MELON BRAWLER 2
All parts for this robot are the same as Melon_Brawler.
This iteration was much smaller than the initial one, opting for less gap between the wheels. This was a bit risky, but the cad seemed to prove that everything could fit, so I decided to send it.
Parts List
Dartbox V2 Drive (Viper) - Drivetrain
The drive motors are Dartbox V2 drive, which were selected since they are, at the time of design, basically the highest end brushed drive motors at the 3lb scale. They conform to the 22mm planetary scale, which means that they contain all the benefits of that platform (increased shock absorption relative to spur gears, relatively secure mounting), but with the added benefits of much more powerful motors, longer shafts, and reduced weight in the gearbox ring.
Quicrun 1060 - Drive Controller
The drivetrain is powered by two Quicrun 1060 ESCs, each of which are advertised as 60 Amp controllers. Each controller drives one side of drive, with splitter cables. I'm not sure if I recommend these, the drive system started going haywire at competition, but I haven't figured out the cause yet. These things did survive getting a battery plugged into the motor leads (Don't robot while sleep deprived!!), so that could be the cause, but it is still impressive that they survived that.
-----—https://www.hobbywingdirect.com/products/quicrun-10-esc-2-3s-brushed
RobotPower Wasp - Lifter Controller
This project used a Robotpower Wasp controller for the lifter. This controller was advertised as a current-limited speed controller, which meant that I wouldn't have to worry as much about pulling too much current at stall and killing the controller. It also had limit switch inputs to prevent the lifter from overdriving and eating itself.
-----—http://www.robotpower.com/products/wasp_info.html
Dartbox V2 HR (107:1) - Lifter Motor
The lifter motor itself is the Just Cuz Robotics Dartbox V2 HR, which boasts an impressive 380 oz-in (2.6 n-m) of torque at only 60g. This motor came stock with a 4mm shaft, which meant that it could interface easily with a number of hubs and gears. It's basically just a higher reduction version of the drive motors.
-----—https://justcuzrobotics.com/products/dartbox-hr-squared
Gobilda Gears - Lifter Power Transmission
The lifter went through an additional 3.2:1 reduction, partly to increase the safety factor on the lifter, and partly to more easily mount the lifter. The pinion mounted directly to the shaft of the drive motor, and the hub gear bolted to the lifter fork.
-----—https://www.servocity.com/2303-series-steel-mod-0.8-pinion-gear-4mm-round-bore-15-tooth-/
-----—https://www.servocity.com/2302-series-aluminum-mod-0-8-hub-mount-gear-14mm-bore-48-tooth/
SCE44 Needle Roller - Lifter and Fork Bearings
Every fork, both powered and unpowered, had one of these needle roller bearings passed through. The 1/4 inch bore is specifically chosen to ride on shoulder bolts. 1/4 was chosen mostly because I was already using 1/4 inch shoulder bolts for Blastwave_IV
Limit Switch - Lifter stop mechanism
The limit switches were selected because of their size, and ease of acquisition. They worked pretty well!
Fingertech Power Switch
I used a Fingertech power switch to turn the bot on/off. It's not strictly necessary, as the ruleset of the competition this was designed for didn't require one, but I wanted to design for SPARC/MRCA rules.
-----—https://www.fingertechrobotics.com/proddetail.php?prod=ft-mini-switch
3S 550mAh Lithium Polymer Battery
This battery was selected to power the whole bot. I wanted to go 3S to run the Dartboxes at their rated voltage. I didn't have any issues with this battery.
-----—https://justcuzrobotics.com/products/3s-550-lipo?_pos=1&_sid=c6008c363&_ss=r
Spektrum Dx6e Transmitter
I originally bought this for Blastwave_I, but this was the only transmitter I have that has spring return on the throttle stick. That lets me drop the lifter stick and stop motion easily, whereas that would be quite the challenge without spring return. I bought it back in 2019, when it was closer to $120 or $150 or something. I would not have wanted to pay $250 for this.
-----—https://www.spektrumrc.com/product/dx6e-6-channel-dsmx-transmitter-only/SPMR6655.html
Lemon-RX DSMX Receiver
DSMX receiver that is super cheap. I used to buy these from Endbots, but unfortunately they closed up shop. You can still get them from Lemon-RX, though the antenna is a bit larger than I'd like. I have used them though with few complaints. They are super light and work pretty well.
-----—https://lemon-rx.com/index.php?route=product/product&path=86&product_id=265
The main change between this and the last version was that I opted to change the heat-set inserts out for 6-32 standoffs, which would run through the whole chassis. They took up more space than the inserts, but should provide a bit more rigidity, and be much less hassle.
Because I was no longer using heat set inserts, I moved the fork assembly over to a peg-lock mechanism, that would be attached to the main chassis with screws. This would enhance rigidity, and allow the plates to be attached to the chassis without requiring the lids to hold everything.
In addition, I decided to embed the passive fork mounts into the chassis instead of having a separate piece that bolts on. This was partly for style points and partly because I didn't want to have to deal with fasteners.
Speaking of style points, I decided to also freshen up the lids and the back of the chassis. I'm still chasing that turn-of-the-century tech vibe I started with Dreamphaze, and this is a bit closer.
After assembly, everything ended up turning out pretty alright! I initially assembled it with 3d printed forks to get a feel for it, though these would be eventually changed over to aluminum forks with the final version.
I also switched from the Fsi6 transmitter to my Dx6e. The reason for this change was that the Dx6e has the ability to change its throttle from the standard throttle (where the stick's vertical axis stays where you put it) to a springback (where the vertical axis springs back to center much like the elevator or aileron channels). This can be accomplished with the switch on the back, and was extremely useful for more accurate lifter positioning. If I wasn't able to return the throttle manually to center with a standard throttle control, the lifter would have continued moving until it hit the limit switches that stop the lifter travel. However, with this, I can simply drop the stick and the lifter will cease movement instantly. (＾_^)ｂ
I did some driving practice with the fork setup, and when attempting to lift heavy objects, the chassis would tip. The solution to this was simple, add some rigid forks to the chassis, inspired by Überclocker.
The static forks can be seen in the below image, along with the finished aluminum active and passive forks. These were all cut from aluminum due to its low weight and availability on SendCutSend. These had SCE44 needle roller bearings sourced from Fingertech press-fit in using an arbor press, which rode on 1/4 inch shoulder screws. I was remarkably happy with how this turned out, the forks did their job of scraping the floor.
