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Offroad Robot - Team AJW - Vic
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Andrew W



Joined: 01 Jun 2005
Posts: 220
Location: Melbourne, Victoria


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Offroad Robot - Team AJW - Vic

Thought I had better make a build thread for my offroad bot.

Drive System: 2 200W Oatley scooter motors chain driving 4 16" wheel barrow wheels
Controller: 28X Picaxe outputting 2 channels of PWM to 2 350W Oatley Scooter motor controllers.
Radio: Spektrum (atm - autonomous down the track)
Batteries: 2 12V 18A Diamec SLA in series.

Got ideas of making it a mobile platform for testing various sensors and ideas.

Looking at putting a computers motherboard in it to provide speech, wireless control (2.4GHz WiFi), onboard image analysis (down the track) and plenty of I/O.

Also playing around with the idea of remote telemetry, although might need to go for 5.8GHz AV to achieve it.

Post Tue Feb 24, 2009 6:56 pm 
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Andrew W



Joined: 01 Jun 2005
Posts: 220
Location: Melbourne, Victoria


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I've already got the motors, chain, sprockets, wheels and got some steel to make a frame (just need to organise connection of the wheels to the 80 tooth Oatley sprockets).

Already got most of the electronic parts, just need to assemble the 5V and 12V regulation circuits (already got the parts for them) and finish building some of the kits.

Using a PC allows easy programming (running DOS Smile), cheap add-ons (Text To Speech via an old sound card), plenty of I/O and heaps of memory (looking at putting at least 256MB of RAM and a CF card for storage).

Post Tue Feb 24, 2009 7:04 pm 
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Fish_in_a_Barrel



Joined: 30 Sep 2006
Posts: 673
Location: Perth, Western Australia


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Advise against Diamec batteries, they don't bounce well. Try to get your hands on some DOSS ones instead.
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Post Wed Feb 25, 2009 11:59 pm 
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Spockie-Tech
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Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


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Agreed.

Diamec are Gel-Cells - My experience is they dont cope with heavy currents (in our out) or mechanical shock at all well.

I dont know for sure, but suspect the Electrolyte Gel probably fizzes a bit or something reducing surface area in contact with the plates, when you push amps through it, The jaycar spec says no more than 5amps charge, which is low for a SLA.

Unlike a wet-cell where the electrolyte just bubbles gas if hammered, or AGM where the electrolyte is "Absorbed into a <fibre>Glass Mat" and pressed against the plate so it cant move easily if things get warm.

Also had (and heard) of them suddenly losing major voltage after impacts - again, suspicion only, but I'm guessing the plates are moving inside the battery, squishing out the gel, and shorting out cells.

The AGM style cant do this, because the mats between the plates act as solid insulators preventing inter-plate contact.

DOSS are Radio Parts cheap chinese brand AGM batteries, but they seem to do pretty well in combat based on our experience prior to moving to NiCds and others.

You can buy them online from http://www.radioparts.com.au/ - The 12v 7Ah bricks are the best ones to get - both power wise, and because they move off the shelves fast (theyre used in lots of things).

If you want another size, or want to make sure you dont get any duds even in 7ah size, I'd visit the city store of Radio Parts in person and ask that the batteries you buy be checked for voltage in front of you before you accept them, since some of the other sizes can sit on the shelf for ages, and if left mostly discharged for ages will sulfate up. Dont accept any batteries with less than ~12.4v on them.
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Post Thu Feb 26, 2009 3:23 am 
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Andrew W



Joined: 01 Jun 2005
Posts: 220
Location: Melbourne, Victoria


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It is mainly as a test bed. When the offroad robot events start in Vic, I'll most likely use it, but I probably won't be using those SLAs.

Post Thu Feb 26, 2009 7:20 pm 
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Totaly_Recycled
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Joined: 15 Jun 2004
Posts: 1346


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I still have some Doss slas in service that Brett got for me at the first and 2nd robo wars i still use them for running compressors and and jump starting ride on mowers and other things they are one of the cheapest sla's i bought but are the best you can get as far am i am concerned i tried the ones from dick smith and ones from super cheap and none of them lasted ort could supply 300 plus amps like the doss ones can these ones have been used in combat running a brigs and straton starter motor as a weapon and were charged back up between battles at about 20 to 25 amps charge current for 10 to 15 mts before going back into battle etc . Sproing will probably be running them in Brisbane at the idea's festival.The main thing with dos bateries ids to recharge them as soon as possible aftere a discharge cycle dont leave them to the next day and also give them al a boost charge about once a month if they aren't getting used and they will last a long time .

Post Thu Feb 26, 2009 8:13 pm 
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Andrew W



Joined: 01 Jun 2005
Posts: 220
Location: Melbourne, Victoria


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Just had a look on Jaycar's website and found they have put the price up of their 18A SLA by more than $10 Evil or Very Mad. It is now more expensive than the DOSS ones, and since I only had one of them I'm now thinking of using 2 of the DOSS 18A.

Post Sat Mar 14, 2009 7:18 pm 
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Rotwang
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Joined: 15 Jun 2004
Posts: 1589
Location: Vic


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Haven’t forgotten your project Andrew, Hope to combine the sprocket adapters for your Bot in with the ones I am getting made for Sidetracked. Get things moving after Ideas.
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Post Mon Mar 16, 2009 5:56 am 
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Andrew W



Joined: 01 Jun 2005
Posts: 220
Location: Melbourne, Victoria


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ok cool, thanks Gary.
Hopefully the 200W scooter motors will be able to provide enough torque to turn it properly. As it appears as though Oatley haven't got any stock of the 300W motors and the 500W motors are a bit dear and would require purchase of their controllers.

Post Tue Mar 17, 2009 6:32 pm 
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Rotwang
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Joined: 15 Jun 2004
Posts: 1589
Location: Vic


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I think they will be ok, might not like trying to spin on the spot in thick grass but gentle turns ok.

Our 4WD bot ultidrum runs really good on the 200W scooters but with smaller wheels.

It started with 100W motors but they weren’t quite good enough.

We might be able to go 9 tooth on the motor sprocket or at least drop back to 10 from 11 so that will help to.

Oatley will probably get other motors in again with a bit of luck.
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Post Wed Mar 18, 2009 6:08 am 
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Andrew W



Joined: 01 Jun 2005
Posts: 220
Location: Melbourne, Victoria


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New Ideas

Finally figured out a way of attaching the 80 tooth sprockets to the 16" wheel barrow wheels.

Just did a bit of a crude cad of it.



The cylinder/circle sitting away from the main wheel is the 80 tooth sprocket and ratchet. They are sitting on a 35mm axel that goes through the wheel barrow wheel (welded to it at either end of the wheel barrow wheel). The 35mm axel has a 20mm hole bored through it. The 20mm solid axel will be welded to the 35mm axel and will have support bearings at each end. I already have some 1/2" mounted bearings, but I think reducing the 20mm shaft down to 12.5mm will cause a stress concentrator where it is reduced.

I didn't really want the hastle of live axels, but doing it with dead axels entails trying to mount the sprocket directly onto the wheel (you need to offset it around 30-35mm). As some of you know, I've been trying to do this for quite a while and it appears as though live axels are the only way to achieve it.

Any suggestions/ideas ?

Post Mon May 07, 2012 9:58 pm 
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Andrew W



Joined: 01 Jun 2005
Posts: 220
Location: Melbourne, Victoria


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So do people think it's feasible ?

Also changed the specs alot:
Batteries are now LiPo 6S 5000mA x2
Motors are now 300w Oatley scooters x4 (one for each wheel)
Speed controller is now the Sabretooth 50HV.

Post Wed May 09, 2012 9:07 pm 
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Knightrous
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Joined: 15 Jun 2004
Posts: 8511
Location: NSW


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Should be do able. Couple of hours on a lathe and a few welds and you can pretty much use any solution Smile
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Post Wed May 09, 2012 9:40 pm 
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Glen
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Joined: 16 Jun 2004
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Got any pictures of the two parts you want joined together?

If it has giant pneumatic wheels it might be worth buying a big diameter rod of plastic and lathing that out as a giant spacer that offsets the sprocket and bolts it to the wheel. Doing it out of aluminium will weigh a done and take an age to machine.
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Post Wed May 09, 2012 9:55 pm 
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Andrew W



Joined: 01 Jun 2005
Posts: 220
Location: Melbourne, Victoria


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I'll try and get some pictures tomorrow and post them up. I'll also get some accurate dimensions of the parts.

Post Wed May 09, 2012 10:11 pm 
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