Problems with robots and ideas needed

Hi I was wondering about my teams robot and how fast it moves. When ever we try to move with a torque design for speed we can turn (12:36) which is one wheel , but when we tried switching it to speed it would not turn (36:12) which is on one wheel. We have a 4 wheel drive robot.
We are using the large wheels.

What is happening?

Why doesen’t it turn?

What is a really good gear ratio to use to be able to move really fast and be able to turn still?

Also should are team have used 6 motors for driving?

Also I would like to know how many motors does it take to lift a conveyor belt arm the strongest and quickest?

Lastly what is a strong but speedy gear ratio for lifting a conveyor belt robot?

The vex motors can output a given amount of power. As you get more speed, you lose torque and as you get more torque you lose speed. It can’t provide infinite amounts of power so you have to choose between torque and speed.

It won’t turn because you don’t have enough torque. The way you describe it, I’d assume you don’t have omni-wheels. The large wheels have pretty good traction and don’t turn very well when four of them are used. You’re very low on torque when you try gearing it 3:1.

How fast you can move depends on how many motors you have and the weight of your bot. 1:1 is about as high as I’d recommend with large wheels unless you have omni wheel.s. With omni’s I’d go with a 60tooth to a 36 tooth, 5:3

Our bot this year had four motor drive and the bot weighed in at just under 15 pounds. We lost most of the pushing matches we went into but we were fast enough to compensate

The length of your arm makes a huge difference in how it should be geared. Whether or not you have counter-balance or counter-weights changes it too. You’ll have to experiment. I’d recommend starting at 1:15 by compound gearing 1:5 and then 1:3

Good luck

My team has found out that using omni wheels in the front and gearing the back 5:3 on a 5" wheel work very well, because the omni wheels let the front slide when it turns and 5:3 is a good speed, because it is about as fast as a regular driver can easily manage.

254A used a 4 motor drive, but a lot of the other 254 teams used a 6 motor drive. We haven’t done enough tests to determine which is better, but we do know that there isn’t a significant jump in power between a 6 and 8 motor drive on a 15 lb robot.

We used 1:7 gearing for our arm with 2 motors for all but one of the robots. This seemed to work really well, although you could probably get by with a 1:5 gear ratio if you make a light arm, or counteract some of the weight with rubber bands or pneumatic tubing.

For Clean Sweep, I think that the focus is going to be on a fast arm and intake, and not so much on a fast drive train, because the field that you are going to be is effectively have the size as last year’s and you don’t have the platform to avoid.

I was thinking of a 4 motor drive with the other 6 motors used for an intake and an arm or a dumper-type thing.

I was considering two drive motors in my annual “mentor’s demo robot.” With no need to push or be 417-fast, I would go with the fewest motors that can drive the robot at 2fps or so.

This year needs no pushing so a 4x omni wheel robot is quite practical for maneuverability. Since manipulators can’t be exothermic-small this year, more motors may have to be dedicated to drive in order to move all the mass.

How about five 4" omnis like the Robo Wranglers? I’ll see if I can dig up a picture and post it. You could then do a drive train with three motors, and still be able to strafe down the length of the wall. Here’s a link to 148b’s Elevation robot with this drive:, although I suspect they use five motors for the drive.

We built a prototype scissor lift launcher today, and it worked alright. Without the addition of pneumatic power(no bike pump at school today), it managed to shoot the small ball 6 feet into the air and 3 feet forward, the football about 4’ and 2.5’ and the large ball about the same. While it remains highly impractical as a scoring mechanism due to the dubious build quality, enormous flexing of metal and inability to shoot with consistent launch power, it isn’t bad for the first day back.

You might also want to be like some of the robots at Dallas that had four omni’s in a square offset by 45 degrees from the rest of the robot. I don’t know how well it worked, but you could look into it if you don’t want to use 5 motors on your drive, but need more than just 2 motors for your regular maneuvering (forwards and backwards).

How can you make a robot turn good and move fast with 4 motor drive. While only using large and medium wheels but not the omni-directional ones?

Keep the robot light, so the wheels don’t sink into the ground. Use four wheels instead of six, make the drive base as wide as possible, and don’t make it too long. Also use wheels of the same size, because if you have a 5" wheel and a 4" wheel at the same gear ratio, they will be going at different speeds.

This is called holonomic drive, and at least two of these robots did very well. 1899 was an alliance captain on Technology, and 508 was part of an alliance on Technology that made it to the finals before stripping a gear in one of their drive motors.

What do you mean drive base.
Please give more idea or pictures of good drive designs and ratios.

Search for the “vex speed chart.” This is a great place to start.

How to move really fast with 4 motor drive with no omni-directional wheel and still turn really good?

Post 10 had your answer – a wide robot with a short length will turn well. This is where the FRC “West Coast drive” concept comes from, too. In this design there are six wheels on the robot – all driven. The center wheel is mounted slightly lower than the ones on the ends, so that only four wheels are usually touching the ground at one time. This has the effect of a robot with a very short wheelbase (great maneuverability), that won’t usually tip over frontwards or backwards because the other two wheels are there if the robot starts to tip. Here’s a link to a Cheesy Poof FRC bot showing a 6-wheel-drive system in action:

Check out this document for an overview of drive bases (including pictures – large file; be patient).

I know this is in the wrong place but idk where to go to make a new post so heres my question.

In Clean Sweep what do u think is better speed or torque?

The reasons are because right now we have speed. Are gear ratio is 3:1 and have only two motors moving the whole robot.
Right now the robot cant move so wondering why and think is ecause its to heavy.
So are instructor says now change to torque because you dont have to move alot of places this year in clean sweep since its half field. But I think thats wrong.

Do u think if we have 4 motors moving are robot with the same gear ratio will it move now or better. Finally this year though are using omni directional wheels so we dont have to wory i think.

I want to say something to my instructor but dont have the facts please help me.

Here is a link to show u are robot are number is 803 during this video
The match number is 135.

(BTW yes this is from panpaficic so people who were there should remember tthis)

Trading speed for torque will make a heavy bot move (slowly).

Adding enough motors to barely make a heavy bot move will probably cause the motors to overheat before a match finishes.

A bot heavy enough to sink deeply into the tiles will make motors overheat quickly when you turn the bot during matches.

Needing to add several motors to a bot’s drive train seems to be a sign of a design that needs to be adjusted.

I recommend speed and accuracy for Clean Sweep. Quickly getting balls and quickly dumping them through holes in your opponents’ defense is a sound strategy.

Too much speed makes a robot hard to drive, especially when you want to drive precisely to pick up balls or maneuver around balls/allies/goals.

Pushing (needs torque) mostly occurs when a defender gets to the wall as fast as you do, and they try to prevent you from dispensing balls.


dont get what ur saying please explain

I think what gblake is trying to say, correct me if I’m wrong, is that you need to find a nice balance.

First off, I do think that 1:3 is speed gear ratio, meaning 1 turn of motor = 3 turns of the wheel.

Secondly you cannot expect to run a robot with that kind of reduction with two motors. Even a medium weight robot needs 4 motors when using that reduction, and you’re robot is heavy. What you’ll find is that your acceleration will be not as good as you hoped with a heavy robot, or in your case, you might not even move.

Thirdly, as gblake said, if your robot is too fast, you’ll have a hard time controlling it, and this year, the drive space is cut in half, so if your robot is too fast, it might be hard to control.

And finally. My personal opinion is that a drive train should be geared for either torque or 1 to 1. Especially with a heavy competition robot, because gblake is also right in saying that if your drive is geared for speed and your motors can’t handle the strain, they will burn out.

Try to find a nice balance in gear ratios to where your robot moves, and it moves well, but you don’t waste speed. Because this year, it’s especially important to be able to out “juke” your oponent at the wall.