|Drive||2 x Propdrive 28301000kv, 1.875" BanebotsT40 Wheels
|Drive||2 x Propdrive 2836 1200kv, 1.55" Titanium "Cleat" Wheels
|-
|-
|Power||2x4S 650mah LiPo
|Power||2x4S 650mah LiPo
Revision as of 19:14, 21 October 2021
Project Liftoff - September 2021 (rev 5.0), pictured before the September 2021 event. The bot went on to go undefeated, winning the 3lb division with 4 KOs and 3 judges decisions.
Project Liftoff is a 3lb MeltyBrain (a robot that moves using translational drift) as its entire body spins at 2000 to 4000 RPM.
As of September 2021, Project Liftoff is in it's fifth major design generation.
Project Liftoff - March 2019 (rev 1.0)
Rev-1.0 : March 2019
Processor: Arduino Nano
Accelerometer: common MPU 6050 (+/- 16g 12 bits)
Receiver Interface: standard RC-PWM into UART
Motor Control: OneShot125 via PWM manipulation @ ~800Hz
External Sensors: none
Rev-1.1 May 2019
switched from 8" Aluminum rings to 9" AR-500 ring with tooth (and hand cut HDPE)
this AR-500 tooth proved to be too pointed and became embedded in arena wall several times
Project Liftoff - May 2019 (rev 1.1)Project Liftoff - August 2019 (rev 1.2)Sir Pops A Lot (derivative) - August 2019 (rev 1.15)
Rev-2.0 : 2020
Processor: Teensy 4.0
Accelerometer: none… used motor eRPM telemetry from ESCs via bidirectional dShot
Receiver Interface: RC-SBUS into UART
Motor Control: dShot600 via SPI manipulation @ 8000Hz
External Sensors: active IR
CNC'd HDPE body
New 8" AR-500 ring and tooth (with a more blunt tip)
Project Liftoff - July 2020 (rev 2.0)Flip N' Cut (derivative) - July 2020 (rev 2.05)Project Liftoff - September 2020 (rev 2.1)
Rev-3 : 2021 Same electronics as Rev-2; improved algorithm, wheel orientation, and return to accelerometer (see March-2021 picture below).Project Liftoff - March 2021 (rev 3.0)
Processor: Teensy 4.0
Accelerometer: H3LIS331DL (+/- 400g 16 bits)
Receiver Interface: RC-SBUS into UART
Motor Control: dShot600 via SPI manipulation @ 8000Hz
External Sensors: active IR
changed to 4S (from 3S)
Other Details:
Switched to a "Motor Pod" that is sandwhich'd by two clam shell HDPE halves.
Put wheels in-line with weapon tooth (what was Jim thinking).
Rev-4 : 2021 (May-2021 and July-2021) Same as Rev-3 except:
Quest for a more durable motor...
May-2021: created a custom motor with internal thrust bearing with "no-name" motors (internal thrust bearing still failed by the third fight).
July-2021: Put a thrust bearing inside a PropDrive motor
Combing a PD-2826 stator with a PD-2830 motor-can gave the needed room. Could do the same thing with a PD-2830 stator and a PD-2836 motor-can (the PD-2836 is really a 2834, 4mm larger than the PD-2830).
This motor sacrificed power for durability. It was durable... however, it changed the failure point to the set screws and motor axle.
Wheel Axis returning to 90 degrees from weapon
when wheels are inline with the weapon, the hockey-pucking is far worse.
Making weight distribution fully symmetric...
a large counter-balance weight opposite (single tooth) weapon increases hockey-pucking... an impact causes the tooth to stop, but the other side of the Bot goes flying due to its own momentum.
change to fully symmetric two weapon teeth, allowing us to avoid a large counter balance weight.
changed to full round HDPE body
prior HDPE cut-outs were to save weight
prior circular AR-500 weapon ring kept wall collisions "safer" and minimized pinning risk, and allowed us to hollow-out the HDPE.
re-design and re-cut of HDPE shell.
weapon ring changes
make weapon ring narrower to decrease weight to offset increase in HDPE
remove bolt holes from weapon ring (to maximize its strength)
July-2021: first usage of titanium wheels. Thank you to Joe Fabbiani (Smeeeeh) and Calvin Iba (Lynx) for sharing the idea and showing the way - see Lynx May-2021 competition.
Rev-5 : Sept-2021 Same as Rev-4 except:
Major Motor redesign
Switched from PropDrive 2830 to PropDrive 2836.
more power.
Changed to a Hub Motor wheel attachment
6mm dead axle
two 626 bearings (1000+ pounds of dynamic load)
custom machined aluminum inner (motor-can) and out (wheel) hubs
done on home CNC machine (0.2mm layer height)
titanium wheels (via send-cut-send)
no more set screw failures!
Thank you to Brian Boxell (Eruption) for giving us some direction, encouragement, and help on Hub Motors.
Yet another AR-500 weapon ring re-design
Needed to find 80+ grams to offset the increased weight from the above Hub Motors.
Same 0.25" AR-500, but...
via send-cut-send.
Previous 326g (almost a full round circle) to 241g (almost rectangular)
Still no holes, very tapered/narrow in the middle.
Both the above required a re-design of HDPE shell.
Annotated Image of Sept-2021 Project LiftOff internals. The accelerometer and RC receiver are on the underside of the PCB.Rev-5 Issues that we hope to address for Nov-2021 :
In the "first attempt" of CNC'ing aluminum I made several mistakes that led to slight defects in the motor hubs (leading to non-alingment in the Hub Motors that were used... rubbing/friction/added heat/lost power).
Over-clamping & un-even clamping.
Slight alignment issues with double sided parts.
We never (software) tuned Project LiftOff... we were making hardware fixes until midnight on Friday.
The controls were upside down and backwards all day on Saturday.
The IR object/wall detection was never used since it was so misaligned.
Possibly make some ESC changes to improve drift performance.
Continue to ponder how to avoid "hockey pucking".
"Save the Arena Floor" upgrade...
We will modify the software to take advantage of the wheel telemetry information we have (via bidirectional dShot) to avoid "spinning our wheels".
This will not only stop us from ripping apart the arena floor (like a saw blade), but:
It will be much quieter.
It should enable us to spin up much faster (using static friction instead of dynamic friction).
The first appearance was at the March 2019 NHRL event. The very first version used an 8" diameter aluminum pipe cut into two 1/2" thick slices with a notch cut out for the AR500 tooth (with two bolt holes).
Since then, Liftoff has used several laser or waterjet-cut AR500 steel rings. These rings have been sandwiched or otherwise mounted to CNC'd UHMW or HDPE bodies that contain the primary electronics and battery. This has proven to be a durable, and adaptable construction method.
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