My copy of Admin's ERP

[Kelpy]

I started in this hobby about 6 months ago, and have built various different simple robots - photovore, line follower, object avoider etc, and always seem to have to build a new chassis from the ground up.
I have decided that I need a platform which can be adapted to all sorts of different "experiments", not least video object recognition.
Having read all about Admin's ERP through it's development, it made sense to me to use his design, which is tried and tested, and make my own ERP.
I don't have the luxury of CNC or machine tools etc, so it will all have to be done using hacksaw and dremel.
I have bought a small  offcut sheet of 6mm HDPE, and will be using this for all the main components of the chassis.
I have made the main chassis, and have fitted 2 continuous rotation servos to it so far, together with a couple of wheels from a child's truck. (No way would I be able to make Admin's wheels using my hand tools - and skill - lack of   )
We'll see how it goes
Here's a picture of it so far.

[Fr0stAngel]

shhhhh...!don't tell admin, i was planning the same thing...! 
Good Luck with yours ..

[Admin]

I'm definitely following this thread!


Remember, if you have four wheels, you need some form of suspension. There are many ways to do it, mine was just a fancy experiment


as a reference to anyone else, the designs are completely open sourced here:
http://www.societyofrobots.com/robot_ERP.shtml#opensource

[Kelpy]

shhhhh...!don't tell admin, i was planning the same thing...!  
Good Luck with yours ..

Thanks, Fr0stAngel. Feel free to hijack this thread for yours, if you want

Remember, if you have four wheels, you need some form of suspension. There are many ways to do it, mine was just a fancy experiment

I am currently trying to cut out the front wheel supports, as per your design, so it will have some suspension on the front. Bit fiddly though, doing by hand.

By the way, Admin, I hope you don't mind, but I'm going to post this "build" thread on another site, as well, LetsMakeRobots. It will get more exposure and hopefully it will encourage more people, especially youngsters, to follow your lead and get involved in robotics.

[Kelpy]

Found some standoffs about the right length, for the AxonII and the 2nd tier.

[raptorwes]

Looks good. Keep it up! I have been thinking about making something similar.
2 questions though
First, I notice some people mount their servos above the bottom plate and others below. Is one way better than the other?
Second, why if you have 4 wheels do you need a suspension, how is it any different than a 3 wheel robot?

[Admin]

First, I notice some people mount their servos above the bottom plate and others below. Is one way better than the other?

Keeping weight low helps with balance, especially when the arms are swinging around.

Keeping weight higher lets your robot go over larger objects when driving around.

Second, why if you have 4 wheels do you need a suspension, how is it any different than a 3 wheel robot?

Three points are guaranteed to be on the same plane, whereas four points are not. If you have four wheels without suspension, and the ground isn't 100% perfectly flat, one wheel will be off the ground. This means a wheel will spin without anything happening, and your robot will rock back and forth.

[raptorwes]

Oh, ok that makes sense

[Kelpy]

After a bit of a struggle, I have managed to cut out the front suspension/wheel supports. There is no way I would have been able to make the axles out of HDPE, but I found some 8mm aluminium tube in my shed. The chrome hubs are in fact left over from when I used to repair prams and buggies (20 odd years ago - I don't throw anything away) 

[Soeren]

Hi,

(20 odd years ago - I don't throw anything away) 

Yeah, that's a curse we all bear... According to our slightly disapproving GF's/Wifes 

Why not stick to a single wheel in front? (especially when considering the price on omni's).

[Kelpy]

Why not stick to a single wheel in front? (especially when considering the price on omni's).

I can actually see the sense in having this set-up, with 2 arms and the possible weight they may carry. If only one wheel was used, there may be a tendency to tip. (But who am I to say - I'm just copying Admin's design  )

[Fr0stAngel]

Thanks, Fr0stAngel. Feel free to hijack this thread for yours, if you want

Thanks , but i'm really in the design phase right now. And i am deficit on budget ( cant really afford an axon right now ), so i'm designing my own cheapo board using the basic AT89S52.  plus ill probably be going for a three wheel setup. i was thinking of an omni base, but then again  $$ ( i think my craving for robotics will compel me to get a job soon  )

I'll be following your work keenly , but just a thought that it might be better if you could modify your first post every time you update about your ERP, ( with day or a timeline), that way it would be all together and easy for newer readers to follow...... but that's just me..

one question though, any idea about the approximate weight of the final thing?

[Kelpy]

I'm not sure about the final weight yet, Fr0stAngel, haven't got all the stuff for it yet.

Anyway, yesterday, I cut out the 2nd tier, and the mounting blocks for the 2nd set of shoulder servos. Assembled them this morning.

The bad news is I've got to cut out the arms, now. That'll take a while

[Admin]

wow

I really like the way you did the axle things, too. I might just copy it on my next ERP upgrade

Also of note, don't bother with that clear plastic sheet that goes above the Axon. There is soooo much servo wiring I can't even close it any more. My recommendation is to make a square plastic sheet, and velcro it over the location of the Axon. Don't bother with the hinge like I did, it didn't work out so well.

Why not stick to a single wheel in front? (especially when considering the price on omni's).

I tried that on an earlier version, but the problem was it couldn't stop from almost tipping over with the arms swinging all over.

[Kelpy]

Made and fitted the upper arm sections.
I have also tested it with a RC setup, to make sure it actually works  



[youtube=425,350]c0c-xlHXPOc[/youtube]

[garrettg84]

Awesome bot! I'm following here and on LMR. Excellent credit to SOR and link ins from LMR as well. Admin will be proud =)

[Ro-Bot-X]

Beautiful! And is powered by WebbotLib! Cool!

[Kelpy]

I've managed to find time to complete the arms and claws.
I have modified Admin's design for one claw, so that it operates in the horizontal plane. My thoughts are, that with the 2 different actions, they should be able to pick up different shaped objects.





I have to say, I find HDPE very difficult to bond, and have tried all sorts of glues, without success. In the end, where I have rotated the right-hand arm through 90deg, I've had to fix it in place using my soldering iron 

[Admin]

I have to say, I find HDPE very difficult to bond, and have tried all sorts of glues, without success. In the end, where I have rotated the right-hand arm through 90deg, I've had to fix it in place using my soldering iron 

LOL
You should use two 90deg brackets.

How'd you cut those claws out? Very nice job!

I'm pretty excited because now we can even share code, as anything you develop I can steal use on mine

[Kelpy]

Hi Admin.
I did consider making a couple of brackets, but thought that may look too bulky.

How'd you cut those claws out? Very nice job!

They don't look so good close up. They were cut with a hacksaw, drill, and Dremel grinder

I'm pretty excited because now we can even share code, as anything you develop I can steal use on mine

Fat chance of that  I find C very hard to grasp, and can only just about use some of yours (or Webbot Designer), modified to what I want 

[paulstreats]

I started in this hobby about 6 months ago

 Well done, considering that you have only been working with robotics for 6 months, you seem to have a "knack" for structural design.

 The robot is looking great, it would be good to have somebody like yourslef to help and advise in the mechanics department on this forum.

 Just out of interest, how much weight are your ERP arms capable of lifting, and is there any point where weight can affect the stability of the robot?

[Kelpy]

I haven't actually done the maths to calculate the lifting ability, but I know they can lift a plastic bottle weighing 200 grams without strain.
It really depends on what servos you use, and as funds were tight, I have not gone overboard with the servos. I did roughly calculate in my head beforehand which ones would be sufficient to lift a tennis ball or a small can.
Admin has conveniently made a calculator for us  here
http://www.societyofrobots.com/robot_arm_calculator.shtml
As for stability, I have not yet had chance to get that far, but I suspect the weight the arms would lift, would not get anywhere near heavy enough to affect it. No doubt Admin will shed more light on that.

[Admin]

paulstreats, he actually just copied the designs I put up (which has measurements for everything).

As for stability . . . its not just the weight of objects picked up, but also dynamics as well (ie picking something up fast vs slow). Mine hasn't fallen over yet, but I can probably get it to happen if I try in certain situations . . .

[Admin]

updates?