This is Cerberus, a robot I made with my team as an engineering design project. It is designed to operate in a simulated Mars terrain. It’s purpose is to pick up and deploy small probes into the ground. For the course, the target soil were cups of sand on top of an incline.
We also had to pick up a wire frame prism and transport it to the other end of the course. Since the objective was to deploy three probes, we built the claw to hold all of them. We were limited to the VEX kit that was provided to us and we had a small budget that we could spend. A lot of time went into designing and constructing the claw. We used one motor to actuate all three pincers and another motor to rotate the claw assembly. The arm extends and pivots.
Compact Rover for Remote Soil Assessment
Time to build: 120 hours
Weight: 2400 grams
Actuators / output devices: VEX Continuous Rotation Servos, VEX 269 Motors
Control method: VEX PIC Processor with Radio Control
Power source: 7.2 3000 mAh
Sensors / input devices: CC Cameras
Target environment: Simulated Terrain Course
It also has differential steering and all wheel drive. The front wheels are smaller than the back because those were the wheels that were given to us. Cerberus is remote controlled and for the competition I to drive the robot by using mounted cameras. One was attached to the end of the arm and one was attached near the pivot on the upper arm.
We didn’t spend much of our budget. We went to the Dollar Store to buy foam for the pincer pads, elastic bands to close the claws, foam core poster board for the extension I-beam and LED lights to help with aligning the claw with the probes and target soil cups. All of the robots competed on the simulated Mars terrain course for the best time. We came in first place! This was my first real experience with robotics and I must say that I enjoyed it.
This Is super cool! Most of my robotics experience is from VRC, but it’s really cool to see how far the classroom aspect is advancing. I especially like your claw system. I love one motor mechanisms, by the fact that you get so many outputs with only 1 input.
Thanks! I was the lead on the claw design. We only had six motors available and we had to use all of them. Most of the other teams we were up against didn’t think that we could pull it off. Did you check out some of the videos of the claw in action?
Cerberus Testing Video
i dont think i did, but i certainly will now!
I like the phone camera on the robot XD my team did something akin to that last year to make a video of scoring/descoring sacks. Though, i must ask, what is all the harsh squealing noises? i assume its the motors, but I’ve never heard motors squeal like that
The phone was a lot of fun. It was also a way to get a feel of controlling the robots. We had to use VEX cameras that were “well used” with old tube TV’s. The picture quality and field of view was better with the phone. It is also a neat way to get video feed from the robot’s point of view.
The claw assembly is very heavy (about 2lbs at the end of a 12" arm. We used a worm gear meshed with a 36-tooth gear that was mounted on the same shaft with a another 36-tooth gear driving an 84-tooth gear attached to the upper arm assembly. There is a lot of stress transferred to the worm gear and it’s that friction causing the noise. We added some silicone lubricant after we filmed the video and the squealing is greatly reduced. We actually broke the 36-tooth gear during one of the practice runs. Fractured it from the center out. Good thing that didn’t happen during the competition.
In the picture there is a 12-tooth gear driving the 84-tooth gear. That was the set up we used during the trials but we found it was too slow.
Here is a picture of the gearing setup for the pivot assembly.
That make’s more sense. I’ve never used a worm gear under a high load. that system is nice though because your arm can’t be moved(read: Rotated) manually. Also, I’ve busted a few motors under stress (internal broken gearing) so it’s nice to see you have a clutch on there! i didnt figure out that clutches saved your motors till i broke my first 296. Your chassis reminds me of the first time I tried (keyword tried) to make a transmission. If you have a servo, it’d be pretty sweet to see a transmission on this thing. High torque for uphill, high speed for flat road. I imagine this is already taken apart, but a transmission is a decent challenge to make well.
The worm gear was essential for the success of the design. We had to use the older R/C transmitter and receiver which only had 4 analog channels. For precise control and added torque we used the worm gear on a digital channel. Once we changed to the smaller gear ratio and greased the worm gear, it worked fine. The claw actuation was also controlled from a digital channel, I had to tap the buttons to make sure I didn’t open all the pincers at once (although that happened a few times during initial trials.
The course was pretty short, 8 feet long. Any longer than that and we would have completely smoked the competition. I agree, a transmission would be cool but hard to create, especially where we had a limited amount of VEX parts. Servos would have been useful but there was no programming of the PIC.
Cerberus still remains intact. We were supposed to go against this semester’s competition but they are abandoning the Mars rover curriculum and they are now doing the Swept Away competition with the same older kits. That should be interesting.
As for me… I have my hands full helping the engineering faculty combining VEX components with the Arduino micro controllers. So far it has been interesting.