# Drivetrain Physics

Over December vacation, my team’s mechanical lead and I are planning on CADing a chassis in preparation for the build season. When I was tasked with designing our drivetrain last year, I basically just used JVN’s motor spreadsheet to figure out what our high/low gear top speeds would be using a supershifter, and based everything else off of what I thought was reasonable and would work. Although this method can probably work out just fine with enough experience, I want to get into doing some in depth calculations about how the drive train would function. I am interested in learning about how to calculate top speed, current draw, traction, maybe acceleration or turning ability, etc.

So my question is if anybody here has some links to tutorials on these kinds of things. I understand that this is a very broad topic, so the tutorials might be pretty lengthy, but I have 2 weeks of no school ahead of me to pick it up.

This powerpoint presentation from Simbotics has been helpful to me for things like this. The beginning slides are just on different types of drivetrains but it gets more into the engineering behind drivetrain design the farther you go in. Hope this helps: http://simbotics.org/files/pdf/drivetraindesign.pdf

I found this to be helpful

http://botsnlinux.net/firstphysics.php

You will find a detailed simulation model that calculates top speed, current draw, traction, and acceleration in this paper:

http://www.chiefdelphi.com/media/papers/2868

… but it may require some study to understand it.

You can find an up-to-date discussion of turning forces for skid-steer vehicles in the following post:

reported

Attached is a spreadsheet project, which is intended to help with understanding related to robot acceleration and rate capabilities.

The relevant parameters are provided on the Parameters tab of the spreadsheet.

Once the robot parameters are specified, the acceleration percentage can be specified (or changed). Given the acceleration percentage, the cruise time is the remainder from the transit time. The shorter the acceleration time, the lower the cruise velocity but the higher the required acceleration - and vice versa. If the cruise velocity is high enough, there won’t be enough battery potential to support the required motor speeds.

To evaluate the acceleration time capability a numerical simulation is included. Simply stated both the motor cruise speed and the required acceleration time must be met in order to have a possible solution.

This work is not presently validated.
There are missing data items within this; in particular most inertia values are computed from other data.

If there are comments to this, please respond; I am interested in feedback!

I hope that this information proves helpful to someone.

Mobility sizing 140102.xlsx (636 KB)

Mobility sizing 140102.xlsx (636 KB)