pic: Hart District Robotics Swerve Drive Prototype

[Garret]

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[Akash Rastogi]

Very nice offseason project. I really like your use of simple design and use of COTS parts. How is that shifter working out for you guys? What is your control scheme (joystick setup and steering functions)? Are you having difficulties with the modules being in a rectangle instead of a perfect square layout? What motors/gearbox are you steering with?
Looks really clean. Nice work!

[xSAWxBLADEx]

Can I see a close-up of the wheel mount?

videos please?

[Peyton Yeung]

This looks really nice and pretty simple. How long did it take you?

[Ether]

Originally Posted by Akash Rastogi

Are you having difficulties with the modules being in a rectangle instead of a perfect square layout?

Why would that cause difficulties?

[Andrew Schreiber]

Originally Posted by Ether

Why would that cause difficulties?

Perhaps with slightly more complex software? I would imagine that there would need to be code in place to keep the robot from trying to turn long ways by scrubbing the wheels (skid style). But this is just an assumption, the last swerve I programmed was a square and had some pretty major mechanical problems.

[Akash Rastogi]

Originally Posted by Ether

Why would that cause difficulties?

I've only heard that there is more difficulty in programming a rectangular swerve for reasons unknown to me.

Never dabbled in programming, so I am asking based on what others have told me.

So, is it easier (easier being a relative term) to program a square swerve in terms of controls?

edit: what Andrew said seems to make sense.

[Garret]

Thanks for the complements about this robot.

We are building this with an extremely limited (nonexistent) budget so this is the original design that my team came up with in January (like week 1 or 2 of build); consequently this robot base isn't perfect. We had the swerve module parts manufactured during the build season. We started actually making the swerve robot during the summer with a 2-3 hour meeting once a week. We have been working on it on and off since June or July. Most of the issues (in terms of why its taking so long) are related to a lack of funds for buying parts or not having easy access to machining equipment, making it so that we have to design so that we don't use anything we don't already have. Overall everything on this robot (excluding electronics) cost us, less than $1200. I know that the overall investment for our planned 2 swerve robots and additional mecanum robot was around $2500-$3500 in parts.

My intent for this offseason project is to use this as an opportunity to teach new members the basics of mechanics and using tools. My hope is that we can get this to function as a crab-drive that can pivot (by rotating the wheels such that they are tangent to a circular path).

I personally like the shifter, the rest of my team isn't so fond of it. For a second version of this robot we plan on having drive gearboxes for each wheel, and because of our very limited machining and budget right now these will almost certainly be CIMPLE boxes.

Our intent with the joysticks is to get it so that we can translate with one joystick and then use a second joystick to control pivoting. For now we will likely make it so that it only pivots when it is not translating (primarily because this version uses two rather than 4 drive gearboxes). We still haven't gotten this really driving yet, this was because we didn't know what type of encoders to get and we didn't have money to buy them. Mechanically we know this works, we are still trying to get our code working though.

I apologize if I am just rambling or I forgot to answer some of the questions.

[Ether]

Originally Posted by Akash Rastogi

I've only heard that there is more difficulty in programming a rectangular swerve for reasons unknown to me.

Never dabbled in programming, so I am asking based on what others have told me.

So, is it easier (easier being a relative term) to program a square swerve in terms of controls?

Not really. The inverse kinematics¹ are straightforward regardless whether it's square or rectangular.

The challenge with swerve is not the inverse kinematics, but how to control each wheel².


¹The problem of figuring out the theoretically correct speed and steering angle for each of the 4 wheels for any given desired vehicle motion is called inverse kinematics. The derivation of the formulas for this is interesting but not beyond the reach of high school mathematics. The formulas themselves are straightforward.

²If you could make each wheel instantaneously go to its theoretically correct speed and steering angle, swerve would be simpler. But there are dynamics involved. It takes time to steer the wheel and change its speed. During this transition time, the vehicle may do unexpected and/or undesired things. So the real problem in implementing a competent swerve drive is how to control each wheel to obtain predictable operation and acceptable response to driver commands.

[Isaac501]

Not a whole lot keeping those chains on the big drive sprockets, and the drive chain in the upper part of the picture looks pretty loose.

You may want to consider a tensioning system of some sort for it. Transferring any sort of power through that chain is going to make it fly off.

Other than that, looks really neat.

[Alan Anderson]

Originally Posted by Isaac501

Not a whole lot keeping those chains on the big drive sprockets, and the drive chain in the upper part of the picture looks pretty loose.

I don't know what you're looking at. I see 180+ degrees of chain wrap on the visible sprockets, and it looks like nearly that much on the obscured gearbox output sprockets.

You may want to consider a tensioning system of some sort for it.

Are we talking about the same picture? In the one I see, the long chain runs do have tensioning sprockets.

[Gdeaver]

I notice that it uses the banesbot transmissions for steering. They are not 1 to 1 on the chain drive. How are you measuring wheel angle?

[Garret]

We plan on measuring wheel angle with encoders or potentiometers mounted coaxially above the banebots gearbox output shaft. We don't have those encoder mounts on the robot in this picture.

[Alex.q]

Originally Posted by Garret

We plan on measuring wheel angle with encoders or potentiometers mounted coaxially above the banebots gearbox output shaft. We don't have those encoder mounts on the robot in this picture.

If you have a picture of the module itself, I would like to see it.

With respect to measuring wheel angle, I just want to warn you to make sure you buy a high quality sensor for this. My team learned this the hard way.