FW Electric hammer - Robo Challenge (no name yet)

**grant_ploughbot** · 26th February 2013, 16:23

It's been too long since I built a robot for myself. Ploughbot needs loads of work doing on it so I've decided to start something new (i'll probably be re-vamping Ploughbot at the same time).

I've always like axe's, and as James has predator as a good spinner, and spent a huge amount of time with Dave on 360 I decided I don't want to do another one. James is also making his hydraulic crusher so an axe/hammer is the way to go I think.

I don't like C02, too much hassle so I'm going electric. So far Basher is the most powerful FW axe, and LH2 isn't too far behind, so I'd like to try and build an electric version that's more powerful than the pneumatic ones out there now. Doing abit of research there's a few ways of doing it well, but the only really impressive electric hammer so far has to be BETA that John Reid designed.
Looking at how it work's is quite impressive. He manages to squeeze out 10kw of power from the motor constantly over the full 180 degree stroke. That is lifting an 11kg lump over at an impressive speed.

The more weight you can get over on an electric hammer is the key. BETA uses just over 10% of its weight on the head. I think i'm going to go with almost 20% of the weight in the head with a 2kg lump of stainless steel. I'll need a fair bit of power for this, and to get it as powerfull as I hope it will be I need 10kw too

http://www.align-trex.co.uk/800mx-brush ... 520kv.html This 11kw brushless motor should do the trick! I have this same motor in my large RC heli so I know it gives the spec's it produces. I'll be running on 12s Optipower lipo's to squeeze everything I can out of it.
ESC wise I think I'll be putting my Kontronik Kosmik in. It's a pretty fancy ESC I have for one of my heli's, but it's a little big to fit in so it may go into this. http://www.modelhelicopters.co.uk/kontr ... v-esc.html

I looked through an old thread on the forum from many years ago when John and Nick posted some interesting equations for working out the energy in an electric axe, and to work out the speed that it goes over. I've made an axe calculator using these equations and a few extra bits thrown in too, and it's looking pretty impressive if this works.
The gear ratio's looking like i need 23:1 from this motor, however I hope to be doing a similar thing to Beta and using a snail cam to change the ratio from around 40:1 down to about 18:1 so that the motor works at its max power the whole way through.

My only concern is the start up torque of the brushless, however it is a big beast and the 40:1 ratio will help that alot. My back up is to run a Mag s28-150 motor on 12s lipo (double its rated voltage) to produce around 9kw reliably. Its not ideal as it weighs do much but if the brushless doesn't work its a good alternative.

I've almost finished designing how the drive will go. It's 4wd using Astroflight motor's http://www.astroflight.com/motors/cobal ... s/640.html through a 16:1/17:1 gearbox and 75mm wheels. I used to run them on 15:1 in ploughbot, but I'll need alot of magnets holding this thing to the floor so the extra ratio will help keep them running cooler.
The plan is for shaft drive from the front to rear wheels, similar to big nipper's. I plan on using ultra light weight arrow shafts for this. Currently deciding if I should run a 2 stage gearbox with the full ratio or run a single stage ratio to the shaft and a seperate 3:1 bevel gear and each wheel. This comes down to cost and weight really.

I have a Mini Vantec to power the astro's, and will run those on 6s as I used to in Ploughbot (I could push a small car with that set-up).

To mount the electronic's I've drawn up a simple method to have them all floating so that any shocks don't go through the ESC/RX etc. It's an aluminium mount with a series of light weight springs/damper's to hold the electronics tray in place. I'll need to use ultra flexible wet noodle wire to make it useful though.

Just about to make up the test bed to try out this brushless set-up before I go much further as I need to know if I'm using brushless or the Mag motor before I can start drawing up the proper design's in Inventor. I'll keep you updated

**ady** · 26th February 2013, 16:54

Be interesting build to follow, grant are you able to supply blue/red wheels in 150mm at all. I need more clearance on k9.

**Ellis** · 26th February 2013, 17:09

Sounds like it's going to be monstrous, Grant. Look forward to it.

**RogueTwoRobots** · 26th February 2013, 21:26

Well I just bought a motor at the weekend for my electric axe, and it's a mahoosive 300W! Good luck defending against that!

In all seriousness this sounds like it's going to be amazing, pushing boundaries once again. Looking forward to seeing how it progresses

**webby** · 27th February 2013, 20:36

Sounds bitchin!

**SamO** · 27th February 2013, 20:45

Sorry to Hijack you thread.
Just out of interest, how much power does Ploughbot have?

Thanks

**grant_ploughbot** · 27th February 2013, 22:13

Ploughbot uses 2x 750w Astroflight motor's on 24v. It runs a 15:1 gearbox with 75mm blue wheels. Thats geared for about 9-10mph and will push a small car at that.