Well, was doing pretty good on RS2, till today. Was trimming some rubber wheels down on the table saw, and one kicked back, threw the plastic pusher I was using into my gut, and left a pretty good mark!
I have the design ready, and drawings for the parts to be made for Ramming Speed.
- Outer Structure
- Inner Structure
- Bottom Armor
- Top Armor
- Spindle Assembly
The following are the DXF files required for water jet cutting of some of these parts:
Parts are rolling in left and right. I’ll try to get pictures up soon. The design is becoming quite modular. Their will be two power modules (the batteries and connections), two controller modules (a master that contains two speed controllers, the receiver, the power converter for the receiver, and the inverter, and a slave that simply contains two speed controllers), and a motor module (contains four Dewalt motors and gearboxes). The modular design allows for easy access when it comes to working on the components, and I can build them without having the frame ready. The metal should arrive in a day or two, so work will begin on the frame then.
Mike will be joining me once again at TI in May. I found a link that describes why it is best to purchase your plane tickets at 1am on a Wed, so I’ll be up late tonight. Cheapest I’ve found so far is $283 ea (round trip from MKE to SFO), but the times won’t work (doesn’t leave till after noon). Found one for $321 that has perfect times. Hoping it goes down tonight, otherwise, I’ll probably buy anyway. I thought flying into Oakland might be cheaper, but it actually costs more. Could get a cheaper ticket out of Midway, but the cost and time involved in getting there out ways the savings.
I’ve already made reservations for the Holiday Inn in Emeryville (Oakland side of the Bay Bridge, a block away from the Sheraton that I stayed at last November). Their will be a lot of builders there, so it should be a good time again.
I’ve added OnlineMetals as an affiliate. I’m getting all of my Stainless Steel from them. If you’re looking for metal, definitely check them out. I found them to be cheaper than going through MetalMart, which is local for me, even with shipping included! Click on one of my links, when you place an order so I can get a commission to use towards my robot!
I’ve also added RoboForge as an affiliate. RoboForge lets you construct gigantic robotic gladiators, train them to think and fight, and then unleash them in massive international tournaments for money and prizes. Try it, it’s almost as fun as building a BattleBot!
I purchase my motors on Saturday. They are 18v Dewalt, but not the version I’ve described so far. This is a new combination though probably just as difficult to mount as the 24v motors I got rid of, offer 38% more speed (which I decided I needed), and are easily neutrally timed. I’m spending a lot of time to come up with a foolproof mounting system so I don’t succumb to the same fate as in previous tournaments. See below for details on the motor and gearbox, including how to take them apart, and change the timing to neutral.
Speaking of tournaments, the dates have been announced. May 21-27 at Treasure Island. I will be in attendance, whether RS2 is ready or not.
Dewalt released a new version of it’s cordless drill 18v motor and gearbox in the spring of 2002. The following description is based on parts ordered from a Dewalt DW988K-2 18v Hammerdrill. Their are other models that appear to have the same combination of motor and gearbox.
The motor provides 450 in./lbs of torque at 18v. The gearbox offers three selectable speeds, with the highest (called ‘MAX 3rd Speed’) being 38% faster than the previous model at 2000rpm. The previous 18v combo was heralded for its ease of mounting, as the gearbox actually attached to the motor with four screws. The new version offers no such luxury. Their is NO physical connection between motor and gearbox, requiring you to create a custom solution. The gearbox, having more capabilities, is much more complex, but offers ALL METAL gears. The motor is easier to disassemble than the previous model, and the magnets are easily removed, so neutralizing the timing is fairly easy, and their is room inside for capacitors.
The part numbers for this combo, available from a Black & Decker service center, are:
Motor & Pinion 396505-03 $39.95 each
Transmission 397892-01 $37.95 each
Overall length is 5.375″ from end of motor shaft to tip of end plate holder. Diameter at widest point is 2.22″. Total weight is 29.2oz.
- Weight: 15.7oz
- Diameter: 1.85″
- Overall Length: 3.5″ (from both ends of shaft)
- Length of case: 2.62″ (from outside of both caps)
- Weight: 13.5oz
- Overall Diameter: 2.22″ (at widest point)
- Diameter: 1.85″ (main case without shifting collar)
- Overall Length: 2.55″ (from base of case to tip of end plate holder)
I’ve decided to go with 21.6 volts. The reasons are as follows:
- The Dewalt motors are rated for 18v, but have been proven in competition up to 24v without problems.
- I’m using Victor 883 speed controllers which are rated to 24v.
- Space constraints prevent using 20 cells to provide 24v, but the layout of 18 cells to form a 21.6v pack does fit perfectly.
With RS1, I purchased Dewalt 18v XR+ battery packs, dismantled them, and constructed my own 24v packs with speaker wire. They worked OK, but were larger than they needed (large wires instead of bars), didn’t involve any kind of matching, and were simply taped together structurally. They have been reworked twice now, and would need to be again for RS2, so I will instead spend a little money to get new, higher amp-hour cells, configured specifically for RS2.
I will be buying custom made packs this time around. The packs will be from Robotic Power Solutions, and are referred to as ‘BattlePacks‘. I will be using 3.6ah NiCAD cells to form two 18 cell packs, each providing 21.6 volts for a total of 7.2ah.
“Nicad batteries are very robust, and they offer high amperage output and proven reliability. These new Heavy Duty packs (HD) are hand built for high current, using #8, #10, or #12 Silicone output wires. They are protected top and bottom with heat resistant foam or Nomex, and they are wrapped in two layers of shrink wrap.”
I will be using 1/2″ Team Delta spindles custom made to fit the Dewalt 18v Gearbox. The spindles are keyed, to allow for a secure connection to the sprockets. It’s made of ETD150, a modified chromoly steel that is not super hard but in fact, quite tough – yielding a 150 KPSI part that can be cut with a hacksaw. Hooked up to a special jig it failed at 2.2x the max output torque of the Dewalt transmission giving you a 120% safety margin.
Description: 18v Dewalt Drive Shaft
Vendor: Team Delta
Part Number: RCM512
I don’t believe I need any gearing, so the sprockets on the motors and the wheels will have the same number of teeth. To keep them small and light, I will be using 11 tooth finish bore sprockets that will have a 1/2″ bore to fit the spindles. The sprockets will be keyed to fit the key in the spindles, and will also have set screws to prevent side to side movement.
I will be using #35 chain (3/8″ pitch). I’ve used this before, it is strong, and it has never caused a problem. The chains will not have removable links, since these can accidentally come off. I will instead properly attach the links permanently.
The sprockets for the wheels will be the same as those for the motors. They will also be keyed and use set screws.
In RS1 I used 3/4″ axles to prevent them from being bent. In RS2, since I will be using softer wheels with low clearance (see Wheels below), the chances of the axles being bent are null (the rubber will compress before any force is transmitted to the axle. The axles will be 1/2″ in diameter.
Wheels are one of the biggest decisions in a bot, and their are many decisions to be made in choosing the correct ones. Here are some of the issues to be decided:
The diameter of the wheel becomes part of the gearing of the drive train. The larger the wheel, the faster the bot will go given the same RPMs from the motor.
Larger wheels will generally weigh more, given more materials are required.
Larger wheels will generally raise the center of gravity of the robot, especially if the bot is invertible (height of the center of gravity generally then linked to the center of wheel).
Larger wheels provide a larger target, especially for horizontal spinners (small wheels may be to low for spinner to hit). Small wheels may also be able to avoid the spike strips (assuming their aren’t bent spikes).
Their is an ongoing debate over what effect width has on traction. It is my belief that width, when combined with a soft compound, will increase traction through adhesive friction (see a discussion of traction in my Tips/FAQs area).
The materials the wheel is constructed of are obviously very important in a combat robot. Pneumatic wheels will tend to go flat due to damage, and are generally foam filled to avoid this. ‘Mold On’ wheels generally have a solid core, with rubber or polyurethane molded onto it. Colson wheels are this type, and have proved to be very successful. Rubber tends to be the better choice when it comes to the wheel surface, the softer the better. The softer compound can ‘grip’ better due to adhesive friction.
Considering these factors, and my design criteria, I’ve settled on a non-traditional item for use as a wheel. I found rubber rollers, used as spindles in spindle sanders. They are 3″ in diameter, 4 1/2″ long, and have a 1/2″ hole for a spindle. The rubber is very tough, and has a low durometer (guessing around 50 Shore A). The typical Colson wheel has a durometer of 65 Shore A, so these should offer more traction than RS1. I will cut them to a 2″ thickness.
Description: 3″ Rubber Spindle
Part Number: 00928122000
Receiver Signal Amplifier
Some radio control receivers require an inline signal amplifier to drive the Victor 883 controller. This is because the Victor was originally designed to be run by the IFI Robot Controller and although the signal interfaces are the same in format, most radio receivers cannot source enough current.
Description: Receiver Signal Booster
Vendor: Team Delta
Part Number: RCE600B
This is a Heavy Duty Futaba J-Series 400mm Servo Extension. This extension goes between the receiver and the speed controller. On one end of the wire is a male connector and on the other end of the wire is a female connector. Connectors slide snugly together to guard against vibrating loose. Gold-plated terminals improve conductivity and prevent oxidation for longer lifespan. Heavier, 20-gauge wire handles higher current loads with ease. Wire Gauge: 20 Length: 15-3/4″ (400mm) (between terminal ends)
Description: Futaba 400mm Heavy Duty Extension
Vendor: Tower Hobbies
Part Number: LXXA47
A solid state DC-DC converter block generates a clean 5v power rail for your R/C receiver and associated interfaces while preserving ground isolation for continued noise immunity. Input is 24v nominal over the range 18v to 36v. Output is 5vdc at 300ma. Impact resistant to 50g at an 11ms pulse.
Description: 5v R/C receiver battery eliminator
Vendor: Team Delta
Part Number: RCE85-24
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