FRC Blogged-Kit of Parts Drive System Option

[Steven Donow]

http://www.usfirst.org/roboticsprogr...em-Option-2014

Please see the update below on the Kit of Parts Drive System Option from Kate and Collin, the Kit of Parts team:

For the 2013 FRC season, veteran teams had the option to opt out of receiving the Kit of Parts Drive System and instead receive a $450 Product Donation Voucher to AndyMark. Nearly 700 teams took advantage of this option. In the 2013 KOP Survey, 83% of teams who knew that it was an option said it improved the KOP experience. (Unfortunately, 10% of teams said they didn’t know it was an option. We need to work on that!)

Given the positive reception last season, the option will again be available for 2014! Veteran teams can choose to receive a Product Donation Voucher (PDV) from AndyMark instead of the KOP Drive System at Kickoff. Rookie teams will automatically receive the KOP Drive System.

The PDV will again be worth $450 and can be used on AndyMark parts. To accommodate orders and lead times, the option to opt out of the KOP Drive System for the PDV will be available ONLY from 10/3 to noon eastern on 10/17. During that time, the option to receive the PDV in place of the KOP Drive System will be found in the “What’s New” section on the right side bar of the TIMS main screen.

NOTE: If teams do not choose to opt out of the KOP Drive System in favor of the PDV by 10/17, they will be assigned the ‘default’ option of receiving the KOP Drive System as part of their Kickoff Kit.

To help you make your decision, we can give you some general information about this year’s KOP Drive System. It will look very different from those of the past and the two major variations include the following:

• The C-Base is gone. In its place is a redesigned frame using sheet metal and extrusion designed to make it easier to attach superstructures to the drive base.
• It is still a six-wheel belt drive robot, with an estimated final drive speed of about 10.5 feet per second. But, with the new design, we’ve changed to a direct driven center wheel powered by ToughBox Mini gearboxes.

The KOP Drive System can still be set up as a six-wheel drive “long robot”, but the redesign also now allows a six-wheel drive “wide” robot out-of-the-box. We are excited to continue to increase the competitive level of the KOP Drive System while continuing to give teams the opportunity to make the Kit of Parts as valuable as possible. We thank AndyMark and Gates Corporation for their support in creating this possibility.

Interesting to see that the new kitbot is a sheetmetal structure.

[coalhot]

Interesting, I wonder if this is any indication on next years game.

Looks interesting though...

[Akash Rastogi]

Excited to see what the new kit frame looks like. Making superstructure attachment easier might make more teams want to stick to the kitbot.

Nice work AM!

[AllenGregoryIV]

I'm guessing the standard 12.75:1 toughbox mini with 6" wheels. That's 10.9fps unloaded and 8.83fps with standard JVN loads.

I really do wish they would give a bit more information. I always like having a KOP drive to build so my team can be trained to help rookies. If I know it was simple enough to not need it I would rather have the voucher.

Giving a direct drive system to teams is very interesting.

[D.Allred]

Originally Posted by AllenGregoryIV

I'm guessing the standard 12.75:1 toughbox mini with 6" wheels. That's 10.9fps unloaded and 8.83fps with standard JVN loads.

10.7:1 looks like the correct option.

Anyway, I'm interested to see a sheet metal chassis that is long or wide out of the box.

[Ether]

Originally Posted by AllenGregoryIV

I'm guessing the standard 12.75:1 toughbox mini with 6" wheels. That's 10.9fps unloaded and 8.83fps with standard JVN loads.

For students with inquiring minds...

In the spreadsheet, the 8.83 number is calculated directly from the 10.9 number by multiplying by a "Speed Loss Constant" (default is 81%).

This constant is not computed within the spreadsheet from user-entered info about physical loads and motive forces in the drivetrain: you get the same 8.83 answer from the spreadsheet if you change the number of motors, stall torque of motors, the mass of the robot, or gearbox/drivetrain friction.

The best way to determine what value you should use for the "Speed Loss Constant" for your drivetrain is to build the drivetrain and measure its top speed, then divide that by the theoretical unloaded speed.

[Whippet]

Perhaps they wanted to make it easier to attach superstructures because this year's superstructures will need a lot of structural support to do some heavy lifting? I'm calling stacking game.

[Ether]

Originally Posted by Ether

This constant is not computed within the spreadsheet from user-entered info about physical loads and motive forces in the drivetrain: you get the same 8.83 answer from the spreadsheet if you change the number of motors, stall torque of motors, the mass of the robot, or gearbox/drivetrain friction

Also worth noting: in the real world, the % of "speed loss" is not constant when changing gear ratios either:

Team 1678 did some testing earlier this year on a bot with a 2-speed gearbox. The "Speed Loss Constant" was 92% in low gear and 72% in high gear.

[T^2]

Originally Posted by Ether

Also worth noting: in the real world, the % of "speed loss" is not constant when changing gear ratios either:

Team 1678 did some testing earlier this year on a bot with a 2-speed gearbox. The "Speed Loss Constant" was 92% in low gear and 72% in high gear.

Ether is correct on most accounts. Keep in mind that JVN's "speed loss constant" comes after a "drivetrain efficiency" (i.e. losses from gearing), therefore the 81% number cannot be attributed to gearbox losses. The testing we did earlier this year found the overall speed loss from the theoretical free speed of the motors. The numbers we found make intuitive sense, given that motor resistance, friction, rolling resistance, and air drag all tend to increase as speed increases.

My conclusion now is the same as it was then: test your drivetrain instead of blowing smoke from your behind about the theoretical speed you think you'll get.

[Ether]

Originally Posted by T^2

Keep in mind that JVN's "speed loss constant" comes after a "drivetrain efficiency" (i.e. losses from gearing), therefore the 81% number cannot be attributed to gearbox losses.

The Speed Loss Constant does not come "after" the drivetrain efficiency (at least not in the 2013 version). It is completely independent. See below:

The testing we did earlier this year found the overall speed loss from the theoretical free speed of the motors.

^^This is exactly what the "Speed Loss Constant" in the JVN spreadsheet is.

My conclusion now is the same as it was then: test your drivetrain instead of blowing smoke from your behind about the theoretical speed you think you'll get.

I love test data too.

But I still think it may be possible to develop a physics-based model that will reasonably predict overall drivetrain performance -- including not only top speed but also time to reach a desired speed, time to reach a desired distance, and accel, speed, distance, motor amps, motor volts, and Coulomb consumption versus time -- based on a priori estimates of a limited number of parameters .

[AdamHeard]

Originally Posted by DevenStonow

Interesting to see that the new kitbot is a sheetmetal structure.

Curious what they mean by this, as the KOP drive (ever since it's inception in 2005) has always been sheet metal

[ttldomination]

I am actually really interested to see the new design of the kitbot.

To that end, I'm wondering what will be the pricepoint for the frame and such. Is the $450 the dollar equivalent of a new kitbot?

- Sunny G.

[bardd]

I wonder if the direct driven wheel means we'll be getting a WCD kitbot this year. My gut tells me yes. I hope it's true, if not for the advantages of WCD then for the sheer coolness of it.

[Thad House]

I think even though it is a direct driven center, I think it will still be a dead axle system. I don't think FIRST would make the kit chassis not have an outer frame member because that outer member is very helpful for both mounting structure and mounting bumbers, and I dont think they want rookies having to worry about how to mount things without that outer member.

[Lil' Lavery]

I just hope it's revealed prior to October 3rd (or 17th at the very latest).