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

[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]

Originally Posted by 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.

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!

[cadandcookies]

Originally Posted by F Elliott

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.

[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.