[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.

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…

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:

https://i.ytimg.com/vi/QL6rHh3uY8Q/mqdefault.jpg](https://www.youtube.com/watch?v=QL6rHh3uY8Q)

Here is the URS for the platform design:

[User Requirements Specification
FTC 2015/2016 Modular Drive Platform](http://simhardware.org//img/FTC 2016 Drive Platform URS-Rev0_cr 19jul15.pdf)

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

http://simhardware.org/img/Matrix 12V GearMotor_CAD_cr 26jul15.png

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).

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 12V GearMotor-50-0014_cr 26jul15.PNG
[http://simhardware.org/img/Matrix 12V GearMotor-50-0014.PDF](http://simhardware.org/img/Matrix 12V GearMotor-50-0014.PDF)

Tests for Matrix 12V motor below:

http://simhardware.org/img/Matrix 12V GearMotor test_cr 26jul15.JPG

http://simhardware.org/img/Matrix 12V GearMotor test rig_cr 26jul15.JPG

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!

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.

Linear extrapolation of the first 3 points would put the stall torque around 450 oz-in. Would you agree?

Yes, my data aren’t linear.

How did you like your DIY experimental setup?
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.

How hot did the wood pieces get?
Didn’t feel with touch any heat generated.

How long did you run the Matrix motor stalled, and did it show any signs of failure (e.g., smoking, or reduced performance afterwards)?

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

Did you measure the voltage of the battery
No, can’t find my volt meter. :slight_smile:

Do you have any comments on the usage and performance of the tachometer
No problems. I also used it to measure the motor speed of about 11,000 rpm.

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.
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.

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

http://simhardware.org/img/FTC Power Module CAD_cr 01aug15.png

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!

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”

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

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.

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

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

Cheers.

OnShape has just published a curriculum package: LINK

Onshape offers a completely free version of its software with all the same functionality as the professional version – and it’s engineered to be easy to set up and get started.

  1. Immediate Access: You and your students can go here and set up your free account in less than two minutes!

  2. Curriculum Guidance: Onshape is creating curriculum for teachers to use in their classrooms. A free Instructor Kit is available now. The kit contains videos, exercises, and quizzes – including an instructional video teaching you how to use the kit – and covers everything that first-time users need to know to learn CAD.

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.

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

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).