Piecing together a budget heavy

[Shakey]

I'm currently in the process of piecing together a heavyweight. So far I have the radio gear A123 34v battery packs and 2 Wheelchair motors (Eventual aim to replace these with Bosch 750's or similar drive).

However I'm lacking any kind of ESC that can handle the voltage (I'd rather not have to break the packs down to drive the temporary Heavy before I put the proper one together!). Any advice on ESC's or if anyone has a suitable one would be greatly appreciated! If all else fails I'll go for the classic Relays and servos ESC for the wheelchair motored robot.

I'm also in need of a weapon, at the moment I'm thinking lifter, pincer, jaw or my personal favourite an axe. However I'm not sure how to go about something like an axe on budget, the others I'd just use a screw jack and something like a scooter motor to drive it.

The frame would be square sections of mild steel armoured with HDPE armour over the top. Not the strongest but I'll try and avoid axes with the first Heavy

This is just a heavy I'm putting together for fun and to get a bit of experience in before I attempt to build a more serious one. So it's also an exercise in roboteering on a budget

Any advice, ideas or parts available would be GREATLY appreciated.

Cheers,
Alex

[geeza]

Suggest you work out the current draw of the motors at that voltage and go from there. If they can handle that voltage?!

[typhoon_driver]

wheel chair motors tend to be 12v or 24v. I would be surprised if they or their gearboxes could handle the 36v from the A123s. Split the packs otherwise you will burn out the motors. You will also then have more options with speedos

[Rapidrory]

If you can find a 34v ESC then you can just limit the voltage on the stick travel like you do with Gimli if need be. As for modding a TZ85, the mosfets in that can only take up to 30v ( http://www.a-power.com.tw/files/AP_P...R403GMT-HF.pdf ), so you'd have to make a separate mosfet driver board.. my plan was to buy some of those £6 20A ESC off ebay then use the drivers on them to drive a separate high current mosfet board.. or just construct my own dual ESC from scratch like usual

[Shakey]

Cheers, Rory. Just sat down with a TZ and an alan key to have a look in them when I saw your post!

I'll just split the packs down into ~12V that way I can just add packs to get 24/36V depending on the bot. That way I don't have to keep making up new ones, just drop in the right number (Plus I can distribute smaller packs around the robot better).

wheel chair motors tend to be 12v or 24v. I would be surprised if they or their gearboxes could handle the 36v from the A123s. Split the packs otherwise you will burn out the motors. You will also then have more options with speedos

As I do on my feather Gimli I'd limit the sticks so that while I am pulsing 34V the effective max voltage is 24V.

Now I do have a charger that can charge A123 (I-Max B6) but it isn't fast and is only 1 channel. What chargers do people recommend for charging A123s en masse?

[daveimi]

There are two main veins of wheel chair motor. The first is 12V and 20A, the second is 24V and 10A. Make sure you remove the brakes from the end and use right voltage etc.

[Shakey]

There are two main veins of wheel chair motor. The first is 12V and 20A, the second is 24V and 10A. Make sure you remove the brakes from the end and use right voltage etc.

Yeah I have 24V and 10A and have already taken the brakes off. And as I said was going to keep the effective voltage correct if I used 34V but will probably split my battery packs to get the right voltage.

Trying to figure out a better charger to use than my current one though.

[craig_colliass]

A123 technology for a cheep HW robot is A bit unusual, I use them on Cherub and Behemoth team use them too but we have an 8s4p configuration keeping the volts around the 24v mark. you could use SLA for this as for low cost HW these are cheep and I have used them for years in my heavies. If you want to get a heavy in the arena I would advise something like this.
2* 12v 16amp/hr SLA batteries charged with a car charger!
2* Botsbitz 85A speed controllers (I believe they will just about go to 24v) http://www.botbitz.com/index.php?rou...&product_id=59
2 24v wheelchair motors. Try to keep the gearing low so the thing has traction 4-5mph doesn't sound fast but it means you might be able to push the other robots about.
Make the robot small so the mild steel armour can be thick at least 4-5mm. and that will get bent! try to make the robot look different and fun. people have spent their money on tickets to see it! make it so the robot can be repaired in the pits easily. you will find a lot of teams make it so the whole body lifts off on a few bolts so access to the parts to be fixed is easy, shock mount everything you can.
Other things to look out for make it so it doesn't get stuck on the arena floor it is not flat or on the side. if it can't self right it must be invertible. Don't get hung up on weapons to start with, in this game there is a steep learning curve if you can make a robot that can get into the arena and drive about with out getting stuck or breaking and then driving back out of the arena, that's about the best start you can hope for.

I would encourage anyone to have a go, remember a lot of money thrown at a robot doesn't automatically make a good machine, design it well build it well and you with a bit of luck might win.

Don't give up

Craig

[typhoon_driver]

Charging wise, when I was using A123s I used a lipodapter

http://www.slkelectronics.com/lipodapter/

Not sure if they still make them but you can use a cheap high charging nimh or nicad charger. I used an old astroflight charger with it that could give a good 10amps charging a pack in no time at all. Never bothered balancing A123s and the cells were never out of balance voltage wise.

[Shakey]

I know A123 is more unusual for a cheap heavy but for the price they were vs. price of SLAs and the fact they'd be useful when I hope to upgrade to a better bot. I'm not aiming high for the first version and by 'weapon' it'll just be a lifter or something (Anything a scooter motor and screw jack can actuate!), just give my robot something to do in the arena really. Another vote for the TZ85/Botzbitz is good aswell (I've run them on a 6cell liPo 25.2V with no problems for a while now).

I'm going to be trying to make sure my robot is interesting for the crowd, I know how much work EO's put into events and I'm sure they'd much rather have a robot the crowd will enjoy watching in the arena (On that note I absolutely love watching team saint robots fight). This is partly the reason my feather has an axe as opposed to a lifter or pusher (Not that there aren't pushers or lifters that can put on a good fight!).

Chassis wise to keep the cost down I was going to go with steel square section to build the frame, reinforce it at all the joints with bits of sheet steel. Then thick HDPE bolted onto the top of it all as armour (With an airgap to help stop axes touching the components), I have a small amount of Hardox I'll try and use to armour the front. I'll be aiming for invertible as I've seen how hard it is to stay upright in the arena. :P I have an arc welder to weld it all together with and can get decent welds going after building my feather. The chassis construction method is based on this guy:

Apologies for the mess but it's pretty immobile after it burnt out a motor so has been living in the same spot since we moved in! but it's a 40kg robot that can (and has accidentally been) run into a tree at 20mph and happily survived with no damage, not to mention far too many falls than a non combat robot should face :P). It's split chassis with a mini wheel bearing in the middle to act as suspension. I think scaling the same method of square section with triangles of steel to support it should work (As long as I reinforce the square section itself not to buckle).

This is what I currently have to work with:

2 24v wheelchair motors of unknown speed
30 A123 cells
0.5x0.5m square of hardox
and my feathers battery charger (which'll do 6 A123 cells)

So far I've spent £60 on the heavy, with 3 TZ's and a screwjack that'll add maybe another £70 and finally the cost of square tube and HDPE.

One thing I am wondering is that the tread don't the wheelchair wheels is pretty worn out, would wide bike tread screwed onto the wheels be any good?

Those LiPodapters look interesting, I'll have to do more digging into those.