Meaty Drivetrain recommendations (aside from Speed 900's)

[daveimi]

As above really, after Doncaster I've realised that I really need a more substantial drive train. At the minute I run 2 x 12V Gimson GR01's which are fab, but I've been running them on 7.2V as that was the only battery I had lying around. I set-to rewiring to 14.4V as I'm now aware I'm drastically under voltage. I will soldier on for the time being at 14.4V, but the motors are tired and the Gimson site isn't doing the GR02's till later on.

My hot favourite for a meaty drive train is 2x18V GR02's with the bearing retainer kit on a 24:1 box. Does anyone know how these compare to the torque and wattage output of say a Speed 900? I've had a go at looking to build around wheelchair motors but at 6kg a piece it's not gone so well. I have searched the forum back to front and the two things that keep coming up are Speed 900's or over-volted drill motors.

Any recommendations other than these, would a pair of 18V drills give enough shove to equal something like Tiny Toon etc. or should I be looking to go bigger than that? I've been stuggling to find actual real-world performance figures of them all on which to base a decision so any help appreciated, recommendations etc.

thanks again, dave

[Ellis]

Edit: wrote a wall of text, sorry!

Two drill-size motors, or 550 motors, can give powerful performance in the right robots. Cobalt is an example, it used two 550 motors on Banebots 16:1 gearboxes, 73mm Banebots wheels, the result was fast and punchy, despite being essentially two drill motors. I think it's safe to put the effectiveness of that machine down to good grip, good driving, and very good design/weight distrib.

However it's hard to get that sort of performance reliably from just two 550s without quite big bucks.

An option is to use 4x 550 motors, like we do in Tormenta 2. It's not in the same league as the likes of Satanix (S900s), but it does the job of shoving most machines around. Reliability is a major issue, but that might well be down to heavy handed driving as much as anything.

775 size motors are kind of halfway between the two. These are also sold attached to Banebots gearboxes, but they're not exactly cheap and only available in the US. They are also sold with gearboxes in "Magnum 775s", also US-only, similar prices to Banebots, and only a 20:1 reduction option. A custom reduction solution is possible but I think most 775-size are high rpm, 20,000 ish, so you're looking at complicated gearboxes there. That's the beauty of S900s, they're very low revving, so single-stage gearboxes are possible - reliable and simple.

There are several S900 clone-ey type motors on Ebay and across the web, as well as similar things like "Torpedo 800s/850s" - I'd love to get a pair of these and experiment but haven't had the opportunity.

A very powerful option, which would exceed most if not all feathers in the UK right now, is using Dewalts. The individual motors can be had on Ebay for not too much, UK based too, but without gearboxes. Once you add Dewalt gearboxes to these the prices rocket. They can be bought with gearboxes and custom mounts, so they are as simple to implement as Gimsons, here. Again, pricey and US based.

There is a motor size between 775s and 900s, of which I have four, called Johnson 885s. These are a little hard to come by now, but they are sometimes available here. At 18v, they do about 10,000rpm under load and can produce up to 600w. Chances are two of these will be going into whatever I/we build next feather-wise, so I will share results if that happens. On that same link there is a variety of Johnson motors in the 700 size range, you may well find something suitable there.

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In short, it's hard to make 550 motors be the basis for a uber-pusher without high cost, both in a money and reliability sense. Most other options with bigger motors that include gearboxes are expensive. There are several options for just the motors themselves that are comparable to S900s, but they will require custom gearboxes.

Hope that helps give some food for thought. I have probably forgotten an entire branch of the options if not a whole tree, sorry if I did!

[Eventorizon]

Since Speed 900's are tricky to get hold of now I would recommend Torpedo 800's. They are not as powerful but only by about 20%. They will destroy a pair of 18V GR02's (As far as I am concerned those are not meaty at all).

Ellis is right, the Banebots with 775 motors will be very powerful (I am using them in Conker 3 on 16:1) but they cost a fortune. If you have the money they are an easy option to bolt right in but if not then look at a belt/gear reduction system for a pair of Torpedo 800's on 24/22.2V. That will be getting on for Satanix levels of thump without the price tag of other systems.

[daveimi]

Thank you for all the replies it’s a huge help. The Dewalt stuff looks awesome but expensive! So does Cobalt run standardish 550 drill setups at 18V etc to get the performance? I’ve watched it on Youtube a few times and always took note of how easily it shoved stuff about. When you talk about weight distribution is that moving the axles and weight to the centre of gravity to put as much grip as possible through the wheels?
Those Torpedo 800 motors look like the real mccoy, they’re only cheap at like £50 for a pair (roughly). If I got hold of some of them would it be a case of getting on the Technobots website (or somewhere similar) and making up a drivetrain of cogs/axles/hdpe bulkheads and so on? Sorry for the noob questions and thank you again for the help!

EDIT: I was working out the wattages of the different motors, I also wanted to ask...is the wattage of a motor a good indicator of power comparison? For examply, the Gimsons run at 12 V and 18 V come out at around 120 - 180 Watt respectively. The Torpedo 800 comes out at around 300 ish. So if you can sort the driveline out its literally twice the amount of power for the money?

[Eventorizon]

Cobalt has been dismantled and its parts sold to various people but it worked great, came 4th in the only year it entered I believe.

As for the cost to power thing, its something like that. You never put all your power down as some is wasted but roughly, yes you do get twice the power.

Don't go to technobots to create a drive train, the belts are no where near strong enough. You need HTD T5 timing belts and Timing pulleys. Search HTD and you will find a supplier. They are not cheap but unlike GR02's you will only have to buy them once. I say that a lot of machines at GSL 2013 had their GR02's fail on them in some way. Some could keep running, others couldn't. It was all rather strange. Then again if they are mounted correctly you shouldn't encounter any problems.

[Ellis]

You can use the gears from technobots and such but they aren't necessarily the cheapest. Some googling will help there. And yes, you can make a single stage reduction with some shafts, bearings and gears, but it won't be as simple as that in reality. Alignment is fairly crucial, etc.

Cobalt used 550 motors, the same size as you get in regular drills, but Banebots gearboxes, which are worlds superior to drills (and Gimsons).

The Johnson 885s are considered 600w motors at 18v; that means pulling about 33amps, which isn't all that much. Stall amperage could well be double that. I am expecting these to be pretty punchy, not quite S900 level but getting there, but more importantly, far cheaper! So that's roughly 1.2kw of potential drive power (nearly 2hp), which is in the region of double Tormenta 2's drive.

[shakesc]

For those who fancy a size comparison

[daveimi]

Struth yeah you can see a difference. Thank you loads and loads for all the options and talking me through it all. I have a really good idea of where I need to be now I'm not hugely confident at making my own drive train but will have a look at it and see where I end up!

[Ellis]

Dewalts, so much want!

[RogueTwoRobots]

Just an additional thing to throw out there relating to drill drives; they are definitely more effective at pushing other robots when your robot is closer to the weight limit.

In 2007 I built a 4WD machine using 9.6V drills running on 14.4V; it's my profile picture on the left. On paper, that should be a reasonably effective machine (no world beater but not the worst) but it only weighed 7.5kg and was outmanoeuvered and outpushed on every occasion, even by machines that only had 2WD drill drive - including one of my own - because they had more weight over the wheels, giving more traction.

I'm not sure of the weight of your robot but looking at pictures I imagine it won't be much more than 6 or 7kg, which is why it will probably have seemed to lack grunt in the arena. Adding weight will improve it but the longer term, more robust options discussed above are definitely more desirable