Building

Hi guys, need some advice.
Ive always wanted to build a heavyweight, and am thinking about building a cheap(ish) sacrificial/comedy one for one of the events by buying a second hand electric wheelchair off Ebay and using the bits from it.
Before I go ahead and get too eagar though, can someone give me some advice. Does an electric wheelchair give me everything I need (except of course, radio gear) to get a heavy going. I just want it to be drivable, dont care about it surviving.
Any help or advice would be great.
Cheers. Dave.

Hi Dave,
if your building something for a laugh then yeah you can use this, you need to do a bit to get a bit more speed etc.... you can use the stick of it as your speed controller just attach some servos to it.

Using old wheelchairs is a proven method of building heavies, not just sacrificial ones. Even though they are not top of the bill motors for heavies, to move your weapon across the arena they are more then adequate.

Like Adrian said, if you want to use the speed controller of the wheelchair, just connect some servos to the steering stick and your off. Do remember to failsafe the servos though.

Hi Dave
Old wheelchairs can give a good source of parts, you can use the speed controller with a couple of servoes, but you may be able to change the gearing on the motors for more speed, you will need some different batteries.

Good building

DaveMac

Cheers guys.
Id be on a really low budget if I do undertake the project, but Id like to give it a go at some point.
As with all my bots, nothing serious, just fun.

Dave, Ill do my best to dig out the motors and controllers I have. Ive found one of the motors. Ill empty out my shed for the other motor and controller tomorrow if I can. Ill let you know.

Cheers Rhys

Hey, I decided to recycle an old thread as Dave Lawrie is the guy who I am building a new heavy with.
We had a test heavyweight at Aylesbury to have a go at building and fighting a heavyweight.
Since we had a blast we decided to have a more serious go. We (well so far I) have been working on a new heavy.
http://img339.imageshack.us/my.php?image=robotbuilding042sy2.jpghttp://img339.imageshack.us/my.php?i...ding042sy2.jpg
So far so good and its coming together well.

I have run into a few issues which I could use some advice on.
First off I have some sprockets with 12 mm bores. These are not sitting on the axel and will be attached to wheels which have bearings in them. Basically what is the best way to bore these out to around 16mm? It doesnt have to be too acurate but I dont fancy making a mess out of it.
Second is speed controlle.
As you may have noticed I have 4 12v 400 watt motors. These will be overvolted to 24v and on paper should give 6.4kw of power.
Now I know that quite a figure. I was origannly planning to use a Wotty controller as they sound very nice. But I doubt they can handle this crazy current.
I could use two vantec or roboteq controllers but I have heard that some models are getting dicontinued and I am not made of cash.
What seems like an option is buying 4 120 4qd pros which mark lumb is selling.
Would this seem good or should I stay away from 4qd which seems to be the advice i get from many roboteers.
Your advice is greatly apreciated
Marco

Hi Marco,

Looking good!

Your best bet for boring the sprockets is either a step drill or a lathe with a four jaw chuck. You could likely use a mill to do the job also if it has the right clamps.

Driving the motors should be fairly straight forward. A Roboteq HE should be up to the job although I wouldnt guarantee it. Perhaps reducing the voltage to the motors would be a good idea?

Hey kane
Reducing the voltage isnt an option I would like to take at this time. The robot was initially going to be invertible. It was going to run on large 8inch wheels till I was informaed that I was doubleing the voltage on the motors so I would have a large increase in rpm. So I changed to small wheels and so shorterned the chassie.
Thanks for your input though.

Quote from John Reid regarding the 12v Bosch motors.
The 400W motors in the catalogue have peak power between 700 and 800 Watts.

So ... 750 watts @ 24volts instead of 12v = 6kw each motor..... will it get anywhere near this calculation in reality ......dunno.

.......are you serious...!?
that cant be true

Yes....I believe so ...could be wrong.

Download Tornados spreadheet....it has the bosche 400w .....alter the voltage ...gear ratio etc.

http://www.teamtornado.co.uk/ssheet.htmhttp://www.teamtornado.co.uk/ssheet.htm

A quick look on mine gives frightening numbers for amps draw.
Also remember the electric motor aint very effecient ....perhaps 60% at best....so youll be throwing more amps in than power out ..... so MORE amps than the motor calculation. power...these missing amps end up as heat ....youll be able to fry an egg on the motors:).

6kw - it will probably get to that if you were to stall the motors but I have a feeling that the wheels will spin on the arena floor before that happens.

In terms of boring out the sprockets, I would recommend doing it on a lathe. If you arent in a rush and the sprockets are small enough I could do it for you. Although my lathe is a small model makers lathe and I am currently busily getting both a feather and heavyweight ready.

Email me at gary.cairns at strath.ac.uk if you want to chat about it.

Spreadsheet says .....Peak motor power 2.68kw
45% efficient and 247 amps draw.

youll be able to fry an egg on the motors. if as Gary says you get anywhere near using the available power continiously.

Tsk BAD Calc not 6kw ...3kw!


(Message edited by woody on June 25, 2007)

(Message edited by woody on June 25, 2007)

ok i think I am done freaking out from how much my motors draw and thanks for the sugestions on how to bore out my sprockets. Gary I might get back to you on that.
What controllers would you recomend?
I cant seem to find any info on a roboteq HE. Sorry if its a bit obveous but I cant seem to find it on the roboteq site or the robot market place

http://www.roboteq.com/ax2550-folder.htmlhttp://www.roboteq.com/ax2550-folder.html
AX2550 AX2550HE AX2550SC AX2550HESC AX2850 AX2850HE AX2850SC AX2850HESC

Another possible is the Ampflow.

http://www.ampflow.com/motor_controller.htmhttp://www.ampflow.com/motor_controller.htm

(Message edited by woody on June 25, 2007)

ooh i like the ampflow. Any paticular reasson why it looks exactly like a roboteq?

Because it is essentially a Roboteq ...