Constructing BigDaddy Competition Robot (Part 3 - Front to Rear) Pro Preview

Based on your feedback we have decided to show you the live process of building a complex LEGO Mindstorms EV3 Competition robot without having the whole robot ready yet. We are continuing from part 2 where we finished the 'front' of the robot and now we will extend it so that we could also attach the rear part. 

  • #72
  • 22 Feb 2015
  • 9:16

The Name

Yes, we have watched the Marvel 'Kick Ass'. And yes, this robot will be big and angry.

The Construction

Again the robot construction has three parts - 'front', 'back' and a frame in between. In this video lesson we are working on the link between the 'front' and the 'back' (also called rear part when we come to vehicles). For the 'rear' part we are using a differential that would help us transfer power to both rear wheels only with one motor.

The Base

Continuing from BigDaddy Competition Robot (Part 2 - Front) we add a base that would extend the construction from the front to the rear part of the robot.

The Process

We construct, experiment and post. You give us feedback and based on the feedback we make modifications on the robot. So, build it with us on the way, try to take up a specific challenge with it and leave us a comment below on what has and what hasn't worked for you in this robot.

Other episodes from the series:

Constructing BigDaddy Competition Robot (Part 1 - Front)

Constructing BigDaddy Competition Robot (Part 2 - Front)


In the previous episode we started constructing the front of a new competition construction and we finished approximately here. In the next few episodes I'd like to show you how we came up with the rear part of the construction and how we've changed it a few times. We had some gear wheels and now we have a differential. And now it's a very stable and very powerful construction that we'll improve in some of the next video lessons.

Since we are now constructing the rear part of the robot, and we have the front part already constructed, I will introduce you to a new mechanism - it's called a differential. I suppose we should have a special video on differentials. So, here I will just use it as an example and I'll let you to think about differentials for a couple of weeks and then we'll give a detailed explanation on how differentials work. Basically, the idea is that you can control both wheels with one motor. And the wheels can turn separately, although they are controlled by one motor. Here's the differenetial part that comes with the LEGO EV3 Mindstorms set; we also have these special gear wheels that are not like the others; and we have a frame. I'd like to attach the wheels to these axles right here.

I'll have one of the wheels attached to one axle and the other - to the other one. I'd like to add the motor to this gear wheel. So, I'll have to find a way to transfer power from this gear wheel to these two axles. I'll use the differential. It's an interesting mechanism. Probably all cars on the market now have a differential. Some have two, others have four.

Now we attach one of the axles here; the other axle there. As a result, we have two axles. We can transfer power to both axles using only one motor. The good thing about the differential is that we can, for example, stop one of the wheels and the other one will continue turning. This is very useful when we have very large wheels - like these. Because when turning, there will be some friction between the tire and the surface, and we should use a differential. Now that we have the differential constructed, it will be used at the rear part of the robot, so we should find a way to attach it to the front part of the robot. We should extend the construction now. It's really convenient that we have these grey frames in the EV3 set and in some of the NXT Mindstorms sets. But probably in some of the next videos we'll explore how to construct the same construction using only beams. But for the time being let's stick with the grey frames. I'll add this frame right here and you'll probably remember from the previous episode that our idea was to use these black parts that are kind of strange but simply very useful and to find a specific example where we can use them. So, I'll add the frame right here. And you can see that the holes here and the holes of this frame are on different levels. So, it's one hole above and we can, for example, extend the construction in the following way: from the left and from the right. And then attach the whole construction to the front. There are six pins and it's not that easy but it's very stable. Now you may be wondering about these blue pins right here (I've assembled them in advance). We need to extend the construction even further to have a larger robot so we can add more attachments, more sensors, etc. I'll use another grey frame. It's very interesting that you should first add the frame and then lock it with the blue pins. Now I have the front part of the robot extended. We can now look for ways to somehow attach the differential to this frame and then the wheels to the differential. I've prepared another construction consisting of three frames. You can find all the instructions below the video. I'll attach the differential to the frame. Now we have a lot of possibilities for attaching the differential. How exactly should we add the rear part to the front part of the robot? There are a number of options. We have the grey frames and we see that we have a lot of holes on them. We can attach the frame like this or like that or probably in another way. We've come up with an interesting solution where we also use these blue pins over here because they are still not used. And it's a good idea to use the pins whenever you have them in the construction and use all the options the pins present. Now I'll add the following construction.

Right here. One is ready. The idea is that this construction will hold the differential. The second one is also ready. Now we can add the differential and attach it to these parts.

So, we've solved the problem with the blue pins. We no longer have unused pins in our construction. However, you can see the differential is not very stable. So, we should attach it to at least one more point so that we can have a stable construction. It's good to attach it to three points. It's also good to have it attached to two points. Probably three would be perfect. Now, following the same principle, we'll again use these angled beams. I'll remove one of the axles.

I'll attach the whole differential frame to the frame coming to the front using this part - following the same principle.

And then again add it. Now it's much more stable, not that fragile. I'll add the axle, the extention for the axle. Then we add the wheel. And we repeat the same thing on the other side.

Now we have the front part of the robot, the extention of the front part, or the base, and we have the rear part. Now we should find a way to attach the wheels and transfer power from the differential to the wheels. But since we are over nine minutes already, I prefer to leave this for our next episode. Stay tuned and see how we continue with this construction.