Team Bitza

**psycho_fling** · 12th September 2012, 08:46

i think its good to have a higher top speed than you would maybe use all the time, however you don't want it crazy so you can't control it. Plus i'm guessing you'll only be using this in the RC arena which isn't huge so i think 10mph top end would be good

**PJ-27** · 13th September 2012, 09:42

PMDC motors have the following characteristics:
They produce their maximum torque at zero RPM.
They produce zero torque at their maximum RPM.
They develop their maximum horsepower at 50% of their maximum RPM.
At 50% of maximum RPM, they produce 50% of their maximum torque.
At maximum horsepower, they are no more than 50% efficient.

Given these statements would it be a good idea to gear for a top speed double what you want so you're running 100-50% Torque and 0-100% Horsepower over the speed range you'll actually likely achieve?

**ewan** · 13th September 2012, 10:14

No... The balance to be made is between torque and speed, making your gear reduction half what it would otherwise be will slow you to a ridiculous extent as your acceleration would be hopeless. 'Horsepower' doesn't really matter, it's just a hint at torque/speed characteristics which you should be designing around. The best thing is to use the tentacle calculator to try some gearing combinations with a motor similar to yours, and enter a realistic tire coefficient then you can click the 'acceleration' button for more information: http://www.architeuthis-dux.org/torquecalc.asp

**PJ-27** · 13th September 2012, 12:55

Thanks for this.

I think I found an appropriate motor, not sure what I'm looking at though or what my tyre friction coefficient would be, or how I can find it.

Any idea how big the RC arena is corner to corner?

Also what's a good effective pushing force figure / time to top speed?

I get 27lbs and 0.7s

Cheers,

**archie2000** · 13th September 2012, 14:55

care to share your link to the mythical motors?
or are they your secret?

**RogueTwoRobots** · 13th September 2012, 18:34

Originally Posted by PJ-27

Any idea how big the RC arena is corner to corner?

Pretty sure it's 5m x 4m

**archie2000** · 14th September 2012, 05:48

Originally Posted by archie2000

care to share your link to the mythical motors?
or are they your secret?

the 3 horeswpower ones i meant
sorry if that was confusing

**PJ-27** · 14th September 2012, 08:31

I was going to keep it a secret, but I think it'll be a bit anti-climatic so I'll just say.
They're car fan motors, overvolted to 24v. Managed to find a matching pair, also found some incredible wide wheels to put the power down with.

Next question!
On a spinning disk with 3 legs connecting the outter rim to the middle will it throw the balance if I put 2 teeth on opposite sides?

**Bodge Job** · 14th October 2012, 19:32

it shouldn't if there even

**PJ-27** · 16th October 2012, 21:35

Since no one wanted to come play with the wooden robot idea and I had already made one I figured I'd do something worth while with it!
And so was born BitzaWood Revo

In keeping with the Bitza theme the disk is a master pulley from a V6 Modeo (Ditching the saw disks as they'll in ineffective against metal)
The armour is 2mm Stainless that I was given (odd shapes hence the multiple parts)
And I'm swapping out the MDF lid for a HDPE one courtesy of Mr Weston!

No disk yet, but shows off the Ti front skid (Left over Ti from Bitza)

Got some Polycarb for the link cover. That way the light can shine through.

Disk, Bush and Tool Steel for the teeth:

Milling the Teeth: