[FTC]: Drive Platform- Design Exercise
 

In this thread, my son and I will document our process of designing and building a drive platform. We hope to finish the build and programming this summer.

The process will consist of the following steps:

1. Establish design environment: CAD software, new Android programming tools, etc...
2. Establish an engineering design process to follow.
3. Design
4. Build
5. Test
6. Repeat steps 3 through 5 until finished

Anyone interested is welcomed to join in the exercise. All comments, critiques and suggestions welcomed.

Re: [FTC]: Drive Platform- Design Exercise
 

CAD Software:

We've found 3D solid modelling software indispensable for designing our mechanical systems. We've used SolidWorks for the past several years, and SW has served us very well.

This year, I'll be exploring converting to a new software: "Onshape". This is a new CAD modeling software where all the computing is done “in the cloud”; computing is done by servers through the internet and does not require special computers or licensing on the computer = no IT overhead. Onshape also has new collaboration tools/capability similar to Google Drive and Google Docs. Onshape is FREE and easy to gain access. See here: Onshape- The Future of CAD


We'll be converting to Onshape and using it for this project. My son has worked with Onshape more than me, and thinks we'll still need SW for some of the functionality not yet available in the current beta version. We'll see...

Re: [FTC]: Drive Platform- Design Exercise
 

Engineering Design Process

Here's a typical approach from Wikipedia (link):

1. Research
2. Feasibility
3. Conceptualization
4. Design requirements
5. Preliminary design
6. Detailed design
7. Production planning and tool design
8. Production

For this drive platform project, we'll use an abbreviated version. We've already decided the platform will be a Mecanum system. The project is based on previous years' platforms. We'll skip to the "Design Requirements" step and capture previous design work in a document called "User Requirements Specification".

Here's a video of our previous version on the modular Mecanum drive platform:

Re: [FTC]: Drive Platform- Design Exercise
 

Here is the URS for the platform design:

User Requirements Specification
FTC 2015/2016 Modular Drive Platform

Re: [FTC]: Drive Platform- Design Exercise
 

I've purchased the Modern Robotics Inc (RBI) new modules from their website as well as 4 of the new Matrix 12V gear-motors. We used the 9V motors for our previous mecanum platform with good success and want to test these. Matrix has yet to publish specs for their 12V motors. There's a lot of information on the AndyMark and Tetrix motors and I want to evaluate and compare the Matrix option.

I've modeled the motor with OnShape (my first use of this CAD software). The model is "public" and may be viewed and copied by anyone with an OnShape account : LINK



I'm setting up a test rig and will publish torque/RPM/power data next week. From what I've tested so far, the motor has the following:

• 52:1 planetary gear set
• Approximately 200 rpm no load speed

The shaft end dimensions are identical to last years 9V motor. Specs here: LINK. I'd anticipate a stall torque above 500 in-ounces (36 Kg-cm).

Re: [FTC]: Drive Platform- Design Exercise
 

OnShape (OS) hasn't yet released the drawing function: "Coming soon for all users". The OS model exported easily to SolidWorks where I made this dim drawing of the Matrix motor:


http://simhardware.org/img/Matrix 12...or-50-0014.PDF

Re: [FTC]: Drive Platform- Design Exercise
 

Tests for Matrix 12V motor below:

Re: [FTC]: Drive Platform- Design Exercise
 

Thanks for the nice data!

Did you test the motor at only the 4 points shown in the plot, or at other points? If only the 4 points, then they would suggest that the stall torque is 516 oz-in or below. Linear extrapolation of the first 3 points would put the stall torque around 467 oz-in. Would you agree? I think if the stall torque were around 467 oz-in, it would also make the power curve end up being closer to the more traditional inverted parabola.

How did you like your DIY experimental setup? How hot did the wood pieces get? How long did you run the Matrix motor stalled, and did it show any signs of failure (e.g., smoking, or reduced performance afterwards)?

Did you measure the voltage of the battery (i.e., was it truly around 12 v or was it higher as they often are when they are fully charged)? Do you have any comments on the usage and performance of the tachometer (i.e., did it work as expected, would you buy it again, and were there any unexpected issues you ran into when using it)?

Given that you went to the trouble of creating such a nice DIY setup, I'd love to see you run the same tests with a Tetrix and Neverest motor to see how they compare on the identical setup, if you'd be willing.

Thanks again!

Re: [FTC]: Drive Platform- Design Exercise
 

At the 4 points; the graph is a connect-the dots type. I’m ordering an in-line Watts/Volts power analyzer and will repeat again with more points.

Yes, my data aren’t linear.

Was easy to use. With power analyzer and scale hooked to PC (USB), I’d like to be able to log force, Watts, Volts and Amps data to a file for plotting.

Didn’t feel with touch any heat generated.

3-4 seconds; long enough to get scale reading. No noticeable effect on motor.

No, can’t find my volt meter. :)

No problems. I also used it to measure the motor speed of about 11,000 rpm.

Will do… other motors are at school and won’t be able to test them until September. We also want to test the secondary gearbox performance we’re adding as part of this project.

Re: [FTC]: Drive Platform- Design Exercise
 

I've been spending some time working with OnShape. I'm having good success doing the typical cadding we done in the past for First. Below is the MRI Power Module. OnShape has the following advantages over other CAD packages:

• FREE
• Cloud Based- works like Google Docs
• Works on any platform- PC, MAC, Tablet, even smartphones. The computing is done "in the cloud", so device is only a browser interface.
• No IT required
• Revision control is very advanced- similar to GitHub
• Collaboration capabilities are terrific- multiple users can work on the same project in real time.
• No files to maintain

Re: [FTC]: Drive Platform- Design Exercise
 

Can you invite a user to use this software? I think it would be interesting to play with and I need an invite to access it. Thanks!

Re: [FTC]: Drive Platform- Design Exercise
 

Once you set up an account, you can invite other users to access private documents. I've set mine up as public, so anyone can view or copy. My project name is "FTC 2015/2016"

Re: [FTC]: Drive Platform- Design Exercise
 

Current design using Matrix 12V motor, Vex 4" Mecanum and Dremel angle drive for gearbox:

Re: [FTC]: Drive Platform- Design Exercise
 

Looks great, and I'm looking forward to playing with Onshape soon! Thanks for letting us know about it.

FYI, if you're considering this CAD model for use on a real robot, you might want to read some of the reviews on the Dremel angle drive complaining of lack of durability. It's probably made for high speed but not necessarily high torque. It would be a shame to buy 4 of them at $20 each, build a robot based on them, and then find that they break the first time your robot runs into a wall or another robot, stalling your motor.

Re: [FTC]: Drive Platform- Design Exercise
 

Hi wgardner,

Thanks for the heads-up. I have read the reviews. I think the failures are due to the very small square shaft that connects to the Dremel. The rest looks substantial enough. I plan to test with torque numbers x 3, and if it breaks, rework the connection to the motor. A nice feature of the square shaft is that it's very forgiving of alignment. I'll post a screen-shot later...

Craig

Re: [FTC]: Drive Platform- Design Exercise
 

Great! I look forward to seeing pix of the final result, and learning how much torque it can withstand.

Cheers.

Re: [FTC]: Drive Platform- Design Exercise
 

OnShape has just published a curriculum package: LINK

Re: [FTC]: Drive Platform- Design Exercise
 

Even if you solve the durability problem, the roller-on-roller transfer of energy from one axle to the other is not likely to transfer much torque (though it would be good for high-speed, low torque applications, like attaching to a dremel). With that device in your drivetrain on the wheel side of the gearbox, I doubt you would be able to get anywhere near stalling the motor; I'd be more worried about not getting enough traction to get the robot rolling at all. I don't know the contact force or coefficient of friction, so I can't even give a rough numerical estimate of the torque, but it's something else you should check before including it in your design.

Re: [FTC]: Drive Platform- Design Exercise
 

The gearbox has straight bevel gears; my model's simplified representation doesn't show the the teeth.

Re: [FTC]: Drive Platform- Design Exercise
 

Nice work!

On a very distantly related note, are there any suggestions anywhere as to how to set up an Android Virtual Device Emulator to closely track the ZTE Speed? Obviously, one wouldn't be able to do more than test out stuff not directly related to motor control, etc, except maybe with some input and output test files...

Thanks,

Martin

(one of the mentors for FTC #7593 TigerBots).

Re: [FTC]: Drive Platform- Design Exercise
 

Hi Martin,

Have you seen the threads at the FTC forum. There's a lot of activity there. Here's an example:

Thread: End to end response times

Re: [FTC]: Drive Platform- Design Exercise
 

Thanks!

Re: [FTC]: Drive Platform- Design Exercise
 

Here's a photo and CAD of angle gear. The square shaft is pretty light, but the design is cool as square drive shaft is routed through the hollow shaft and press fitted at the gear end. There's a lot of flex which make alignment with motor easy. I'll test for ability to handle about 1500 in-oz.

Re: [FTC]: Drive Platform- Design Exercise
 

Looked at stress in square shaft. Assumed round shaft 2.5mm diam and 500 in-oz (3.53 Nm) and plugged into this on-line calculator: TORSION OF SOLID AND HOLLOW SHAFTS

It returns 160 kPSI (1100 MPa). That about 5x the the stress to break a steel rod. It's not looking good for the square shaft. Now I need to look at the gears; they probably aren't designed for the torque either...

Re: [FTC]: Drive Platform- Design Exercise
 

If the dremel drive doesn't work out, you could probably make your own version using the bevel gears at ServoCity and some Actobotics parts, like what is shown at the bottom of this link. So far, we're quite happy with the 1/4" axles of the Actobotics set: they're much stronger than the Tetrix axles and the bearings for the Actobotics axles seem much nicer than the bronze bushings used in the Tetrix set.

Re: [FTC]: Drive Platform- Design Exercise
 

Thanks for the link, and the price is right. The same steel gears from mfgr are about $25 ea.

Re: [FTC]: Drive Platform- Design Exercise
 

I tested the angle drive for torque strength. I jigged it up and applied force with a torque wrench set at 20, 25 & 30 in-lb (480 in-oz). At 30 in-lb, the shaft started "unraveling", twisted and broke. It's a bundle of wires formed into a square shaft.

I'll drill out the wire shaft and make a coupling to press fit into the 4mm ID/6mm OD bearing shaft.

Re: [FTC]: Drive Platform- Design Exercise
 

I'm looking for CAD models of the Modern Robotics components and your nice picture is all that I can find so far.

Did you make that model yourself or get it from somewhere? Are there models for the other components? If you made them yourself, would you be willing to export them and share them?

Thanks!

Re: [FTC]: Drive Platform- Design Exercise
 

I've modeled the new motor, servo and main power modules. They are "public" at OnShape. I can export to most file types; what do you prefer?

Re: [FTC]: Drive Platform- Design Exercise
 

Great! I'll just find them myself on OnShape! Thanks!

Re: [FTC]: Drive Platform- Design Exercise
 

Re: [FTC]: Drive Platform- Design Exercise
 

Modern Robotics Inc. has posted CAD files for the new controls modules here:Download Files


Core Modules STEP files
Core Device Interface PDF
Core Device Interface 3D PDF
Core Legacy Module PDF
Core Legacy Module 3D PDF
Core Motor Controller PDF
Core Motor Controller 3D PDF
Core Power Distribution Module PDF
Core Power Distribution Module 3D PDF
Core Servo Controller PDF
Core Servo Controller 3D PDF

Re: [FTC]: Drive Platform- Design Exercise
 

Made the coupling:

Re: [FTC]: Drive Platform- Design Exercise
 

Thanks for posting this, Craig. To anybody else who is interested in downloading these, just grab the STEP files - this zip file includes all the PDFs.

The PDFs are a little disappointing - they don't include an orthographic projection or dimensions.

Re: [FTC]: Drive Platform- Design Exercise
 

Hi John,

Yes, the PDFs don't help much. Have you worked with CAD solid modelling software? I recommend checking out OnShape. It's free and requires no software installation or difficult IT maintenance. Projects at OnShape can be "public" and anyone can view & copy. The MRI files have been imported to OnShape and are available for anyone to use.

Craig

Re: [FTC]: Drive Platform- Design Exercise
 

Yes, I took a look at OnShape based on your previous posts. It looks interesting, but my CAD skills are quite rusty, so I can't give it a fair evaluation. I'm going to show it to my team's CAD person to see if he's interested.

Re: [FTC]: Drive Platform- Design Exercise
 

Completed the basics of the platform design. Trying to maximize the open space inside the 18in square limit. Additional structure, particularly front, will be designed as determined by the game functions. If the open space is not required, a simpler straight drive design could be used. We built and competed with the straight drive and had no failures other than a broken mecanum roller from dropping during transport.

Re: [FTC]: Drive Platform- Design Exercise
 

Oh well, the mecanum design is pretty much worthless for this year's game; back to the drawing board. I'm thinking BIG tires:

Re: [FTC]: Drive Platform- Design Exercise
 

A 30 degree slope is bad. Sixty is quite a problem.

Re: [FTC]: Drive Platform- Design Exercise
 

I get 30 & 50 deg from CAD model. Yes, keeping the COG low enough to climb the 50 deg bars will be a challenge.

Re: [FTC]: Drive Platform- Design Exercise
 

I don't have the exact measurements, and not currently in the room, but I would agree that the angles are around 30 and 50 degrees.

Who said you had to "climb" the 50 degree section.... (I see the more advance bots just dragging themselves past that section in the endgame, I.e. starting from the low zone, and reaching to the bar.) (During the regular 2 minute time period, just driving to the low zone, and extending to the high goal as well, over the churros)

Re: [FTC]: Drive Platform- Design Exercise
 

Where's the term churro come from?

Re: [FTC]: Drive Platform- Design Exercise
 

They look like the churro fried-dough pastry: https://en.wikipedia.org/wiki/Churro.

Re: [FTC]: Drive Platform- Design Exercise
 

FRC came up with the term for them. I think it was an intern at Andymark actually. Well known little product, used mainly in the Kit of Parts drive train for FRC.

Re: [FTC]: Drive Platform- Design Exercise
 

:) Yeah, that. Must be a regional thing.

I lived for a long time in San Diego and I understood the reference immediately as my kids grew up eating them with their Mexican food kids meals.
http://www.rubios.com/menu/other-fare-and-kids/churro/

Re: [FTC]: Drive Platform- Design Exercise
 

The bars running across the mountain are known in FRC as a churro.
http://www.andymark.com/product-p/am-churro.htm

Re: [FTC]: Drive Platform- Design Exercise
 

Yeah, but they're called a churro in FRC too because they're just like the mexican dessert. It's not like FRC came up with the term out of nowhere. ;)

Re: [FTC]: Drive Platform- Design Exercise
 

Here's a revised version of the drive platform User Requirements document: FTC 2016 Drive Platform URS-Rev1

Re: [FTC]: Drive Platform- Design Exercise
 

:) I was just trying to explain the origin of the term that most FTC teams wouldn't know about.:)

Re: [FTC]: Drive Platform- Design Exercise
 

Really? Are there that many FIRST teams in places without Taco Bell or Panchos? I know they aren't "real" churros, but when I read the name on an AndyMark parts list, I knew sort of what to expect. Maybe if the world were a bit more like Demolition Man, where "all restaurants are Taco Bell now"...I'd still like to know how the three seashells work without massive chafing.

Re: [FTC]: Drive Platform- Design Exercise
 

What I mean is that in the post that was first questioned about the term "churro" came from. (To my knowledge) he was asking what a churro part was and not the actual piece of food.

But hey, I might be totally wrong.:) Because we seem to be talking about two different issues. I am talking about what the actual part a churro is. While everyone else is talking about the food term and what type of food it is.

Re: [FTC]: Drive Platform- Design Exercise
 

Drive Platform Design Strategy

My son and I have been thinking about this season's game vs. drive platform design. The "Mountain" element provides new and difficult challenges that are very different from previous years. Here are some of the issues we've been thinking about:

1. Scoring- The scoring capability related to drive design is challenging related to climbing the mountain. We estimate that purely driving/climbing ability can score 80 points by driving up to the "Mountain High Zone" (40 autonomous & 40 tele-op). And... if the robot can climb to the High Zone, we'll be able "hang" using fairly simple mechanisms (80 points hang & 20 points "All Clear Signal"). So... climbing could affect a total of 180 points for the team.
   
   
   
   
2. Drive vs. Climbing- To climb into the High Zone, the robot has to climb the 30 deg angle ramp and drive over the "churros" (rungs), and then climb the rungs at 50 deg. We're thinking of the High Zone as a ladder leaned at a 50 deg angle with rungs spaced at 5.33" intervals. Possible drive types:
   • Standard 4" wheels- will fall through the rungs
   • Big wheels- approximately 8", wheel base is only about 8" and center of gravity (COG) must be low or robot will flip. Wheels could "trip over" debris; hindering autonomous navigation.
   • Tank treads- much more complex system to design than wheels.
   
   
   
   
3. Physics- Any wheel or tank tread design will not have enough friction to climb at 50 deg with smooth contact with the rungs (assume < 1 coeff friction) . The treads or wheels must be able to "grab" the charro or the charro's ribs. The power required to climb 50 deg is much higher than previous years’ 15 deg incline. It’s complicated, but we’ve done a rough estimate for a 30 lb robot with wheels, and got about 500 in-lb torque at each axle.

Re: [FTC]: Drive Platform- Design Exercise
 

Big Wheel Design

We did some design and testing. We modeled the AM-0420 8" Wheel with an automotive "cogged V-belt", model # AX-23. The idea is that the belt will be flipped inside out and snugly fit the wheel OD. We're thinking well cement the 2 rubber surfaces together.

The auto parts store didn't have this small a fan belt, but I got a longer one with the same cog pattern and cross-section. We mocked up the 50 deg angle with a churro at the correct alignment, rigged the belt around an 8" wheel and rolled the wheel per design by hand. It felt like it should work; worked well enough that we ordered 4 wheels and 4 belts.

Re: [FTC]: Drive Platform- Design Exercise
 

Time to review the concept of center of mass with the students. Both static and dynamic. Saturday we let the students go on design for different aspects of the game. Half way into the meeting, we gave them a power point presentation on COM that we give the FRC students. After a little playing on the mountain with this summers practice bot, the concept of COM really sunk in. We can "crash" the practice bot up the 30 degree slope. To drive up the 50 degree slope is challenging.

Re: [FTC]: Drive Platform- Design Exercise
 

My quote then was a response to the side discussion about familiarity with the food. I fully understand that the original question was about the aluminum stock, not the fried dough. My point was that if you are familiar with the food, you wouldn't ask the question about the aluminum.

This looks like a great solution - if you can find the right pitch timing belt, it should interface well with the churros even at the steep angle. If rubber cement doesn't do the trick for you, you might want to check on glues meant to hold a patch in a tire. These glues are usually painted on, set in place, and then partially burned to form a solid joint. Of course, I suggest doing the burning outside, on a metal pad, away from other combustibles, with a class A+B fire extinguisher handy just in case things go awry.

Thanks! I'll incorporate a bit of this into our FRC pre-season training this year.

Re: [FTC]: Drive Platform- Design Exercise
 

I have one of these arriving tomorrow:

Gates 255L050 PowerGrip Timing Belt

Re: [FTC]: Drive Platform- Design Exercise
 

Thanks for all the information on this thread. We are a rookie team of 6 with mostly 7th graders this year. While the team is starting to use PTC, I came across this thread and got quite interested in onshape. We are using tetrix kit. Are there tetrix models available on onshape? How does that work? Thanks in advance for the help.

-Manoj
FTC 10295 - Yellow Jackets

Re: [FTC]: Drive Platform- Design Exercise
 

Hi Manoj,

Yes, there are Tetrix as well as Modern Robotics Inc. and Matrix models that have been added to OnShape. You asked: "How does that work?" Are you asking about how use OnShape? Or... specifically how to use the "Public" models at the OnShape site?


Craig

Re: [FTC]: Drive Platform- Design Exercise
 

Looking at that spreadsheet, I might consider re-reading the rules. To my knowledge you cannot score points for both hanging and parking in the high zone during the same match-- see 1.5.3-4 in the Game Manual Part 2.

I'm also interested in your numbers for debris scoring-- were you able to fit 20 pieces of debris in the goals? My team isn't meeting again until Thursday, so I can't check this myself.

Thanks, and have a great season!

Re: [FTC]: Drive Platform- Design Exercise
 

Hmm... looking at the scoring table in Scoring Summary 1.7, it looks like you can. I don't understand what 1.5.3.4.e means: "e. Cliff Zone: See End Game scoring". But... we'd be in the "High Zone", not the "Cliff Zone", at the end of Driver-control period.

We haven't set up the field; just eye-balling it from the CAD models.

Re: [FTC]: Drive Platform- Design Exercise
 

I took a closer look at the CAD model and it looks like about 10 pieces will fill the bin.

Re: [FTC]: Drive Platform- Design Exercise
 

According to the manual:
Also relevant:
and I'm not sure what conditions you could find where you could be scored to be both fully supported by the mountain High Zone and the Pull-Up Bar at the end of the match, as they're mutually exclusive conditions, since the End-Game is part of the Driver Controlled Period.

Could you explain how you came to a different conclusion?

Nice! This is a bit higher than my estimate, which was 6 based on the CAD model.

Re: [FTC]: Drive Platform- Design Exercise
 

The statements below seem to conflict, but I agree your interpretation makes more sense.

"The Driver-Controlled Score is based on the location of the Scoring Elements, all Clear Signals, and Robots at the end of the Match after all objects have come to rest."

"Robots earn points based on where they are Parked On the Mountain at the end of the Driver-Controlled Period."

I was assuming,and the Scoring Summary (1.7) seems to indicate, that "Driver Control Period" and "End Game" are 2 different periods. But... the robots are under driver control during the End Game.

Re: [FTC]: Drive Platform- Design Exercise
 

Hi Craig, thanks for confirming that. I meant if those models are readily available to use or do I need to do additional importing of the models. I guess when I start using it might become more clearer. Let me try it tonight and I'll get back if I've more questions.

Thanks
Manoj

Re: [FTC]: Drive Platform- Design Exercise
 

Thanks Nick (cadandcookies) for pointing out my error in scoring related to driving/climbing of the robot, as well as capacity of the goals for Debris. Below is revised scoring:

Scoring- The scoring capability related to drive design is challenging related to climbing the mountain. We estimate that purely driving/climbing ability can score 40 points by driving up to the "Mountain High Zone" in Autonomous Mode. And... if the robot can climb to the High Zone, we'll be able "hang" using fairly simple mechanisms (80 points hang & 20 points "All Clear Signal"). So... climbing could affect a total of 140 points for the team.

Re: [FTC]: Drive Platform- Design Exercise
 

They are available in 2 ways within OnShape.

1. Any "Public" workspace can be copied by anyone using OnShape. Parts and assemblies created with OnShape have all the attributes of the original.
2. Models created in other CAD software can be uploaded and used within OnShape, but don't have the original detail (e.g. sketch dimensions). Tetrix, AndyMark, Modern Robotics Inc, McMaster-Carr, etc. CAD models are available at their websites as STEP files and are very useful for CADing.

The above is true for all the mainstream CAD packages: Solidworks, Creo, Inventor and more. My opinion is that OnShape is ideal for FIRST as all computing and file handling is done "in the cloud" and eliminates the IT headaches for PC installed software. OnShape can be used from any machine and any OS using web browsers: Safari (Mac OS only), Mozilla Firefox, Google Chrome & Opera (not IE). And... it's FREE with easy account set-up.

Re: [FTC]: Drive Platform- Design Exercise
 

Thank you so much for your help. I was able to import the field setup from Andymark.

Re: [FTC]: Drive Platform- Design Exercise
 

We've done some work on the "Big Wheel" concept design to look at the center of mass (CoM) issues:

• 8" wheels result in a narrow wheel base ~8"
• When climbing the 50 deg churros rungs, the contact point of the wheels narrows to 5.3" and the vertical distance inside the wheel base narrows to ~3.5"
• Not only must the CoM be kept inside the 3.5" zone, torque from the rear wheel can flip the robot.
• We want to maintain 2" clearance between robot bottom to floor. This prevents lowering the motors, battery, etc. This will allow "debris" to pass under without obstructing travel of the robot. "Tripping" over the blocks could hinder autonomous navigation.

We sketched a design where the motors are set forward and battery is at front. Even this does not put the CoM in the "safe zone".

Re: [FTC]: Drive Platform- Design Exercise
 

Have you moved your arm fully forward and/or down? That could move your CoM a good bit.

Another thing that might help would be to make your wheelbase (distance between axle centers) a multiple of the churro spacing (4.8"?). This would keep you from rocking back and forth as you climb, though you would need a bit of extra torque as you come up out of a trough. In order to do this and remain under the size limit and not fall into the spaces, you may have to have more than one plane of wheels on each side.

Re: [FTC]: Drive Platform- Design Exercise
 

So my team is playing with this also, and while the problems of weight distribution are important, we feel that you can get around it because there is no weight limit on FTC bots. While you want to keep the robot as light as possible since power is limited, it also is very realistic to add ballast exactly where you need it using things besides the battery and motors. With a few lbs of steel riding right on the front of your chassis you should be able to compensate to make this concept work.

Re: [FTC]: Drive Platform- Design Exercise
 

Yes, extending arm forward, with 1lb weight, moves CoM to about centerline of safe zone. And... has better distribution when level.

Re: [FTC]: Drive Platform- Design Exercise
 

Yes, ballast will be used after the other mechanisms are chosen. We've found weight balance and precise alignment of the wheels make a big different in how the drive platform tracks.

For this design exercise, we're looking at using the arm as follows:

Re: [FTC]: Drive Platform- Design Exercise
 

Cool - almost exactly what I had in mind when I suggested moving the arm forward and down. Glad to see it's working out.

Re: [FTC]: Drive Platform- Design Exercise
 

Hi,

Any chance for these tests to be rerun with the Tetrix and Neverest motors now that school is open and the motors are presumably available? Thanks so much!

Re: [FTC]: Drive Platform- Design Exercise
 

I've been preoccupied with the new controls and changes in drive platform requirements. Hopefully I'll get to it this weekend.

Re: [FTC]: Drive Platform- Design Exercise
 

We received the AndyMark wheels and v-belts. The inside-out v-belt fits snugly over the wheel. The cogs grab the churro nicely.

Re: [FTC]: Drive Platform- Design Exercise
 

Looks like a good fit, on both the wheel and the churro! Are you planning to use adhesive between the wheel and the belt?

Re: [FTC]: Drive Platform- Design Exercise
 

It's tight enough not to slip in rotation. I'm thinking a thin bead of heat glue would keep the belt from moving laterally. Rubber cement would work too.

Re: [FTC]: Drive Platform- Design Exercise
 

Same two primary answers I was thinking of, with a slight advantage towards the rubber cement. CA is too likely to be brittle under game stresses. Hot glue doesn't really stick to anything, and might not grab the smooth tire tread well. Rubber cement is more flexible than either, and would provide more friction even if it doesn't serve as an actual adhesive on one side or the other. Contact cement is flexible, but would be a royal pain to get right. Silicone glues are also worthy of consideration, for the same reasons as rubber cement.

Re: [FTC]: Drive Platform- Design Exercise
 

OK- time to start building the prototype. The plan is to build one half of the chassis; Chassis Rails, 2 wheels & 2 motors. We'll test on "Mountain" for ability to climb.

Re: [FTC]: Drive Platform- Design Exercise
 

Here's a Bill of Materials (BOM) for the prototype:

Link to Excel spreadsheet with BOM and other analyses: Chassi Build_cr 03oct15.xls

Re: [FTC]: Drive Platform- Design Exercise
 

We've made some modifications to the design:

1. We had used 2" for chassis clearance of balls and blocks. This is incorrect as the ball is 2.8" in diameter. We raised the motors to clear 3".
2. We made the Chassis Rail 4" tall and symmetrical about the wheel axle. This allows a standoff at top of Rail.

The BOM in the previous post has been updated.

Re: [FTC]: Drive Platform- Design Exercise
 

The first fabrication activity will be to modify the 8" AndyMark wheels. They will be turned on the lathe to narrow to 1" and allow the hub to attach within the 1" width.

Re: [FTC]: Drive Platform- Design Exercise
 

Re: [FTC]: Drive Platform- Design Exercise
 

I found an interesting robot with similar design. The video may shed some light on how the bot will drive on tiles...

LINK to video

Re: [FTC]: Drive Platform- Design Exercise
 

Rubber cement is fast drying, but Shoe Goo urethane adhesive is way stronger in the key spec of its => peel strength.

We are evaluating a strange design that uses four overlapping pairs of half wheels that have their flat sides oriented 180º out of phase within the four pairs, and each pair is driven by one of four motors..

By correctly spacing the axles within the pair and by optimally separating the pairs on each side (front to back), we expect them to roll over the churros where we have plastic and them climb them on the high zone churros.

Our Plan B wheels are going to be 8" AndyMark, like yours, but with thick walled pieces of 5/8"-3/4" OD surgical or urethane rubber tube pieces tied around the circumference to function as as large and somewhat individually "floppy" cleats.

Notches in rim will keep the cleats' tied on with the capture cord at properly equal spaced locations around the circumference of the wheel. Shoe Goo adhesive may be needed to better stabilize cleats against the wheels' urethane if cleats flex too much. with just cord holding them on.

We considered your style of cogged belt too, but felt the cogs might be a little too shallow for maintaining good grip engagement with the churro bars.

Appreciate all the time spent documenting your design and build process here.

-Dick Ledford

Re: [FTC]: Drive Platform- Design Exercise
 

A good quality CA will bond belts and wheels in this application. Medium set will give a little more work time. Be fast if you use it.

Re: [FTC]: Drive Platform- Design Exercise
 

Good idea using Shoo Goo- thanks!

I converted the above robot's SolidWorks model to OnShape here: ASME CMU Robot 2004

The design has nice mechanisms for arm using servos.

Re: [FTC]: Drive Platform- Design Exercise
 

We tested the chassis & wheels on the "Mountain" today; no motors yet:

• It's not certain that the rig will climb as hoped. Turning the wheels by hand doesn't give enough info about slip, as the front and back wheels work together and we couldn't apply the torque on both in sync.
  
  
• When a wheel is resting on 2 rungs, I'm concerned that the bot will get stuck; the notches could bind on the churros and not climb forward. Momentum will probably be a factor in this.
  
  
• We did have a problem with the chassis hitting the churro as shown below. Something's off with my CAD model, the mountain CAD, or both.

Re: [FTC]: Drive Platform- Design Exercise
 

Re: [FTC]: Drive Platform- Design Exercise
 

Almost done with the prototype...

Re: [FTC]: Drive Platform- Design Exercise
 

Prototype is ready to test, but having problems with App Inventor. Old programs won't run with newly installed Driver Station App. Where's IT when you need them? :)

Re: [FTC]: Drive Platform- Design Exercise
 

I got the App Inventor program working by installing the latest Driver Station app and reinstalling "LocalAppInventor_win.ova" to the newest version. I've got to say, the programming platform has worked well for me; given my limited programming ability. I'm having fewer configuration issues compared to RobotC.

The prototype ran nicely on the floor. I like the belt drive for efficiency and smoothness. We tested on a whiteboard and it had no problem driving up 30 deg. It started slipping at about 40 deg. We'll test on the mountain at today's meeting.

Re: [FTC]: Drive Platform- Design Exercise
 

We ran two test for the prototype yesterday:

1. Climb Test
2. Wheel/Tile Damage Test

Both were unsuccessful. :(

I wasn't able to attend the meeting and can only view the videos my son made. There are a couple of additional things I'd like to test and will set up a home test rig for the churro climb. Here are links to the videos:

FTC 2016 Prototype Climb Test
FTC 2016 Prototype Wheel Test

The damage inflicted was worse than the picture obelow shows. The wheel abraded the surface about 1/16th inch depth. This seems to be a "show stopper" for the cogged belt idea.

Re: [FTC]: Drive Platform- Design Exercise
 

Thinking about the wheel design and passing the tile damage test. I posted the following to the build Q&A forum:

I'm concerned that it's going to be difficult to design a wheel or tread that can both climb the mountain, and not damage the floor tiles.

Re: [FTC]: Drive Platform- Design Exercise
 

Yes, The mountain is a beast of a problem. We have invested allot of time and money into a Irobot style tank tread robot with wheels. Early prototypes show it should work. If it doesn't what do we do?

Re: [FTC]: Drive Platform- Design Exercise
 

We can always do this: YouTube Scrimmage

Re: [FTC]: Drive Platform- Design Exercise
 

You don't have to go over any churros to score in the goals or even to "climb": you just need to be on the low part of the mountain with your drive train above the tape on the bottom 2 inches.

Everybody seems to be obsessed with driving over the churros, but you can do pretty much everything without driving over any of them...

Re: [FTC]: Drive Platform- Design Exercise
 

I totally agree, if you analyze the scoring potential, being able to climb the churros is worth a max of 80 (not including chin-up). Blocks in the bins are worth a lot; 300 point by my calculation (10 pieces in 1 low, 1 med, 1 high).

Re: [FTC]: Drive Platform- Design Exercise
 

We built a test rig to simulate the 30 deg ramp and curros. We thought that the cogs didn't have enough bite on the churros' ridges. We ran the prototype on the test rig and got a repeat of Thursday's failure. We ground off every other cog of the drive belt (inside out on wheel) and got a bit better performance. See link to YouTube video):

https://youtu.be/glkYs-dqP5I

We only had a long enough churro to make 4 stubs. We'll move the lower stubs up and test for the 50 deg High Zone.