In order to have companies manufacture parts of our robots, they first need to know what the parts look like and their specifications, which is why it is important to know how to make a proper technical drawing. This section will tell you how to make such drawings along with tips and tricks to make them look nice and easy to read.
In February 2022, we got a workshop about making drawings by two people from VDL (one of them was from the first RTT year). Here is the presentation they made for this workshop: drafting_course_20220228.pdf. Please read it before you continue reading here since this page will talk about things introduced in that presentation.
The first thing you need to do when making a drawing is to place the datum features, which you can think of as being the anchors for your part. They are the surface or feature where the other features are referenced from. It is usually an important functional feature that needs to be controlled during measurement as well. They need to be placed first because it is the first thing the manufacturer will look at to be able to position your part in his software which he uses to make the part. In fact, in that software, he will have to position the datum A of your part on a big flat plane which corresponds to the surface on which the part will be manufactured. Therefore, it is important to place the datum A on a large flat face (for example, the part of the motor mounts on which the motor is attached). The other datum features need to be place on important features of your part (for example, the hole for the motor and the surface touching the bottom plate for the motor mounts)
Then you need to fill in the title box. Give it a proper name, and write your name and the date so that the manufacturer knows who to contact if he has questions about your drawing. An important thing to make sure the drawing will not get too busy and messy is to fill the “Unless otherwise specified” section, like that you won't need to specify the tolerances on certain dimensions, or the fact that each dimension is in mm.
Finally, edit the grid reference on the drawing (the numbers and letters on the border) so that it is easy to reference to a specific feature on the drawing (it is good to have at least 10 of each like in drawing_frontleftmotormountv4.pdf)
Now, you need to write the dimensions of every feature of your part (hole sizes, how far from the datum features, length of each edge, etc.). Make sure each and every feature of your part is given a value! Otherwise the manufacturer will choose it by himself and it will probably not be what you want. To make sure the drawing does not get too messy, there are several things you can do. First, round values don't require numbers after the comma (eg 6,00=6 and 0,00=0). Then, if two features have the exact same values, you can reference only one and add a (x2) after the dimension (eg, in drawing_frontleftmotormountv4.pdf, the two threaded holes in [B9] and [B7] have the same depth, so only the one in [B9] is referenced, with a (x2) so that the manufacturer knows this dimension applies to both holes. Same thing for the chamfered holes in [G5], only one is mentioned but it applies to the three holes since there is a (x3)). Also, certain dimensions in a part need to be exact (so without tolerances). To mention this, you need to add a box around the dimension. For example, in the motor mount drawing, the distance between the motor's hole and the datum C needs to be exact so that both the wheel and the motor are placed correctly, so the 28,16mm in [G7] is put in a box. Same thing for the angle between the wheel and motor's holes, the 19 degrees is in a box in [G7]. However, manufacturing these exact dimensions makes the part more expensive, so for dimensions which don't need to be exact make sure you use tolerances, like the width of the motor mount in [J6].
Finally, you need to add Geometric Dimensioning and Tolerancing (GD&T) as introduced in slides 6 to 10 in the presentation mentioned at the top of this page. By using various GD&T symbols, you can make sure certain features of your part will be exactly as you want them. For example, we wanted the surface of the motor mounts which touches the motor to be as flat as possible, so we used the flatness GD&T symbol in [J6] to mention that. Another useful GD&T symbol is the position one, which makes sure a feature is located exactly where you want it, so it is very useful to place holes in the right place (see [B7] and [F9] in the motor mount drawing), but also good for surfaces (eg, [F8], the position symbol is used as a flatness symbol for that surface, but it is also used to make sure the surface is located correctly with respect to the Datums A and B). For more information about these symbols and how to use them, click here: https://www.gdandtbasics.com/gdt-symbols/
Get feedback. Ask the people you work with to double check your drawing, make sure that every feature is defined correctly, and that all the GD&T symbols are used correctly. Ask people from previous RTT years if they can have a look at it, especially Rick Timmer who helped me out a lot to make my drawings and who makes drawings for his current job so he will definitely give you great feedback. You can also contact me (Corentin Monat) and I'll try to help as best as I can.