[FTC]: Can I add non-slip material to 4" Tetrix Wheels?

[F Elliott]

Rookie Coach alert!

We had our robot on a ramp for the first time tonight and the traction of our rear-wheel gear drive 4" Tetrix wheels is not what we are wanting. We wanted to use 4" Hi-Grip AndyMark wheels but we ran into difficulties mounting them in a satisfactory way so we went to the Tetrix wheels. Now we are having to rethink.

Reading various forums, it sounds like teams attach (glue?) strips of non-skid to their wheels. I know sheet materials are legal (and several non-skid sheet materials have been posed and approved in the rules forum) and glue/adhesives are legal... but how does increasing the diameter of the 4" wheel come into play and aren't we modifying a standard part by doing something like this?

I'm posting here before I ask in the rules forum because: (a) I'm a total FTC novice and I'm not even sure I'm asking the questions correctly, and (b) I get great answers fast here on Chief Delphi! :)

THANKS!

[Al Skierkiewicz]

R5
o. Wheels of any type up to 4” diameter. Wheels that have exposed features likely to cause damage to field and/or game elements are not allowed.

Emphasis mine. My opinion, in addition, is the non-slip makes the wheel larger than 4".

[maths222]

As long as you add the padding and did not purchase it pre-attached, it should be OK (we do something similar with special Lego tires on the 4 inch wheels). For an official answer post on the official FTC forums.

[Al Skierkiewicz]

Jacob, I believe your team was asked to return the wheels to stock for this very reason, they were too big.

[maths222]

I had my coach post on the official forums for a ruling.

[aklego]

The 4" limit only applies to purchased non-Tetrix/Matrix/Lego wheels. Teams can modify or build wheels to be > 4" as desired, subject to the allowed materials, field damage, and 18" size constraints. There are several official forum post dealing with this issue and it might be a good idea to have printouts handy as the above posts make it sound like some teams have been wrongly failed at their tech inspection.

All that said, if you have a quick way to make your robot 4 wheel drive (chains or gears?) you will likely get HUGE improvements in traction and drivability.

[maths222]

And an official answer...
http://ftcforum.usfirst.org/showthread.php?1923-Robot-Parts-and-Materials-Answer-Thread&p=9028&viewfull=1#post9028

[maths222]

Jacob, I believe your team was asked to return the wheels to stock for this very reason, they were too big.

I think another team from our school had this happen. For whatever reason, we were not called on it.

[Al Skierkiewicz]

I have asked for a better explanation. The revised rules and the inspection checklist still imply 4" as a maximum. So there is at this point some confusion.

[CougarRobot]

Al,
We asked about this in post #71 on the official forum.

http://ftcforum.usfirst.org/showthread.php?1923-Robot-Parts-and-Materials-Answer-Thread&p=7778&viewfull=1#post7778

The answer was "A: Yes, you may modify a legal COTS wheel with a custom tread and make it larger than 4" diameter."

[F Elliott]

... All that said, if you have a quick way to make your robot 4 wheel drive (chains or gears?) you will likely get HUGE improvements in traction and drivability.

We qualified for our regionals! We are in shock.

We definitely need to improve our drive system. We are too slow and we have unpredictable traction around and on the Ramp. Should we go for driving all four wheels? Do we need to go for four motors or is two motors on a chain/gear drive enough?

How do you analyze this sort of question?

[cadandcookies]

We qualified for our regionals! We are in shock.

We definitely need to improve our drive system. We are too slow and we have unpredictable traction around and on the Ramp. Should we go for driving all four wheels? Do we need to go for four motors or is two motors on a chain/gear drive enough?

How do you analyze this sort of question?

In my experience working with the ten Eagan Robotics FTC teams this year, either of the setups you mentioned would be just fine, especially considering your main problem is "unpredictable traction"-- the main solution for which is making sure your wheels have the same or similar traction and are getting the same or similar power from your motors.

If I were you, I would ask the question of which fits into your existing robot with the least amount of work.

That being said, under nearly any normal circumstances, a 4-motor drive will beat out a 2-motor drive in terms of pushing power. If your only goal is behaving predictably around the ramp and you have a better use for two DC motors, by all means a 2-motor chain drive should behave just fine.

Unfortunately I'm not at our workspace right now, but I'd be happy to get you pictures of our various drive setups if you'd like.

On another note, good job qualifying for (I presume) your super-regional tournament, and good luck when you get there!

EDIT: You can also check out some of the pictures in the FTC link in my signature for photos, but most of them don't focus on the drive trains.

[aklego]

We qualified for our regionals! We are in shock.

We definitely need to improve our drive system. We are too slow and we have unpredictable traction around and on the Ramp. Should we go for driving all four wheels? Do we need to go for four motors or is two motors on a chain/gear drive enough?

How do you analyze this sort of question?

Congratulations!

Without knowing all the details of your robot, I think the best advice I can give is to experiment and find what works. We had a very successful 2 motor, 6 wheel drive bot two years ago. It was slow but our design was such that we didn't need much speed. That said, if we hadn't spent our allotment of motors elsewhere, we definitely would have added them to the drive train.

Again, congratulations on your advancement!

[MattRain]

We qualified for our regionals! We are in shock.

We definitely need to improve our drive system. We are too slow and we have unpredictable traction around and on the Ramp. Should we go for driving all four wheels? Do we need to go for four motors or is two motors on a chain/gear drive enough?

How do you analyze this sort of question?

Having a good drive base is really where every robot needs to start. TOO many times does our team see rookies with only two wheels motorized, usually direct driving them. Direct driving the wheels is really bad on the motors. Ypu really need to either gear or chain drive every wheel you have.

To give you an idea on a good drivebase, we use 6 wheels, all geared together, using the medium 80tooth gears on the motors, and the 120 tooth gears on the tires. Reason being for 6 wheels, one falls off, you can STILL drive. Not stuck. Along with all the wheels being geared, we run to motors per side of the robot, wired into the same motor port. 2 Motors left, 2 motors right. Alot of pushing power as well! Any robot that tries to play defence against us, just gets pushed out of the way. If you want to see our bot in action, look on youtube, Valley X Robotics, or here, www.valleyx2844.com <--- pictures of it on the website.

[F Elliott]

We currently have two 40:80 gear driven 4" AM Hi-Grip wheels with two dual omni wheels on the other end. It works but...

Thinking through Saturdays events, it became obvious a lot of our weaknesses are traceable to inadequate traction, being too slow, and not being able to smoothly and reliably transition over the ramp edges.

I think having four driven wheels would be a big step to better.

We only own one motor controller so that is what we started with. Later I was able to borrow a motor controller for our lift motor and flag motor. For regionals I think I can borrow another motor controller.

We are definitely going to undertake a major whale dive into drive systems during the off season.

[MattRain]

Our team personally stays away from the tetrix Omni-wheels. They just dont do well on the wood. As you said as well, they have a hard time with even getting ONTO the wood. Yes they are easier to turn with, but you loose certain things.

Diving into different drive bases is a good idea. Try to get ahold of another DC Motor Box. It will help you later on as your team grows.

[F Elliott]

The team spent some time tonight discussing the drive question. It's been very interesting as a teacher listening to and letting these debates play out. Someday I'm going to record a few and let our administrators here them --- these are engaged passionate students!

I think the choice is between two mortors driving four wheels via a gear train or four motors, one on each wheel. The debate was intense. I vetoed chain drives, mechanum, and tank treads since we have none of the parts and no experience with them.

During the discussion the areas we were lacking information and experience were the following:

1. Four wheels driven independently by four motors... This would be the simplest mechanically and lowest cost approach since would just replicate the two drive wheels we have. We were not sure how you synchronize the two wheels on each side if each wheel is driven by its own motor. In the software? Would this mean we would need a total of four motor encoders as well? And PID control? If so we only have one encoder and we were never able to get PID to work with our two current motors.

2. Two wheels on each side driven via a gear train by one motor on each side. Minimal SW impact but this means lots more gears and axles. Will there be enough power now with one motor powering two wheels and all the gears if we gear 1:1? Seems unlikely. Robot weighs 20 lb

3. If we tried to drive a geared side with two motors wouldn't they fight each other if they weren't somehow synched using encoders and PID?

I can we us doing all kinds of cool experiments in the off season!

[TRWSHSHLX]

To synchronize the motors on one side, you can electrically wire both motors into the same motor port.

Four wheel independent driven is fine but I personally had great experiences with all wheel drives (all wheels geared together). You are correct in there will be difference in motor performance but as long as you send the same power signal to both motors on the same side; the effect is insignificant compared to most of the other issues.

Chains on the drivetrain are acceptable as long as it's tensioned correctly and robust enough for shock loads. However it is less robust and requires a bit more maintenance than gears.

As for a 2 motor all wheel drive; it's totally doable however if you have the extra motors, put them on. Back four to five years ago when only 4 motors were allowed total, a robot from my region had an AWD and advanced very far in elimination at the world championship with a 2 motor AWD.

Record all the discussions in the engineering journal! In the real world, it's a critical and essential part of the industry.

Good luck!

[F Elliott]

Thanks Henry! I had forgotten that we could wire two motors to the same controller port. We have the motors and mounts. Lets see if I get it...

Two mirrored assemblies: Left Side Drive & Right Side Drive
Parts list for ONE Assembly:
2 wheels with bearings and axles
2 DC motors and mounts
1/2 Motor Controller
1 Encoder
2 Wheel Gears, one per wheel with axle and hub
2 Motor Gears, one per motor with motor hub
TBD Gears as needed to connect the gears attached to the 2 motors and 2 wheels into one meshed drive train

Wire both the motors onto the SAME Motor Controller Port.
Final gear ratio is determined by wheel gear/motor gear.
Size of intermediate gears does not matter.
Make note that each intermediate gear reverses the direction.

QUESTIONS/ASSUMPTIONS
1.Can we run all four motors off one motor controller, ganging them up two motors per port? We can borrow another motor controller. CAREFUL of the wiring!

2. Is it better to mount the motors closer to the ends near the wheels or put them in the center near each other and drive gears out to the wheels?

3. I'm assuming the fewer intermediate gears the better?

Now I see how you could have the six wheel configurations with the two motor per side. Raise the ends an 1/8, which helps transition the edge... makes much more sense now!

This would be a LOT more fun if we didn't have deadlines LOL

[TRWSHSHLX]

1. You can run all four motors off one motor controller. My team did it every year we were in competition and worked great. However make sure you get the polarity correct depending on how your gearing is setup.

2. Doesn't matter. Preferably minimal transition gears to reduce slop but the slop is very little to minimal. Think of motor placement more in terms of how you want the weight distributed around the robot.

3. Yes - to reduce slop between all the wheels and to save money. However again in the grand scheme of things, it doesn't matter much if at all.

[Al Skierkiewicz]

F,
I recommend that teams do not mount the wheels directly on the motor output shaft. The bearings are not meant for that and the friction increase with robot weight. It is suggested that wheel shafts be mounted using the bearings that are part of the kits. this reduces friction, gives more predictable and repeatable performance and lowers battery draw.

[MattRain]

F,
I recommend that teams do not mount the wheels directly on the motor output shaft. The bearings are not meant for that and the friction increase with robot weight. It is suggested that wheel shafts be mounted using the bearings that are part of the kits. this reduces friction, gives more predictable and repeatable performance and lowers battery draw.

I second this. Putting the wheel directly on the motor shaft is not good for the motor at all. Most of the time that I have seen them mounted straight to the motor shaft, the gear box shatters inside, making the motor useless.

If you would like, I can upload some pictures of some of the 4 motor drive bases that we have had in the past with our team.

[F Elliott]

I think we have a prototype for one side of our new drive system.

The washers under the motor mounts will be replaced with 3/16"x1/2" spacers, the shoulder bolts will get shortened 3/4" (eliminating the Al spacers currently outside the wheel), and the lengths of the bolts securing the motor mounts to the channel will get sized properly. We'll reinforce the channel near the wheel mount area.

We put press-in bearings in the hubs of the AM Hi-Grips, which ride on the shoulder bolts. Its very smooth. Overall, everything spins pretty well.

These two motors will get connected to one channel of the motor controller and we'll duplicate everything to the other side onto the other channel.

Are we headed in the right direction?

Thanks!

http://friedbits.com/downloads/DriveTrain-20140117-1.JPG

http://friedbits.com/downloads/DriveTrain-20140117-2.JPG

http://friedbits.com/downloads/DriveTrain-20140117-3.JPG

http://friedbits.com/downloads/DriveTrain 20140117-4.JPG

http://friedbits.com/downloads/DriveTrain-20140117-5.JPG

[cadandcookies]

Are we headed in the right direction?


Definitely looks like it to me!

If you can figure out a gear or spacing to replace those three middle gears with a single gear, that would probably be more efficient.

You guys are definitely headed down the right track!

[TRWSHSHLX]

Looks very good! A few notes to think about:

1. Fine tune the spacing between the two wheels to find a good balance between stability (from a longer wheel base) and turning ability (from a shorter wheel base)

2. It's been a while since I've played with TETRIX gears but I'm fairly certain you don't need all four screws to mount the gears to the shaft collars. Two will probably suffice but four doesn't hurt

3. Find a spacing such that there's the least number of axles as possible (for simplicity and maintenance sake)

Keep up the good work!

[F Elliott]

I was able to borrow some 80T gears yesterday!

1. Replaced the 3 40T center gears and their axles with one 80T. This also allowed us to eliminate the spacers under the motor mounts and gave us some adjustment range between the two motor gears and the driven gears. This drive train runs smoother and feels "right".

2. Wheel base increased from our original 10" to 11.25". We tried eliminating the remaining two small gears (the next increment smaller) but couldn't get the gears to mesh correctly. I'm okay with the increase.

3. I think the larger gears might run a little truer when all four bolts are used on their hubs. I don't think it matters with the 40T gear.


http://friedbits.com/downloads/DriveTrain-20141118-1.jpg


http://friedbits.com/downloads/DriveTrain-20141118-2.jpg


http://friedbits.com/downloads/DriveTrain-20141118-3.jpg


http://friedbits.com/downloads/DriveTrain-20141118-4.jpg


http://friedbits.com/downloads/DriveTrain-20141118-5.jpg

[Al Skierkiewicz]

F,
Over the years, one of the things I have often seen on FTC and FLL robots is the wrong spacing on gears. Often they are spread too far apart which allows them to skip but at other times I have seen them jammed together which causes high frictional loss and heavy battery loading. If it looks better and sounds better, I think you have a better design. I am a firm proponent for "the robot is talking to you" philosophy. If it is making funny noises, it is telling you something is wrong.

[F Elliott]

Last night we got the new drive and the modifications finished. Straight line tests were awesome. We were so psyched! He can even pop a (albeit small) wheelie!

But then...

We started testing tank drive pivot in-place... OH NO! He now has so much torque and traction with his four motors and four AndyMark HiGrip wheels he tears up the mat! Yikes!

1. To those of you driving all four wheels, what wheels are you using? We could replace the HiGrips with four 4" Tetrix regular wheels. That might work or it might tear up the mat as well.

2. We could use two HiGrips on the back and two Dual Omnis on the front. That is the same wheel set we had initially but we were not driving the Omnis. Would that work?

THANKS!

[maths222]

Either should work ... unless your robot is really heavy. Then I would suggest option number 2 (or a 6wd with a dropped/larger center wheel.)

[F Elliott]

Robot weighs 10 kg.

[maths222]

If you have the tetrix wheels, try them and see how turning is. If it is slow or makes the battery get really low, switch to omnis.

[Al Skierkiewicz]

Robot weighs 10 kg.
Really 10 kg? Wow! We need some pics please.

[F Elliott]

The robot as shown in these photos is 9.5kg. The bottom section is 5.8kg and the top section is 3.7 kg. Missing is the little bucket scoop on the front and the flag mechanism interior to the top portion facing the rear of the robot. They don't weigh much. The yellow cord is normally attached and wrapped around the lift axle you see in the center of the top section.

http://www.friedbits.com/downloads/Robot-20140130-5.jpg

http://www.friedbits.com/downloads/Robot-20140130-6.jpg

http://www.friedbits.com/downloads/Robot-20140130-3.jpg

[F Elliott]

http://www.friedbits.com/downloads/Robot-20140130-7.jpg

http://www.friedbits.com/downloads/Robot-20140130-8.jpg

http://www.friedbits.com/downloads/Robot-20140130-9.jpg

http://www.friedbits.com/downloads/Robot-20140130-4.jpg

[Al Skierkiewicz]

F,
You didn't say you were a Ham. Nice option using the Rig Runner. I have been trying to get West Mountain involved in First for many years. I recommend the CBAIV to teams all the time.

[ash5919]

this is all neat :)

anyways are we allowed to use Tetrix motors? :confused:

[MattRain]

anyways are we allowed to use Tetrix motors?

Um, its the only "motor" we can use in FTC.

[F Elliott]

F,
You didn't say you were a Ham. Nice option using the Rig Runner. I have been trying to get West Mountain involved in First for many years. I recommend the CBAIV to teams all the time.

Not a HAM... I actually got onto Anderson Powerpoles from this website! Then I saw the RIGrunners and got a ruling to use them. The fused distribution panel has saved our bacon three times now. We do so something stupid, a fuse blows, we figure out what we did, we replace the fuse, and all is good. I think a lot of teams burn stuff up because they're not fuse protected.

[WIREDFTC]

Our team uses a 6-wheel drive system, using 4 TETRIX V2 motors, 2 on each side, and each side connected to one motor port on the controllers. We have 120 tooth gears on the motors, and 80 tooth gears on each wheel, which drives rather quick. (You can kind of see it in the picture) We had to put steel weights in the bottom of our robot to counteract all the torque, making it weigh 38 pounds. It's no fun to carry it to the competition field. https://s3.amazonaws.com/ksr/assets/001/560/804/dbc88e06fc51c52fd77c6acf07890bed_large.JPG?1390610 304

[WIREDFTC]

Not a HAM... I actually got onto Anderson Powerpoles from this website! Then I saw the RIGrunners and got a ruling to use them. The fused distribution panel has saved our bacon three times now. We do so something stupid, a fuse blows, we figure out what we did, we replace the fuse, and all is good. I think a lot of teams burn stuff up because they're not fuse protected.

When our team gets the funds, I am MAKING us switch to a RIGrunner and PowerPoles if we make it to the Super Regional, because it will help with many electrical problems, but I have a question for you. What rating fuses did you use for the motor controllers? I know it's 20A for the DC in, and all the fuses on the bot have to be <= 20A but I couldn't find ratings for the motor controllers and such. (Also I LOVE the sub-assembly held to the robot with the quick-release pins!)

[Al Skierkiewicz]

Wired,
This device will help identify problems that are causing shorts on the robot but it is a rather expensive alternative. The motors are drawing a few amps a piece. So a 5-10 amp fuse for each controller is likely what you need. PTC claims each controller can effectively feed 4 motors, two for each output. Inefficient mechanical designs would push that limit in my opinion.
One of the issues with many teams is the way they distribute power on the FTC robot. When daisy chaining power from one controller to the next, any problems with wiring will affect everything down stream from the problem. My suggestion is to individually feed each controller using something like the Rigrunner or other power distribution block. Another area I see in inspections is teams 'tinning' the wire before insertion into the screw terminals on the motor controllers. This is the wrong way to terminate these wires. Screw terminals of this type require un-tinned wire so that the wire will actually conform to the terminal as the screw is tightened. This gives the maximum current transfer and minimum series resistance to the connection. While the FTC rules do allow smaller gauge wire, I recommend at least #18 and #16 preferred for all wiring carrying power to controllers. This gives you predictable performance from your motors, less chance of brownout faults and minimum issues with the controllers.

[F Elliott]

When our team gets the funds, I am MAKING us switch to a RIGrunner and PowerPoles if we make it to the Super Regional, because it will help with many electrical problems, but I have a question for you. What rating fuses did you use for the motor controllers? I know it's 20A for the DC in, and all the fuses on the bot have to be <= 20A but I couldn't find ratings for the motor controllers and such. (Also I LOVE the sub-assembly held to the robot with the quick-release pins!)

We went with 20A for the Main, 10A for the motor controllers, 5A for the servo controllers, and 3A for the Samantha. We've blown three fuses. One time we had something get caught in our gears and that blew the motor controller fuse, one time we got the Samantha power plugged into the wrong place (don't ask) and that fuse saved our Samantha module, and another time we blew a main fuse when a student cut the power wire from the battery while the battery was still connected.

The Quick Release Pins are one of our favorite features. We can break the robot completely apart in under 30 seconds with no tools. In addition to the four pins, there are two Anderson power connections and two NXT control connections. The base is fully functional as a driveable chassis when separated.

[WIREDFTC]

Wired,
When daisy chaining power from one controller to the next, any problems with wiring will affect everything down stream from the problem. My suggestion is to individually feed each controller using something like the Rigrunner or other power distribution block.

That is EXACTLY why I want to do it as soon as possible. It would isolate electrical problems, make wiring easier and prettier, and make our connections rock solid. Thanks!


We went with 20A for the Main, 10A for the motor controllers, 5A for the servo controllers, and 3A for the Samantha. We've blown three fuses. One time we had something get caught in our gears and that blew the motor controller fuse, one time we got the Samantha power plugged into the wrong place (don't ask) and that fuse saved our Samantha module, and another time we blew a main fuse when a student cut the power wire from the battery while the battery was still connected.

The Quick Release Pins are one of our favorite features. We can break the robot completely apart in under 30 seconds with no tools. In addition to the four pins, there are two Anderson power connections and two NXT control connections. The base is fully functional as a driveable chassis when separated.


Thanks! Hah I won't, but I am very curious to how it happened.

That's a fantastic idea, I really really like it! It's quite innovative! In FLL I tried to keep the robot semi modular, but I never even thought of it for FTC, that's great!