EV3 TrotBot, Ver 1
Below is the same version with toes:
Mindstorms TrotBot with Active Toes
The toes used in the following video smooth TrotBot's gait and lower the torque requirements so that the metal axles mentioned below aren't necessary.
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Update: simplified instructions for building TrotBot's legs with toes are here. This leg will work for all 8 legs of Mindstorms TrotBot. |
Adding Toes Lowers Torque Requirements, Allowing LEGO's Plastic Axles to be Used Instead of Steel Axles
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Note: for better performance, consider building Mindstorms TrotBot Ver 3. It's less wide so it turns more easily, and it has a lower center of gravity.
Overview
Linkage: TrotBot uses the linkage developed by Team TrotBot
Build Difficulty: Hard. These instructions cover building a frame for TrotBot with an EV3 brick, and the steel axles described below are over-sized and so are difficult to push into parts. I use a piece of wood like the above Kapla blocks to push the axles into parts, and needle nose pliers to help take parts off. Also, you will still need to build the legs, transmission, and outer frames. Also, this version's lower leg pins tend to detach when turning on high friction terrain (see this post), so I recommend using version 3's stronger legs , the directions for which can be found here.
Trobot's Characteristics:
1. 8 Legs, or 4 "horses" with a gait that mimics a galloping horse
2. When building TrotBot with the EV3 brick make sure to add its "heels" to smooth its gait and lower the power requirements, which I show in my weight-bearing experiment.
3. Steerable? Yes, by driving one side forward and the other in reverse, like a tank.
Linkage: TrotBot uses the linkage developed by Team TrotBot
Build Difficulty: Hard. These instructions cover building a frame for TrotBot with an EV3 brick, and the steel axles described below are over-sized and so are difficult to push into parts. I use a piece of wood like the above Kapla blocks to push the axles into parts, and needle nose pliers to help take parts off. Also, you will still need to build the legs, transmission, and outer frames. Also, this version's lower leg pins tend to detach when turning on high friction terrain (see this post), so I recommend using version 3's stronger legs , the directions for which can be found here.
Trobot's Characteristics:
1. 8 Legs, or 4 "horses" with a gait that mimics a galloping horse
2. When building TrotBot with the EV3 brick make sure to add its "heels" to smooth its gait and lower the power requirements, which I show in my weight-bearing experiment.
3. Steerable? Yes, by driving one side forward and the other in reverse, like a tank.
Parts Used: In addition to the Technic beams, pins, gears, etc. this build requires a programmable EV3 brick, and 2 EV3 Medium Servo Motor (45503). For batteries I recommend using Lithium Ion AA batteries as they are lighter, last longer, and will improve walking performance. Also, to better bear the robot's weight I used 3/16" OD brass tubes for the leg's long connections to the frame (aluminum rods are fine too) rather than LEGO's plastic axles, cut to 21" in length because the EV3 brick is so wide.
A change for this EV3 TrotBot is I replaced the plastic LEGO axles with steel axles to transmit the higher torque of this EV3 build. You can check out my experiment in the blog section, where I show how much LEGO's plastic axles can twist under the higher torques seen in builds like this EV3 TrotBot. Axle twisting delays leg movement, which can change the gait to the point that robots walk poorly.
NOTE: If you don't want to use the below steel axles consider adding toes.
A change for this EV3 TrotBot is I replaced the plastic LEGO axles with steel axles to transmit the higher torque of this EV3 build. You can check out my experiment in the blog section, where I show how much LEGO's plastic axles can twist under the higher torques seen in builds like this EV3 TrotBot. Axle twisting delays leg movement, which can change the gait to the point that robots walk poorly.
NOTE: If you don't want to use the below steel axles consider adding toes.
Plastic LEGO axle permanently twisted by a LEGO XL motor (geared down by a 5:1 ratio)
I purchased the plastic LEGO parts from Bricklink
I purchased the additional servo motor from Amazon
I purchased the metal support rods from my local hardware store
UPDATE: the maker of the metal axles Brick Machine Shop is no longer on Bricklink, but you can find them on Ebay under the store name "CNCgear"
How to Build
General Comments:
1. The build instruction below show me building just one side of the EV3 frame, with the other side already completed. The other side can be built the same way but flipped because the motors are on the opposite sides of the EV3 brick.
2. As mentioned above, I replaced LEGO's plastic axles with steel axles due to the heavy and wide EV3 brick.
We'll start by attaching the motor to the EV3 brick.
Four 9-hole Technic beams will be attached to the underside of the EV3 brick to support the motors.
Notice the middle idler gear below uses a black plastic axle, which is fine since it only holds the gear in place and the axle does not transfer torque. But I recommend that the two outer gears use steel axles since they drive the legs.
Time to put the motor on!
I used a steel axle here, but plastic axles would work fine since the torque is lowest coming out of the motor.
Next we'll begin adding structure to the side of the EV3 brick. First, I'll add 7 hole beams.
Now add pins to a 15 hole beam that will become the base for your gear train, and attach it. The two pins to the left will go on the outer Technic beams of the structure you just made, 3 holes from the bottom, highlighted in the next image.
Attach an 8 tooth gear to the axle.
Attach two, 9 hole Technic beams to the pins.
Now you can begin to make the gear train in earnest!
Now that the gear train is done, it is time to truss this thing up. Below is a picture of the finished product:
...and below are some of the parts you will need to build each truss system, and instructions on how to build them:
Make the same structure for the opposite side, and then attach, making sure to put bushings on the outside of the axles:
The frame is done, all that needs to be added now are the support rods and whatever sensors you choose to use.
Note: you may have noticed that the 9 hole beams I chose to use for the frame's diagonals aren't exactly the correct length, but are close enough, and are described here.
Note: you may have noticed that the 9 hole beams I chose to use for the frame's diagonals aren't exactly the correct length, but are close enough, and are described here.
The brass support tubes have an outer diameter of 3/16", and were cut to 21" in length. Be sure to file down the cut edges so that the LEGO parts can slide on easily.
There's the TrotBot frame with EV3! The final step is to add the leg sections you made from the TrotBot instructions:
