Direct Drive Four Motor System
 

I am looking at possible drive trains for next season. One thought I had was to run each CIM motor directly into each wheel (after running through a transmission). With a 12.75 reduction, you get about 9 ft/s with 6" wheels.

If you're having problems visualizing, think crab drive system without the wheel assemblies rotating and the motors running the same direction the wheels are turning (sorry I can't explain it more).

Does anybody have any experience with this type of drive? What were your problems?

Thanks!

Re: Direct Drive Four Motor System
 

No experience Collin ... but thanks .... you've got me thinking ...

We did talk about doing something similar (CIM on each wheel - using DeWalt gearbox and short chain X 4) last year but we couldn't afford the weight hit of those 4 assemblies ...

Re: Direct Drive Four Motor System
 

I would think the weight and size of four trannys might be a problem. We had four wheel drive robots in the past and turning was very hard. We have switched to six wheel drive with a lowered center wheel and turning is very easy. I know you must have your reasons, but can you tell us the advantage of having four trannys.

Re: Direct Drive Four Motor System
 

The weight that you would gain using four tranny's could be lost from not having to use any chain.

I understand that turning is hard...but I feel that can be lessened by using wheels with lower traction.

Re: Direct Drive Four Motor System
 

I understand that the four seperate transmission setup would give you a slight increase in pushing power, but using a wheel or tread with a lower coefficient of friction would just hurt you in pushing matches. You would be more likely to just spin your wheels without gaining any traction, therefore loosing any pushing power you gained through this setup. Based on the weight, pushing, and turning factors I would personally go with a 6 wheel drive setup. But this all really depends on what resources your team has to work with.

JT
229

Re: Direct Drive Four Motor System
 

not necessariyl. if one of those tires lose contact with the carpet, you only have a 3motor powered robot. 2 motor powered if 2 tires leave ground.. but if oyu have a chain connecting the wheels, even if one wheel leaves the ground, there are still 4 motors torquing the wheels still in contact with the groudn.

Re: Direct Drive Four Motor System
 

1213 used this:


Each was a bit over built at 7-1/4 lbs. Should be able to take 1/2 lb. or so off.

Speed was 7-1/2 FPS with 4" wheels - that's with the Chippy driving the pins on the first stage of the DeWalt - I.E. planet gears replaced with adaptor keyed to the Chippy output shaft.

Mobility was outstanding with 95A durometer urethane wheels. Pushing was not much of an issue last year, but we managed to push when we needed to.

A chain added to connect front to back wheels would transfer power in case one end got lifted - but, I'd rather stay low a use a ramp than bother with chains.

Re: Direct Drive Four Motor System
 

Jack -

Thanks for the info...that's exactly what we're looking at doing.

Re: Direct Drive Four Motor System
 

Biggest issue is holding onto the naked DeWalt tranny. The leg between the motor and tranny is actually two pieces. One (1/4" Al) is the motor mount. The other is 3/8" and fully keyed (water cut) to fit the base of the tranny. I've got the DXF of the pattern if you go with something like it - saves weight - naked DeWalt is only 0.85 lbs.

We used 1/2" high-carbon keyed axles - machined 3/4" from one end to fit the 0.3 x 0.25 double-D tranny output. We found early on that unhardened shafts snapped. Heat treating solved that.

Re: Direct Drive Four Motor System
 

I'd like to offer two strong opinions on this subject.

1.) Direct drive is good! We have been doing this up in Saginaw for a couple years (teams 902, 703, and 49). I love not have any more chain tensioning/jumping off issues! We just make the holes in the right places, but the thing together, and it works for the whole season. No adjustments!!

2.) I have always been a strong advocate of coupling the wheel rotations to each other. We do it with tank treads, but even with wheels you should make it so all of the motor power can go to both the front and/or the back. The problem comes with the inevitable pushing match. We all start with the same limits on power (same battery/fuses/motors). The trick is to put as much of it to the ground as possible. If you have a motor powering each wheel independently and you get a weight shift on your bot such as climbing a ramp or a pushing match, the wheels that get unloaded are no longer helping and you suddenly went from a 4 motor bot to a 2 motor bot.

(sorry, long winded)

Matt's $0.02

Re: Direct Drive Four Motor System
 

yes and no- if a wheel leaves the ground it will also spin freely,

which means it will draw far less current, your battery will be less loaded, and therefore there will be more voltage (power) available to the other three wheels

probabally not 25% more power, but it will be a significant amount.

Usually in a shoving match the wheels mnaking contact with the floor start spinning anyway - once a wheel starts to spin it doesnt matter how fast it spins, the force it applies is the same. Having twice the HP on a spinning wheel gets you no increase in pushing force.

Re: Direct Drive Four Motor System
 

that would be driver. whenever my tires start slipping, i let off on the power a bit till i get my tires gripping again.

Re: Direct Drive Four Motor System
 

//Only read if you care about off topic posting
OK, so I know that by posting what I am about to post I am not following the original intent of the thread BUT this topic was brought up and has enough relevancy for me to justify my single subject post.
//

I have been thinking about the pushing thing for a long time, and I believe it boils down to simple physics. If all robots have the same maximum weight to be pushing on the Normal force, the only other factor affecting a NON STALLING (from lack of torque required to turn wheel(s)) is friction. F=uN if I am not mistaken. To get the greatest force, you must have the greater amount of friction applied to the floor.
*This next part is a really long sentence with many side notes in parenthesis, it is hard to follow, but bear with me.**
I don't care how much horse-power you put into a drive system, as long as there is enough power to not stall the motors (or trip the breakers), which I find is EASILY accomplished with 2 CIMs per side (seeing as how my team doesn't think about stalling with 1 per side), you will win a pushing match with a highest amount of friction with the robot to carpet interface (wheel(s), tread, gum rubber roller ;)....etc.)

Pretty much
If you don't trip breakers and stall your motors, and you have a higher amount of total friction applied to the floor, you will have the great force in the desired direction, therefor win any pushing match.


Thats my long winded-off topic $.02.
-Henry

Re: Direct Drive Four Motor System
 

Henry's post got me thinking about this

the robot with the greatest force (most friction) will win the pushing match

but I have to admit now that is not the end of the story

OK, you are pushing another robot backwards, against their will. There is a good chance your tires are not slipping and his are

now the issue is, how fast are you pushing him backwards? if you have more HP available (more motors on your drivetrain) then you can get that torque at a higher wheel RPM, which means:

if you have superior traction to win the shoving match, the more motors you have, the faster you can push other bots around

and in a FIRST match, time (speed) is of the essence!


my 2¢ :^)

Re: Direct Drive Four Motor System
 

Collin:

I have one pretty significant concern about using direct drive on each wheel - load sharing. In an ideal world of equal force and weight distribution, direct drive isn't a bad idea and it's not a bad idea in the 'real world' either, others will testify that it has worked for them!

However, take for example a robot that doesn't have weight evenly distributed, say it's 70% in the back and 30% in the front. You will need to set your ratios based on the largest amount of torque you'll see - in this case, the back wheels. Since you want to ensure the front and back wheels are spinning at the same rate (roughly, it's an open loop system)... you'll have to gear the front wheels to this same ratio. You will essentially be running slower than you would with a combined motor system.

To put this in a better frame of reference (numbers!)...

Let's say it takes 70 inch pounds of torque peak to turn the the back wheel and 30 inch pounds peak on the front wheel, and your peak current draw is at 10 inch pounds of torque from your motor. You will end up gearing both sets of motors at a 7 (plus some) to 1 ratio because you don't want your breakers to trip in a pushing match.

However, if you had these two motors combined on a single shaft that was linked via chain to two separate wheels, things change. Though each motor would still put out peak torque at 10 inch pounds, their combined torque would be 20 inch pounds at peak current. The max torque this pair of motors would see is 100 inch pounds. Thus, you'd gear the motors at 5 (plus some) to 1 ratio. This is a significant increase in speed (the difference between slow and average or average and fast!!)

Another case is assuming that your robot is lifted by another so it's only on it's back wheel- you now have two motors in the air doing no work, and you have the two rear motors seeing almost twice the load they were geared for - you'll be tripping breakers. That's no fun either!

For the two reasons above, I don't design direct drive robots. I also don't like the idea of creating 4 individual gearboxes, but it's mostly the load sharing benefit that keeps me sticking with motors in parallel. Others do direct drive and it works for them.

Fighting Words: It comes down to a mater of weight, and I think that if you're smart about your chain size (#25) and sprocket materials (aluminum) you'd be hard pressed to say the weight difference is enough to over come the disadvantages. I don't considering creating a good chain tensioning system upfront and spending a few minutes to tighten it every few matches at the first regional to be terribly inconvenient vs. the tolerances and assembly requirements of building 4 robust gearboxes.

Just some thoughts and fighting words,

Matt

Re: Direct Drive Four Motor System
 

And there you have it. Over the years, I have seen SO MANY chain drives that are WAY oversized (we used to be guilty of this charge as well). There are certainly reasons to use larger chain and/or larger spockets, but try to imagine it being smaller/lighter, and then put forward some effort into making that happen.

This past year on our 6 motor drive robot with the very grippy "McMaster tread" and we used #25 (1/4 pitch) chain and tiny 13 tooth sprockets to link the wheels. Only broke one chain (of four on the machine) once ever and that was due to a very rare circumstance. If we can do #25 with six motors, you can definitely do it with four.

All we had to do was develop a good way to get and keep the sprockets inline, and develop a good tensioning system and we were virtually trouble free from then on out.

There is no good reason to link together your wheels with huge and heavy sprockets. We had the most powerful drive setup you can have, and we had pretty much the most grippy tread you can have and we had the smallest sprockets of anyone, and it worked! And it is no stroke of luck. Small chain, and small sprockets, CAN work for you too.

For all of you stuck in the world of #35, please, step into the future. A future full of wonderful weight savings.

If you aren't using #25 chain in your drive system, either it is an 8 motor drive system, or has 16" wheels, or you are doing something wrong. At least just try it and I think you'll be surprised. #25 chain is wonderful.

Re: Direct Drive Four Motor System
 

Guilty as charged; 6 motors with 8" wheels, and relatively small sprockets (for reduction purposes) breaks #25 chain. 6 motors with 4" wheels, and 1:1 sprockets doesn't, because the stress in the chain is considerably less. (Speaking in general terms, for both cases, with the math and experience to back it up!)

Now, if you want to consider the 8" wheels a bad design choice, that's probably fair enough—but it doesn't necessarily mean that there's anything wrong with the chain installation itself, even if it breaks #25.

Re: Direct Drive Four Motor System
 

Excuse the off-topic nature of this post, but I feel it needs to be said… again

Sanddrag

You take every possible opportunity to plug your own drive train. I know I speak for many members of the CD community when I say we are getting a little tired of hearing about it. You built a 6 motor shifter… congratulations. Your design was elegant and very robust, but adding an extra motor in your drive train doesn’t make your robot all-powerful. Try to set an example for the students reading CD and stop bragging about your own drive train.

Re: Direct Drive Four Motor System
 

its a little early in the year to be deciding or debating which drive train configuration is the best

seeing how the game itself wont be announced until early NEXT YEAR! (january :^)

every year presents new challenges. What worked well last year might well be a clunker-bot this year

keep an open mind!

Re: Direct Drive Four Motor System
 

Wise words from Ken.

Re: Direct Drive Four Motor System
 

Things like this I don't just "excuse." Maybe you should "set an example for the students reading CD" and not publicly call someone out as you have in your above post.

But since we've already crossed that threshold, why stop now. (hold on to your seat belts ladies and gentlemen. ;) )

I have every right to plug my own team's drivetrain any chance I get. Just as you have every right to ignore all my "bragging" about the HexaMax.

And actually adding another two motors in the drivetrain does make the robot all-powerful. I am unaware of any robot as powerful as this one this past year.

I try to set an example by sharing my knowledge and expertise with unique systems like the HexaMax. There are teams who would have never attempted building a shifting transmission until they saw ours, and I showed them how it works. So, THAT is how I set an example, not by bragging. I don't come on here for my afternoon cheap thrills; I come on here to help people, and to inspire people, and occassionally get the reverse for myself. If my methods haven't worked for you, I'm quite sorry.

Do you know how many people don't even know that FIRST offers scholarships? Probably a similar number of people don't know that they ARE capable of building something really cool like a shifting transmission. The more exposure to it they get, the more comfortable with it they will become. It is all about exposure. In my mentions of the HexaMax, I intend not to flaunt it as the greatest drive system ever in FIRST. Clearly it is not. I use it to "raise the bar" for all the other teams. Why did we build a 6 motor drive? Because we knew no one else would. Simple as that. Now it has been done, and it has been refined. So maybe next year, there will be multiple teams that do so. I now leave it up to other teams to take it above and beyond. A six motor shifting crab drive, a six motor 3 speed, a six motor shifting walking robot, a 6 motor drive that weighs 12lbs, heck, I don't know. But I believe my design inspires others to strive for more (as we had) in their future designs.

Now, as for the credibility of Holtzman's post, I remind you that it comes from someone that chose to buy a gearbox instead of building one. Not that their's anything wrong with that; it is a quite strategic decision. However, it does make for an interesting conversation point in the sense that I don't think buying a gearbox as opposed to building one provides anything to brag about. This is where our two teams differ. We have a drivetrain that is worthy of bragging about whereas I believe they do not.

Re: Direct Drive Four Motor System
 

Sanddrag,
Although your team did pull of an interesting drive train, there are plenty of other teams that have as well. Many even more impressive than yours. I can always post about how wunderbar my drive trains are, and how awesome the teams are I have built them for are. For example, last year's drive train on 1072's robot was seen to push two opposing robots at the same time, in low gear. We had amazing traction and huge torque off 4 CIMS and six skyway wheels rethreaded with wedgetop, and each transmission was 8 pounds flat. Not too many people can pull that off. However, there was a time for discussing this drive train, and I took full advantage by posting pictures and talking about actual performance, not just saying "how good our drive train was" or "it never broke"

When bragging about a drive train, use numerical facts. 8 pounds. High/low speed, minimum pressure it took for shifting, torque it took to slip the wheels, etc. Make your post relevant to the discussion. Also, do not assume that just because you have 6 motors, you can outpush anyone. I have seen teams using 2 drills (a while ago) effectively bully a robot with 4 motors. Or six.

Although I personally find many areas where your drive train could see improvement, I am not here to diss your drive train. It worked fine. I am here, however, to "diss" how you constantly use your one Hexamax drive train example to justify how six motors two speeds is the way to go, and how people that use any other system (like #35 chain) are doing something wrong. This shows to me that you may be a little narrow-minded, not willing to try other things, things you may think are unorthodox. While I have never used #35 chain for drive train, I have used direct gearing to the wheels, and plenty of other things you may think hideous.

As for influencing other teams, you may be giving teams a false impression of your drive train by always bragging about it. True, you have the right to. But should you? Not everyone else brags about their drive trains, I don't. Because I know that my drive trains are only good for a very select few teams, and they will make their own decisions about what to make. You don't need to always tell people how good your drive train is. For the people that saw it in action, let THEM chose if it worked well or not. And let THEM decide if they want to base their designs on yours. Pounding it into our heads isn't going to help is, it may mislead us.

We aren't trying to compete for who's drive train is copied by rookie teams the most. It is a bad idea to think your drive train is so good it can apply to anyone. As you see, the kit drive train is very generalized, and was made by engineers to serve the purpose of a drive train anyone can use. I do not think "sanddrag's hexamax" can be compared to the kit, nor can it be advertised like the kit. Your drive train worked well for you. It would not work well for anyone who tried it. The kit was designed to work well for anyone. I can always say my swerve drive from my sophomore year in high school was good. But I think it sucked, it was a terrible design and I made a million improvements during the past few years. It would be a disaster for some teams to try it.

My point is, we can do other people on Chiefdelphi forums some courtesy and DISCUSS our drive trains, not brag about them. We can not post things we have posted in dozens of other threads. We can at least admit to ourselves that our own designs arent perfect, simply because we can always improve on them. We can humble ourselves and not think we have made the ultimate, full proof drive train. Because remember, we may be wrong about some of the things we say here on Chiefdelphi. #25 chain has been known to break, 2 speed transmissions are not always so great, and 6 motor 2 speed gearboxes are not so impressive when they weigh 12 pounds, because they have been known to weigh 8. Just look at my drive train for team 100. You don't see me bragging about how amazing my six motor drive is, do you? Anyway... we should all just be humble, courteous, and act like gentlemen (or ladies) on these forums, and not fill it with yakking about who's drive train is better. My two cents.

Re: Direct Drive Four Motor System
 

Sanddrag,

First off, Tyler has never bragged about our drivetrain. He's a young man, who knows much about respect and humility. He would never would come here and make arrogant boasts about the drivetrain he helped design. That's not the way he, or our team operates.

As to your comments that our drivetrain isn't worthy about bragging about because the gearboxes were purchased, that is true we did buy AM shifters. This does not mean there wasn't any original engineering in our system. Your comment demeans all the hard work put into our design by our students and mentors. I don't believe that bragging on CD is in good taste, nor am I that desperate for attention to do so. But I do take pride in my team's design and work, as we all should be.

I urge everyone to be proud of their own designs. We all should take ownership of our work. I also urge people to share their designs, in hopes of inspiring other as Sanddrag mentioned. That being said, there is a line between sharing/explaining a design and repeatedly glorifying one's design in a self-admiring way. Let the design speak for itself. There's no need to shove it down anyone's throat. Follow the examples of people like JVN and Ian Mackenzie. These guys have designed amazing drive systems, and made the designs available to all. Do they come on CD and plug their design everyday? No of course not. Why? Because they're above that. Their egos don't need constant stroking, so they have no reason to resort to bragging.

Humility tends to take people places, pompous boasts tend to get people left at home by themselves.

Re: Direct Drive Four Motor System
 

I'd really like to point out that this isn't a very credible way of arguing the point. After all, are we saying that ChiefDelphi had nothing to brag about when they first stuffed their robot full of DeWalts?

More to the point, Simbotics in 2003 and 2004 definitely had something to brag about, using those criteria—but should the fact that the rest of their 2005 drivetrain was innovative, succesful, and built and designed by the team be overshadowed by the fact that they bought AndyMark's products?

Sometimes, you have to defer to the convenience of the prebuilt system, and sometimes you need to do it yourself, in order to get the job done. You can't, however, categorically state that all prebuilt gearboxes are less notable than the team-built ones, after all, it's not hard be proud of an off-the-shelf part that works well, as opposed to a custom part which doesn't.

Re: Direct Drive Four Motor System
 

actually, engineers prefer to use off-the-shelf components

if you have to redesign the wheel (or the transmission/gearbox) to make your robot come together, you have not done as good a job, as someone else who is able to put together an effective robot with off the shelf components.

from every perspective, custom designs are expensive

another 2¢ from Ken :^)

Re: Direct Drive Four Motor System
 

A Ferrari is very expensive, but a gokart works almost as well, so I'll just buy that instead?

And as for redesigning the wheel, I direct you here

We did better than off the shelf. Did we have to? No. But we wanted to and that's what makes us different.

Re: Direct Drive Four Motor System
 

If you're on a go-kart track. YES!

I have no problem with people pimping their designs. I know that when someone asks me for help on a gearbox, the first thing I do is send some examples to talk around; and yes, they are examples of my own design.

Where I have a problem, is when people repeatedly disparage those teams that designed simple systems, with the goal of elegant completion of the design challenge. You keep badmouthing teams that didn't design something like your system. Look, I'm sorry 229 didn't build a 6 motor shifter. We've had the design since pre-season 2004, but... WE DIDNT NEED IT FOR THE GAME!

This is terribly off-topic; and I appologize.
I suggest everyone gets back to helping Collin.

-JV

Re: Direct Drive Four Motor System
 

I think it makes them pretty credible.

After all, they were smarter than you. They paid $300 for something that accomplished the game goals just as effective as yours ever could have, seeing as pushing power was never needed, whereas you spent six weeks designing and building a drivetrain that's living in 2002.

While you were off adding extra motors, they were busy building one badass robot.

Re: Direct Drive Four Motor System
 

Actually, they built four.

Re: Direct Drive Four Motor System
 

+1 if you count the prototype drive base.

Re: Direct Drive Four Motor System
 

Actions speak louder than words (said or typed) and a winning season speaks for itself. Whether you custom built every piece or assembled from "the shelf," having a successful season allows your performance to speak for you. Many teams have great features/machines, but arguing about the best is in many ways missing the point.

Back to the true topic at hand, I have a question:

Is it feasible for the 4 independent motors to be electronically controlled/programmed to have the same output speed?

Re: Direct Drive Four Motor System
 

I fail to see the point of bragging and insisting who is better than who. Are they supposed to make people feel better about themselves or gain respects from others?

There are plenty of opportunities to prove yourself in this program, the least of which are the myriad technical awards, the chance to win regionals and Championship, not including the more prestigious Chairman’s and Engineering Inspiration awards, and the ultimate price of FIRST: the inspiration and motivation of students into Science and Engineers, as well as just being decent human beings. I would assume those are the places to compete and strive to be the best, not the brief moments you spend so much around here.

In a community that boast inspiration above all else, the evidence of which is shown here: http://www.chiefdelphi.com/forums/sh...threadid=40485 , I am very disappointed that people are spending so much time on such trivial issues. I suggest you reexamine your reason for participation in this program if you intend to continue these kinds of discussions.

Inspiration is a way of life, not a show in front of others. Quality and excellence come from within, from what you do, from who you are, not from what you look like.

Now please, go have some meaningful discussions that will inspire us all.

Re: Direct Drive Four Motor System
 

Y'know, I'd fully intended to split this thread in two -- one that focuses on the initial question at hand about direct-drive and its merits and a second that focuses on... well, I'm not sure. I couldn't think of a thread title that was less derogatory than, "Fighting over when, how, and why you should mention your past work, who decides if it's worth mentioning at all, and discussing why we feel compelled to tell people it's annoying when overdone -- repeatedly"

The point's been made, I think, and I'm certain that your criticisms of Sanddrag's behavior have been duly noted. Do I need to make y'all play dumb team-building games that make you say things like, "I liked... I didn't like... I wish you would have..."? I'll do it.

Re: Direct Drive Four Motor System
 

any drive train that can allow your robot to move around the field in a reasonable manner, be very reliable, and allow you to complete the game objectives is a good drive system in my book. Just my 2 cents
like Mr. Bill Beaty says: "Drive train, Drive train, Drive train, Drive train"

Re: Direct Drive Four Motor System
 

Absolutely, but it requires feedback, such as an encoder, resolver, tachometer, and a good controls algorithm, especially to control the speed of four different axis. However, I'll ask another question for you:

It is worthwhile to electronically control the speed of each individual tire in a closed loop fashion on FIRST robots?

This is an interesting question, and there are a few distinct and divided groups on these forums about drive wheel feedback / controls in general. There are some very adamant people who swear up and down that closed loop control (position and/or velocity feedback on the wheel) is critical, others who deem the resources / benefit are too small, and still others who ask, "Closed loop? What's that?" I consider myself to be in the 2nd group.

My thoughts are merely, "Can't a good driver with some practice on the robot before it is shipped 'aim' an open loop drive system 'straight enough'?" The advantage of a closed loop system is pretty nice if you have two pairs of motors controlling two wheels on each side - you can essentially ensure that when you push both joysticks full forward, that the robot will move straight and not veer off by say up to 10 degrees or so as it might in an open loop system. Driving is more intuitive, this is a very good thing.

Correct me if I'm wrong, but this thread has sort of now technically spun into a suggestion about a 4 wheel robot with independently driven wheels, each with an independent gear box, as well as a closed loop feedback setup on each axis to ensure that the wheels all spin at the same rate.

Others may disagree, but my opinion about this can be said in a single word: Overkill.

Matt

Re: Direct Drive Four Motor System
 

Back to the main topic,

Both the times I have done direct drive to four wheels with 4 motors, I used a very similar setup.

I had a gear bolted to the wheel and the wheels rolled freely on bearings and shafts. The gearing was as follows: small gear on the CIM output mates with a larger gear, which is on the same shaft as a smaller gear. The smaller gear then mates with the larger gear that is bolted to the wheel. EX: CIM speed of 5342 x two 12:40 reductions = 480 rpm = about 12 feet per second on 6" wheels.

The reason for the two reductions being the same was so the first gear (on the CIM, 12 tooth) and the last gear (on the wheel, 40 tooth) could be on the same rotational axis. This proved for a very small drive train, and if you mess around with the shafts and gears, you can pull it off with very few parts, meaning less fabrication.

My reason for using a gear on the wheel itself is so it can act as the final reduction, instead of having extra bearings and shafts to have that reduction inside the transmission, only to run a shaft out to the wheel.

I really like the 4 wheel 4 motor independent direct drive system, it doesnt clutter your robot with drive shafts or chains, it makes everything modular. Also, fabrication is a blast, you're making 4 of the same part for the drive trains, and the gear reductions arent that complex or anything. No CNC required (unless you have interesting cheeseholes) and I would say this is a really reliable system, very low maintainance if done right.

The only way you can go wrong is if you use a face width that is too small for the gears. Then you start snapping teeth. I used .375 on all the gears, it worked quite fine. Also, it is a must to have your wheel on stable bearings and shafts, because if the gear on the wheel and the gear on the transmission misalign, the teeth get worn down or they snap. And the last rule of thumb, use loctite! When direct driving like this, there tends to be more vibrations through the drive train (it is usually dulled by the chain in chained transmissions). These vibrations make set screws and bolts back out and your drive train to misalign.. etc. Keep your drive trains screwed together!

Re: Direct Drive Four Motor System
 

In my opinion, answer is: Maybe! But before you go piling on a whole bunch of complexity, you should try to design something simple that’ll go straight all on it’s own – build it – test it – if it works, you’re done.

That’s what we did with the above example of our experience, as Collin was asking, with four-wheel direct drive. It was a low risk experiment for us. The CIMs were known to be unbiased, and they gave us four. The parts were water-cut from scrap in about two hours – including the welding jig, which made for 30 minutes to weld. The DeWalts cost $21 each. The wheels cost $17. So, with a $200 investment, the kit frame, and some assembly, we had it on the ground in two days. It went straight.

OTOH, suppose that this year’s game has an autonomous that is worth doing and requires precise positioning… Who knows! Except that one thing we’re sure is we’ll try to keep it as simple as we can.

Re: Direct Drive Four Motor System
 

You're missing something relatively important in your thinking here. Yes, a good driver can effectively be the element that closes the loop, but only when there is a driver at the controls. However, a reliable autonomous routine pretty much requires closed loop software control of motor speed.

Re: Direct Drive Four Motor System
 

I'd qualify that a bit with "an autonomous routine that has a decent chance of screwing up."

If you're just knocking off the hanging tetra, you can go open-loop (as the only thing you have to do is drive forward a smidge and raise an arm). There's very little chance of this screwing up, as you're not going far, and the hanging tetra is a big target.

Now consider the 10-point ball from FIRST Frenzy. Tiny target, really far away. Break out the encoders, folks.

Re: Direct Drive Four Motor System
 

Please don't tell our robot. We took the encoders off the drive wheels and mounted them on two boggie wheels about 6 inches each side of dead center - got better distance measurement that way. Direction was not a problem. Ask the folks at Rah Cha Cha or Novi - it would cap the center side goal dead solid perfect, or, with the gyro telling it when to stop turning, it could snatch a tetra from the autoloader and hold it over the center goal. The motor control was binary - on, then off.

Re: Direct Drive Four Motor System
 

Collin:
Sorry I didn't see your post until just now.

S.P.A.M used 4 CIM's, 4 NBD gearboxes, and 4 "half tank treads" last year, and we loved it. We'll probably go with a similar design this year if it fits the game. It's the fastest we've ever assembled our chassis and drive system. The biggest drawback was the cost of 4 Breckoflex belts; they don't get much cheaper even though they are half the length.

side view

top view

Sorry, these are the best pictures I could find on our website. We drove the center sprocket on each tread with the output of the Dewalt gearboxes so we theoretically had 4 wheel control although we just ran them in pairs like a full tank tread. The treads are slightly angled down to the center to give the same "boogie wheel" effect that allows turning without dragging the treads.

We have always build our own custom gearboxes and other than the omniwheel drive system we built in '04 we have always used tank drive, but with 4 identical motors this was the first year we split them up that way. As has been posted, this system seemed more powerful than Fluffy. Credit of course goes to Gary and James Jones (James was a featured presenter on drive trains at the '04 FIRST conferences).

Re: Direct Drive Four Motor System
 

On a similar topic, our six wheel "direct" drive originally started out as a 4 motor/ 4 wheel design, which we then expanded to six wheels, and used driveline to connect all of the wheels. Upside, no chin/belts/tensioning . . . Downside? Weight, it was fairly heavy, but it worked well, and we were able to add encodes to get a good idea of where we were. Not quite as modular as a moter per wheel design, but we did it with just the 4 cims, and it did work quite well.

I would strongly encourage teams to try out more designs which use direct/line drives instead of chain/belt.

P.S. here is a picture of the front 4 wheels of our system: http://www.chiefdelphi.com/forums/sh...highlight=1097

Re: Direct Drive Four Motor System
 

Ok, there is all this talk of "tripping breakers" and such... So I ask what does it take to trip the stock breakers?
Also, because last year was my rookie year... I only have experience with one drive train... but I don't remember all these sorts of problems to do with it.
We had 2 stock trannys, with 2 cims per tranny. 4-wheel drive with the stock skyway wheels, i.e. your standard 4-cim 4-wheel drive slip steering set up.
We didn't ever trip anything... I pushed people around quite a bit, i flew down the field, and I always drove strait. Oh, and we never broke a chain.

Somehow we where amazingly lucky and evaded all of the aforementioned problems... if anyone knows how, I'd like to know!!!