Starting a new build... something...

[ChILd_ReBoRn]

So. After a long, long time tinkering with various cable driven machines, and finally setting up a small utility vehicle that I called a Poor Man's Dozer, or PMD for short, i decided to embark on a long journey called RC tech. I have absolutely no experience in RC technics, so I'm a total noob in everything related.

I've decided to build another all purpose vehicle, with a blade, and with a 3 point hitch for some implements. Speaking of witch, I just realized I forgot to order a 3rd ESC for the implement motors. Blah.

So, what do I have already:

flysky 6 ch remote
2 ECS's
2 drive motors (40 RPM worm gear, hopefully enough torque)
4 10 kg servos (metal gear)

I still need 3rd ECS, 11,1V LiPo and some kind of drive train.

My current dozer has heng long plastic tracks from a panzer III tank. They work great, have enough grip, but look silly with a narrow footprint. I found some new ones, rather cheap, plastic or metal ones with a 45mm width, but I'm not sure what sprockets they need.

If I managed to connect everything as it should be, in my head, this setup should work:

blade servo to one channel
3 point hitch servo to another channel.
Left motor to ECS, and ECS to servo and battery.
Same for the right motor.

That leaves me with 2 free channels

One channel would go to another ECS and a jack port for implements (a mower, logging winch and a tipper), and that leaves me with one channel. I think I'd use it for lights or something. How do I connect the lights? is there any kind of an interface or do I directly plug them in into the receiver?

And last thing.. how do servos work exactly? are they always self centering, or are they reliant on the TX stick position?

for an example.. if I put the blade control on a non spring loaded lever, and push it all the way one side, would the servo move to one side and stay put? Would it stop in all positions respectively of the lever position? When I push the directional stick forward, does it work like a throttle? slight push motors moves slowly, bigger push motor runs faster? same as a potention meter regulated PWM?

thank you for now.

I have no fancy tools, nor any money, so this will be a simple build.. no fancy milling and expensive parts, but.. to each his own. As long as it's pushing dirt.. I'm happy

PMD V 1.0

PMD V2.0








video

everything is rather crude, but it's functional. As I said.. only basic tools used

[Wombii]

Looks like a fun project! I especially like that control box.

For your servo questions:
Servo angle = stick angle. The servo will move proportionally to the stick. Move the stick to 40% and the servo will move as quickly as it can until it reaches the 40% position and stop. It does not self center unless the stick self centers. If the servo is connected to a channel controlled by a 3 position switch instead of a stick, the servo will move to the 0% position with the switch down, 50% position with the switch in the middle and 100% position with the switch up (The exact positions can usually be adjusted in the transmitter setup with trim, dual rate, mixes and End Point Adjustment).


Bonus technical answer:
Internally, a servo is a motor, ESC and a feedback potentiometer connected to the output gear. The feedback pot works in the opposite direction of the signal from the receiver. If you open the servo and mechanically disconnect the pot from the gear, you can actually control the speed of the motor either with the stick or by adjusting the pot. If you use glue on the pot or replace it with fixed resistors it will work exactly like an ESC and motor. When the pot feedback and stick signal cancel each other out the servo motor stops.
In other words: If stick signal is lower than pot signal then spin motor left. If stick signal is higher than pot signal then spin motor right. If signals match then stop.
Because of this a hacked servo can be used as a motor/ESC combo or a PWM dimmer for lights.

To control lights from a receiver channel you'll need a control board of some kind. This can be a hacked servo, an Arduino, an RC light kit like this or an RC switch like this. Frizzen has a great servo light controller hacking tutorial here in the electronics section.

I hope this helped, but I'm not always good at explanations outside of my own head, so feel free to ask more

[skeeter]

I love the PMD! It's a neat lil budget friendly machine!

[frizzen]

Very cool project! That looks fun.

Each track drive motor only needs an esc, it doesn't need a servo also.

If you want the lights on any time the models turned on you can tap RX voltage and not use a channel to turn it on/off. If you want to switch lights on/off from the remote, check out the links wombii posted.

This will be fun to watch

[ChILd_ReBoRn]

Thnx guys. Can't wait to get the stuff, and start building

[ChILd_ReBoRn]

So, after a lot of thinking, I decided my build would go something about this:

https://www.riverlandequipment.com/u...ginal/4660.jpg

I really can't fathom why did they make the track setup the way they did, but, since it will put the motors in the back, it will leave a lot of space up front for electronics, servos and battery.

I have a few questions:

1. How do you calculate chassis size? I made it 33cmx16cm, but when I placed the idler wheels I had as spares... they looked ridiculously small, so I downsized the chassis to 24x10cm. That looks small, but since the tracks are 45mm wide, that would give me an overall width of 190mm which is enough, and with the blade up front, it will be around 30cm long. Since my motors are only 8kg/cm (stall torque) better to keep things in the right size department.

How do you make your cabs? I saw people using styrene, but that's way to brittle. How do you mold plastic? or is there another way I'm not aware of?

[Wombii]

I love these forums. I feel like I learn about new machines every week. That is the fastest dozer I have ever seen. https://www.youtube.com/watch?v=N3K9-Mwhd6M

I know nothing about building scale construction equipment from scratch, so I can't help you with the chassis, but I'm curious as to why you feel styrene is too brittle. In my experience it's a very good mix of flexible and strong. I could probably stand on some of the pieces I've made for my fire truck from 2mm plates.

[ChILd_ReBoRn]

um.. when I type sytrene in google, it gives me a lot of sytrofoam links. Including food trays and stuff. That all looks very soft, and breaks easily

[ChILd_ReBoRn]

ok.. I've googled a bit more.. and found what you guys are talking about.. it's some dedicated modeling plastic... that styrene... not sure where to acquire that here...

[ChILd_ReBoRn]

As I said, finding plasticard here in Croatia is near impossible. I'll either order it or make do with something else. It's really expensive for a piece of Styrofoam.

I managed to get the chassis assembled and motor brackets mounted. I can't really do anything else until sprockets and tracks arrive. I will try to figure out how how to make track tensioners.

[Wombii]

Ahh, yes. That would explain it. These polystyrene materials are chemically the same as Styrofoam, but completely different in structure. They are not a foam at all. More like a credit card. I've only tried Evergreen, but Plastruct is another popular hobby brand. You may be able to find the same material in large sheets from a plastics material distributor or a store for construction materials. I like it because it's easy to cut (score with a knife, then bend to break it off) and makes a very solid bond with a solvent based glue. I don't have experience or a suitable work space for working with metals, but you seem to be good with it. I'm sure you can make a very nice metal cab if you prefer that. Brass is a popular material for detailed work as it can be soldered with normal tools.

This is a good intro to working with styrene: https://www.youtube.com/watch?v=uJQ71o1qqWw

[skeeter]

What You've got made so far for the chassis looks pretty good.

[ChILd_ReBoRn]

Ok. MY Tx came extraordinarily fast. It even avoided customs, so it was really cheap. I managed to mix the channels so moving the stick up both motors drive in one direction, moving the stick down, they both reverse. When moving stick side to side, motors work in alternating directions, so I can steer on a dime. I will see if the need arises to lower the response of individual motors to simulate better steering.

I made the rear idler wheels, and now I have to tackle the front ones. They should be able to tension up the tracks, so they can't be fixed. I'll see will thgey be tensioned by screwing them or with spring loaded system like my old PMD has...Really cant make much progress until my tracks and sprockets arrive. Keep you posted...



The axles will be shortened when I see the exact track position.

[ChILd_ReBoRn]

Blah. I don't like it. Will redo it. I have a vision..

[ChILd_ReBoRn]

I like this way better.

There are 3 road wheels going between the idlers. Still haven't sourced them..

Will see if they can get some sort of suspension, or will they be rigid.

[ChILd_ReBoRn]

I think the last one is to far to the front. I'll have to move it back and possibly add another road wheel

[ChILd_ReBoRn]

So, prototype chassis is done. Have to thread the axles when I cut them to size. Decided to go full rigid, like a normal dozer.

[ChILd_ReBoRn]

Weeee.. Got the esc's, Tx, LiPo and xt60 connectors.

Voila.. My first ever RC vehicle.. Lol



My new motors still didn't arrive, so I had to jack the PMD v2.0 for testing.

Reverse is slower that forward movement, and because of the brake, there's a delay while operating motors. A bit annoying. I have to double tap the stick to move the motor in reverse..

[skeeter]

The PMD is looking pretty good!

[ChILd_ReBoRn]

thank you. It's still early to give it true judgement