dogdish community on orkut

If you're on orkut, then join the dogdish tribe:

http://www.orkut.com/Community.aspx?cmm=4235

if you need an invite let me know: dogdish at REMOVE.dogdeit.com

More battery lore

I had a great conversation with Lars' friend Greg this evening and got a much better sense of what we need. Here's the summary.

Battery type
We need Golf Cart batteries, NOT deep cycle batteries. GC batteries are designed for our application, and are way cheaper than what I've been looking at up till now.

Configuration
One string of 8 6V batteries is better than two strings of 12V batteries. More capacity for the money. We could also consider one string of 6 8V batteries, but I don't know that there's any advantage. We are not constrained by size limitations on batteries.

Power Consumption
A typical 200 amp-hr 6V battery costs $60 and weighs 60 lbs. If power consumption at the batteries (taking into account mech./elec. losses) is 2KW (2.7 HP), and assuming we only get about 100 amp-hr out of the batteries due to the discharge rate we can expect to get 2.5 to 3 hours of continuous operation before a recharge. Fortunately, nothing is continuous on the playa, so I'm betting we can get 4 to 5 hrs between charges.

Chargers
We can buy a small on-board 110V charger from Greg for about $300 that allows the vehicle to plug in anywhere. We should have a 1.5KW (2HP) generator in camp for the purpose. Recharge time is about 4 hours. We could also trade off recharge time for ride time, i.e. 3 hrs on, 3 hrs. off.

When to re-charge
An outstanding issue is determining WHEN to recharge! It's not easy. There are expensive devices that measure current vs. time to calculate it. Being kind to the batteries is key to the success of the vehicle so we will have to research that one.

Maintenance
New batteries need to be charged/discharged about 20 times to break them in. They also need to be "balanced" occasionally. I think that means charging them all the way up until they're venting some gas. Have to verify that.

battery estimate

Here's a quick estimate of battery reqs based on what I've learned about batteries in the last while:

Assume 4 hours of operation at 2HP continuous power consumption.
Assume 75% mechanical/electrical efficiency.

So amperage at 48V = (746x2/48)/0.75 = 41amp. But we have two 48V battery strings, so that's 21amps.

Consider the Trojan 27RV battery.
http://www.absak.com/pdf/trojanspec.pdf

12V 115 Amp-Hrs. 115/21 = approx. 5, so Usage rate is C/5 which is reasonable. They advertise reserve capacity at 25amps as 200min (3hrs 20 min.) So at 21 amps maybe closer to 4 hrs.

This battery is 60 lbs and is $98. We're only running this for a week, so we could probably go with cheaper Costco batteries with somewhat greater capacity.

workshop ready

On saturday, Kevin got the trailer and made a run to Home depot. He met Simon, Geoff and I at Jen & Scotto's 6 car garage. We made quick work of cleaning out the space and after 3 hours we had a functional shop with 2 new tables.

steel order

This is our first order of material placed to a local steel supplier.

Steve,

Here is the list of material I would like to purchase. I excluded items you said you did not carry stock in. I've also changed some quantities from your original quote. I will call you tomorrow to arrange payment. I won't take delivery until next week.

Do you carry 1/4" plate? If yes, in what dimensions?

Kevin MacDonald



FLAT BAR Qty
3x1/4 x 3' 1
1.5 x 1/8 x 1'-0" 1
2.5x1/4 x 1'-0" 1
2x1/8 x 1'-0" 1
2x3/16 x 10'-0" 1
2.5x3/16 x 2'-0" 1
3x3/16 x 3'-0" 1
4x3/16 x 2'-0" 1


ANGLE
L3x3x3/16 x 6'-0" 1
L2x2x1/8 x 10'-0" 5
L1.5x1.5x1/8 x 10'-0" 30
L1x1x1/8 x 10'-0" 2

HOLLOW TUBE
SQ. 3X3X3/16wall x 4'-6" 1
3 1/2" pipe (4.0 O.D. x .226wall) x 1'-0" 1

Tool Survey

Could everyone please post a list of tools they have that could called upon for use? We need items like extension cords, power tools, metalworking tools, carpentry tools, assorted hand tools, anything at all that you have. I want to make sure I don't buy something we already have.

Set up shop starting Saturday Jan. 24

I'll be renting a trailer Sat. morning. By 11:00am or so I could meet folks at Home Depot and pick up lumber for benches. Here's what I have in mind:
Jan. 24 - Clear work area and build two work benches. Possibly buy a chop saw, bench vise & drill press from Home Depot. Would be good to have three bodies from 11am till 5 or 6. Two would do.
Tools needed:
- Circular saw.
- hammer & nails.
- saw horses.
- misc. carpentry tools. Would be good to leave some stuff there.
- Long extension cords. 110V power might be a problem if the entire garage is on one circuit. Might be necessary to run extension cords to the house to a 2nd circuit and leave them there ready to go.
Purchases (or at least check out prices)
- chop saw + disks
- bench vise
- drill press with vise
- 2 hand grinders with grinding & slitting disks.

Feb. 1 TBD.

the beginning of the work

kevin and i met yesterday to set up rough schedule and go to jen and scotto's. Jen & Scotto's will be perfect! It's not insulated but we will have plenty of room (15x20).
Is everyone ready to work this weekend? We need to get the shop set up. We also need to get a combo lock.

The schedule that we created is very rough and is broken into 2 week increments. Based on the schedule we have 2 weeks to get the shop up and running and to have ordered some of the supplies. Hopefully tomorrow I will be able to type it up.

When are people available this weekend? Kevin, can you blog your vision for setting up the shop the next two weekends (time needed by how many peeps ata any given time, toools, etc...)

I think i have a boombox that we can use!

Link to all DogDish CAD drawings

This site shows all details drawings.
Art car drawings

Dogdish motion equations

If you check out the URL you'll find my analysis of the math for the motions of the three wheels of the dogdish vehicle. Basically this math describes the constraints that must be satisfied when steering the vehicle along any path. Although there are six controlling degrees of freedom (the steering and speed of three wheels), the motion of the vehicle has only three (rotation and xy velocity). Only a subspace of steering configurations are wheel-slip free. I analyse this relationship. Any potential movement of the vehicle can be re-parameterized as a time varying rotation speed and ground velocity. I do this for the simple case of tricycle motion. If rotation and horizontal motion are specified independently then there are some funky spirograph motions and I analyse these in the document.
URL: http://research.microsoft.com/users/swinder/dogdish.pdf