive wheels
<AndrewLawrence> Aaron, you must drive wheels.
<thefro526> < Can't drive Arcade to save his life...
<wing1002> teh Logitech extreme
<SuperNURDs3255> My team prefers tank.
<mattc9> 3 axis joystick 'nuff said
<SabreBytes772> yea i want to :P
<Guest 46> what does 16 use? cheesy?
<Bryan33> we use derivitive cheesy drive as well
<SabreBytes772> wait what did you do? is there someway we can see it???
<AndrewLawrence> We have a modified version of cheesy drive.
<Meredith16> 16 uses joystick for throttle and steering wheel
<wing1002> the Logitech Extreme is such a nice joystick. I like it better than the xbox 360 controller just because the joystick can twist.
<wing1002> i used that for driving
<wing1002> http://www.logitech.com/en-us/gaming/joysticks/extreme-3d-pro
<SabreBytes772> oh so you used a logitech, broke the stick off and used to turn?
<AndrewLawrence> We use Stang-Positioning-System for auton
<Bryan33> got to go. Nice talking to everyone!
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<AndrewLawrence> Bye Bryan!
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<BREO> SPAM!
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<Guest 33> Is the sps easy to get running?
<wing1002> clsed loops people
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<schreiaj> too slow 
<wing1002> use your closed loops
<wing1002> ;9
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<Meredith16> Well, it was a cheetah after all...
<SuperNURDs3255> I know this is kind of a dumb question, but what are the advantages of gyros? Disadvantages?
<wing1002> well
<wing1002> in what case do tyou want to use it>?
<wing1002> gyros are good for rotational feedback
<Guest 33> Weight
<wing1002> i.e. precise angles for autonomous
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<AndrewLawrence> Guest 33, we use steel tubing instead of aluminum. Because it's so much stronger, we run 1/16" thickness and 3/4" diameter and it's super light and su
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<wing1002> it's better than solving a 2nd order Differential Equation constantly from an accelerometer to determine your angle
<SuperNURDs3255> Better than using encoders for angles?
<Guest 33> Thanks andrew
<wing1002> and encoders aren't immune to robot wheels sliping
<Guest 18> we had problems with gyro drifting in angle measurement
<Guest 51> 2 stick tank
<Guest 33> How feasible is center to center belts for a team with a cnc?
<schreiaj> what about it?
<schreiaj> can it hold tolerances?
<Guest 51> its very nice to use
<wing1002> I personally can't use tank effectively
<Guest 33> Does it confer enough advanteges to attempt?
<wing1002> how do peopel find it effective?
<mattc9> didn't 33 do something like that?
<schreiaj> I always run tensioners and chain. Simper
<schreiaj> And yes matt, 33 used an asymetric design in 08
<Guest 33> But what about efficiency?
<Guest 33> Or parts count?
<AndrewLawrence> Can we touch on efficiency?
<schreiaj> IKE has some great posts about rigidity, CoG, and asymetric wheel placement
<schreiaj> Sure Andrew
<Guest 33> Yay!
<SabreBytes772> how do you get more efficent?
<AndrewLawrence> Thanks
<AndrewLawrence> Aaron, from what I know, less stages = more efficient
<AndrewLawrence> But that's all I know
<SabreBytes772> yea
<AndrewLawrence> 973 2009 = favorite non equally-spaced robot of all time
<SabreBytes772> 33 had a weird drive this year with 3 different wheels i think
<schreiaj> yes, but they were symetric
<SabreBytes772> mhmm
<mattc9> what about this year?
<SabreBytes772> and how did they do?
<mattc9> for 33
<wing1002> so
<Guest 18> http://www.frc-designs.com/btd.html
<SabreBytes772> http://www.frc-designs.com/images/btd/2012_33(3).jpg
<SabreBytes772> theres the pic i was talking about with 33
<wing1002> how long should it take for an ideal team to build a drivetrain in the season
<schreiaj> How long does it take to put together the kitbot?
<AndrewLawrence> We're planning on doing it in a few days
<SabreBytes772> http://www.youtube.com/watch?v=YGTwp3hjVI8
<SabreBytes772> 1918 2010
<wing1002> like 1 hour for our team
<schreiaj> then there you go
<wing1002> well, a custom built
<AndrewLawrence> Then you have pre-cut parts. Even faster
<wing1002> hmm
<SabreBytes772> 3 days
<wing1002> i want to say one week
<SabreBytes772> oh at 3 weeks done
<Guest 51> have we talked about why someone would want to use a 14 wheel dirve?
<schreiaj> I'll bring it back up
<SabreBytes772> 3 days to build drive train. by the end of week 3 you should have the drive built
<SabreBytes772> 40 lbs max
<AndrewLawrence> I'd prefer done by week 1, moving by mid week 2
<SabreBytes772> I'm not even done the design by the end of week 2....
<SabreBytes772> its pretty much done... but still
<AndrewLawrence> That's why we design ahead.
<wing1002> yea
<SabreBytes772> how do you design ahead?
<AndrewLawrence> Come on Aaron, you gotta get in the game
<wing1002> 1648 is using the next 6 weeks to finish our drivetrain concept
<Guest 41> it depends on what you include in the drive base.
<wing1002> basically
<AndrewLawrence> It's like 254 - they have a drivetrain down to a science. Look at a game, and know any small changes they'll do to it by a few hours after kickoff.
<schreiaj> The trick is that 99% of teams are NOT 254
<SabreBytes772> is it just canadians that call is C.I.M. or what?
<wing1002> I know 2415 has used the same drivetrain with different wheels for the past 4 years
<AndrewLawrence> Very true Andrew
<schreiaj> copying them is not a great idea for the rest of us
<AndrewLawrence> No, but it's fun to do
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<AndrewLawrence> Excellence is contagious, after all.
<wing1002> what 1002 used to do is that we had one drivetrain design
<wing1002> and modified it to the game
<AndrewLawrence> ^That's the plan
<wing1002> from 2006-2008 we used the same custom drivetrain
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<SabreBytes772> my chassis was done design by start of week two and sent out to get machined by mid week 2
<wing1002> in 06 we used performance, and in 07 and 08 we used colson
<wing1002> that's all that changed
<AndrewLawrence> We machine everything in house, so we can get it made and start construction as soon as it's done
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<alecmataloni111> 1538
<SabreBytes772> ours in water-jetted, and bent
<wing1002> put it up in chat
<SabreBytes772> in a sponsors place
<AndrewLawrence> Ours is steel, and cut
<wing1002> 1648 uses 8020
<schreiaj> 703 in 07 http://www.chiefdelphi.com/media/photos/26312
<wing1002> the frame literally goes up in 30 minutes
<SabreBytes772> what the heck!?!?!
<Guest 51> thats a lot of wheels o.o
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<AndrewLawrence> 852 has them
<SabreBytes772> no body does treads its just a bad idea...
<AndrewLawrence> for 2012
<Guest 41> i think what he's saying is its a study of tribology. the large shapes of the surface roughness on roughtop and carpet make it so you cant use
<Guest 41> basic friction rules
<SabreBytes772> 2010 was logical... kinda...
<Guest 41> what about 195
<Guest 23> Scrub is rough on tread
<AndrewLawrence> 195 in what year?
<Guest 23> They like to come off
<Guest 41> theyve had ssome fast dread designs if i remember right
<AndrewLawrence> Efficiency?
<Guest 41> maybe 05-06??
<wing1002> ooh
<wing1002> blue nitrile
<SabreBytes772> battery boxes?
<Guest 41> yes battery boxes!
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<AndrewLawrence> We had an illegal motor at Central Valley, and Andrew didn't catch it while inspecting our bot.
<schreiaj> specific questions about them?
<AndrewLawrence> Although we didn't know it was illegal
<SabreBytes772> what if they dont ruin carpet or break any rules?
<schreiaj> You'd have to prove they dont
<schreiaj> And Andrew, what motor did I miss? If I recall I only checked part of your robot
<SabreBytes772> you dont have any proof they do.
<wing1002> bring a sample of carpet
<AndrewLawrence> It was on the shooter
<wing1002> ruin the robot on it
<wing1002> and pass inspection
<AndrewLawrence> We didn't know until later (I didn't attach it)
<schreiaj> Yeah, all I checked was your bumper perimiter if I recall. The rest had been signed off
<SabreBytes772> Gates sponsors us :P so we use that
<AndrewLawrence> Really? My memory must be bad
<SabreBytes772> like our team not just FIRST
<SabreBytes772> GROUND CREARANCE?!
<schreiaj> Recall, SPECIFIC questions... kthx. just concepts are pretty general, what do you want to know about them?
<SabreBytes772> 0.003
<Guest 39> do you think you could talk about using a harmonic gear system for gear ratios?
<wing1002> ooh
<wing1002> i have a good one
<wing1002> frame materials
<wing1002> sheet vs bar of any type
<schreiaj> harmonic gear systems? I'm a programmer... assume I'm not smart
<Guest 39> its pretty cool, i found it on youtube one day
<Guest 41> battery box. materials? whats a good weight? securing?
<schreiaj> wing, the general rule is use what you have experience with and resources with
<wing1002> right
<schreiaj> obviously if you have no sheet capability don't do it
<wing1002> but if you want to make the transition
<SabreBytes772> yea but is sheet stronger than bar?
<wing1002> are there any advantages?
<schreiaj> dependent on shape
<SabreBytes772> yes thank you...
<Guest 23> Also dependent on your machining resources. Breaker and such.
<Meredith16> and we got killed by the plates in 2008!
<alecmataloni111> Did you guys do Cantilevering vs Not cantilevering?
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<schreiaj> No we didn't excellent
<wing1002> oh yeah west coast vs standard
<SabreBytes772> was more or less better for 2012?
<SabreBytes772> for ground clearance i mean
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<SabreBytes772> whats cantilevered?
<AndrewLawrence> Cantilevered is no outer support for the wheels
<AndrewLawrence> Like West Coast Drive
<Guest 23> West Coast vs. East Coast
<SabreBytes772> oh got it.
<SabreBytes772> I like Non-Cantalilevered
<AndrewLawrence> We prefer not to cantilever wheels, since the weight loss isn't too great for us with the steel, and the outer support is really great.
<Guest 51> is the only reason to use cantileverd weight?
<alecmataloni111> No.
<AndrewLawrence> Plus Colsons, so no need to change wheels
<Guest 51> what other reasons?
<alecmataloni111> Cantilevering helps maintenance
<AndrewLawrence> If you're like 254, and exchange your wheels for brand new ones every match, it's helpful
<Guest 23> Easier to get to chains in some cases
<schreiaj> Andrew, I didnt know they did that. I know 118 was switching all the time though
<Guest 51> oh ok
<AndrewLawrence> Yeah, 254 switches every match. It was pretty cool to watch the pit crew at CalGames do it.
<AndrewLawrence> They let us play with their used wheels. They're so cool.
<avanboekel> every match is a bit much
<AndrewLawrence> They can do it
<AndrewLawrence> Probably not EVERY SINGLE match, maybe every other.
<Guest 23> Amen
<SabreBytes772> I like this chassis
https://www.facebook.com/photo.php?fbid=10150594575556124&set=a.403091396123.209982.653091123&type=3&theater
<SabreBytes772> tell me if you can see it
<schreiaj> yes we can
<SabreBytes772> 6 wheel / Macanum lol
<AndrewLawrence> I tell people: All in all, unless you can prove your custom chassis is sufficiently better than the kit chassis, then you should build Kbot on Steroid
<SabreBytes772> TANK FTW!!!!
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<Guest 23> Octa wheel setup with a direct drive center? Interesting
<SabreBytes772> WAIT!
<SabreBytes772> 8 wheel, transmission in center or off center
<AndrewLawrence> STOP
<AndrewLawrence> Hammer Time
<Guest 23> Thanks for your time!
<Guest 18> When will the new white paper come out?
<SabreBytes772> lol sorry had to ask
<SabreBytes772> I'll send examples
<SabreBytes772> https://www.facebook.com/photo.php?fbid=10151009577441124&set=a.403091396123.209982.653091123&type=3&theater
<SabreBytes772> https://www.facebook.com/photo.php?fbid=10151079736456124&set=a.403091396123.209982.653091123&type=3&theater
<SabreBytes772> this or this
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<Guest 20> guest18: good question - still up in the air
<Guest 58> when will the recording be available for download?
<Guest 23> Depends on how you want to ride
<schreiaj> 58, the best way to snag it as fast as possible is subscribe in itunes
<SabreBytes772> k so for 8 would you prefer having COG in middle or off center
<Guest 51> i like the second one
<schreiaj> https://itunes.apple.com/us/podcast/ewcpcast/id477122221?mt=2
<Guest 51> because if you lose a chain off the gearbox
<SabreBytes772> i was told off center but idk...
<Guest 51> you only lose 2 wheels
<schreiaj> even though it appears to be being weird
<Guest 51> imean thats my opinion
<Guest 23> It is a wholisitc question. You could possibly use the gearbox or transmission as usable weight to balance or sway.

Thanks to everyone for a great podcast! I would have liked to hear a bit more talk about exact center to center belted drivetrains (which teams could benefit from them), but that’s what the discussion on CD is for.

I agree, I’d like to have had more discussion, unfortunately our guests weren’t terribly familiar, I’ll see if I can get one of the guys who has done a system like that before to chime in here if you have specific questions.

I heard it was a pretty good cast, looking forward to the recording.

  • Sunny G.

Well, today’s your lucky day then? http://recordings.talkshoe.com/TC-98466/TS-681568.mp3

And, as always, it is available (along with all our casts) in iTunes. https://itunes.apple.com/us/podcast/ewcpcast/id477122221?mt=2

Very sorry I missed this talk. A couple of add-ins:

In the discussion of torsional stiffness with the “noodle vs. stiff”, a noodle frame is generally harder to turn. While less maneuverable, it can hold position better. This is generally true though of the more vs. less traction. I would more often than not prefer a stiffer frame, but the holding position is one area where a less stiff frame can be better.

With regards to “the Bizarre collection of wheels”:wink: . In 2008, we went with the asymmetric set up because it was a turn left game. We tried a lot of different combinations that year. In rcing terms, some were too loose, and most were too tight. Too loose was difficult to drive in the straight lines on the back side once you had acquired a piece. Too tight refers to being too slow when turning. In a turn on skid steer trying to turn a radius, the inside wheels tend to scrub more than the outside wheels. With most of the CG over the middle wheels, we had those two as high traction. We had Omnis on the inside outer wheels to reduce the latteral scrub friction. We had KOP wheels on the outside outer wheels too keep it from being too loose. Eventually we went Omnis on both fronts as the drivers skill increased during the season, and he could handle a “looser” set-up. This is often true in racing as well.
In hindsight there were plenty of robots with stiffer frames and possibly better controls that did not have to go to the extreme we did of alternate wheels. We were still utilizing skid steer controls in 2008, and a steering based control scheme would have likely worked better.

I will do a seperate post on 8wds.