3 motor drive train
 

I was wondering if teams will start going to 3 motor drive trains since first made it sooooooo easy to have 2 motor drive trains.

Re: 3 motor drive train
 

Why would you use an odd number of drive motors?!

Re: 3 motor drive train
 

3 per side. 6 Total.

Re: 3 motor drive train
 

i think he means three motors per side, totaling six motors. i guess you would add the fisher price motor somehow. i dont think it would be worth the trouble. in that case, you might as well design it from scratch, which most teams are already capable of.

Re: 3 motor drive train
 

why not

Re: 3 motor drive train
 

yes i mean 6

Re: 3 motor drive train
 

You'd need a whole mess o' differentials and torque converters and all sorts of nasty stuff to make an odd number of motors work...

Re: 3 motor drive train
 

not really just the right gear ratio

Re: 3 motor drive train
 

Says who? all you have to do is match their speeds. Plenty of teams have done it. 45, 494, 188, etc.

And there's definitely an advantage. If you figure out how to keep the FP's cool, and not draw a ton of current with them, you've got a 5th and 6th CIM in your transmission, for all practial purposes

Re: 3 motor drive train
 

i think changing gears on the fly is over rated.

Re: 3 motor drive train
 

It's surprisng how many people post without reading the whole thread. Phrontist is talking about an odd number of motors total. The thread starter meant 3 motors per side, 6 motors total. An odd number of motors total in a normal skid steer design would definitley be no easy feat.

As for 6 motors, I do not expect a great increase in the number of them. First of all, I don't think the gain is that great because every 4 motor robot i have seen loses traction before it puts too great of a load on its motors. Also, if you use your FPs, you aren't left with much power for your arms between the remaining motors.

Re: 3 motor drive train
 

In my opinion it will be better to have 3 motors on each side, however that just gives you more stuff to worrie about and more things that can go wrong. I'll rather stay with two reliable ones, also the FP motor burns easily.

David

Show us your numbers...
 

Decisions concerning the number of motors in a drivetrain (2, 4, 6, 8, 10, 12... whatever!), the number of speeds in a drivetrain, and what speeds to gear at, are engineering design decisions.
These decisions are dependant on a robot's gearing, wheel traction and many other factors.

The output power from the motor must be modified (via gearing) to be "optimized" to achieve desired performance. Sometimes more power must be added (more motors) and sometimes the gearing must be modified for different tasks (multiple speeds). There are many different definitions of "competitive performance". There are also many different combinations of drivetrain components tha can be used to achieve these levels of performance.

Note: for more information on drivetrain physics, shifting gears, or multiple motor drivetrains, please click the *search* button.

To imply that this decision can be universally made for all drivetrains, without showing any calculations
(i.e. "6 Motor drive is stooopid. Long Live 4-motors...") is foolish.

I urge everyone: keep your opinion to yourself; unless you have some calculations to back it up.

Thanks,
John

Re: 3 motor drive train
 

Wouldnt that be a 6WD?

Re: 3 motor drive train
 

well wouldn't it be a waste of power, as well as weight, because, the weight of the gearbox that FIRST gave us this year is heavy, imagine adding another moter to, as well as the gears needed to get the ratio and the speed right. and the power part, well six motors drawing the power all at the same time, which 2 motors could do, or even 4 is, well alot, leaving little power for the arm, but it might work if you are a pushing robot only. also the chances of something breaking or screwing up are greatly increased. which is always bad in the competion.

Mohsin
Team 772
If it aint broke, get INCENTIVE

Re: 3 motor drive train
 

Im going to go out on a limb here and guess that with efficient weight reduction, you could make a 6 motor transmission that weighed the same amount as the current kitbot one, or slightly more. It's all a question of whether it fits the design criteria of your team's robot.

What do you mean by power? Draining the battery? sure, it does, but any team that makes a 6 motor drive will have considered that and deemed it an acceptable penalty.

You don't need motors for arms, you can use pneumatics, and there's still multiple motors left over if you use 6 drive motors.

Re: 3 motor drive train
 

Would a 6-motor drive train offer any significant advantage over a 4-motor? It wouldn't be any faster, but you would get more torque. But wouldn't you also need some hi-traction wheels to take advantage of that torque? And then there's the extra weight...

So my question is... is it worth it?

Re: 3 motor drive train
 

You can have a higher top speed, with more torque at that speed than a drive system with fewer motors would have.

Re: 3 motor drive train
 

Or some high traction treads :D . BTW I would like to thank JVN personally for creating his spreadsheet motor calculator. It helped me tremendously in designing my teams gearbox this year. John, i'll be shaking your hand at one of the competitions, good work man.

Re: 3 motor drive train
 

Please everyone read JVN's post previously in this thread. It is all in how you gear it. Very few conclusions about drive systems can be made in general. You can go much faster with a six motor drive, you can much slower. You can have lots more torque, or a lot less. Adding more anything (motors, gears, etc) to a drive system doesn't amount to any generality other than more weight, but even that is debatable.

If we are looking to discuss a specific drive system, lets do so but lets refrain from making such general coments as "it wouldn't be any faster."

Re: 3 motor drive train
 

remember the CMI motors have weight, and if you use the other motors, the gears would have to use weight, but as for pneumatics well if you want to use them a lot, a compressor would be the best choice, but it adds weight and drains more power from the batteries, we found that out last year. and i will agree with you in the desigh criteria, whatever you wnat and think best suits your needs, build it

Mohsin
Team 772
Civil Engineers = Tree Huggers

Re: 3 motor drive train
 

From what I can tell (since I've never built a 3 or even a 2 motor transmission) the only thing to gain from a 3 motor transmission would be to push hard at high speed. After seeing the coefficient factor of different wheel types, your going to be hard pressed to keep any wheel/tread from breaking loose with 4 motors. I may be off ( I did some math, but I don't completely trust it ) I think if you took the kit bot setup and also used the highest traction wheels you could find (what's been used in the past anyway, unless you've got some new space age material you need to tell me about) - all 4 cims - 21-28 sprockets - You're still going to be able to break the wheels loose in a pushing match. That's without shifting - plain ole kit gearboxes. So, putting another motor on there... If you wanted to break your tires loose while pushing at 5'/s maybe? OK but why? Usually your just trying to hold some ground, not send an opponent into orbit. Or maybe you want to go 20'/s but you could forget about controlling it. Maybe you'll get close to stall if you increase your weight with a bunch of tetras or using the opponent bots weight to leverage it. Anyhow, like John said - I think most of the hype on 3 motors is just that - hype. Do the math and you'll see. I know of a team that seriously knows what they're doing, and they're considering 1 cim/side , 3 speed NBD's and tank treads.
Although we did modify the kit gearboxes to take the FP motors (and lightened them up), just because we could. They haven't been run with 3 motors yet, but it will be fun just to see how they perform. We aren't planning to use them for our competition bot though. If anyones interested in how to do this it's pretty easy. You need to mill that fat 50 tooth in half. Then you can put a 60 tooth 32 pitch gear on the end of one of the cim shafts. We welded the 14 tooth to the 60 tooth, then key it back on the cim shaft. Then you penetrate the other side of the gearbox for the FP to mate with that 60 tooth. It took us 2 days to do it. Maybe later in the season I'll host a vid of our comp bot pushing the 6 motor practice bot around :D

Re: 3 motor drive train
 

well on a similar note. 118 is actually going with only 3 chips powering all 4 wheels. Although they arn't coupled, you still can say it's a 3 motor drive train.

Re: 3 motor drive train
 

Care to enlighten us on exactly how this will work. It sounds very intriguing. :)

Re: 3 motor drive train
 

If you want to be able to push and do burnouts while using "tall" gearing, using a Fisher-Price on each side along with the CIP's would give you an additional 50% or so in horsepower. Of course, doing this could get you dangerously close to tripping the 120A breaker while doing high speed pushing.

Re: 3 motor drive train
 

well its a swerve/crab drive and only three of the wheel boxes are powered by chips. The forth wheel box just turns via the steering motor (separate from the drive motors) and drags along for the ride.