[FTC]: FTC weight and number of drive motors

[Frank Neuperger]

Apologies if this is a double post on this. My earlier post seems to have vanished.
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We are an FTC rookie team and are wondering :
1. What is the more common drive configuration for winning robots. 2 or 4 drive motors?
2. What is the the weight of 2 drive motor bots vs 4 drive motor bots. Understood that the motors and controller weigh more?

3. What is the most common gearing ratio for 2 and 4 drive motor bots?

4. Comments on battery life with 4 and 4 drive motor scenarios.

Just trying to get a feel for the robot speed/agility that is most common place and looking at number of motor to bot weight ratio as well as gearing strategy of successful bots.

Frank Neuperger
FTC 4314
Gilbert AZ

[Andrew Remmers]

Its not always about what the drive train does to make the robot successful, yes it is a very important part of the robot since you wouldn't do anything with out it. But it really depends on what you design your robot to do. A great number of drive trains are variations of a "tank drive" Take for example Exploding Bacon last year started with a fast 6 wheel 2 motor drive robot. By the end of the season we had outfitted it to a 1:1 Geared 6 wheel 4 motor drive robot. We did this because we wanted to have a robot that was strong in pushing matches. The drive train is a big discussion with our team, last year we talked about it for on the upperside of 3 weeks.

As I said It really is up to you what you want your attributes to be. Anything you build can be successful if it is implied correctly, there really isn't a "golden drive train" in any application of mechanics really, each has its own weaknesses and strengths. Also I wouldn't worry about weight, there is no weight limit. Battery power, we didn't have any problems we ran 5 motors almost constantly during matches.

But thats my $0.02

Andrew

[Chris is me]

I can't speak specifically for FTC (you can mathematically calculate drive load for your motors if you want, I could help with the math if you're looking for that much precision), but I can say a few things that should be helpful from what I've picked up:

1. Test everything. Build a chassis, put some weight on it, and figure out if there's a big difference between 2 and 4 motors. There's no substitute for figuring out how the platform in front of you works.

2. I can say you probably won't / shouldn't be draining a battery in 2 minutes. FIRST generally uses circuit breakers to make sure you can't draw that much current for that extended of a period of time. In any robot game, you shouldn't be anywhere near that number because 2.5 minutes with a perfect battery is 1 minute with a shot battery. Also, you would take a major performance hit at the end of the match.

[JesseK]

Fast drive trains have tended to be big let-downs in FTC from my experience and witnessing. Standard 1:1 with 3" wheels typically does the job, or if you want a little faster then 1:1 with 4" wheels may do it better. FTC is more about control than flying around the field; strategy can more than make up for lack of relative speed.

The weight differences between 2 motors and 4 motors is nominal; simply split the wiring at the controller for 2 motors per side instead of 1 motor per side.

The difference in power of 2 motors vs 4 motors comes into play during pushing matches, of which there are many. It also comes into play for motor longevity; 4 motors tend to last longer than 2 simply because there are more motors to spread the load. As for raw pushing power, there is a noticeable difference, yet only if your bot maintains traction over the other bot. Push traction is a derived characteristic of wheel tread, center of gravity, and the height/direction of the contact point between your bot and another bot.

As for battery life, it's been my experience that continuously-run or overloaded manipulators have more effect on the battery than a drive train does. Your design may not have any continuously-run components though (conveyor, intake roller, etc). Additionally, the difference in current draw between 2 drive train motors vs. 4 drive train motors is nominal.

[normalmutant]

We put 4 motors on our prototype robot during the middle of the season to test it, and even though it probably got run more than our bigger robot at demos, it barely ever burned out. Our 2 motor robot would burn out at the most inconvenient times, i.e. finals. We haven't tested it for sure, but we think 4 is better.