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Drivetrain Type Comparator

Take one set of motors, gears and wheels, and see what each drivetrain layout would do with them. Same parts, four very different robots.

Inputs

Diameter across the wheel. Mecanum and flex wheels share a diameter with the plain ones, so pick by name rather than by size. Anything not listed can be typed in.

Results

LayoutForwardStrafePush vs tankMotorsWheels

Drive in any direction

Drive in any direction
0° from forward

Each shape is how fast that drivetrain can go in every direction with the same motors, gears and wheels, seen from above with forward at the top. The line is the direction you picked and the dot is the top speed that way. Straight ahead and straight sideways match the table. In between is what the table cannot show: an X-drive is slowest on the diagonal, a mecanum drive is slower still, an H-drive is fastest there because its forward and sideways wheels work separately, and a tank drive has to turn to face the way it wants to go.

How this is calculated

Every layout here is handed identical motors, gears and wheels. The differences are entirely in how the wheels are pointed.

Tank

Wheels aligned with the robot. Everything the motors produce points forward, so it is the baseline for both speed and force, and the only layout that can use traction wheels everywhere. It cannot move sideways at all. To go left you turn, drive, and turn back.

X-drive

Four omni wheels at 45°. Because no wheel points where the robot is going, each only needs to roll at cos 45° of the robot's speed, so it travels √2 faster than tank, forwards and sideways alike. The same cos 45° works against you for force, giving about 71%.

Note that the √2 is not unique to the layout: gear a tank drive up by √2 and you get the same trade. What an X-drive actually buys is strafing.

Mecanum

Wheels stay aligned with the robot, and angled rollers on each wheel let it slide sideways when the four are driven in opposing pairs. Forward speed and strafe speed both come out at wheel speed, so unlike the X-drive there is no speed bonus and no speed penalty. You gain sideways motion and nothing else changes.

The cost is grip and complexity. Mecanum wheels are expensive, heavy, and hold poorly, and strafing scrubs the rollers hard enough that it is noticeably less efficient than the geometry suggests.

H-drive

A normal tank drive with one extra wheel mounted sideways in the middle. Forward performance is untouched, with full tank speed, full tank force and traction wheels allowed, and strafing is bolted on.

The catch is that strafing has one motor doing the work while dragging the tank wheels sideways across the tiles. It is slow and weak, and it costs a motor from a budget that is already capped. Good when you need occasional alignment rather than genuine sideways mobility.

Choosing

There is no ranking here because the answer depends on the game. If matches are decided by contact, tank's grip advantage is hard to argue with. If they are decided by getting into position quickly and precisely, the ability to strafe can matter more than any of the numbers above.

What this table is good for is checking that you know what you are giving up, and for noticing when a layout is chosen because it looks impressive rather than because it wins.

Sources & assumptions

Cartridge speeds and wheel diameters are VEX published figures. The cos 45° and √2 factors for the X-drive are exact geometry. Mecanum forward and strafe speeds follow from standard mecanum kinematics, in which the four wheel contributions sum to wheel speed in both directions.

Roller friction, scrub losses and the grip differences between wheel types are not quantified, because no VEX figures exist for them. They all work against the non-tank layouts, so treat every push figure other than tank's as an optimistic ceiling.

Every source the site uses, and when it was checked

Make a notebook page

Turns this calculation into a dated engineering notebook page: the setup, data, results, figures, working and sources, numbered and cited. You add the goal, the decision and the reflection in your own words, plus photos and sketches. Print it, paste it into Google Docs, or download a Word file or slides.

My notebook

Notebook page

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    This page

    Our own layouts

    A layout remembers how a page is set up: its type, its system, which parts print and which of your tables it uses. It never remembers a word, a number or a photo.

    Your team kept on this device
    Add someone to the team list
    Your words never written for you

    These are the parts a judge or teacher reads to see your thinking, so the page leaves them to you. Leave a box empty to get lined space for writing by hand. Start lines with "- " for a list. The notes under each box only count and point things out; they never change what you wrote.

    Rough notes

    Rough notes

    Rough notes

    Rough notes

    Rough notes

    Rough notes

    Rough notes

    Rough notes

    Rough notes

    The word counts can be measured against a target your team sets on My notebook. The reading level is Flesch-Kincaid grade level = 0.39 × (words ÷ sentences) + 11.8 × (syllables ÷ words) − 15.59. Syllables are counted by vowel groups, so the grade is an estimate of the school year the writing reads at. It says nothing about whether the writing is any good.

    One part at a time, with a clock. At the end of practice, while you remember it.
    How you tested your details

    Fill in what applies. These print as a small table under the method.

    Before and after

    Compare this calculation with a run you saved earlier on this tool (under “Saved runs”). The page shows what changed and by how much.

    A line through the data from your recorded table

    Pick two measured columns from the same table. The page plots them and draws the least-squares line, only across the range you measured.

    Robot log a CSV from the robot's SD card

    Load a CSV your robot saved. Pick the time column and up to three columns to plot, and type their units. Only those columns go on the page; the file stays on this device.

    Two versions' trials your data, compared

    Pick a column of recorded trials for each version, from this page or another saved page. The page shows both averages and a 95% range for the difference. The numbers are copied in when you pick them, so later changes to the other page don't change this one.

    Options compared your scores

    Score each option 1 to 5 on each criterion, and weight each criterion 1 to 5 by how much it matters. The page only multiplies and adds.

    Photos and sketches stay on this device

    Up to 4. Paste a screenshot with Ctrl+V, drop pictures here, or pick them. Photos are shrunk before they’re kept, and an unsaved page keeps them in its draft. Use Mark up to draw arrows, labels, dimensions and numbered callouts on a photo. Mark one photo Before and one After to print them side by side.

      Test plan written before testing

      Write this before you test: the question, what you expect with a number, and what result would make you drop the idea.

        Build steps our build

        One row per step, in order, so someone could rebuild from this page.

          Parts used our parts list

          Lengths in holes are also shown in inches between the end holes. Weights are only added up where you type them.

            Plan the cuts: packs every piece of one part (sizes in holes, or inches on the hole grid) onto whole sticks of the stock length you type.

            Ways it could fail our scores

            List the ways this could fail. Score how likely (1 to 5) and how bad (1 to 5); the page multiplies them and puts the biggest risks first.

              Designed against built our measurements

              What the CAD or the plan said, and what you measured on the robot. The tolerance is yours.

                Changes from the last version our changes

                What changed since the last version, why, and which result it was meant to move.

                  That page’s settings, results and first photo are copied in and set beside this page’s. The result each change should move is looked up on both pages.

                  Tasks our plan

                  What needs doing, who, and by when. Open tasks carry to the next meeting page until someone ticks them done.

                    The pages behind this idea our evidence

                    The pages in this notebook that show the idea being tried, measured or changed. A judge reading the claim can turn straight to them.

                      Time spent our hours

                      Who worked on this and for how long.

                        Session log what we did, as we did it

                        Notes taken during a session. The time comes from the clock when the note was taken; every word is yours.

                          Size limit does it fit?

                          Type the starting size limit from the current game manual, and the robot's size as designed or measured, in inches. The site doesn't store the limit, because it changes with the game.

                          What broke from your breakage log

                          The breakage log is on My notebook. Copy it onto this page as a table, as it stands now; later entries don't change this page.

                          CAD model which version this page is about

                          Paste a link to the model (Onshape, Fusion or anything else) and the name you use for this version. For Onshape, the page reads from the link whether it points at a saved version or a workspace that keeps changing. Nothing is fetched.

                          Your code
                          Comments notes for the team, not the page

                          A teammate or coach can leave a note here. Comments stay beside the page, travel with it in exports and links, and don't print unless you tick them under Include.

                            Sources you used besides this tool

                            Videos, other teams, manuals, people. The tool’s own sources are cited for you.

                              Sign-off
                              Include

                              Press a ? to see what an option is for, or read them all on How the notebook tools work.

                              What “The calculator’s figures” is for

                              The calculator’s own diagrams and charts, numbered as figures and drawn from your numbers. Judges look for pictures that explain a design.

                              What “How it was calculated” is for

                              The formulas and steps the calculator used, so a reader can check the arithmetic for themselves.

                              What “The calculator’s warnings” is for

                              Things the calculator flagged, such as a motor near stall. They’re quoted and credited to the calculator, so they never read as your conclusion.

                              What “The calculator’s notes” is for

                              The calculator’s plain-language notes on the result. Off at first, because they read like conclusions, and the conclusions on a page should be yours.

                              What “Lined space” is for

                              Ruled lines under any part you haven’t written yet, so a printed page can be finished by hand.

                              What “Writing space as” is for

                              The blank space for handwriting as ruled lines, a dot grid or quarter-inch squares. Dots and squares suit sketches and hand-drawn graphs.

                              What “A summary under recorded data” is for

                              The number of readings, the average, the spread, the lowest and the highest under each table you recorded, worked out from your numbers. It shows every run counted, not just the best one.

                              What “Words used” is for

                              A small box with the site’s one-line definitions of glossary terms the calculator used, for readers who don’t know them. It never looks at your own writing.

                              What “Robot at the time” is for

                              The Robot Profile as it was when the page was first saved, so weeks later you can tell which version of the robot a test was run on.

                              What “Long tables in full” is for

                              Long calculated tables printed complete on an extra page, instead of every few rows on the page itself.

                              What “Fit on one sheet” is for

                              Smaller type and shorter tables, aiming for one printed sheet. Use it when every entry in your notebook should be a single page.

                              What “Wider left margin” is for

                              A wider left edge, so the page can be hole-punched or bound without losing any words.

                              What “Larger type, for reading aloud” is for

                              Bigger print with more room between lines, for the team member who reads the page to a judge. It overrides Fit on one sheet.

                              What “Our rubric scores” is for

                              Your own scores against the rubric, on a sheet of their own, for checking a page before a judge does.

                              What “When this page was first saved” is for

                              The day the page was first saved, printed beside its date. It shows the notebook was kept while the work happened.

                              What “Teammates’ comments” is for

                              Prints the comments teammates left on this page at the end, marked as not part of the page. Off at first, because comments are notes for the team, not for judges.

                              What “Show every table and block” is for

                              Shows every table and block in the editor, not only the ones this type of page usually uses. It changes the editor, not the printed page.

                              Rubric check

                                This checks what is on the page, not how good it is. Clear, specific writing in your own words is what earns the top marks.

                                Preview, letter size

                                Write it now

                                Where this goes next

                                Explore further on the full map

                                Where the answers on this page can be used, and which tools could have given you the numbers it asks for.

                                Comes after

                                Pushing Force & Traction Limitfills in your gear sizes here

                                You are here

                                Drivetrain Type Comparator

                                Where your answer goes

                                X-Drive Speed & Strafeif X-drive wins, see its speed in any direction you pickbrings your gear sizes with itDrivetrain Speed Calculatorget the full speed picture for the layout you pickedbrings your gear sizes with itPushing Force & Traction Limitadd wheel grip, which the push column here leaves outbrings your gear sizes with itRobot Profilesave the drive you picked so every tool starts from it

                                a number carries across the next question it raises

                                Keyboard shortcuts

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                                Copy a link to these exact numbers
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                                Letter keys do nothing while you're typing in a box.