I spent the weekend working on one of the paintball markers
and wiring the batteries. The marker is coming along well and is almost ready to
test out. I had two small problems: the solenoid is too little and weak to
disengage the sear, the barrel came out a little rough. I ordered an undersize
drill and reamer for the barrel and a bigger solenoid for disengaging the sear
from Mcmaster. The description of the reamer says it will leave a mirror-like
finish. I calculated the new solenoid will pull with about 25 lbs of force at
48V with a 1/8" stroke. I chose .6875" for my final barrel diameter as this
coresponds to "medium" diameter paint.
I also got started on the wiring using 6 AWG wire and
soldered-on heavy duty ring terminals. The battery side of the wiring is about
half way done. In order to charge the tank at 12V and run it at 48V, I'll be
using an 8-pin connector between the battery and ESC.
Gene
From: tanks-admin-at-rctankcombat.com [mailto:tanks-admin-at-rctankcombat.com] On Behalf Of Gene Burbeck
Sent: Friday, November 03, 2006 12:29 PM
To: tanks-at-rctankcombat.com
Subject: RE: Gene is building a tank! [TANKS]
Cross post form RFL forum:
I bought a Tippman 98 Custom paintball marker from a friend at work. I dissasembled it and designed a billet reciever to hold the bolt, valve, barrel, etc. The aluminum and tooling for making it are on the way from Mcmaster. For triggering the marker, I am using a small overvolted solenoid in place of the sear (the sear is the piece which releases the bolt). The marker's valve, front and back bolts, springs, and barrel will be stock. This stuff fits in the aluminum housing that I will machine. In order to save machining time and cost, I designed the reciever to be all made from .25" wall 6061 tube stock. For the barrels I'm starting out using the stock 98 Custom barrel. If I have the money later, I'll get a pair of Flatline barrels to help minimize trajectory and keep the shots parallel to the ground. This type of barrel is slightly curved to put backspin on the ball. I have Paul, my friend from work coming over this evening to help more with frame construction for the tank.
Progress last night with Paul:
We put the "roof" on the tank.
The
roof is bent from thin sheet steel and fastened to the bulkheads with #10-24
screws. We also made the back bulkhead and back cover out of 1/2" Lexan. I've
been using all 1.25" long #12 sheet metal screws in the Lexan so there is no
need for tapping. Those screws are VERY hard to put in the first time! The motor
goes over the ESC, up under the sheet metal roof.
In
other news, I traded two of these:
for
one of these:
This
is the team Whyachi version of the 48V 330A Sevcon speeed controller. The two
reasons for using this is reverse is built in (no need for contactors for
reversing) and 48V capability. At 48 volts, motor heating is only half as
bad as it would be at 24V for a given power output level - at double the motor
rpm, only half the current and torque is needed for a given ammount of
horsepower. At the same time, AVAILABLE torque goes way up since stall current
goes up when supply voltage goes up (assuming the batteries will source enough
current).
I've
been playing around with the calculations for running the tank at 48V, similar
to the calculations I used to do in order to design spinning robot weapons.
Armature resistance of the LEM130 as per Lemco spec is 5m (5 milliohoms), KV is
150 rpm/volt and current/speed is 10 rpm/amp. The batteries are rated
at 1800 amps short circuit.
no
load speed at 48V = 48V X (150 rpm/volt) = 7200 rpm
skipping a few steps...
rpm
drop at 350 amps = 350 amps X (10 rpm/amp) = 3500 rpm
So,
peak horsepower occurs at about 3700 rpm and 350 amps. Since the batteries
deliver 1800 amps through a short circuit, thier voltage drops to 39V under 350
amps of load (48V - (48V X (350A/1800A) = 39V). At peak output power, therefore,
the input power is 350A X 39V = 13.7 kW. At peak output power, effiency is only
about 50%, so mechanical output power is about 6.8 kW - or 9 HP. Wow! That
sounds about right, since the continuous rating at 36V is 4 HP. What this all
means is that tank *could* be geared to go way faster than nessesary. However if
I want the batteries to last longer than 5 minutes, I'll need to gear for
something a little more sane.
With
4" track sprockets, 10 mph corresponds to 800 rpm. To get that rpm I need to
gear about 9:1. Thats reasonable to do in a 2-stage reduction. I won't know
until I start experimenting, but I'm expecting the gearing for a battery
life of longer than 45 min to be at least 10 mph.
Gene
From: tanks-admin-at-rctankcombat.com [mailto:tanks-admin-at-rctankcombat.com] On Behalf Of Gene Burbeck
Sent: Tuesday, October 24, 2006 10:38 AM
To: tanks-at-rctankcombat.com
Subject: RE: Gene is building a tank! [TANKS]
Got my speed controller today and installed it. This thing
is a beast! It is Curtis model number 1205-111:
36 volts and 400 amps oh my! It fits just right, lying down
in the center of the tank. I fastened it to the lexan baseplate with four
5/16"-16 torx screws. The esc is overspeced enough that it shouldn't need any
cooling. However, if it turns out to be nessesary there is room to put it up on
standoffs to get the flat bottom surface of the esc up off the lexan. The
controller is in good condition, and assuming it doesn't have any problems, I'll
be very pleased with the deal I got.
Gene
From: tanks-admin-at-rctankcombat.com [mailto:tanks-admin-at-rctankcombat.com] On Behalf Of Gene Burbeck
Sent: Wednesday, October 18, 2006 11:12 AM
To: tanks-at-rctankcombat.com
Subject: RE: Gene is building a tank! [TANKS]
I'll make my tracks slightly to short to fit on the
track guides, then trim down the red side plates until the tracks fit nicely. In
other builders' experience, do roller chain tracks stretch at all over
time (I'm using 2 strands of #50 chain per track). I would tend to think
roller chain doesn't stretch.
Gene
From: tanks-admin-at-rctankcombat.com [mailto:tanks-admin-at-rctankcombat.com] On Behalf Of Chrysanthos Kanellopoulos
Sent: Wednesday, October 18, 2006 10:20 AM
To: tanks-at-rctankcombat.com
Subject: Re: Gene is building a tank! [TANKS]
Only out of curiosity:
How would you tension the tracks of the Mark
-Liberty "closed type" track configuration?
CHrys