Tray Torque Calculator

Please welcome, the BarcBots Tray Calculator

At the tournaments, especially early in the season, I have seen quite some teams struggle with lifting the tray.
My students initially designed a monster compound gearbox for that task. It was slow, unreliable (gear clicking) and used a lot of space inside the robot, but it worked. We thought there must be a better way. After trying few different designs, we have thrown a bit of science at the problem and figured out that a lever mechanism represents a kind of variable gear. To help my students better understand this complex lever and gear interaction and to help them find a good design, I wrote a simple HTML/Canvas/Javascript simulator, in which you can play with various aspects of your design and observe the changes it makes to the torque needed to raise the tray.

Some usage tips are directly on the page. Details of the internals are in the page source. Feel free to modify if it doesn’t fit your use case. Feel free to ask if something isn’t clear.

After evaluating different configurations, we ended up with the powered lever attached to a simple 1:7 gearbox (~14Nm available torque with the red cartridge), 7Nm computed maximum torque needed to raise our fully-loaded 12-cube tray and actually verified that the motor behind the 1:7 gearbox never needs more than 1Nm during 12-cube scoring.

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That is a nifty little tool!

I had good time playing with it.

Is there any chance you could modify it to rotate arm through the lower left quadrant and, maybe, display an additional curve for bottom side rotation? I suspect that it might be slightly more efficient for some geometries.

Thanks this is a great tool, I had been trying to calculate the right gear ratio and this helped a lot.

Quite a simple change, you can grab the HTML (use “view page source”, then save as. Direct save page might show some nasty dynamic HTML artifacts) and change the limits at line 305.

305: var armAngle = makeInput(“angle”, “Arm angle [degrees]:”, 90, 0, 360, 1);

(Edit: and also the limit of the loop at line 258)
I understand it might also need to change the axes on the chart, since the arm torque would be considered mostly negative in that quadrant, but with the default setup, it reveals interesting behavior in that quadrant - it was a great teaching opportunity I missed by initially dismissing that quadrant as useless (you’ll see why once you try).

I’ll try to improve it a bit next week. Also, I don’t have direct access to the team web, I’ll need the students to update the page.

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