slow Drive system
 

We're a rookie team, and so far we are working on making a tank drive system with just 1 of the cim motors on each side. gear ratio of 1:3 . Is this not gonna be enough? I'm seeing alot of other teams using two motors together, or a transmission.

Thanks,
Nerdlingers

You will be slow, but you should have lots of power.

P.S. dual motor transmissions add weight, and complexity it is a good choice for most rookies to go with a one motor non shifting drivetrain
[edit] I didnt see that you said 1:3, I automatically assumed it was 3:1. Anyways, yeah what Jimmy said


Cory

Uh, shouldn't a 1:3 gear ratio make the output rpm greater than 12600, assuming 4200rpm at the output shaft of the motor?

3:1, on the other hand, would equate to approximately 1400rpm, still assuming 4200rpm.

Last season, with the Atwoods, we had two gear ratios. The high speed selection was geared at 10:1, and the high torque selection was 100:1. We moved at a nice 12feet/sec, I would estimate, in high gear. It moved like a snail in low gear, but boy was it hard to stop.

<edit>
I'm leaving the post as it was, but I'm just acknowledging that I am dumb, and that I was thinking in terms of rpm, not teeth per gear.

Thanks to M. Krass and Jon Lawton for clearing that all up for me.
</edit>

don't the cims only produce 2.2 Nm of torque at stall, and you will not reach due to your 40 Amp limit, so you will only have maybe 6 Nm of torque on either side . . . .

I'd say go slower.

Actually you have them reversed. A three to one gear ratio would triple the speed of the robot and a one to three gear ratio would increase the torque of the robot by a factor of three. I believe your confusing the speed ratio and the torque ratio which simply enough are inverses of each other.

For the most part, there is almost always a team that is slower and/or less powerful than you.

You shouldn't lose any sleep over it;)

Lord Nerdlinger, how big are the wheels you are planning on using?

Because the way i am seeing it assuming 4200rpm output, geared 1:3 puts you at 1400rpm on the wheels which is 23.3 rps multiply that by the circumference of your wheels.

If you are using 6 inch wheels that gives you a top speed of 36.65 fps which is way too fast.

I would recomend having a speed of about 10 or 12 fps. Which would mean you would have to gear it 1:10

We are using the 9" neumatic wheels, with the 1 gear on the motor shaft and one w/ 3x the teeth on the wheel shafts. I thought the cim motors were 1500 rpm? so that would make the wheels only 500 rpm, right?

I think the drill motors in high gear are ~1500 RPMs

I thought the CIMs ran it up to about 5000 or 5500 or so.

Yah, reduce it more, way more.

Yes, the CIM motors have a max rpm of about 5500.

Using the CIM motors geared 1:3 with the 9" pnuematic wheels will give you a top speed of 55 fps,

That is way too fast!

I would recommend gearing 1:10 and using the 6" skyway wheels, this would give you a top speed of 11 fps, much more manageable

Our drive is using 2 CIM's and we have them at a 10 to 1 "gear" ratio...
We are very fast, and we have torque to back it up...

Whatever ratio you do decide upon, please remember to make sure that it puts out enough torque at 40 amps to move your robot.

the breakers are different this year - i think they're all the way up to 120 amps

Hey. Very interesting. CIM is being sued by Motion Systems ( a New Jersey Corporation) beacuse CIM is supposedly bringing in cheap Chinese knock-offs of Motion Systems wheel chair actuators. Read all about it at http://www.levinhawes.com/1/pr/Motio...PrelimInj.pdf.

First, the CIMs are 5500rpm, not 4200. http://www2.usfirst.org/2003comp/Specs/Chiaphua.pdf.

Second, the breakers will not let you get 120amps for a single motor. That is limited to 40. The 120 is the total number of amps the entire robot can draw.

Third, you need a MUCH better reduction than 3:1. With 9" wheels, you probably want a wheel speed of approx 250rpm. This can be accomplished very easily be using the gearboxes FIRST provided with the drill motors in low.

Fourth, until you get a few years under your belt and have been to a few competition to see what works on what doesn't, I wouldn't even recommend attempting a two-motor transmission. Along those same lines, when you do go to a regional, assign at least one person to go talk to other teams and see how they did their drivetrains. It should give you some good ideas for next year.

Hmmm
 

You know tank treads arent a bad Idea because you will have a O degree turning radius. but I really wouldnt only use 2 Cim's I would use 2 Cim's and 2 drills at the same speed. Err I dunno if that would work, but I was always a huge fan of 2 wheel rear drive with 2 Cim's with 2 Pneumatic shifted gears.

But I bet most rookie teams will try to go direct drive with the drills. I always use a multi speed tranny with any motor!

P.S. Anyone have a good design for a 3 speed thats Pneumaticly shifted, I can only manage a 2 speed in the given space. And Im also having a down shifting problem its a lil rough, but thats expected from helical gears right?

According to that paper, the freespeed is 5342rpm, but it's 4356rpm under normal load. 4200rpm is a conservative estimate.

No....do NOT use a 3:1 reduction and call it a day

We're using similar wheels and I'm reducing the CIMs by ~20:1

Yay, we finished mounting the motors to the 5/8" coupling gear shaft and found that we could easily hold the shaft in place and trip the fuse, so we def need more torque. 1:20 sound excesive, I'll look into a 1:8 ~ 1:12 range.

Thanks

Rather than guess, use this White Paper as a starting point.

Then, take the information you learn about speed and apply it to torque and see where you end up.

Math is better than guessing. (Only marginally.)

I think you have it reversed, according to dictionary.com here is the defenition of "gear ratio":

The ratio of the speed of rotation of the powered gear of a gear train to that of the final or driven gear.

Lord,
I have to go with everyone else on this. The gear ratio sounds too high especially with the 9
' wheels. The chalupa motors are strong but the gear ratio will allow you to go fast only if you can get the robot moving. That is a big "if" since the gear ratio will provide so little torque. 8-12 feet per second is a good guide.
As to the electrical draw, the 40 amp breakers are the dominant factor and I would predict some heavy action on their part with this design. Turning will be your greatest draw.

Like I've stated before, Our Team has (somehow) managed to get 15 feet per second with a 10:1 ratio using the 2 Chiphua Motors, and we still have loads of torque. We aren't a speed based robot...
Anyway, OUr drive is really nice and (if only) if chiefdelphi had a section dedicated to video clips, I'd show you our drive in action!
I might be able to get a file server and post a link in a while...
Anyway, we Haven't had any issues with it, and it works great!