Using Multiple Kinds Of Motors

Since some motors have a higher torque, others have higher speed, isn’t it a good idea to use both to drive the same robot? My team has never attempted this (or that I am aware of), would it be a good idea? According to the First Wiki, the Fisher Price motor has a higher speed, significantly higher. The CIM has a significantly higher torque. Now isn’t it possible to make a mechanism that will switch the motors? Switching the motors to fit the needs of the situation. Car manufactures do it, for example the hybrid vehicles. They use both electrical motors and the traditional engines. They must have a mechanism to switch gears.

I have an idea for a mechanism that uses pneumatics and gears, but does not seem very reliable.

Now would it be really worth the trouble to make a mechanism to switch motors? Does the benefits outweigh the drawbacks?

Pros:
Best of both worlds

Cons:
Weight
Mechanism can be the weak point (more moving parts mean more chances of breaking down)
Seems like a redundant way to do something while gears ratios can be adjusted

I can think of a way to do that without switching motors. Several, actually, but one should provide the idea.

http://www.andymark.biz/am-0114.html

Also see the Nothing But Dewaltswhitepaper and team 33’s 4-speed design.

Simpler than switching motors.

Ultimately, all motors contribute is power. To paraphrase the great Dr. Joe, who posted something pretty cool that I couldn’t find searching, speed and torque are “accidents of birth” - motors really only contribute power. You can trade speed for torque and vice versa with gear reductions. That’s the whole idea behind transmissions and shifting gears. If you want more torque and more speed than you could find at a single balance point, you shift gears.

Shifting actual motors makes a lot less sense. First, when would you ever want less power in your drivetrain? Putting an FP in a CIM’s place would just mean you would have to gear it slower to get the same torque. I just can’t see a situation you’d ever want less torque.

In addition to that, you’re limited to a fixed number of motors, and using more of the “best” motors when you could just shift gears seems a little trivial.

Analogous to how batteries or a wall outlet supply power in an electrical circuit (power=voltage x current), motors only provide power into an mechanical system (power = torque x rotational speed). Since they use similar amounts of power you could use one to for slower speeds and one for faster speeds. All your doing is making a two speed shifter almost copying the effect of the AM Super Shifter or any other two speed transmission because all you are doing is changing the output speed but not the power. This isn’t practical because you could just get a shifter and put both motors into it (compensating for different speeds of course) and get the same effect but double the power. Though you are correct that you could do it really just isn’t practical.

About the Hybrids depending the type of drivetrain (parallel, series, or power-split) they may or may not necessarily switch between the motor and ICE (internal combustion engine). In a parallel hybrid the Motor and the ICE are simultaneously providing power to the drivetrain. In a series hybrid the motors provide all of the driving power and the ICE can act as a generator. The power-split hybrid is what you are talking about and yes they are more efficient than the others but only because the differences in energy consumption allows the motor to work for lower speeds (lowering power consumption) and the ICE and Motor to work at high speeds/loads (consuming more power) are so vast compared to the Fisher Price and CIM. This really results in having lower (than a conventional ICE car) torque at low speeds and higher torque at high speeds.

I recommend looking at Paul Copioli’s Motor Drive presentation as it does a good job explaining the relationship between speed, torque, and power. It also explains how to match different motors into a single gearbox which is what I think you really want to do instead of swapping motors.

BTW you all realized “Team Role: Programmer”.
I have had different types of drive trains on my mind, but I want to incorporate the most unique and strange drive systems. What about a system without wheels at all? I want to take the whole “Innovate not imitate” to the max here. I thought using multiple would be cooler than just one

I can understand your desire to innovate so here is something to think about.

A fundamental problem with FIRST robots are that not all the motors are being used all the time. This means that there is a lot of untapped power at any given time. If one was able to put all motors into whatever function(s) were needed at the time, it would be revolutionary.

That would be about as good as a drivetrain could get motor/power wise.

The trick to designing is to identify the problem before finding a solution.

Engineering isn’t always about innovation.

I would suggest that you look at all you options, but the 6 and 8 wheel drivetrains that have been created recently are a very strong base on which to build an optimized system. I also wouldn’t be so quick to allocate a bunch of motors to drive, seeing as how drive barely ever scores points on its own.

Also, FPs seem to like blowing up under heavy load, so if you are going to drive a robot with just FPs in ‘high gear’, I would recommend significant amounts of loaded testing.

Before we were able to use more than two CIMs, everyone had to improvise. I believe our 2003 Championship robot had Cims in two wheels and FP in the other two wheels, geared accordingly, of course.

First, what ChrisIsMe said.
Then, what BJC said.

The issue is defining the problem. Do you really want all possible energy being put into the drivetrain? Is it needed and, if so, to what end? Can the drivetrain do something useful(er) with all that power?

Way back before small electric motors were available, workshops all worked off one single power source - a water wheel, steam engine, gasoline engine or (large) electric motor - with a shaft that ran the length of the shop. Each machine had a long leather belt that took power from the shop shaft (with a clutch that could be disengaged when desired). In this way, all of the power was available to any machine that needed it, or a fraction was available to every machine in the shop.

What if you built a robot that shared ALL the mechanical power like that?

Brooks “Design of Design”

“He who seeks originality will often find novelty, but not great design.”

The Pet Rock was very original, but not necessarily a great thing.

As BJC said, good design begins by asking questions.
What would you want to create? The most agile? The fastest? The most powerful pusher? The best balance? Even “most original” would require knowledge of what others have done. Otherwise, you would find yourself talking about this great, original design that someone else ahs done.

Study “good” examples. What do you like about them? What do you not like about them? How could you/would you do things different?

For the 2010 season, the 968/254 robots used a power takeoff to have one set of motors/gearboxes powering both the drivetrain, and the lifting arm. I believe 973 used a similar design as well.

Team 60/254 had a power takeoff in 2004 to power a winch which lifted the robot from the ground at the end of the match.

I’m not aware of any FRC robot that has been centrally driven through one power unit.

You do make a great point, one great example is the Shake Weight… Its useless.

Now if I wanted to innovate what would be the best thing to innovate? Depending on the game, I would have to talk to my team about it. Most will think I am crazy, but I got to say, I can make a big impact by getting the new people on my side. I really wanna be crazy this year, have a blast while making a non relevant robot. I want people to way “WTF is that?” kind of response and then kick @#@#$@# at the competitions. I really want to move away from the traditional chassis too, maybe having a triangular pyramid?

Innovation is not inherently bad, but I feel you may want to master the basics first. Once you do, you can understand why certain shapes, techniques, methods, etc… are effective and commonly reused.

^ this guy is a fun one to bug :stuck_out_tongue: . I love starting to have our team known for playing the game in crazy ways. But regardless of how we accomplish a task, if a way exists to be better at that task we will do it (even if it stresses out the team moms and makes them want to strangle me).

Lots of crazy ideas are thrown into our design discussions, but our filter of what could possibly work is a lot less restrictive than most teams. Which yields some pretty fun and odd things making it through, but they have to have potential in reality to make it to the next step.

Regardless of how much I want to make some really crazy things, they’ll only happen if they fit that task at hand.

Dave, have you ever considered that perhaps having a rock solid drive system would be beneficial to something complex? Perfection of a system comes not when you can add nothing more but instead when you can remove nothing. As you said, you are a programmer, as a programmer you aren’t terribly familiar with mechanical systems (this is an assumption). Perhaps you should start by figuring out what you can remove from last years drive train to make it better. This would allow you to learn more (which will help you in the future when you show us your awesome new drive system) and help your team because a better drive system is ALWAYS a good thing.

I just noticed your usertitle… Don’t go stirring up trouble now, simple, simple, simple. It’s the way to go.

Our drive system was very basic, I mean very basic… 6 wheels with 2 motors, what can you take away from that? I did not like how it was so basic, it was too much of a conformist approach for me. Of course, me being the new kid with no idea how the competition would be, I did not speak out as much as I should have. It was a terrible system, can’t go over bumps, can’t drive under tunnel (well it can but it can take a while to get it right). Now the leader graduated (he never liked my ideas LOL) I can step it up even more.

I might even hold off on forcing my ideas a bit though, me talking too much last year might have intimidated some people.

Yea I am not a very mechanical person, well its not awfully hard to learn.

Going back to the problem before the answer thing. What do you want out of you drivetrain? It sounds like you currently just want it to be different then normal?

I would suggest looking at things that could be improved within your current drivetrain.

How to increase your robots tractive force?

How to make your robot more manuverable? (strafing or just turning)

How to make it weigh less?

How to make it more easily repairable?

How to get your CoG lower?

How to get up an incline?

How to make it able to stand its ground when hit from the side?

Ect.

So if your robot needs to be a triangle to better do some of these, then you should make it a triangle.
Because I gurantee you that if you can do some of these things, even if they arn’t visible at first glance, you will have a more competitive robot and people will notice the difference.

It was clear that a standard tank drive system could do everything in Breakaway and more this year. If you want an effective drive, take what you had last year and make it do the things it didn’t. Conforming to an intelligent design is almost always a good idea.

And if you think being a Mechanical guy is easy, you are right. But being a great one takes just as much work as being a great programmer. The only way to really know what you are doing mechanically with an FRC robot is hands on experience, reading good mech threads on CD, learning a lot of physics and engineering concepts, and being able to weave it all together into a basis for common sense decisions (which, although known to be ‘common’, never is).

If you intend on building a winning robot, simplicity in the drive is one of the best ways of getting there. Ask 1114, they have been doing it since 2005.