Rango - Build diary

**harry hills** · 6th April 2014, 11:09

Have a little faith in Ellis, I think he is capable of working out speeds correctly.
Also these aren't "fake speed 900s" I think that was just used as an rough approximation as they are large motors.

Maybes we need to look at fan cooling rather than just spamming numbers?

**Max** · 6th April 2014, 11:30

I think these are the data sheets:
http://www.pollin.de/shop/downloads/D310507D.PDF
They say 21 000 rpm no load,
10 700rpm 67A at max torque
and 132A stall

**Ellis** · 6th April 2014, 12:05

Hi Max. Yep that does look like the specsheet, actually from the site I bought the motors, and indeed, you're right, it says 20,000 odd rpm and a massive stall draw. Well, crap. Pollin.de on their selling page list the motors as 10,700rpm @ 18v as did another source from which we purchased last year. Their selling pages are wrong then, and that is where the problem lies, they're misinformed and as such so was I. I never even saw the button to see the datasheet but of course it's obvious as day now.

So I built this around what I believed to be motors running at 10,700rpm @ 18v as per the listed specs on the website. Lol. People will have to believe me when I say I would not have built this like this if I had seen that specsheet sooner. It's of course, way way off, 6:1 is nothing like enough. I'm now surprised it even moves under its own power. It does, and very well, wheel spin was easy for the short time I tested on rustic grippy tiles. I'm still kinda surprised the ESCs get hot whilst the motors are pretty much room temperature.

Well it's way too late to help now, robot is kinda doomed haha.

Thanks again for the help. I had fully intended to run different motors for next year anyway, looks like that upgrade process will be a rapid and automatic one.

This whole project was an experiment and an exercise, so I could learn as much as possible for my first featherweight build. It has succeeded in that respect. Shame it'll probably eat itself in fight 1! Blarg!

edit: 21000 @ 18v, no bloody wonder

edit2: anyone got any speed 900s

with access to the right tools they could be dropped in quite quickly.

**plargen** · 6th April 2014, 12:28

i have 1 of the cheap ebay 1s if you can find another, shaft seems to be 5mm

**Eventorizon** · 6th April 2014, 12:33

I have one I found in a box, I think it was a spare from Conker 1 that I lost. It smells fine, I will bring it to GSL.

Would something live this do? http://www.cornwallmodelboats.co.uk/...mfa1114_1.html

Here is the Data sheet: http://www.mfacomodrills.com/motors/800.html

And here are some real Speed 900's: http://www.westbourne-models.com/Mod...-2084-ext.html

I am sure if you ordered them to have them rapidly posted to the Robochallenge building that Grant could bring them in for you on the morning of the event.

**harry hills** · 6th April 2014, 12:35

We're looking at similar things now. Would using one and using the dual rates/fancy arse magic on the DX6i make those a viable choice?

**plargen** · 6th April 2014, 12:42

spotted these on ebay

http://www.ebay.co.uk/itm/MODEL-BOAT...item2ec7531693

**Ellis** · 6th April 2014, 12:54

The 885s are 49mm in diameter and the width between bulkheads is 100mm, so to fit larger motors (the torpedo 800, 850s, or any 900 size can) the main bulkheads would have to be pocketed a bit and the bolt pattern in the mounting plate moved/slotted to the side a few mm. So not something that can be done on the day sadly. A powerful enough 775 could work but I can't find many that are between low revving and gutless and the fast ones such as the banebots ones.

Will try the existing setup on radically reduced rates from the tx as Harry suggests and see what effect that has.