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.

Re: [FTC]: Drive Platform- Design Exercise
 

We moved the lower churro stubs up to the 50 deg part. See video below. It gets stuck most of the time with the back wheel locked in and doing a wheelie. A few pounds force on the front enabled it to climb past (not shown).

Prototype Climb Test 2.5

I think the performance warrants going the next step to make the other side rail and test full functionality. This will ensure our holding the cross bar hasn't introduced something to the test that doesn't represent what a 4 wheel platform does.

If we get a positive ruling on using code or clutch to limit torque while on the floor, we'll proceed with the design.

Re: [FTC]: Drive Platform- Design Exercise
 

It's possible to do the chinup without driving over churros. About the only thing you sacrifice by not driving over the churros is possibly 40 points in autonomous for getting to the high zone, but you get 10 for getting in the low zone and you get more points anyway by going for the beacon, putting the climbers in the shelter, maybe scoring debris during autonomous (which counts at the end of the driver period, but if you score some in autonomous then you can keep piling it on during driver control), etc.

For teams that can climb the mountain, awesome and kudos! But for teams that can't, there are other ways to score as many points (or more) with different types of scoring mechanism designs. Don't give up!

Re: [FTC]: Drive Platform- Design Exercise
 

Amen brother! Often the simpler, less glamorous strategies win the day.

Ok... time to check our progress against the "User Requirements Specification" written after the game was revealed.

5.1 All materials. Components and controls must be legal per “2015-2016 FIRST® Tech Challenge Game Manual Part I” and “2015-2016 FIRST® Tech Challenge Game Manual Part II”

The prototype failed the first wheel test of "against wall for 15 seconds at full power". Plans are to limit torque to the wheels while on level ground to prevent slipping and abrading the tiles. A question has been posted on the Q&A forum regarding this strategy.

5.2 The control system will be based on the new Modern Robotics Inc. control modules. The legacy module will not be used.

Requirement meet

5.3 The platform must be no larger than, or collapsible to 18 inches square.

Requirement meet

5.4 The motors will be one of the allowed 12VDC gear-motors.

Requirement meet

5.5 The platform, when loaded to a total weight of 35 lb, will be able to climb a 50 degree incline with ladder rung spacing per game manual and field design.

The prototype (1/2 bot) will be loaded and tested at approximately 18 lb

5.6 The platform should have a loaded (35 lb) full speed of 2 ft/sec on the level field.

Requirement meet so far by estimate of speed from motor testing and drive train calculation:
*Motor RPM @ 20% of max power = 175 RPM (see test data)
*Wheel diameter = 8.75"
*Wheel to motor ratio = 0.5 rot/rot

Calculated speed = 0.5 rot/rot x Pi x 8.75 in/rot ft/12 in x 175 rot/min x min/60 sec = 3.34 ft/sec

5.7 The platform should have a pushing force of 20 lb.

To be tested if prototype completed

5.8 The platform should be able perform with the field littered with “debris” game elements and still meet all user requirements.

To be tested if prototype completed

5.9 The platform must be capable of supporting navigation systems for the
autonomous period with driving through the “debris”.

To be tested if prototype completed

Re: [FTC]: Drive Platform- Design Exercise
 

FYI, I've asked a few questions on the official Q&A forum that have gone unanswered for weeks. Maybe they'll answer you and maybe they won't.

My opinion only: there's nothing in the rules to prevent you from doing the things you described (as long as they're not COTS with 2+ DOF, etc). If you don't hear back, I'd suggest that you go forward with your plans. After all, you're following the rules in an attempt to prevent field damage.

Limiting the power so the motor stalls is a little dangerous as it can heat up the motor/ smoke the motor/ prematurely drain the battery/ etc. Finding that power setting may also be tricky as it will depend on robot weight, battery charge level, etc.

Adding a clutch is a good idea if you can pull it off without limiting your power when you need it.

Another option is a software mechanism that detects wheel slippage and kills the power when it is detected until the gamepad controls are released and re-engaged. I think there are threads on this on CD on the FRC side. Then during inspection, your robot drives, detects wheel slippage and then stops the motors so there's no way for it to grind into the field for 15 seconds. This can be demonstrated to the inspector.

Also keep in mind that field damage is going to be dependent on robot weight. I fear many teams may build tread-based robots, test the light drive-train-only chassis and find it to be non-damaging, then add another 20 pounds of scoring mechanisms, and then find at the tournament that their new, heavier robot damages the field.

Good luck!

Re: [FTC]: Drive Platform- Design Exercise
 

Hi wgardner - thanks for the thoughtful feedback; much appreciated! This "design exercise" has been a project my son (FTC alum) and I have been working on for over 2 years. It's not my FTC team's design, so won't be going into competition. My team is leaning toward a tank tread design.

If this project is successful, anyone could use the info to inform their designs. If not, I hope they can learn something from our dead ends. We're posting the work here as an example of applying engineering principles to the design/build process.

Roger that- I've tested the Matrix 12V gearmotor direct from battery, stalled for about 3 seconds. But... 15 seconds is scary.

... and complicated. :(

Great idea about kill and reset from the game pad! If we get that far, we'll try that. I'll look for the posts in the FRC threads.

We're working on weight testing today. We've added weight to simulate a 35 lb bot (~18 lb for the 1/2 bot) and tested on the test ramp. We're seeing the motors loose power when they get near stall speed; <~ 10 rpm @ motor pulley. We're not getting enough power to climb 50 deg with the added weight. That was with encoder control of speed. We're making another Op Mode to run straight power control while we charge the battery to full.

I've calculated we should get about 350 in-ounces (21 in-lb) torque from the motor; so should be seeing about 9 lb tangential force at each wheel. The dynamics are complicated and 9 lbs probably won't be enough. We can always increase the driven pulley diameter. and design for a super-light build.

Thanks!- we're going to need some luck. :)