| Author |
Message |
Robin Hoad (Robinh)
Member
Username: Robinh
Post Number: 1
Registered: 2-2008
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| Posted on Tuesday, February 5, 2008 - 12:53 pm: |
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Hi Paul,
My dad is building a electric powered 7.25" guage model railway locomotive. Its about 1.2m long and weighs around 70KG with its twin 12V leasure batteries installed. He has already bought three MY1018E 24V 400W motors from you. He is mounting these with one driving each of three axles via an appropriate chain drive, with gearing set to give about 7mph at 2500 motor rpm. I guess that we expect the all-up rolling weight to be about 200-400Kg. He is looking to choose a speed controller now. Assuming all three motors are wired in parrallel we are looking for a 24V controller which is well capable of giving the motors as much as they can handle. The motors are mounted to the metal chassis and can even be given some forced air cooling if needed. Proportional forward and reverse is required, perhaps with re-gen breaking if possible. We were thinking of a 4QD Pro-120 series (24V). Do you think this would be suitable? Other options? Cheers
Robin
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Admin (Admin)
Board Administrator
Username: Admin
Post Number: 700
Registered: 10-2004
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| Posted on Tuesday, February 5, 2008 - 8:01 pm: |
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Hi Robin,
Always nice to see what projects our products are being used on.
Three motors will draw 64A at the rated load and could draw more during periods of acceleration when under maximum load although the power to weight ratio with the max speed does look good.
The Pro-120 would be a good choice but you will need a heatsink which could be the loco body if feasible. A boxed Pro-150 would also be suitable and without any additional heatsinking (just) but cooler the better if you can incorporate a heatsink.
Regards
Paul |
ian reddall
Unregistered guest
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| Posted on Tuesday, February 5, 2008 - 3:25 pm: |
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Thanks for the reply
I need to get moving with this project and will use a 750w bosch motor.
Please provide details of what is required i.e Speed controller, any leads, fuses, control boxes for speed and forward/reverse inputs etc and availability as need to be placing order on thursday
Regards
Ian Reddall - Chatsworth pneumatic solutions ltd |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 701
Registered: 10-2004
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| Posted on Tuesday, February 5, 2008 - 8:17 pm: |
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Ian,
For the Bosch we would always recommend a 4QD Vortex 75A but as your application is going to be a relatively light load for the Bosch you could get away with the 35A version but we would still recommend the 75A version.
Both versions are available boxed with leads, after that you need fusing (our maxi range (50A) with matching fuse holder should be ideal. We also have multicore cable and pots to suit (two types of pot, the miniature 16mm 10k pot would offer the best performance). For forward reverse, you will need a toggle switch or similar which we currently do not stock. Use our quick search on the website which should bring up the items referred to above. |
Chris Chellingsworth (Ccworth555)
Member
Username: Ccworth555
Post Number: 5
Registered: 1-2008
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| Posted on Wednesday, February 6, 2008 - 2:58 pm: |
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Paul,
Thanks for your useful post of February 4, 2008 - 9:00 pm.
Unfortunately I’m stuck with a 12 Volt system for this robot for many reasons, not just the alternator, I do understand the very good reasons for moving up to 24, 36 volt though.
After your expression of concern that the 480w S2 motor pair may not be man enough, I’ve done some investigation and I may have to move to a pair of 750w S1 Bosh motors.
Would the pair of VTX-75 12v controllers handle the 750’s ?
If I have to move up to a pair of Pro-120’s would these be OK with the 480w motors in the interim ?
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Have I gathered correctly, from browsing other areas of the tech’ support forums, that there are some compatibility issues between Pro-120’s and the Futaba 6EX 2.4GHz gear ?
Or have I got the wrong impression ? Do RC gear compatibility issues simply relate to the 3401-005 interface rather than the motor controllers ?
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As I need a pair of controllers, would it be possible to totally separate the 12v systems for LH & RH motors and use two unconnected 12v batteries ?
If this is possible I’d implement the battery charging / topping up with two 17 Amp 14.4v alternators. The only connection that I can envisage would be mechanical I think.
Your advice always appreciated !
Many thanks
Regards
Chris |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 704
Registered: 10-2004
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| Posted on Thursday, February 7, 2008 - 5:51 pm: |
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Hi Chris,
VTX-75 depending on final load would be right on their limit, for a 12V 750W Bosch I would suggest the Pro-120 as a minimum.
The only issue that I can see with using the smaller motors on this controller is the lack of motor protection afforded by the current limit. Be careful with your driving, i.e. avoid stalling the motors and you should be fine.
There are some concerns from some users of problems with 2.4GHx radio with electronic interfaces rather than servo's but we have not been able to replicate these problems ourselves. At this time, we have no reason to doubt that the 4QD interfaces will not work and if any problem was found, we would cover that under our guarantee terms.
You can run the batteries and motors as you describe apart from the need to common the two negative terminals together otherwise you will effectively common them via the RC interface or receiver (unless using opto isolation).
Reagrds
Paul |
Chris Chellingsworth (Ccworth555)
Member
Username: Ccworth555
Post Number: 6
Registered: 1-2008
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| Posted on Friday, February 8, 2008 - 12:57 pm: |
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Paul
Many thanks again for your very informative response.
I’ll certainly go for the separate LH & RH 12v systems allowing two of your largest batteries to be used. It’s useful to know that I should have a common negative, thanks.
This robot application is such that it will be unavoidable to regularly stall the robot, thus wheels and thus the motors. Either by softly colliding with objects or trying to climb banks / humps that are too steep.
Consequently, whichever motors or controller combination is used, I need a workaround that will protect the motors from damage and the controllers from overheating in the event of stalling.
I had thought that I may be able to use an automatic resetting (or modified resetting) circuit breaker in the +ve line between each motor and it’s controller.
I’m unable to use a standard manual circuit breaker as it will not be possible to physically reach the robot to reset the circuit breaker during operation. If there is a small time delay for the circuit breaker to reset this is quite acceptable.
Perhaps you know of another solution to this issue ? I’m even still unable, as yet, to locate a UK source of automatic resetting circuit breakers possessing sufficient capacity. Although they do appear common is the US. Please refer below.
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From your comments regarding compatibility, I’m happy to purchase the Futaba 6EX 2.4GHz, 4QD interface and controllers from Technobots.
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Regards Chris
Chris |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 708
Registered: 10-2004
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| Posted on Friday, February 8, 2008 - 6:51 pm: |
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Hi Chris,
The controllers will look after themselves so you can focus the protection towards the motors.
My view of circuit breakers can be found here http://www.technobots.co.uk/discus/messages/6/402.html?1201202270
It may be possible to lower the 4QD current limit, check out their website 4qd.co.uk as they have a wealth of info on there.
Regards
Paul |
Chris Chellingsworth (Ccworth555)
Member
Username: Ccworth555
Post Number: 7
Registered: 1-2008
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| Posted on Sunday, February 10, 2008 - 6:21 pm: |
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Hi Paul,
Many thanks for your reply.
Your advice regarding fuses and circuit breakers is very informative.
I’ll go for the Pro-120’s and protect the 480w motors accordingly as they are an interim measure.
Also I’ll contact 4QD as I’ve found the following data on their site, just as you suggest:
“Drive current can be reduced from the standard value by altering a resistor and can be altered over quite a wide range. Details on request.”
In the slightly longer term I’ll need to protect the motors, perhaps the Bosch 750w pair, as stalling of the drivetrain will be regular.
The robot will be working in a hazardous area, with no access for personnel or other vehicles to either change fuses or pull the robot out.
The robot will need to extract itself from the hazardous area under it’s own power
Consequently I can’t blow a fuse and loose drive in the longer term.
We are trying to utilise ‘commercially off the shelf’ components rather than ‘industrial’ control and motor gear as in certain (hopefully rare) circumstances the robot will be disposable. Consequently they will need to be built down to an affordable cost.
Do you know an electrical / electronic solution to this issue ? i.e. allowing stalling but protecting the motors without access to the robot and keeping it moving.
Would the Bosh 750’s overheat the Pro-120’s if they are set (probably as standard) to produce sufficient current to utilise their power ?
If this issue is a 'brick wall' then I need to design in a mechanical slipping clutch mechanism into each motor – wheel drivetrain.
The proper drivetrains are not designed as yet as I’m just using the caravan shifters as an interim measure in order to conduct testing on the other robot systems.
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May I ask, will the two Pro-120 still use the same 3401-005 interface as you suggested for the two VTX’s ?
The Pro-120’s that you are selling for £130 on your website, are they boxed or not ?
(The site is not too clear to me on this matter, the VTX page depicts this difference quite clearly.)
Using the Pro-120 with the 12 volt 750w motors ‘on the limit’ as you suggest, do I need to use both of the double 9.5mm spade connectors for each motor pole ?
Your comments are much appreciated as always, thanks for your valuable time.
Regards
Chris |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 710
Registered: 10-2004
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| Posted on Tuesday, February 12, 2008 - 9:09 am: |
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Chris,
The issue for a controller is deciding when a motor is stalled and when it is under heavy load or simply accelerating hard. A stalled motor can quickly start smoking even with the current limit set to 100% of fall load just due to the lack of cooling. Naturally motors difer and some are more tolerant than others with a number of influencing factors such as case size. One technique used to prevent stalling is to make sure you have far more torque than you need so that the wheels will spin before they can stall.
We had a commercial customer who used this approach with success. There are other methods such as measuring motor temperature and using this to regulate power to the motor. Some controllers use a time / current method to estimate temperature rise. For you, I would suggest looking to see what current you need to achieve the performance required and this may well be much lower than it's full load current (especially with the Bosch) then limit the current to this. Then it's a question of how long it will take for the motor to suffer at this current under stall conditions.
Yes, use the same boxed interface. A base and cover are available to house the Pro-120 series, I'll look to get them added to our website but budget on £16-20.
You do not need to use both 9.5mm tabs if you do not wish to, this is where you can run a pair of motors from the same controller.
Regards
Paul |
Chris Chellingsworth (Ccworth555)
Member
Username: Ccworth555
Post Number: 8
Registered: 1-2008
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| Posted on Tuesday, February 12, 2008 - 12:59 pm: |
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Hi Paul,
Thanks for your useful response. I’m unable to let the wheels themselves spin as I need traction for climbing small humps or hills. The limit of the robot climbing ability will need to be limited by the torque durably supplied by the motors.
An idea of the purpose / duty of the robot can be gained if you scroll to the very bottom of this very long page:
http://www.nolandmines.com/machinespart1.htm
I’m in the process of building the prototype concept robot in the UK for development use. This is for AVS-MAC with a meagre funding of my own.
It’s not intended that this project evolves into a profit making venture. Although it’s a given that companies need to make a profit by selling us equipment.
Hopefully, finally on the subject of motors and controllers, may I ask two more questions:
Is it possible to limit motor current by using a fast response electromechanical torque sensor that feeds a limiting signal back to the Pro-120, or another inline current limiting device / auto resetting trip ?
You say that motors can overheat and smoke when overloaded, however what is the normal failure mode of a 12 volt motor that is repeatedly stalled without any current overload protection ?
Your comments are much appreciated as always, thanks for your valuable time.
Regards
Chris |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 716
Registered: 10-2004
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| Posted on Tuesday, February 12, 2008 - 3:57 pm: |
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Hi Chris,
Relying on wheel spin to avoid stalling does depend on traction but assuming you have designed the transmission so that the torque does not exceed the nominal duty rating, stall torque could be 3 to 5 times that value which could then break traction.
Sorry but not familiar with the phrase AVS-MAC or what you are asking in relation to the machine you linked to?
It is quite possible to modify the signal to the speed controller (either at voltage level or at RC pulse level) using some extra interface electronics. Gyro's do this in robots to keep them in a straight line. You would effectively need the equivalent but for torque. If you have a suitable transducer, the electronics would be quite simple.
I did not know Bosch made a 12V 750W motor but I have the spec of a 630W motor. Just a quick point, note that our Bosch 24V 750W motor is designed for bi-direction use but all others I have seen are uni-directional (although you change the timing on some). Anyway, a 12V 630W motor would dissipate 270W at nominal load and is fan cooled. Stall the motor without current limiting (either electronic or limited by the battery technology) and the motor would have to dissipate over 3kW without any forced cooling. Each time you stall a motor, the windings would heat up very quickly and ultimately result in the insulation breaking down and shorting out goodbye to the motor. Short term stalls will bring about a premature failure. In the early days of robot combat, the battery technology limited the effects of stalled motors, then batteries with a much lower internal resistance were used which gave improved acceleration but also increased the probability of motor failure under stall conditions. As you are looking to use high capacity batteries, this would give a lower internal resistance and compound the risk of damage to a stalled motor. |
Chris Chellingsworth (Ccworth555)
Member
Username: Ccworth555
Post Number: 10
Registered: 1-2008
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| Posted on Tuesday, February 12, 2008 - 9:41 pm: |
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Hi Paul,
Many thanks for your reply.
Your information regarding the Bosch 630 w 12 v motors is most appreciated, as is all of your other advice and explanations.
I apologise for not being clear in my previous post. The prototype machine we are building now is the continued development of the machine I referred to in the link. I was endeavouring to explain the potential robot duty cycle and working environment by referring to the link.
Sorry for falling into jargon nomenclature also. AVS-MAC refers to the following:
Regards Chris
Chris |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 719
Registered: 10-2004
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| Posted on Wednesday, February 13, 2008 - 8:57 pm: |
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Hi Chris,
This is really interesting stuff and a really commendable project. We are more than happy to provide as much technical assistance via this forum as you may need.
Regards
Paul |
Chris Chellingsworth (Ccworth555)
Member
Username: Ccworth555
Post Number: 12
Registered: 1-2008
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| Posted on Thursday, February 14, 2008 - 12:00 pm: |
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Hi Paul,
Many thanks for your comments and support.
I just thought, if realistically the 630w Bosch motors are going to be the largest suitably available at 12v, do I still need to move up to the Pro-120’s ? Or would the pair of VTX-75’s suffice.
I’ve read that Bosch tend to be realistic with their quoted wattages, but I’m unsure if this is relevant or not.
Regards
Chris |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 722
Registered: 10-2004
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| Posted on Thursday, February 14, 2008 - 7:53 pm: |
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Bosch motors have in our experience been very realistic in their ratings. A VTX-75 is on its limit but only if you run in flat out which you are unlikely to be doing so on balance with good heat sinking, go with the VTX-75. Whilst we do not stock the 12V 630W Bosch, we can I would imagine get them but do remember the issue about motor timing and unlikely the 750W version, the 12V version has a screwed output shaft. |
Hugo Marques (Marques850)
Member
Username: Marques850
Post Number: 1
Registered: 3-2008
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| Posted on Friday, March 14, 2008 - 11:26 am: |
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Hi there!
Im Hugo and I am trying to build a electric scooter using 2x12V batteries and your 24V 300W DC motor(part n.1470-024),and your throttle lever unboxed (part n. 1520-006) but not sure which motor controller to use. Can you help? |
Hugo Marques (Marques850)
Member
Username: Marques850
Post Number: 2
Registered: 3-2008
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| Posted on Friday, March 14, 2008 - 11:52 am: |
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I forgot to mention that the batteries are 2x12V 18Ah.
Regards
Hugo |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 736
Registered: 10-2004
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| Posted on Saturday, March 15, 2008 - 7:51 pm: |
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Hugo,
I assume you do not need reverse for a scooter so I would recommend the 4QD Uni Series 4 24V 40A - Part No: 1514-424. A base and cover is also available for this controller.
Regards
Paul |
R.A.Sourbutts
Unregistered guest
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| Posted on Thursday, March 13, 2008 - 8:39 pm: |
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Dear Sir, I recently bought 2 electric motors off you.36v750w geared 6.1 600rpm.My1020zx3.
part no1471118.I'm now looking for a regulated output generator to drive the 2 motors.it's for a min loco. if you could help it would be very much appreciated. •••• |
