Still Here (Just about!)

Greetings all,

Feels like ages since I last posted on this forum. Since starting uni I just have not had the time or money to put into the robots like I used to.

This was by no means a choice, but a consquence of the changes in circumstances surrounding my every day life.

For me, building a robot relied on being able to spend an hour or so a day, tinkering away in my workshop to create somthing cool at at the end.

Living 200miles away from home meant I didnt have this workshop access, and when the holidays came up I was just too busy with other things to be able to work all day every day on bot building to make up for lost time.

Dont worry, this is not another post to say Im quitting; quite the oppsite infact. Its just a post to let you all know im still alive :lame: and that sooner or later I will build another robot and get back into the roboteering hobby.

Currently Im working on a project restoring and retrofitting a 20 year old 2.5ton bridgeport CNC mill.

Hopefully it wont be too long before I have the thing running. Despite the vast scale of the thing, I was able to apply most of what Id learnt from building robots to make this work.

I have a blog of my progress here for those of you who are interested. http://www.ukcnc.org/forum/viewtopic.php?t=4http://www.ukcnc.org/forum/viewtopic.php?t=4

(If you choose to join the forum, please post somthing so I can tell you apart from the spambots :-))

The other thing I wanted to do was ask you all for a bit of advice on another mechanical project I will be starting soon.

Next month our village is holding the annual Whacky Races event where we close off the road from the top of the hill by the church down to the village hall.

Entrants have to build a gravity powered kart (no other forms of propultion allowed) which will be raced all day in a series of time trials.

Winner is the one with the fastest time.

I need to build a kart to enter in this race and I would welcome any design tips that would help me build a winning kart.

My idea is to build somthing as low and light as possible whilst keeping it quite wide to increase stability. The hill is quite steep so i dont think extra weight will be needed to provide additional inertia.

I would welcome any sugestions on materials to use, what type of chassis, brakes steering etc. I suppose it needs to be similar to the robots in many ways .. light as possible but still strong enough to survive a crash, and more importantly in this case, minimal ammounts of friction and wind resistance.

I suppose wheels are a important consideration. Would wide tyres cause noticable frictional losses ? Last year I used road bike wheels but Id prefer not to use these again as they have to be supported from both sides which makes the chassis much bulkier and heavier than it otherwise need be.


Any suggestions will be much appreciated.


Dom

if you do not need to go around corners, have solid ali or steel wheels running on the rims, with as big a diameter as possible.
Making it heavier helps.
but then this all goes out of the window if you have corners as lighter with grip is better.
good luck with it.

http://www.stotfoldscouts.org.uk/soapbox/instruct.htmhttp://www.stotfoldscouts.org.uk/soapbox/instruct.htm
:proud:

lol

is that the new renault F1 car?

There is one corner at the bottom of the hill but it is quite substantial.

I will try to upload some footage from last year to give you a better idea of the course.

Lots of stuff on the redbull site.. I saw one a few years back which suspended the driver inside a cage shaped like a red bull.. absolutley mad
http://www.gravityengine.co.uk/redbull/http://www.gravityengine.co.uk/redbull/

Dom, I am seriously impressed. Very good work. As you know, we both have the same mills and I love my TNC 151 controller.

First of all, I will point out that the mill only uses single phase. I had better explain that. ALL the various different parts are run from single phases ie:- the Spindle motor is on phase one, the servos on another and the TNC on the other. The only thing that uses all three phases is the spindle brake. The spindle drive upon braking momentarily puts all 3 phases onto the motor.

I did read your blog but not in great detail. Did you get your manual? If not give me a call and you can borrow mine and copy it.

I hope you get as much fun out of your machine as I get out of mine. However, I now have another mill as well! Greedy me. lol.

Mike.

Mike, thanks for the words of encouragement. I saw you had posted and was thinking to myself, oh no .. hes going to have a go at me for not using the machine in its original configuration :lol:

Im not too sure about the power thing. On the old bosch drives there were power inputs on the PCB labled 415v.

As for the spindle motor, it is a shunt wound dc motor which according to the data from contraves needs 400v on the armature to operate at the correct max speed.

While our machines may look similar, I think internally there could be differences.

Does your spindle motor have a 24v electromechanical (wheelchair style) brake as well?

Thanks for the offer of the manual but I do have one of my own. It was one of the first things I bought. Didnt come cheap, but the time it saved was priceless.

I already have my mind set on a VMC, but this one will have to pay for it so I have a good incentive to get this one done.

The good thing is that when I got this one home I found it wouldnt fit in my workshop so I had to find an alternative home. As a result, I now have space for about 6 VMCs with room left over for a cnc laser or waterjet :proud:.

I cant wait to cut out my first part, though if progress carrys on at the current rate that time might be as soon as 4 weeks from now!

Back on the subject of gravity karts, is it more advantagious to have the back wheels with separate axles (one per wheel) or a single one running between the two ?

With one axle I could get away with just two bearings, but then id have the weight of the extra length of axle, with independant axles id save weight on axle length but would gain it on two more bearings. Which one would have the frictional advantage? Would there even be a noticable difference between either config.

I guess the main reason im asking this question is because I want to go for a single rear axle congfig so when im not using it on the race day I can bolt a gurt big motor to it, but i dont want to include this option if itll give me a disadvantage when running on gravity power.


(Message edited by Ukrobotics on March 18, 2007)

Funnily enough I investigated something similar to what you are planning a while ago, gave it up but here are some points that may be useful to you.

Remember that as you go around a corner, the outside wheel travels further than the inner wheel. This obviously causes problems with a single axle configuration. There are two ways to get around this,

1) Use a differential - expensive, heavy and not really viable

2) Use the same method as a go kart. A go kart has a single axle across the back. When it goes around a corner it is light enough and powerful enough to spin one of the wheels as it goes around the corner. This does mean that your tyres wear down quicker but the saving you make on a diff makes it worthwhile.

As for the axle itself, you can get a hold of some light aluminium hollow axles on ebay. I have just bought a solid steel one for the front of my new heavyweight for a fiver plus a few quid for delivery.

Good effort on the mill! Looks exceptionally impressive.

(Message edited by typhoon_driver on March 18, 2007)

Yes Dom, it does. and if left for a while without running it does seize. The 400V is for the brakes as I said.

I looked at your pis. Its all the same stuff.

BTW, your old TNC 151 was a 4 axis controller. All you were missing as the drive units.

Mike.

Mike: The tnc was blown as was the spindle drive the price of getting those repared/replaced alone was equal to the cost of an entire retrofit; thus why i chose that option.

Its going to be good though as everything is being done properly. Removed the spindle motor and took it to a specialist and they cleaned out all the carbon dust, skimmed/undercut the commutator, replaced the brushes etc... That reminds me one more thing that definatly is 3 phase is the blower motor on the back of the spindle motor. They have made a capacitor based phase conversion circuit to make that work off single phase.

Thanks gary, I hadnt thought about that. When under power it would be fine, but as its gravity powered in the race i think i will go for separate axles. (one per wheel).

Last year I tried to make my kart skid steer. I figured with really narrow wheels with quite low friction I might be able to get away with it. No such luck though. As soon as i stopped one wheel, all the others stopped too!

Dom, you may wish to use wind power in your favour. If you made the floor pane like an aerofoil, you could use the resulting lift to reduce your drag.
just a thought.

just a small point, on a properly set up gokart, the solid axle works by actually lifting the inside rear wheel, not by spinning it. the best way to get this effect in your soapbox is to use an inclined front kingpin, so that turning the steering wheel moves the wheels slightly up and down as they move side to side, lifting one off the floor. this allows you to wiggle your inside rear in the air, even when static, if you get it right. this lets you go around a corner with a solid rear axle.

James, I do believe that MacLaren are looking for you.

Mike

they had their chance mike :)

Im struggling to find a cheap but effective brake solution for this soapbox.

Ideally Id like to go for disc brakes, but they seem to be prohibitively expensive. A front & rear brake disc set-up for a mountain bike seems to start at about £100 on ebay. Is there a cheaper way of doing disc brakes, or an alternative that will be just as simple and nearly as effective ?

Last year I used bike wheels and was able to use the V/caliper brakes that came with the bike. This year I want to move away from the bicycle wheel idea as they have to be supported from both sides which means the chassis has to be much larger , heavier and less rigid than it would be for use with wheels supported from one side only.

Does anyone have any suggestions for building/obtaining a cheap but simple and effective braking system ?

what wheels are you using ?

the traditional soapbox brake is a wooden lever that acts directly on the tyre... if you fitted two you could have tank steering!

get that rotten constrictor thing off your profile pic, and put up a pic of your racer

Si: Not 100% sure about the wheels. The £5 sack truck wheels from northern tool seem like the ovbious choice though im a little concerned the small 10 diameter might reduce my top speed too much.

(That is assuming that the wheel diameter affects the speed in a gravity kart in the same way it would a powered one)

Rob - Tried the skid steer idea last year on the grounds of minimal moving parts and maximum simplicity but it didnt work!. When one wheel stopped all 3 others did too.

Im thinking the lever on the tyre might be the better appoach ..the more I look into it the more I realise discs are complicated and expensive.

As for calling constrictor a rotten; how dare you! :P Ill remove it if you remove the rotten carrot from yours.

I actually have nothing to show right now as everyting is just in my head or scribbled on paper. Once ive made some progress ill share some photos.

What if you used two moped wheels on the rear, then you could use their drum brakes.

PS, how long is the course ?. A heavier cart might be slow on the take off but would be faster later in the course

Finding a cheap scrapped moped might be difficult and I guess it would be excessivly heavy.

Course is no more than 200m.

This approach seems simplest..
http://www.gravityengine.co.uk/redbull/viewer.php?id=153http://www.gravityengine.co.uk/redbu...wer.php?id=153

Tiller for steering ...std push bike brakes ...reclined seat.

Perhaps you could get clever and add a lean mechanism?

Someone made one like that last year - it was very unstable and buckled two of the 4 wheels.

Heres the video from the 2006 event: http://www.youtube.com/watch?v=AgLngG9rUychttp://www.youtube.com/watch?v=AgLngG9rUyc

Another idea for brakes is just the flinstones method . Just cut a hole in the floor and put your feet in to stop or alternatively just something that would create friction .

it was very unstable and buckled two of the 4 wheels.

Sling yourself LOW ,reclined with bum just off the floor....cut the frame and cant the rear wheels in a little at the top ....make a foot rudder bar to steer.
Edit :- A long hand tiller and foot operated brakes might be better ... a lot of probs seem to come with oversteer.

Come on your an engineer!

Or just get a racing wheelchair.

(Message edited by woody on March 31, 2007)

(Message edited by woody on March 31, 2007)

LOL ....A similar design at approx 4 mins in to the video didnt do very well!

His rear wheel buckled under the side strain before he crashed.

(Message edited by woody on March 31, 2007)

:lol: - The kart at 4mins into the video is my kart being driven by me!

Whoops!

Here ya go Dom, ready to rock
http://cgi.ebay.co.uk/NEW-DEMON-BOGEY-GO-CART-DEMON-70_W0QQitemZ280098436680QQcategoryZ137893QQrdZ1QQc mdZViewItemhttp://cgi.ebay.co.uk/NEW-DEMON-BOGE...0098436680QQca tegoryZ137893QQrdZ1QQcmdZViewItem

Nice shot Dom - but not quite.

My suggestion
Use wheels that can take sideway force for the back axle.
Use 1 heavy wide tyred wheel at the front - use wind pressure to increase its apparent weight.
Use wings beteen chassis and back axle to lift up body and redce apparent weight on other 2 wheels.

was looking for somewhere too post couldnt of found a better place, my apologies for my resent absence missed alot of events but there is a valid reason.

Ive not long got out of hospital after being treated for bactiral Meningitis, pretty much knocked me for 6 and i only just got it in time before i was too ill. Im not quiet upto events atm but will be back soon

best of luck too all

Get well soon Craig