Monster Truck Rover - Semi-teQ II

[seesoe]

i started a blog for the project, but ill probably end up finishing it here

here is the intro and the plans

http://forums.trossenrobotics.com/blog.php?u=1529

i was trying to figure out the best drive system setup. as of now this is how i have planned. i will have 2 stationary shafts acting like front axle and back axle, then on each side of the axles i will have dual roller chain idler sprockets, one chain will go down to the tire, and another will go to the motor positioned in the middle of the bot, this said, that means the motors will have 2 sprockets on them, one to go to the rear axle sprocket and the other to the front, then the wheels will have their own drive system with a set of pillow block bearings, axle, and sprocket.

if you were keeping track, that's a total of 16 sprockets for the bots drive system!, i don't know where you get your sprockets from but that is pretty pricey

so i came up with another idea, i was thinking to get rid of the back axle, and put the motors there instead of the middle. still having 2 sprockets on the motors shaft, this time one goes straight down to the tire, and the other to the front axle. this will still be a hefty 12 sprockets but that's not to to bad...


so my question is what do you guys thinks would be a better drive setup? having the motors in the back or in the front?

[seesoe]

here is a quick drawing i made in paint

[crabfu]

I don't think that it matters if drive is front center or back, since they are all chained together. If it needs to do some serious rock crawling, then weight should be as forward and low as possible. Motors don't weigh much, so battery, and other electroics placement, are probably a lot more important. You could also do axle driven system with steering, instead of skid steering and dealing with all the sprockets and chains. But locking differentials at such a long chassis would make turning difficult, even with 4ws.... As I foun out the hard way myself lol. However, there are many options for that, as there are lots of rc crawlers in the market now, lots of great parts to choose from.

-crabfu

[seesoe]

I don't think that it matters if drive is front center or back, since they are all chained together. If it needs to do some serious rock crawling, then weight should be as forward and low as possible. Motors don't weigh much, so battery, and other electronics placement, are probably a lot more important.
ya, i didn't think it would make a difference either, i learned my lesson with battery placement with my first robot, as i have 2 40 pounds SLA's and i think the 3rd is 10 pounds, and if im not mistaken the motors are a little under 15 pounds each. so about 120 pounds of motors and batteries, and i was thinking to make weight distribution as even as possible, unless it won't really make a difference of the motors are in the front or back...

You could also do axle driven system with steering, instead of skid steering and dealing with all the sprockets and chains. But locking differentials at such a long chassis would make turning difficult, even with 4ws.... As I found out the hard way myself lol. However, there are many options for that, as there are lots of rc crawlers in the market now, lots of great parts to choose from.
what do you mean about locking differentials at such a long chassis, and skid steering/ can you elaborate more please.

the setup will be like tank style steering.

cheers
seesoe

[Adrenalynn]

Those are some big motors. I have 1000wt, 36v motors that weigh less than half that, and each one will accelerate an adult to 18mph.

Skid steering = tank-style-steering = skid-steer.

Ref: http://en.wikipedia.org/wiki/Skid_steer
Ref: http://www.howstuffworks.com/skid-steer.htm

[seesoe]

sorry my mistake, i just went out an weighed them, they are 16.5 pounds each.

they are wheel chair motors so they have a gearbox too

[crabfu]

I mean if you need 6 wheels, then you have 2 choices that I can think of....

1) tank like system like you're thinking of.... either one power source with a clutch for skid steering for either side, or a power source on either side. Turning is made by powering right or left wheels in forward or reverse.

2) using axels like a car...it'd be a rock crawler truck with 6 wheels. So you'd have either one power source and using axles to route the power to each of the wheels (like a 4x4 truck, but in this case 6x6) or use multiple power sources to drive the wheels. Turning then is done by steering like you would with a car. You can make it 4 wheel steering for better turning. The problem with this, as I was pointing out, is that in order to turn well, you'd need a differential between each wheel axle, because right and left sides will be running at different speeds as you turn. But because of having differentials, it makes climbing difficult, as the diff will allow free spining wheels to accept all of the power, and the stuck wheel to have none. So if you are climbing rough terrain, it gets stuck easily. This is why crawlers usually have the diffs locked, meaning they act as a single rotating thing, not allowing right and left to spin at different speeds.

I've built a contraption before with 6x6 with 4ws as described above. It carries a lot of weight with not much power, and with the diffs locked, it will not turn.... the chassis is way too long. Here is the link: http://www.crabfu.com/steamtoys/rc_steam_rover/

the videos shows the diffs unlocked, and it can pull quite a bit of weight, and does fine in grass and minor bumps, but does not do well at climbing rocks.

Here is a video of my electric r/c mini rock crawler: http://www.youtube.com/cfhelis#p/a/u/0/Btob_YW2xb0 it does have the diffs locked all around, and is 4x4 with 4ws. It works well because it is low weight, all of the weight is as forward and low as possible, and turns ok. It can climb just about anything, and is just a traditional axle driven truck with a lot of very soft suspension travel :)

-Crabfu

[seesoe]

those are some pretty nice projects!

my bot will have only 4 wheels. the axles are bolted down and not meant to spin. this is why im going to use idler sprockets with a bearing in them. the left motor controls the left front and back tires, and the right motor controls the right front and back tires, the controller has built in differential mode settings.

[seesoe]

i was kinda iffy on the dimensions that i picked for the bot, so like i did with the first semiteq, i threw together a quick cardboard mock up of everything so that i can see how parts are going to fit and get a real idea and feel of the whole thing.

(sorry for the bad iphone pics)
i put a spray paint can, one of the motors, and a battery so that you can get an idea of the size:)

EDIT:
i also decided on putting the motors in the center, later on down the line i am going to try and implement a suspension or hydraulic system.

[crabfu]

Wow that is huge... awesome!

[seesoe]

ya:P

its all designed around the wheels, i think the size of the body to wheels ratio worked out nicely:)

cheers
seesoe

[seesoe]

hello all,

i been busy searching parts and stuff, i got some new tires and ordered a big order for the drive system.

TheBigBearingStore.com is an amazing place, i love to buy from them, here is the stuff i ordered.
8 - pillow block bearings 3/4 shaft
4 - 4 bolt flange bearings 3/4 shaft
1 - 3' 3/4 keyed shaft
1 - 20' #40 roller chain
8 - #40 roller chain connector links
12 - 18 tooth 3/4 bore sprockets (4 for the wheel axles, and 2 for each drive side)
4 - 18 tooth 5/8 bore sprockets (will be milled to 17mm, 2 for each motor)

i have a local friend that has a contract with a hospital and he gets all their junk, i got my old robots back tires from there.

so i revisited him and got 4 more tires, 2 of them were the same size and but wrong style hub. the other 2 where to big but the right hub, so i bought all of them and changed out the hubs.

the top 2 tires in the picture below are the original tires
the middle 2 tires are the ones that im going to swap the rims with the bottom rims
if i do find 2 more tires the same size as the bottom ones ill go with those instead, they are i think 15 inches, and the tires im using are 13 inches.

till the shipment comes, for pictures:)
cheers
seesoe

[seesoe]

bought the controller, my old robot's AX2550 controller unfortunately messed up (tear, $500 bucks)

I bought the AX3500 (http://www.roboteq.com/brushed-dc-motor-controllers/ax3500-dual-60a-brushed-dc-motor-controller.html) this time, it has more features, however it is half the amps of the AX2550, which is 120amp

some weight specs of the bot will be as follows
2 X 55 AH 12V SLA's - 40 LB each
1 X 33 AH 12v SLA ~ 24 LB (might have 2)
2 X geared motors - 16.5 LB each
55 pounds worth of chain, sprockets, bearings and shaft. (says ups)
4 X 13 IN Tires - 9.5 LB each

so about 230 pounds with no frame, so maybe a little over 250 pounds with frame

till next week
cheers
seesoe

[Adrenalynn]

That's a pretty expensive 40A controller (60A peak, but that's marketing for ya)

I'm a big fan of the RS-80D in that size range (80A continuous per channel, but I've peaked them much higher before) for about $100 less.

[seesoe]

yeah it was, but i like them, im used to their system, and im not a good programmer yet, and their product comes with software that gets the bot moving, so i can learn at the same time.

those are nice controllers, I'd probably change it up with my next robot and use one of those. I've seen them before, on this tank http://www.eigenspace.net/robot/ (nice work he has done i might add)

cheers
seesoe

[seesoe]

well its Monday, drive parts came in

now i need to more the wheel hubs to a standard size and then the first column of sprockets on the right need to be bored about a millimeter bigger (17 mm)

you'll notice there is 10 pillow blocks, guess someone got confused with all the stuff i had bought and put 2 extra in:P bill said 8

anyways still Wednesday when the controller comes in:)
cheers
seesoe

[seesoe]

here is the controller, the serial cable, and the rc outputs

im going to try and start building the frame this weekend so stay tuned:)